wood research @ upm

Physical | Elasticity | Dielectric

S i d e k A b A z i z

Pertanika. J. Sci. & Techno!. 3(2): 389-399 (1995)ISSN:0128-7680

© Penerbit Universiti Pertanian Malaysia

COMMUNICATION II

Penggunaan Kaedah Dinamik Ultrasonik bagiMenentukan Pemalar Kenya! Kayu Tropika

Diterima 7 May 1994

ABSTRAKKertas ini melaporkan penentuan pemalar kenyal 56 spesis kayu-kayan tropikamenggunakan teknik dinamik ultrasonik. Gelombang membujur (45 kHz)digunakan untuk mengukur halaju pada arah ketakisotropan jejarian (R),tangen (T) dan longitud (L) bagi setiap sampel kayu. Pemalar kenyal bagisetiap spesis kayu ditentukan dengan menggunakan nilai halaju ultrasonik danketumpatan menerusi persamaart Christoffel. Hasil k~ian menunjukkan terdapatsatu korelasi yang linear diantara pemalar kenyal dan ketumpatan kayu bagiarah L, R dan T. Perbandingan hasil pengukuran ulrasonik kepada hasilpengukuran statik menunjukkan teknik ultrasonik juga mampu digunakanuntuk menilai kualiti sampel-sampel kayu tropika jenis sederhana dan keras.

ABSTRACTThis paper reports the determination of elastic constants for 56 tropical woodspecies using the dynamic ultrasonic technique. Longitudinal waves (45 kHz)were used to measure the velocity in the radial (R), tangential (T) andlongitudinal (L) anisotropic directions of each sample of wood. The diagonalelastic constants of each species of wood studied were estimated using thevalues of ultrasonic wave velocities and their mean densities via the Christoffelequations. The results show that there is a linear correlation between the elasticconstants in the L, Rand T directions and density of wood. Comparisonbetween the ultrasonic measurement and static measurement indicate that theultrasonic measurement technique is also capable of assessing the quality oftropical medium and heavy hardwood.

PENGENAlANTeknik ujian memusnah biasa diguna bagi mendapatkan sifat fizikal bahanyang boleh dikaitkan dengan kualiti kayu (Szymani and McDonald 1981;Bucur 1985). Kaedah yang berkesan, kos yang rendah dan kepentingankajian merupakan faktor-faktor yang harus dipertimbangkan bagimendapatkan hasil pengukuran yang memuaskan. Teknik ujian memusnahdikatakan kurang efektif kerana memerlukan banyak sampel kajian disamping kos penyelenggaraan yang tinggi dan hanya dapat dilakukan dimakmal sahaja. Teknik ujian tak memusnah ultrasonik merupakan satualternatif bagi tujuan pengujian, pemiawaian dan kawalan mutu kepadabahan kayu (Bucur 1983; Bucur 1985; Bucur and Rocaboy 1988). Teknik

Sidek Hj. Abdul Aziz, Abdul Halim Shaari dan Chow Sai Pew

ini tidak memerlukan banyak sampel kerana sampel kajian tidak mengalamikemusnahan dan sampel yang sarna dapat diuji semula bagi mendapatkanparameter fizik yang lain. Di samping itu ia berupaya untuk memberikandata-data fizik dalam masa yang singkat di makmal atau ujian seeara in situ.

TEDRI DAN TEKNIK PENGUKURANKayu adalah bahan ortotropik kenyal dengan eiri kimia dan strukturbinaannya yang kompleks serta berbeza pada arah longitud (L), tangen (T)dan jejarian (R) seperti yang ditunjukkan seeara skematik pada Rajah 1.Kayu menunjukkan sifat kenya! dan berkemampuan mengatasi sebarangtegasan luar seperti ketumpatan dan ketegangan sehingga ke had kenyalnya;ia mematuhi hukum Hooke iaitu

dengan Cijkl adalah pemalar kenyal bahan uj

dan ek1

masing-masing mewakilikomponen tegasan dan terikan (Bueur 1983; Bueur 1985). Model ortotropikCartesian digunakan bagi memudahkan kajian perambatan gelombangultrasonik bagi meneirikan aspek-aspek kekenyalan bahan kayu. Data-datapemalar kenyal kayu ini sangat penting bagi menganggarkan ataumenentukan pemalar-pemalar teknikal yang digunakan olehjurutera bahan.

Arah L Arah T Arah R

\1

390

Rajah 1. Arah rujukan bagi sampel kayuTatanda L mewakili longitud (arah pemanjangan), R

mewakili jejarian (arah pembesaran cecincin) dan T merujukkepada tangen terhadap arah pembesaran cecincin).

Pertanika J. Sci. & Technol. Vol. 3 No.2, 1995

Penggunaan Kaedah Dinamik Ultrasonik bagi Menentukan Pemalar Kenya! Kayu Tropika

Pemalar kenyal bagi komponen normal (diagonal) iaitu Cll

, CRR

danCrr bagi bahan kayu dapat diperolehi menerusi data masa perambatanhalaju gelombang ultrasonik yang merambat dalam arah L, R dan T.Indeks pertama dan kedua masing-masing merujuk kepada arah perambatangelombang ultasonik dan arah sesaran zarah-zarah. Pemalar kenyal C

j.

dapat dikaitkan dengan sebutan halaju gelombang utrasonik V melaluipersamaan berikut:

Persamaan ini sebenarnya merupakan hasil penyelesaian persamaanChristoffel (Bucur 1985; Sidek et at. 1990) iaitu

C.·kl n·n· - pV28'k = 0lJ ! } 1

dengan npj merujuk kepada arah perambatan gelombang, p adalahketumpatan sampel kayu dan 8ik adalah delta Kronecker yang bernilai 1apabila nilai i bersamaan dengan nilai k.

Matlamat utama kajian ini adalah untuk menentukan pemalar-pemalarkenyal kayu tropika menggunakan kaedah dinamik ultrasonik. Konsepasas pengukuran adalah begitu mudah dengan gelombang ultrasonik 45kHz yang dipancarkan menerusi tranduser piezolektrik ke dalam bahankajian. Gelombang ini akan dikesan oleh alat pengesan gelombangultrasonik yang juga diperbuat dari bahan piezoelektrik. Bagi bahanpepejal seperi kayu, di samping gelombang longitud (membujur), terdapatjuga gelombang ricih (melintang) dan gelombang Rayleigh iaitu gelombangkenyal yang merambat pada permukaan bahan. Dalam kajian ini kaedahpemancaran terus digunakan bagi pengujian bahan kayu yang mempunyaistruktur butiran kasar. Frekuensi 45 kHz digunakan supaya gelombangultrasonik dengan jarak gelombang yang panjang mampu dirambatkan didalam sampel dan dapat melalui halangan-halangan kecil. Alat ultrasonikBPV Steinkamp (buatan German) dengan operasinya berdasarkan kaedahpemancaran mampu mengukur masa perambatan gelombang ultrasoniksehingga 999.9 f.Ls telah digunakan bagi mencirikan sifat kenyal kayutropika. Rajah blok bagi keseluruhan set eksperimen ditunjukkan padaRajah 2. Dua buah prob berbentuk kon dipilih disebabkan keadaanpermukaan kayu yang kasar dan tidak sarna rata jika ditinjau secaramikroskopik. Dengan mengetahui jarak dan masa perambatan gelombangyang merambat dalam kayu pada arah-arah tertentu, maka nilai halajugelombang ultrasonik diperolehi melalui sebutan V (=jarak/masa). Bagisetiap arah L, R dan T, lebih dari dua puluh nilai pengukuran halaju

Pertanika J. Sci. & Techno!. Vol. 3 No.2, 1995 391


dilakukan untuk setiap sampel kayu dan nilai purata halaju digunakanbagi mendapatkan nilai pemalar-pemalar kenyal.

Penjana DenyutlITtrasonik

Dellyuf600V

Sampel kayuSet PengukurMasa Rambatan

I 261.7J1sl...... ..... Transduser

Penerima

Rajah 2. Rajah skema bagi peralatan ultrasonik BPV Steinkampyang digunakan untuk mengukur masa perambatan gelombang

ultrasonik dalam Sfl;({!J sampel kayu tropika.

BAHAN KAJIANSampel kayu tropika yang dikaji diperolehi dari Institut PenyelidikanPerhutanan Malaysia (FRIM) Kl'pong yang dikeringkan seeara pendedahanpada udara. Kandungan kelembapan bagi sampel-sampel kayu inidianggarkan antara 12-15%. Jadual 1 menyenaraikan sampel kayu tropikayang dikaji berdasarkan nama tempatan dan saintifik serta nilai ketumpatanpurata setiap satunya. Sampel-sampel kayu tropika yang kering mempunyaidimensi 11 em (panjang) x 7 em (lebar) x 1 em (tebal) (ralat pengukuran± 0.01 em) dan setiap satunya mempunyai arah longitud L, tangen T danjejarian R yang merujuk kepada arah utama ketakisotropan kayu (lihatRajah 1). Nilai pemalar kenyal normal kayu dapat ditentukan dari nilaiketumpatan dan halaju gelombang (V) ultrasonik melalui persamaanberikut

dengan indeks L, R dan T mewakili arah-arah paksi utama kayu iaitulongitud, jejarian dan tangen (Rajah 1).

392 Pertanika J. Sci. & Techno!. Va!. 3 No.2, 1995

Penggunaan Kaedah Dinamik Ultrasonik bagi Menentukan Pemalar Kenyal Kayu Tropika

JADUAL 1Nama tempatan, spesis, nilai ketumpatan purata dan pemalar kenyallongitud bagi sampelkayu tropika yang dikaji menggunakan teknik dinarnik ultrasonik (dalam unit 1010 N/m2)

Sampel Nama Nama Ketum-Tempatan SaintilIk patan eLL Crr CRR C

LL(kgm·3)

Kayu kerasAl Tembusu Fagraea fragrans 800 1.47 0.20 0.23 1.40A2 Merbau Intsia palembanica 800 1.57 0.19 0.20 1.54A3 Giam Hopeaspp. 975 1.67 0.21 0.24 1.65A4 Balau merah Shorea spp. 880 1.74 0.19 0.23 1.70A5 Resak Vatica spp. 945 1.88 0.18 0.24 1.81A6 Kekatong Cynometra spp. 975 1.87 0.22 0.24 1.84A7 Chengal Neobalanocarpus heimii 945 1.96 0.23 0.24 1.96A8 Keranki Dialium spp. 960 1.56 0.22 0.23 2.01A9 Balau Shoreaspp. 975 1.73 0.21 0.23 2.01

AI0 Bitis Madhuca utilis 1105 2.19 0.24 0.26 2.38All Bakau Rhizophora spp. 1040 1.99 0.23 0.25 2.07

Kayu sederhamiBl Meransi Carallia spp. 800 1.41 0.17 0.22 1.34B2 Simpoh Dillenia spp. 735 1.49 0.16 0.19 1.43B3 Rengas Glutaspp. 835 1.52 0.20 0.23 1.49B4 Kulim Scorodocarpus 835 1.51 0.19 0.22 1.49B5 Punah Tetramesrista glabra 720 1.54 0.17 0.19 1.54B6 Merawan Hopeaspp. 690 1.62 0.19 0.23 1.55B7 Keledang Artocarpus spp. 800 1.57 0.16 0.21 1.55B8 Mengkulang Heritiera spp. 755 1.65 0.18 0.20 1.60B9 Mata ulat Kokoona littoralis 880 1.76 0.19 0.24 1.63

BI0 Kasai Pometia spp. 800 1.84 0.15 0.23 1.70B11 Kelat Eugenia spp. 800 1.77 0.17 0.23 1.76B12 Tualang Koompassia excelsa 835 1.81 0.17 0.20 1.78B13 Merpauh Swietonia spp. 755 1.87 0.15 0.19 1.81Bl4 Kempas Koompassia 880 1.90 0.19 0.24 1.86B15 Kapur Dryobalanops spp. 755 1.98 0.18 0.21 1.80B16 Keruing Dipterocarpus 880 2.01 0.19 0.23 2.23

KayulembutCl Terentang Campnosperma spp 435 1.09 0.17 0.18 0.70C2 Jelutong Dyera costulata 465 1.19 0.13 0.18 0.80C3 Pulai Alstonia spp. 465 1.39 0.14 0.20 0.71C4 Sesendok Endospermum 530 1.40 0.16 0.19 0.85

malaccensis

C5 Melantai Hopea macroptera 530 1.21 0.17 0.21 0.79C6 Geronggang Cratoxylon 545 1.25 0.20 0.22 0.80



Uadual 1) sambungan

Sampel Nama Nama Ketum-Tempatan SaintiIIk patan C

LL CIT CRR CLL(kgm·3)

C7 Meranti Shoreaspp. 545 1.40 0.21 0.24 1.94merah muda

C8 Petai Parkiaspp. 545 1.13 0.12 0.23 1.07C9 Perupok Lophopetalum spp. 560 1.38 0.20 0.22 1.26

C10 Machang Mangifera spp. 560 1.45 0.18 0.21 1.43C11 Kedondong Burseraceae 575 1.45 0.13 0.24 1.29C12 Terap Paratocarpus spp. 575 1.34 0.16 0.22 1.20C13 Panarahan Myristicaceae 595 1.45 0.16 0.18 0.94C14 Medang Lauraceae 610 1.53 0.16 0.22 1.26C15 Ramin Gonystylus bancanus 625 1.46 0.17 0.23 1.64C16 Kayu getah Hevea brasilliensis 640 1.32 0.17 0.20 0.92C17 Mersawa Anisoptera spp. 640 1.37 0.18 0.21 1.26CI8 Melunak Pentace spp. 655 1.31 0.18 0.20 1.20C19 Meranti Shoreaspp. 655 1.38 0.20 0.22 1.21

kuningC20 Meranti Shoreaspp. 675 1.46 0.17 0.20 1.94

putehC21 Kungkur Pithecellobium spp. 675 1.26 0.17 0.22 1.07C22 Meranti Shorea uliginosa 675 1.50 0.16 0.18 1.47

bakauC23 Sepetir Sindora spp. 675 1.49 0.16 0.20 1.36C24 Merawan Hopeaspp. 690 1.59 0.11 0.19 1.55C25 Cerutu Parashorea lucida 690 2.06 0.17 0.20 2.06C26 Bintangor Calophyllum spp. 690 1.84 0.19 0.22 1.43C27 Durian Durio spp. 690 1.62 0.18 0.21 1.58C28 Kembang Scaphium spp 705 1.64 0.20 0.22 1.70

semangkokC29 Meranti Shoreaspp. 705 1.54 0.21 0.24 1.39

Data pemalar kenyal CLL* dilaporkan oleh (MTIB) Malaysia Timber Industry Board(1986) .

HASIL DAN PERBINCANGAN

Perubahan nilai-nilai pemalar kenyal terhadap ketumpatan pada arah L, Rdan T bagi sampel kayu tropika yang diukur pada suhu bilik ditunjukkanpada Rajah 3 (a)-(c) dan nilai puratanya dinyatakan dalam Jadual 1.Perbezaan nilai pemalar kenyal bagi satu spesis kayu dengan spesis yanglain adalah kerana kayu merupakan bahan yang bersifat tak homogensamaada pada jenis yang sama atau jenis yang berbeza. Struktur asasbinaan kayu akan menentukan nilai ketumpatan dan sifat fizik kayu yanglain. Secara amnya struktur kayu keras terdiri dari bahan molekul makro

394 Pertanika J. Sci. & Techno!. Va!. 3 No.2, 1995

Penggunaan Kaedah Dinarnik Ultrasonik bagi Menentukan Pemalar Kenyal Kayu Tropika

(40-45% hablur polimer alfa selulos, 15-35% hemiselulos dan 17-25%amorfus lignin) dan bahan bermolekul rendah (bahan organan - ekstraktifdan bahan tak organan). Manakala kayu lembut pula mengandungi 4045% selulos, 20% hemiselulos dan 25-35% lignin. Peratusan ini berbezadari satu jenis dengan jenis kayu yang lain. Kandungan selulos tidakbanyak berbeza bagi kayu jenis keras berbanding dengan kayu lembut(Desch 1980). Molekul selulos diorientasikan sepanjang paksi serabut(atau sepanjang butiran kayu) bagi menghasilkan kekuatan serta kekenyalanyang maksimum pada arah L (Patton 1986). Hal ini jelas diperhatikan dariRajah 3(a)-(c), corak pemalar kenyal bagi kayu-kayan tropika adalah C

LL

>CRR>Crr sepertimana yang diperolehi oleh Bucur (1983) yang mengkajikayu beech. Perbezaan inilai CLL' CRR dan Crr bagi setiap spesis kayu kajian(lihat Jadual 1) adalah di antara lain bergantung kepada struktur binaankayu, ketumpatannya dan juga kelembapan bandingan persekitaran. Datadata ini adalah unik bagi setiap sampel kayu kajian dan amat berkait rapatdengan kualiti kayu berkenaan. Analisis korelasi linear ke atas nilai pemalarkenyal dan ketumpatan bagi sampel-sampel kayu tropika setiap satunyapada arah L, R dan T menggunakan komputer menunjukkan terdapatnyaperkaitan yang berikut;

i) CLL

=1.2758 X 1O-3p + 0.643228 (r= 0.59), arah Lii) CRR = 7.1621 X 1O-5p + 0.16402 (r = 0.31), arah Riii) Crr = 9.43053 x 1O-5p + 0.112512 (r = 0.31), arah T

dengan CLL'CRR'~ diukur dalam unit (x 1010 Nm2) dan p dalam unit kgm-3.

2.50

N

E........Z

~2.00

x'--"

o>cQ)~

'- , .50ooEQ)

0...

1.00400

Arch L

600 BOO 1000 1200Ketumpatan Kayu (kgjm 3 )


Sidek Hi .\hdul A~iz, Abdul Halim Shaari dan Chow Sai Pew

0.30

N

E'-..z~o 0.25

o>.cQ)

.Y

L 0.20ooEQ)

rArch R

j-11J

i....--'" ._~.~._~,._~'U'__"-J.'~·_L'~· ~,'_',~;_'_L, ....., '-,Wi'U'__"-1.'-.L.J,i

0.30

40(1 600 800 1000Ketumpatan Kayu (kg/m 3)

1200

E'-..0.25Z

o-0

00.20>.cQ)

.Y

LoE0.15

~ I

0.10400

Arch T

600 800 1000Ketumpatan Kayu (kg/m 3)

1200

396

Rajah 3. Perubahan pemalar kenyal terhadap ketumpatanpada (a) arah L, (b) arah R dan (c) arah T

bagi 56 spesis kayu tropika

Pertanika J. Sci. & Techno!. Vo!. 3 No.2, 1995


Nilai pemalar kenyal longitud kayu yang didapati dari eksperimenultrasonik lebih tinggi berbanding dengan nilai pemalar kenyal kayu yangdilaporkan oleh MTIB (1986) menggunakan teknik statik. Rajah 4menunjukkan perkaitan di antara pemalar kenyal C

LLyang diukur

menggunakan kaedah ultrasonik dan kaedah statik bagi menentukan sejauhmana penyisihan kedua-dua teknik bagi sampel-sampel kayu tropika. Darieksperimen ultrasonik didapati nilai pemalar kenyal CLL bagi kayu tropikayang berketumpatan kurang dari 840 kgm3 lebih tinggi berbanding dengannilai pemalar kenyal kayu yang dilaporkan oleh MTIB (1986). Analisisseterusnya terhadap data-data ini menunjukkan terdapat penyisihan yangagak tinggi bagi kayu tropika yang mempunyai ketumpatan yang rendah,tetapi bagi kayu jenis sederhana dan keras, nilai purta perbezaan antarakedua-dua teknik ini tidak melebihi 5%. Bagi kelompok kayu sederhana dankeras, teknik ultrasonik berkeupayaan memberikan data-data pemalar kenyalsepertimana dari teknik pengukuran statik. Perbezaan yang ketara inidisebabkan oleh isyarat gelombang ultasonik yang meranlbat di dalamsampel kajian diterima dalam masa yang amat singkat, menyebabkan tegasanyang amat kecil terhasil dari gelombang ultrasonik yang berfrekuensi antara40 hingga 45 kHz ini. Hasil yang diperolehi bersesuaian dengan hasil yangdiperolehi oleh Bucur (1985) iaitu nilai pemalar kenyal bagi kayu beechyang dikaji dengan menggunakan kaedah dinamik ultrasonik didapati lebihtinggi berbanding dari kaedah statik (lihatJaduall dan Rajah 4). Bodig andJayne (1982) juga melaporkan bahawa nilai pemalar kenyal kayu yangdiperolehi dari kaedah dinamik agak tinggi (sekitar 10-15%) berbandingdari kaedah lenturan statik bagi sejalur kayu; proses pelenturan kayutersebut akan melibatkan canggaan ricih. Faktor ini disebabkan olehperbezaan keadaan termodinamik bagi ujian statik dan ultrasonik. Secarateorinya pemalar kenyal yang terlibat dalam pengukuran statik adalahbersifat isoterma sedangkan bagi pengukuran dinamik ultrasonik ia lebihmematuhi hukum adiabatik terutama apabila frekuensi gelombang ultrasonikmeningkat. Corak taburan data-data pengukuran dari kedua-dua teknikadalah seragam dengan sisihan taburan tidak melebihi 10% dan inimenunjukkan bahawa teknik ultrasonik berupaya menyediakan data-data pemalarkenyal sebagai suatu faktor pencirian untuk menentukan kualiti kayu.

KESIMPUIAN

Secara keseluruhan dapat disimpulkan kaedah dinamik ultasonik dapatdigunakan bagi kayu tropika. Teknik ini dapat digunakan bagi tujuanpengujian dan pempiawaian bahan berkayu kerana nilai pemalar kenyalyang didapati melalui kaedah ini walaupun lebih tinggi tetapi peratusanralatnya kecil iaitu kurang dari 10 peratus dari nilai yang diperolehi menerusikaedah statik. Bagi kayu tropika corak pemalar kenyal adalah CLL>CRR>CTI

dan terdapat satu korelasi yang linear di antara nilai pemalar-pemalarkenyal dan ketumpatan bagi 56 sampel kayu tropika yang dikaji.



2.50

Aroh LN

E~2.00

5?O

•

o

• : 2

• IV./"

o /"/"

/" .

...... o. • 0...... s o. •

"01.50>,cQ)

.Yo

L

..2E1.00Q)

0.. .. ..,..

9 'U' 'U' Kcedch Ultrcsonik~ Kaedah Statlk

12000.50

400 600 BOO 1000Ketumpatan Kayu (kg/m 3)

Rajah 4. Perbandingan hasil pengukuran pemalar kenyal CLL

menggunakan kaedah dinamik ultrasonik dankaedah statik (MTIB 1986)

PENGHARGAAN

Projek penyelidikan ini dibiayai sepenuhnya oleh Kementerian Sains,Teknologi dan Alam Sekitar Malaysia menerusi geran penyelidikan jangkapanjang IRPA/RME, Kod no. 1-07-05-062. Ucapan terima kasih ditujukankepada Encik Zaidi Hassan, Cik Tijah Pardi dan staf Jabatan Fizik di atasperbincangan dan bantuan teknikal.

SIDEK HJ. ABDUL AZIZ, ABDUL HALIM SHAARIdan CHOW SAl PEW

Jabatan Fizik, Fakulti Sains dan Pengajian Alam SekitarUniversiti Pertanian Malaysia43400 UPM Serdang, Selangor, Malaysia.

RUJUKANBODIG, J. and B.A. JAYNE. 1982. Mechanics of Wood and Wood Composites. New York: Van

Nostrand Reinhold.

BUCUR, V. 1983. Ultrasonic method for measuring the elastic constants ofwood incrementcores bored from living trees. Ultrasonics May: 116-126.

BUCUR, V. 1985. Ultrasonic, hardness and x-ray densitometric analysis ofwood. UltrasonicsNovember: 269-275.

398 Pertanika J. Sci. & Techno!. Vo!. 3 No.2, 1995


BUCUR, V. and F. FOCABOY. 1988. Surface wave propagation in wood: Prospective method fordetermination of wood off-diagonal terms of stiffness matrix. Ultmsonics November:344-347.

DESCH, H.E. 1980. Timber Its Structure, Properties and Utilisation. London: McMillan.

MAL4,.YSIAN TIMBER INDUSTRY BOARD (MTIB). 1986. 100 Malaysian Timbers. Kuala Lumpur:MalaysianTimber Industry Board.

PATTON, WJ. 1986. Materials in Industry. NewJersey: Prentice Hall.

SIDEK H]. AB. AzIZ, H]. SALLEH HARON, ABDUL HALIM SHAARI, CHOW SAl PEW, GAZALI AHMAD danMOHD. SALLEH MOHD DEN!. 1990. Pendekatan ujian tak memusnah bagi penganalisaanciri kenyal bahan kayu. In: Seminar Kebangsaan Fizik Dalam Industri, 19-20 September(1990) Universiti Teknologi Malaysia, Sekudai,Johor.

SZYMANI, R. and K.A. McDoNALD. 1981. Defect detection in lumber; state of the art. ForestProductsJournal31 (11): 34-43.

PertanikaJ. Sci. & Technol. Vol. 3 No.2, 1995 399

Ultrasonic detection of knots, cross grain and bark pockets in wooden pallet partsKabir, M. F..1, Schmoldt, Daniel L.2 and Schafer, Mark E.3

ABSTRACT

This study investigates defect detection in wooden pallet parts using ultrasonic scanning. Yellow-poplar (Liriodendrontulipifera, L.) deckboards were scanned using two rolling transducers in a pitch-catch arrangement to detect unsound andsound knots, bark pockets and cross grain. Data were collected, stored, and processed using LabView™ software. Sixultrasonic parameters—three involving time-of-flight, two involving ultrasound pulse energy, and one using ultrasoundpulse duration—were measured for each defect type. Four of the six parameters were affected by transmission throughunsound knot regions. Sound knots also showed decreased values forthe energy-related parameters. All ultrasonicparameters changed sharply for bark pockets. Cross grain also affected ultrasound energy transmission. Smallcoefficients of variation for repeated measurements indicates that this scanning arrangement is stable and scanning ratehas little effect on the measurements. Results indicate that on-line detection of these defects is possible by ultrasonicscanning.

INTRODUCTION

Wooden pallets are the largest single use of sawn hardwood logs, consuming around 40% of all US hardwood lumberproduced. Every year, over 400 million wooden pallets are manufactured using 4.5 billion board feet of hardwoodlumber. Pallets are integral to the US transportation infrastructure, and wood is the primary raw material used in pallets.Most wooden pallets consist of two parts, stringers—the structural center members that carry the product load—anddeckboards—the top and the bottom members that provide dimensional stability and product placement. There are manytypes of pallet designs—depending on the size, number, and position of stringers and deckboards—but most are producedfrom solid wood, lumber, or from the center cant material of logs. Most solid wood material, that is manufactured intopallet parts, is low quality (having a high percentage of defects) and therefore has less market value for other solid woodproducts.

The most common defects in pallet parts are knots, cross grain, reaction wood, bark pockets, insect holes, splits, decay,shake, and wane. For quality pallet production, it is necessary to detect defects during manufacturing and then grade andsort parts prior to pallet assembly. An economic analysis by Schmoldt et al. (1993) indicated that improved palletdurability and performance imparts much greater value to carefully manufactured pallets. Current pallet manufacturingoperations, however, do lend themselves to manual grading and sorting of parts. Therefore, this research program aims todevelop automated techniques that include scanning, defect detection, and grading.

Previous work has investigated a variety of ultrasonic waveform parameters to detect defects in wood (McDonald 1980,Lemaster and Dornfeld 1987, Patton-Mallory and DeGroot 1990, Ross et al. 1992, Schmoldt et al. 1994, Fuller et al.1995, Kabir et al. 1997). Most of these studies were conducted using laboratory samples or surfaced lumber, whereas inpractice, conditions may be quite different. This is especially the case in the pallet industry where low quality, unsurfacedwood must be scanned. Furthermore, simple ultrasonic propagation velocity alone may not be sufficient to detect mostdefects. Other ultrasonic parameters, e.g. peak amplitude, time to peak amplitude, centroid time, root mean square of thetime domain, pulse length, energy, frequency domain modes, frequency domain energy, etc., may be required. Recently,Halabe et al. (1993, 1994, 1996) conducted a study using ultrasonic frequency analysis for decay detection in wooden

1 Postdoctoral Fellow, Dept. of Wood Science and Forest Products, Virginia Tech, Blacksburg VA 24061-05032 Research Forest Products Technologist, USDA Forest Service, Biological Systems Engineering Dept., 460 Henry Mall,Madison WI 53706-15613 Vice-President, Ultrasound Technology Group, Forest Products Division, Perceptron Inc., 2935 Byberry Road, HatboroPA 19040

timbers. They reported that frequency domain analysis can significantly increase prediction sensitivity for modulus ofelasticity and strength of clear and defective wood under controlled laboratory conditions.

More research needs to be done comparing different ultrasonic parameters’ sensitivities to defects. The final goal of thisstudy is to develop an automated ultrasonic scanning system for defect detection in pallet parts. This initial experimentwas carried out to determine which ultrasonic parameters respond well to particular defects and also to observe thereliability and repeatability of data collection using pressure-contact rolling transducers.

MATERIALS AND METHODS

Scanning equipmentA materials handling system was designed by the Forest Products Division of Perceptron and purchased by the USDAForest Service. It consists of in-feed and out-feed roll-beds and an ultrasonic scanning ring where rolling transducers aremounted. Perceptron provided the necessary electronics and software to control material movement, signal generation,and waveform capture and analysis. Pallet parts move through the system lying on a face and pitch-catch ultrasonictransmission propagates through the part’s thickness. The transducers can be operated using a range of frequencies in 90-180 kHz. A single scan line of data is collected during each pass of the part through the scanner. The desire resolution ofthis scan line (number of waveforms per inch) can be achieved by controlling roller speed and number of pulses/sec. Datawere processed to create six ultrasonic parameters—time of flight-centroid (TOF-centroid), time of flight-energy (TOF-energy), time of flight-amplitude (TOF-amplitude), pulse length (PL), energy value (EV), and energy/pulse value (EPV),to be discussed further below.

Definition of the ultrasonic parameters4

The most important parameters relate to the energy in the received signal. Wave energy is expressed as the time integralof the voltage squared:

E = v2 (t)dt� (1)

Because of the wide variation in transmitted energy levels between sound wood and defects, it is more convenient toexpress the energy on a logarithmic basis. The energy value (EV) is derived from the energy E, and is expressed indecibels (dB). By convention, this is a negative number, with lower signals (containing less energy) being more negative.

The pulse length parameter (in units of microseconds) is simply the time for which the pulse is “on”, and depends uponthe transmitted ultrasound frequency. These two parameters, energy value and pulse length, can be combined to provide asingle parameter, which is known as energy/pulse value (EPV). Again, because of the wide range of energy levels, EPVis also expressed on a logarithmic scale (in dB).

TOF-energy is calculated as the time at which the energy integral (Equation 1) crosses a threshold value—as a percentageof the final (maximum) value. If the threshold value is, for instance, 40%, then TOF-energy is simply the time at whichthe integral value reaches 40% of the final value. Similarly, TOF-amplitude is the time at which the amplitude of thesignal first reaches, for instance, 40% of the maximum amplitude. TOF-centroid is the time to the centroid of the timewaveform, which is based on the ratio of the first- and zero-th order moments. No frequency domain parameters werecalculated in this study.

Data collectionTwelve, fresh-cut yellow-poplar boards 40 inches in length and approximately 1/2 inch thickness were collected from apallet manufacturer. The boards were kept in cold storage to reduce their drying rate. A line was drawn on each boardthrough a defect of interest and scanning was performed along this line. All parameters were calculated for each scan.Three boards were scanned for each defect type. The boards were scanned with two scanning rates—10 waveforms/inch(70 ft/m roller speed) and 4 waveforms/inch (220 ft/m roller speed). Each board scan line was repeated ten times for eachdefect type and scanning rate. All measurements were made at 120 kHz transmitting frequency and 500 kHz samplingfrequency.

4 For proprietary reasons, full details regarding the ultrasonic parameters and their measurement cannot be released at thistime.

RESULTS AND DISCUSSION

Fig. 1 depicts graphs of ultrasonic parameters plotted against board length for a scan line that includes an unsound knot.These data are taken from one of the sample boards; other boards behaved in a similar manner. Data collected at 10waveforms/inch and 4 waveforms/inch are also shown. The graphs show that PL and TOF-centroid increase sharply withthe unsound knot. TOF-amplitude and TOF-energy seem relatively unaffected, however. On the other hand, the presenceof an unsound knot causes a dramatic decrease in EV and EPV. Scanning rate does not appear to affect parametermeasurements (Figs. 1c & 1d); both, EV and EPV have nearly identical values at scanning rates of 10 waveforms/inchand 4 waveforms/inch. In addition to a dramatic loss in transmitted energy, unsound knots also tend to spread out thereceived waveform, increasing the pulse length and centroid value.

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Figure 1. Ultrasonic measurements taken at 10 waveforms/inch along the length of a scan line (x-axis) are shown for allsix parameters (a, b, c). An unsound knot is present between the 5- and 10-inch locations. For comparison, the last graph

(d) shows measurements made at 4 waveforms/inch for EV and EPV.

The effects of sound knots on ultrasonic parameters appear in Fig. 2. PL, TOF-centroid, TOF-amplitude, and TOF-energy seem unaffected by the sound knots, but EV and EPV exhibit a sharp decrease around the regions of sound knots.While unsound knots contain incipient or advanced decay or have a complete separation of knot from surrounding wood(loose), sound knots influence wood properties by interrupting the longitudinal direction of wood fibers (Anon 1987).Wood fibers around a sound knot are distorted, developing localized cross grain which may have substantial impact onultrasonic measurements. While it is well established that TOF measurements can detect the presence of sound knots(e.g., McDonald 1980, Kodama and Akishika 1993, Schmoldt et al. 1996; Kabir et al. 1997), it appears, from this study,that energy losses (Figs. 2c & 2d) are more sensitive than TOF measurements (Figs. 2a & 2b). Like unsound knots,sound knots do not have any noticeable effect on measurements at different scanning rates (Figs. 2c & 2d).

Bark pockets contain some bark in place of wood, so one would expect them to have a significant effect on ultrasonicmeasurements. Fig. 3 illustrates how the ultrasonic parameters vary with bark pockets. PL, TOF-centroid, and TOF-energy increase sharply with bark pockets whereas EV and EPV decrease. The tremendous increase or decrease of theparameters may be associated with the presence of a small split and decay in the bark pocket of this sample board.

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Figure 2. Ultrasonic measurements taken at 10 waveforms/inch along the length of a scan line (x-axis) are shown for allsix parameters (a, b, c). Sound knots are present between the 12- and 18-inch locations and also between the 32- and 38-

inch locations. For comparison, the last graph (d) shows measurements made at 4 waveforms/inch for EV and EPV.

Cross grain represents a generalized slope of grain; it is often measured as a ratio of perpendicular deviation versuslongitudinal reach, e.g. 1:10 or 1:6. Deviations from longitudinal (X direction) are measured in both the Y (dy) and Z (dz)directions, with the resultant cross grain d calculated as in (2). Ultrasound propagation is known to differ with graindirection (anisotropy), so one would expect several measured parameters to be affected. PL shows high variability in thecross grain region (Fig. 4a). There are also some decreases in EV and EPV measurements, but not as dramatic as barkpockets or knots. Again scanning rate showed no effect on data collection.

d = dy2 + dz

2 (2)

To test the repeatability of measurements and the reliability of the data, boards were scanned ten times with coefficientsof variation calculated. These are presented in Fig. 5 for a bark pocket scan line using the board appearing in Fig. 3. Thelow CV% values suggest that the repeatability of data collection using pressure-contact rolling transducers is very good.Some inflation of CV values likely occurs because of errors in data point registration between repeated scans.

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(d) shows measurements made at 4 waveforms/inch for EV and EPV.

CONCLUSIONS

There appear to be significant, defect-specific differences in several ultrasonic parameters for yellow-poplar deckboards.Most of the ultrasonic parameters examined here change rapidly in the region of defects, which can be used for on-lineinspection of defects. Because species and individual pallet parts will vary in the magnitude of various ultrasonicparameters, relative changes may prove to be the most informative and diagnostic characteristic of ultrasonic signalpropagation. Energy value and energy/pulse value were found to be the most sensitive ultrasonic parameters for thedefects examined in this study. Bark pockets and unsound knots are more easily detected compared to sound knots andcross grain. Small values for coefficients of variation indicate that repeatability and reliability are acceptable. Scanningrate has little effect on data collection, which means that it should be possible to scan at relatively high industrial speeds.

Continued work in this project will expand data collection further. Other wood species will be tested to determine ifsignificant inter-specific differences exist with respect to the ability of ultrasonic parameters to distinguish defect types.We also plan to examine still other ultrasonic parameters, e.g., in the frequency domain, that have been shown todiscriminate between certain defect types. Eventually, multiple scan lines will be collected for each board to enable us tocreate ultrasonic 2-D maps (images). Such maps will actually be 3-D (multi-dimensional), as the 2-D maps will havevalues at each scan point for a variety of useful ultrasonic parameters. The contribution of several parameters shouldproduce fairly accurate defect characterization at each scan point on the pallet part.

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measurements made at 4 waveforms/inch for EV and EPV.

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3 are the source of the data.

REFRENCES

Anon. 1987. Wood Handbook: Wood as an Engineering Material. Agriculture Handbook 72, USDA Forest Service,Madison. 460pp.

Fuller, J.J., Ross, R.J., and Dramm, J.R. 1995. Non destructive evaluation of Honeycomb and surface check in Red Oaklumber. Forest Products Journal 45(5): 42-44.

Halabe, H.B., GangaRao, H.V.S., and Hota V.R. 1993. Nondestructive evaluation of wood using ultrasonic frequencyanalysis. Pages 2155-2160 in D.O. Thompson and D.E. Chimenti, (Eds.) Review of Orogress in QuantitativeNondestructive Evaluation Vol. 13. New York, Plenum Press.

Halabe, U.B., GangaRao, H.V.S., and Solomon, C.E. 1994. Non destructive evaluation of wood using ultrasonic dr-coupled trasducers. Pages 2251-2256 in D.O. Thompson and D.E. Chimenti, (Eds.) Review of Progress inQuantitative Nondestructive Evaluation Vol. 12. New York, Plenum Press.

Halabe, H.B., GangaRao, H.V.S., Petro, S.H., and Hota V.R. 1996. Assessment of defects and mechanical properties ofwood members using ultrasonic frequency analysis. Materials Evaluation 54(2): 314-352.

Kabir, M.F., Sidek, H.A.A., Daud, W.M., and Khali, K. 1997. Detection of knot and split of rubber wood by non-destructive ultrasonic method. Journal of Tropical Forest Products 3(1): 88-96.

Kodama, Y. and Akishika, T. 1993. Non-destructive inspection of of defects in wood by use of pulse-echo technic ofultrasonic waves. I. Measurements of enclosed knots. Mokuzai Gakkaishi 39(1): 7-12.

Lemaster, R.L and Dornfield, D.A. 1987. Prelimanary investigation of the feasibility of using acoustic-ultrasonics tomeasure defects in lumber. Journal of Acoustics Emission 6(3): 157-167.

McDonald, K.A. 1980. Lumber defect detection by ultrasonics. Res. Pap. FPL-311, Madison WI: USDA Forest Service.Forest Products Lab. 20p

Patton-Mallory, M. and DeGroot, R.C. 1990. Detecting brown-rot decay in southern yellow pine by acousto-ultrasonics.Pages 29-44 in Proceedings of the 7th International Nondestructive Testing of Wood Symposium, September 27-29, 1989, Madison WI, Conference and Institute, Washington State University.

Ross, R.J., Ward, J.C., and Tenwolde, A. 1992. Identifying bacterially infected oak by stress wave non-destructuveevaluation. FPL-RP-512, USDA Forest Service, Madison

Schmoldt, D.L., McCleod III, J.A., and Araman, P.A. 1993. Economics of grading and sorting pallets parts. ForestProducts Journal 43(11/12): 19-23.

Schmoldt, D.L., Morrone, M., and Duke Jr., J.C. 1994. Ultrasonic inspection of wooden pallets for grading and sorting.Pages 2161-2166 in D.O. Thompson and D.E. Chimenti, (Eds.) Review of Progress in QuantitativeNondestructive Evaluation. Vol. 12. New York, Plenum Press.

Schmoldt, D.L., Nelson, R.M., and Ross, R.J. 1996. Ultrasonic defect detection in wooden pallet parts for quality sorting.In S. Doctor, C. A. Lebowitz, and G. Y. Baaklini (Eds.) Nondestructive Evaluation of Materials and Composites,SPIE 2944: 285-295.

Dielectric and ultrasonic properties of rubber wood. content, grain direction and frequency

M.F. Kabir, W.M. Daud, K. Khalid, H.A.A. Sidek

Holz als Roh- und Werkstoff 56 (1998) 223-227 �9 Springer-Verlag 1998

Effect of moisture

Dielectric properties of rubber wood have been studied at low and microwave frequencies with different moisture content and grain direction. The ultrasonic properties were studied with pulsed longitudinal waves of frequency 45 kHz. Two anisotropic directions have been considered for this study - parallel and perpendicular to grain. The low frequencies were of 0.01, 0.1, 1.0, 10 and 100 Hz and microwave frequencies were of 1, 2.45, 6, 8, 10, 14 and 17 GHz. The moisture content affected the dielectric constant and dielectric loss factor both at low and microwave frequencies. The moisture content above 30% showed little influence on dielectric properties whereas it increases linearly from 0 to 30% in both the grain directions at low frequencies. A continuous increase of dielectric properties was obtained with the increase of moisture content at microwave frequencies and the trend becomes concave upward. Dielectric properties increase as the frequencies increase except dielectric loss factor at microwave frequencies where reverse trends were observed. Little change of dielectric loss factor was obtained at frequencies above 6 GHz. The parallel to grain direction showed higher dielectric constant and dielectric loss factor compared to perpendicular to grain direction. This dielectric anisotropy of wood may be attributed due to the microscopic, macroscopic molecular as well as chemical constituents of wood. Ultrasonic properties were also affected considerably by the moisture content and grain direction. The dried wood showed higher ultrasonic velocity and elastic stiffness constant compared to green wood. The parallel to grain direction exhibits higher ultrasonic velocity and elastic stiffness constant than perpendicular to grain.

Oielektrische und UltraschalI-Eigenschaften von Hevea brasiliensis: EinfluB yon Feuchte, Faserrichtung und Frequenz

Die dielektrischen Eigenschaften yon Hevea brasiliensis wurden bei niedriger und Mikrowellenfrequenz sowie unterschiedlichen Feuchten und Faserrrichtungen unter- sucht. Die Ultraschalleigenschaften wurden mit gepulsten Longitudinalwellen von 45 kHz bestimmt. Beide Bestim- mungen erfolgten parallel und senkrecht zur Faser. Als niedrige Frequenzen wurden 0,01, 0,1, 1,0, 10 und 100 Hz eingesetzt, im MikroweUenbereich 1, 2, 4, 5, 6, 8, 10, 14 und 17 GHz. Die Feuchte beeinflu~t die Dielektriziffits- konstante und den Verlustfaktor in beiden Frequenzbe- reichen. Zwischen 0 und 30% Feuchte steigt die Dielektrizit~itskonstante bei niedrigen Frequenzen linear

M.F. Kabir, W.M. Daud, K. Khalid, H.A.A. Sidek Department of Physics, Universiti Putra Malaysia, 43400, Serdang, Selangor, Darul Ehsan, Malaysia

mit der Feuchte an. Ober 30% ergeben sich nur geringe Anderungen. Im Mikrowellenbereich steigt die Dielektri- zit~itskonstante fiber den gesamten Feuchtebereich expo- nentiell an, wogegen der Verlustfaktor bei hohen Frequenzen bis 6 GHz abnimmt; oberhalb davon wurden nur geringe Anderungen beobachtet. Auch die Ultraschall- Eigenschaften werden deutlich yon der Feuchte und Fa- serrrichtung beeinflut~t. In trockenem Holz sowie parallel zur Faserrichtung sind Geschwindigkeit und Elastizitiits- modul hSher als in feuchtem Holz und senkrecht zur Fa- ser.

1 Introduction The dielectric properties of rubber wood are important for understanding the structure of wood and cellulose at molecular level as well as for measuring the density, moisture content by nondestructive method. It was reported that the detection of knot, defects, spiral grain, etc. are also possible by measuring dielectric properties (Martin et al. 1987). The dielectric properties of wood are essential for its efficient use in engineering application where it is subjected to alternating fields, such as in large power transformers. It plays a significant role in heating, drying and gluing and thus, improving the quality of the wood and wood based materials.

The dielectric properties of wood vary with physical parameters such as moisture content, density, grain direction and temperature. They also vary in an extremely complicated fashion with frequency. The overall effects of these parameters on dielectric properties of wood interact with each other and add to the complexities of the dielectric properties. Though there are some reports on the variation of dielectric properties with these parameters, most of them deal with low moisture content and with few frequencies (James 1975, 1977; Kroner and Pungis 1952; Nanassy 1972; Norimoto and Yamada 1976; Rafalski 1967; Skaar 1948; Vermas 1974, 1976; Venkateswaran and Tiwari 1964). The present work deals with the variation of dielectric properties, such as dielectric constant and dielectric loss factor of rubber wood with moisture content, grain direction and frequency.

The conventional static test (destructive) for evaluating the wood properties is quite an expensive, time consuming process and it would take decades of work to accomplish the test for various species. As an alternative to the static test, several methods such as vibration, X-ray radio graphics, pilodyn wood testers have been employed for evaluating wood properties (Parker and Kennedy 1973). The ultrasonic technique may be suitable for the rapid determination of the mechanical properties. It is also reported that the detection of defects such as honeycomb, check, split, knot, etc., are also possible by ultrasonic method (James et al. 1995; Kabir et al. 1997). The effect of

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moisture content and grain direction on the ultrasonic properties have also been discussed in this paper.

2 Materials and methods Rubber wood ( H e v e a b r a s i l i e n s i s ) was supplied by the Farm Department of Universiti Putra Malaysia. Specimens were prepared in the form of discs of 35-40 m m in diameter and 3.0-3.5 m m in thickness for the measurement of dielectric properties at low frequencies; and 22-30 m m in diameter and 3.5-5.0 m m in thickness at microwave frequencies. Two main anisotropic directions have been considered for this study - parallel to grain and perpendicular to grain. Both surfaces of the specimen were smoothed with sand paper so that it made good contact with the electrodes. The low frequency measurements were carried out with a parallel plate electrode at frequencies from 10 -2 to 102 Hz by using Dielectric Spectrometer consisting of Chelsea Dielectric Interface (CDI 4c/L-4, Dielectric Instrumentation, UK) and Frequency Response Analyzer (SI 1255, Schumberger, UK). The microwave experiments were done with a 4 m m open ended coaxial sensor (HP 8507 M) and computer controlled Network Analyzer (HP 8720B). Frequenices used for this study were of 1, 2.45, 6, 8, 14 and 17 GHz. Following the proper ca- libration method, the accuracy of the measurement is about +5% for dielectric constant and +3% for dielectric loss factor.

Ultrasonic measurements were carried out with a commerical ultrasonic tester (BP V - Steinkamp, Ger- many) of 45 kHz pulsed longitudinal waves. Two conical transducers were used for transmitting and receiving the pulses. Transmission times were digitally displayed and recorded manually. The ultrasonic velocity was calculated by dividing the specimen length with transmitting time. The elastic stiffness constant was determined using the following equation:

e l i = p V 2

whereC/j is the elastic stiffness constant, p is the density of the wood specimen and V is the ultrasonic velocity.

To measure the dielectric and ultrasonic properties at different moisture content, initially the specimens were fully soaked in water for a sufficiently long time to achieve full saturation. After that the weight of the specimen was taken and measurement was carried out. It was then dried in air to reduce the moisture. This cycle of measuring, drying and weighing was repeated until the specimen showed no change of weight by drying. Finally the oven dried weight of the specimen was taken by drying in an electronic oven at 100 + 3 ~ for 24 hours.

3 Results and discussions The dielectric constant of rubber wood at frequencies 0.01, 0.1, 1.0, 10 and 100 Hz in parallel and perpendicular to grain directions are presented in log scale in Figs. 1 and 2 respectively. Figures 3 and 4 show the variation of dielectric loss factor with moisture content in both directions. Regardless of grain direction, two distinct regions of moisture content have been found for the variation of dielectric properties at low frequencies- one below 30% and the other above the 30% moisture content. The dielectric constant and dielectric loss factor increases as the moisture content increases form 0 to 30% and thereafter a slight increase of the dielectric properties are observed

8

7 . . . . . . . . . . . . . . . C I + = I

E 6 . . . . . . . . . . . . ~'.i . . . . / . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 ......

...... .iiiiiii iii ii iiii iiii iiii iiii il - . t 2 . . . .

i i i i i i i i i

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Fig. 1. Dielectric constant vs moisture content in parallel to grain direction at low frequency [] o.oi Hz, + o.1 Hz, * 1.o Hz, �9 zo.o Hz, x lOO Hz Bild 1. Dielektrizitiitskonstante parallel zur Faser in Abh~ingigkeit yon der Feuchte bei niedriger Frequenz

8

7 . . . . . . . . . . . . . . . . . . . . . . . . r . . . . . . . . . . . . . . . . . = . . . . . . . . . . . . .

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~5

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Fig. 2. Dielectric constant vs moisture content in perpendicular to grain direction at low frequency [] o.ol Hz, + o.I Hz, * x.o Hz, �9 IO.O HZ, X 1OO HZ Bild 2. Dielektrizit~itskonstante senkrecht zur Faser in Abh~ingigkeit yon der Feuchte bei niedriger Frequenz

-2 ! , , i i i ~ i i i

I0 20 30 40 50 60 70 80 90 1 O0 Moisture content (%)

Fig. 3. Dielectric loss factor vs moisture content in parallel to grain direction at low frequency [] o.ol Hz, + o.1 Hz, * x.o Hz, i lo.o Hz, x lOO Hz Bild 3. Verlustfaktor parallel zur Faser in Abhiingigkeit yon der Feuchte bei niedriger Frequenz

with the increase of moisture content. The increase of dielectric constant with the increase of moisture content upto 30% was also observed by Mkhaiovskaya (1972) and ]ames (1975). Lin (1976) stated that the polar groups in the cell wall and cellulose have increased freedom of rotation when moisture content increases and thus increasing the dielectric constant. The free water, i.e. the moisture content above 30% does not have much effect on the dielectric properties.

Dielectric constant of rubber wood at microwave fe- quencies of 1.0, 2.45, 6.0, 8.0, 10.0, 14.0 and 17.0 GHz in parallel and perpendicular to grain directions are shown in Figs. 5 and 6 respectively. Dielectric loss factors in both the directions are shown in Figs. 7 and 8. The dielectic constant and dielectric loss factor increase with the increase of moisture content throughout the whole ranges. The abrupt change of the dielectric properties are observed at very high moisture content and the curve becomes concave upward. The dielectric constant and dielectric loss

factor vary almost linearly at low moisture content. Free water molecules interact with the microwave field inde- pendently of the cell wall substances and bound water. Therefore, the change of dielectric constant and dielectric loss factor is determined mainly by the dielectric properties of free moisture and its volume.

It is observed from Figs. 1-4 that the dielectric constant and dielectric loss factor in parallel to grain direction is greater than in perpendicular to grain direction. The variation of dielectric properties between parallel and perpendicular to grain direction is due to the difference in the arrangement of cell wall and lumen in addition to the anisotropy of cell wall substances (Norimoto et al. 1978). The greater dielectric constant in parallel to grain direction may be explained in terms of the transition proba- bility of dipole jump to an adjacent site when the field applied to parallel to grain direction is considerably higher than that when the electric fields were applied in perpendicular to grain (Norimoto and Yamada 1970). The che-

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g } . . . . . . . . . . o 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

~ ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " J . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

o , . . . . .

-4 n ' ' ' ' ' ' ' ' ' ' 0 20 40 60 80 1 O0 0 10 20 30 40 50 60 70 80 90 100 110 Moisture content (%)

Moisture content (%)

Fig. 4. Dielectric loss factor vs moisture content in perpendicular to grain direction at low frequency [] o.o1 Hz, + o.1 Hz, * 1.o Hz, �9 10.0 Hz, x zoo Hz Bild 4. Verlustfaktor senkrecht zur Faser in Abh~ingigkeit yon der Feuchte bei niedriger Frequenz

Fig. 6. Dielectric constant vs moisture content in perpendicular to grain direction at microwave frequency [] 1.o GHz, + z.45 GHz,

6.o GHz, �9 8.o GHz, x zo.o GHz, �9 14.o GHz, A 17.o GHz Bild 6. Dielektrizit~itskonstante senkrecht zur Faser in Abh/ingigkeit yon der Feuchte bei Mikrowellenfrequenz

35

3O

25 t -

2o

._ a l O

5

0 I I

o 2'0 4'0 6'0 ao loo Moisture content (%)

Fig. 5. Dielectric constant vs moisture content in parallel to grain direction at microwave frequency [] 1.o GHz, + z.45 GHz, * 6.o GHz, �9 8.o GHz, x lO.O GHz, �9 i4.o GHz, A 17.o GHz Bild 5. Dielektrizit~itskonstante parallel zur Faser in Abhtingig- keit yon der Feuchte bei Mikrowellenfrequenz

o ( . ]

~5

14

1 2 -

1 0 -

8 -

6 -

4 -

2 -

O~ 0 10 20 30 40 50 60 70 80 90 100


Fig. 7. Dielectric loss factor vs moisture content in parallel to grain direction at microwave frequency [] x.o GHz, + 2.45 GHz, * 6.0 GHz, �9 8.o GHz, x lO.O GHz, �9 14.o GHz, A 17.o GHz Bild 7. Verlustfaktor parallel zur Faser in Abh/ingigkeit yon der Feucht bei Mikrowellenfrequenz

226

mical constituent of wood may also be responsible for the dielectric anisotropy. According to Norimoto and Yamada (1972), the dielectric properties of wood are strongly influenced by cellulose and mannan in parallel to grain direction whereas in perpendicular to grain direction the dielectric propert ies are influenced by lignin.

The measurement frequency also affected the dielectric properties considerably. At low frequencies, the lower the frequenices, the higher the dielectric constant and dielectric loss factor (Figs. 1-4). This is also true for the dielectric constant in microwave frequencies. But for dielectric loss factor at microwave frequencies, higher values were obtained at higher frequencies. A little variation of dielectric loss factor was observed above 6 GHz. The interaction of the electromagnetic field with the molecules of the wood substance at higher frequencies differs from those at lower frequencies, as the period of field oscillation at microwave frequencies can be compared with relaxation t ime of the molecules (Torgovnikov 1993). A phase shift, therefore arises between the field strength

140

12o- % ~xlOO-

E 80-

8 6 0 -

E

,-n

4 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

o i t i ~ i i t

0 10 20 30 40 50 60 70 Moisture content (%)

80

Fig. 10. Elastic stiffness constant vs moisture content in different grain direction: [] Longitudinal, + Radial, * Tangential Bild. 10. Elastizit/itskonstante bei verschiedenen Faserrichtun- gen in Abh~ingigkeit yon der Feuchte: [] longitudinal, + radial, �9 tangential

12

1 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

o 6 =o . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ * ~. .~ ....

-~ 4 t5

2

0 0 2'0 4'o 6'0 8'o t60


Fig. 8. Dielectric loss factor vs moisture content in perpendicular to grain direction at microwave frequency 1.o GHz, + 2.45 GHz, * 6.0 GHz, [] 8.0 GHz, x lO.O GHz, �9 14.o GHz, A 17.o GHz Bild 8. Verlustfaktor senkrecht zur Faser in Abh~ingigkeit yon der Feuchte bei Mikrowellenfrequenzen

5000

ii ii iiii ii 3500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

= 3000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o o

2 5 0 0 . . . . . . . . . . . . . . . " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 0 0 0 - ~ - - - - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15oo . . . . . . . . . . . ~ : ~ ......... L §

1000 . . . . 5'O io 0 10 20 30 40 60 80


Fig. 9. Ultrasonic velocity vs moisture content in different grain direction: [] Longitudinal, + Radial, * Tangential Bild 9. Uhraschallgeschwindigkeit bei verschiedenen Faserrich- tungen in Abh/ingigkeit yon der Feuchte: [] longitudinal, + radial, �9 tangential

vector and the polarization vector resulting in a reduction of dielectric constant and an increasing of loss factor with the increase of frequency were also reported by James and Hamil (1965), Torgovnikov (1993) and Tiuri et al. (1980).

Empirical equations of the type Y = a x b have been determined for calculating dielectric constant and dielectric loss factor from the moisture content at low frequency. The value calculated from the equations are shown by the solid lines in Figs. 1-4. Fourth order polynomial equations of the type Y = a x 4 + b x 3 + cx 2 + d x + e were found suitable for the curve fitting at microwave frequencies. The value calculated from the equations of curve fitting were shown by solid lines (Figs. 5-8).

The ultrasonic velocities and elastic stiffness constant in parallel and perpendicular to grain directions at different moisture content are shown in Figs. 9 and 10 respectively. As the moisture content increases, the ultrasonic velocities were found to decrease for all grain directions, and cons- equently elastic stiffness constant. A sharp rise of the ultrasonic velocities and elastic stiffness constant was observed as moisture content decreases from 30% in- dicating fiber saturation point. Similar results were also obtained by Sakai et al. (1990). But Nakamura and Nanami (1993) obtained continuous decreasing of velocity instead of getting any sharp division line in the region of fiber saturation point. The ultrasonic velocities and elastic stiffness constant in parallel to grain were found to be greater than the perpendicular to grain directions. This result agrees well with findings of the previous workers (Kamioka 1988; Bucur 1983, 1988; Bucur and Feeny 1992). The higher acoustic velocity in parallel to grain direction may be due to the longitudinal orientation of cell along the axial directions since cell walls provide a continuous wave path. Polge (1984), on the other hand, found a strong correlation between the fiber length and ultrasonic velocity that permits the possibility to develop a non destructive methodology for fiber length. The radial and tangential directions both of which are perpendicular to grain also have substantial effect on the ultrasonic velocity and elastic stiffness constant. The radial direction showed higher ultrasonic velocity and elastic stiffness constant compared to tangential direction.

4 Conclusions Moisture content of rubber wood affected dielectric properties considerably at both low and microwave frequencies. The dielectric constant and dielectric loss factor increases as the mois ture content increases from 0 to a round 30% and thereafter increases slightly for both parallel and perpendicular to grain directions at low frequency. In microwave frequencies, the dielectric constant increases cont inuously with the increase of moisture content with concave upward. In low frequencies, the dielectric constant and dielectric loss factor increases as the frequency increases. The dielectric constant also increases with the increase of frequency but dielectric loss factor decreases. The dielectric loss factor almost remains constant above 6 GHz. Fourth order polynomial equat ion can be used for est imating dielectric propert ies of rubber wood from mois ture content at microwave frequencies whereas exponential equat ions were found suitable at low frequencies. The grain direct ion plays an impor tan t role for measur ing ultrasonic propert ies . The parallel to grain direct ion showed higher ul trasonic velocity and elastic stiffness constant compared to perpendicular to grain. This result can be used for detect ing grain defects of wood.

References Bucur V (1983) An ultrasonic method for measuring the elastic constants of wood increment cores bored from living trees. Ul- trasonic 21(3): 116-126 Bucur V (1988) Wood structural anisotropy estimated by acustic invariants. IAWA. Bulletin 9(1): 67-74 Bucur V, Feeny F (1992) Attenuation of ultrasound in solid wood. Ultrasonics. 30(2): 76-81 lames WL, Hamil DW (1965) Dielectric properties of Douglus Fir measured at microwave frequencies. Forest Prod. I. 15(2): 51-56 lames WL (1975) Dielectric properties of wood and hardboard. Variation with temperature, frequency, moisture content and grain direction. Res. Pap. USDA Forest Service. Forest Prod. Lab. Madison, Wisconsin lames WL (1977) Dielectric behaviour of Douglus-fir at various combination of temperature, frequency and moisture content. Forest Prod. J. 27(6): 44-48 lames IF, Robert IR, Drum JR (1995) Nondestructive evaluation of honeycomb and surface checks in Red Oak lumber. Forest Prod. I. 45(5): 42-45 Kabir MF, Sidek HAA, Daud WM, Khalid K (1997) Detection of knot and split of rubber wood by non destructive ultrasonic method. Journal of Tropical Forest Product 3(1): 88-96

Kamioka H (1988) Effect of ultrasonic bonding materials on velocity and attenuation of sound in Red Lauan wood lpn. J. Appl. Phys. 27(2): 188-191 Kroner K, Pungis L (1952) Zur dielektrischen anisotropie des natureholzes im frequenzbereich. Holzforschung 6(1): 13-16 Lin RT (1967) Review of the dielectric properties of wood and cellulose. Forest Prod. I. 17(7): 61-66 Mikhailovskaja KP (1972) Investigation of moisture characteristics of wood electric parameters. Author's paper on Thesis for Candidate of Science degree, LTI, CBP, Leningrad. (in Russian) Nanassy AJ (1972) Dielectric measurement of moist wood in a sealed system. Wood Sci. Technol. 6:67-77 Nakamura N, Nanami N (1993) The sound velocity and moduli of elastic in the moisture desorption process of Sugi wood. Mokuzai Gakkaishi. 39(2): 1341-1348 Norimoto M, Yamada T (197o) The dielectric properties of wood IV. On the dielectric anisotropy of wood. Wood Res. 50:36-49 Norimoto M, Yamada T (1972) The dielectric properties of wood VI. On the dielectric properties of the chemical constituent of wood and the dielectric anisotropy of wood. Wood Res. 52:31-43 Norimoto M, Yamada T (1976) Dielectric properties of wood. Wood Res. 59/60:106-152 Norimoto M, Hayashi S, Yamada T (1978) Anisotopy of dielectric constant in coniferous wood. Holzforschung. 32(5): 167-172 Parker ML, Kennedy RW (1973) The status of radiation densi- timetry for measurement of wood specific gravity. Proc. IUFRO, Pretoria. 5(2): 882-893 Polge H (1984) Essais de caracterisation de la veine verte du merisier. Ann. Sci. For. 41:45-58 Rafalski J (1967) Dielectric properties of compressed Beech wood. Forest Prod. J. 17(8): 64-65 Sakai H, Minamisawa A, Takagi K (199o) Effect of moisture content on ultrasonic velocity and attenuation in woods. Ultra- sonics. 28:382-385 Skaar C (1948) The dielectric properties of wood at several radio frequencies. NY State Coll. For. Syracuse NY, Tech. Pub. 69, 36 pp Torgovnikov GI (1993) Dielectric properties of wood and wood based materials. Springer Verlag, New Work. Tiuri MK, Jokela K, Heikkila S (1980) Microwave instrument for accurate moisture and density measurement of timber. Journal of Microwave Power. 15(4): 251-254 Vermas HF (1974) Dielectric properties of Pinus pinaster as a function of its Alcohle-Benzen-soluble content. Wood Sci. 6(4): 363-367 Vermas HF (1976) The dielectric constant of solid wood substances calculated with two different methods. Holzforschung. 30(3): 97-98 Venkateswaran A, Tiwari SY (1964) Dielectric properties of moist wood. Tappi. 47(1):25-28

227

COMPARATIVE STUDIES OF ELASTIC PROPERTIES OF COMMERCIAL-TYPE WOODS

BUREAU OF RESEARCH AND CONSULTANCY UNIVERSITITEKNOLOGI MARA 40450 SHAH ALAM, SELANGOR

MALAYSIA

By

AZMAN KASIM AMRAN SHAFIE

AZHAN HASHIM @ ISMAIL

January 2006

i) u R i: A i; O P R E . S C A « C H A CONSULTANCY

Biro Penyelidikan dan Perundingan Universiti Teknologi MARA 40450 Shah Alam. Malaysia Tel : 03-55442094 / 5 / 3 / 2 Website : www.uitm.edu.my/brc

Fax : 03-55442096 -i

UNIVERSITI

TEKNOLOGI

MARA

Penolong Naib Canselor (.Penyelidikan) 03-5544 2094/5 [email protected]

{Coordinator Penyelidikan (Sains dan Teknologi) 03-5544 2091 '[email protected]

[Coordinator Penyelidikan (Sains Kemasyarakatan & Kemanusiaan) 03-5544 2097 [email protected]

[Coordinator Perundingan (Kewangan) 03-5544^2090 [email protected]. my

(Coordinator Perundingan '3-5543 5120

[email protected]

Penolong Pendaftar 03-5544 2092 [email protected]

Pegawai Eksekutif 03-5544 2098 rohani734 @ salam. itm.edu. my

Pentadbiran 03-5544 2093

Surat Kami Tarikh

600 - BRC/ ST. 5/3/491 11 September 2002

Encik Mohd Halil Marsuki Penolong Akauntan Unit Kewangan Zon 17 Universiti Teknologi MARA Shah Alam

Tuan

GERAN PENYELIDIKAN -

Merujuk kepada perkara di atas, bersama-sama ini dimajukan salinan surat kelulusan menjalankan penyelidikan untuk para pensyarah dari UiTM Cawangan Pahang;

1. Kajian Sifat Mekanik Komposlt Ferit {Lio.sFeo.5)o.4Nio.3Zno.3Fe204 Getah Asli Termoplastik Ketua Projek Abdul Aziz Mansor KosProjek RM 9.980.Q0

2. Comparative Studies of Properties of Commercial-Type Woods Ketua Projek Azman Kassim KosProjek RM 9,930.00

Diharap tuan dapat menghantarkan geran penyelidikan ke Universiti Teknologi MARA Cawangan Pahang.

Terima kasih.

Yang benar

lAls-jlX/U

DAPEAH AHMAD Penolong PeTicJaftar b/p Penolong Naib Canselor (Penyelidikan)

s.k: 1. Pengarah Kampus Universiti Teknologi MARA Cawangan Pahang

2. Dr Azhan b. Hashim @ Ismail Pensyarah/ Koordinator UPP Universiti Teknologi MARA Cawangan Pahang

3. Penolong Bendahari Universiti Teknologi MARA Cawangan Pahang

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Tarikh : 1 Februari 2006 No. Fail Projek : 011000030019

Prof. Dr. Azni Zain Ahmad Penolong Naib Canselor Biro Penyelidikan dan Perundingan UiTM,ShahAlam

Yang Berbahagia Prof.,

LAPORAN AKHIR PENYELIDIKAN^ COMPARATIVE STUDIES OF ELASTIC PROPERTIES OF COMMERCIAL-TYPE WOODS'

Merujuk kepada pekara di atas, bersama-sama ini disertakan 4 (empat) naskah Laporan Akhir Penyelidikan bertajuk ' Comparative Studies on the Elastic Properties Of Commercial-Type Woods', untuk makluman pihak Prof.

Sekian, terima kasih.

Yang benar,

AZMAN KASIM Ketua Projek Penyelidikan

n

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RESEARCH COMMITEE

AZMAN KASIM Head Of Researcher

Signature

AMRAN SHAFIE Researcher

DR. AZHAN HASHIM @ ISMAIL Researcher

Signature

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ACKNOWLEDGEMENTS

I would like to express my utmost gratitude to the institutions and the following

individual for their direct or indirect support, constant monitoring, enthusiasm,

encouragement until the completion of the research.

Institute of Research, Development & Commercialisation (IRDC), UiTM

Prof. Madya Dr. Jamaludin Kasim

En. Wan Mohd Nazri Wan Abd. Rahman

Wood Technology Dept., Faculty of Applied Science,

Universiti Teknologi MARA Pahang

En Tajuddin Mokhtar

En Azizi Md. Yasin

Science (Physics) Laboratory Assistant, UiTM Kampus Jengka

Prof. Madya Dr. Sidek Hj. Ab. Aziz

Ultrasonic Research Laboratory, Physics Department

Universiti Putra Malaysia, Serdang, Selangor Darul Ehsan

Semoga segala jasa baik tuan-tuan hanya ALLAH sahaja yang dapat

membalasnya.

AMIN.

iv

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TABLE OF CONTENTS

Page

ACKNOWLEDGEMENT iv

TABLE OF CONTENT v

LIST OF TABLES vii

LIST OF FIGURES viii

LIST OF ABREVIATION ix

ABSTRACT Xi

CHAPTER

I INTRODUCTION 1

1.1 Problem Statements 2

1.2 Research Objective 2

1.3 Literature Review 2

II WOODS PROPERTIES 4

2.1 Introduction 4

2.2 Definition of Wood Strength 5

2.2.1 Density 5

2.2.2 Stress 5

2.2.3 Strain 5

2.2.4 Elasticity 6

2.2.5 Modulus of Elasticity (MOE) 6

2.2.6 Modulus of Rupture (MOR) 6

III NON DESTRUCTIVE ULTRASONIC TESTING 7

3.1 Introduction 7

3.2 History of Ultrasonic 7

3.3 Propagation of Ultrasonic Waves in Wood 8

3.3.1 Bulk Waves 9

3.3.2 Rayleigh Waves 9

3.3.3 Lamb Waves 12

3.4 The Correlation of Ultrasonic-Elastic Properties . -

v

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IV RESEARCH METHODOLOGY 15

4.1 Introduction 15

4.2 Sample Preparation 15

4.3 Ultrasonic Measurement Techniques 16

V RESULTS & DISCUSSION 17

5.1 Introduction 17

5.2 Data of Measurements 17

5.3 Discussion 24

VI CONCLUSION AND PROPOSAL 27

6.1 Conclusion 27

6.2 Proposal 26

BIBLIOGRAPHY 28

APPPENDIX 29

vi

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Table

LIST OF TABLES

Page

3.1 Definition of elastic modulus and its respective equation.... 14

5.1 Data of ultrasonic measurement of Kempas 18

5.2 Data of ultrasonic measurement of Chengal 19

5.3 Data of ultrasonic measurement of Tembusu 20

5.4 Data of ultrasonic measurement of Simpoh 21

5.5 Data of ultrasonic measurement of Rubber wood 22

5.6 Data of ultrasonic measurement of Meranti 23

5.7 List of modulus of elasticity for different categories of 24

commercial wood

5.8 Comparative MOE results of different commercial wood 25

5.9 Comparative density results for selective commercial wood 25

vn

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LIST OF FIGURES

Figure Page

3.3a The propagation of compressive wave 10

3.3b Shear wave propagation 10

3.4 Rayleigh wave 11

3.5a A symmetrical Lamb wave 11

3.5b A asymmetrical Lamb wave 12

4.1 Ultrasonic measurement system 16

viii

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LIST OF ABREVIATIONS

MOE

MOR

GPa

AU

N

DT

NDT

SOEC

FRIM

UiTM

UPM

Modulus Of Elasticity

Modulus Of Rupture

Giga Pascal

Acousto-ultrasonic

Newton

Destructive Testing

Non-Destructive Testing

Second order elastic constant

Forestry Research Institute of Malaysia

Universiti Teknologi MARA

Universiti Putra Malaysia

IX

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COMPARATIVE STUDIES OF ELASTIC PROPERTIES OF COMMERCIAL-TYPE WOODS

ABSTRACT

Wood-based industries has been extremely expanded in develop country like

Malaysia as one of the major contribution to the economic growth of the country.

Since wood has become popular in our daily usage, one should conscious about

the quality of the wood as natural raw materials. Talking about the quality of

woods normally we are talking about the type of woods been used.

Conventionally, to identify the quality of wood people look at the prices of the

woods, which high in price indicated the woods are in a good quality.

Scientifically, by going through certain high technological approach, the quality of

woods could be identified. In this project, the ultrasonic technology has been

used to identify the quality of commercial-type woods by determine the elastic

properties of the woods. Ultrasonic measurement technique is apart of non

destructive testing without damaging the targeted samples. Many papers have

been discussed nor published regarding the non-destructive testing of woods and

forest product industries previously. The objective of the project is to estimate the

elastic properties of the selective commercial woods in collaborations with

Woods Technology Department, UiTM Pahang. The selected commercial woods

have been used are Kempas (Koompadia malaccensis), Chengal

(Neobalanocarpus heimii), Tembusu (Fagraca Fragrans), Simpoh (Dillenia Spp.),

Rubberwood (HeveaBrasiliensis) and Yeliow Meranti (Shorea Spp.). Thus, the

data of elasticity could estimate the quality of woods macroscopically.

X

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CHAPTER 1

INTRODUCTION

Wood is a natural raw material which is known scientifically as an isotropic

inhomogeneous material. So the properties of wood and wood products show a

wider variety than the synthetic materials such as concrete, metals, plastic etc.

Therefore, the strength and the stiffness characteristics of woods product have to

be assessed individually in order to sort the material to grade classes.

Traditionally the grading of the structural wood was based on the visual

inspection of defects on the surface of the material (Balazs, 2001). But nowadays

as the science and technology progressively fast forward, a new method has

replaced the traditional one by introducing the ultrasonic non-destructive testing.

They are more reliable and repeatable to classify the commercial-type woods

than visual grading.

Ultrasonic inspection is used to determine whether or not a test piece

might be used according to it intended purposes. By this inspection, one could

determine whether the inspected commercial woods are free of defect or any

discontinuities. In this project several commercial type woods had been selected

such as Kempas (Koompadia Kempas (Koompadia malaccensis), Chengal


Rubberwood {HeveaBrasiliensis) and Yellow Meranti (Shorea Spp.)., Chengal


Rubberwood (HeveaBrasiliensis) and Yellow Meranti (Shorea Spp.). In order to

identify elastic property of each wood a non-destructive ultrasonic testing has

been approached to measure the wood physic and wood mechanics. This report

will discuss the elastic properties of each selective commercial type woods by

using ultrasonic measurement techniques.

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1.1 Problem Statements

Studies on the elastic properties of the selective commercial type wood

are well established but by difference NDT approached. A lot of works related to

the hardness and the toughness of the wood has been carried out especially by

using the destructive testing (DT) yet only few reports on the NDT were

published. The determination of quality of commercial wood in term of ultrasonic

approached is still new to our country.

1.2 Research Objective

The main objective of this research is to identify the correlation between

the elastic properties and the wood categories. It also to determine the

correlation between the ultrasonic waves propagation and each categories of

wood. By having this we could estimate the quality of the commercial type wood

in term of the hardness and toughness. Beside, it could also been introduced and

familiarized among the public a systematic way to grade the wood in this country.

1.3 Literature Review

The ultrasonic nondestructive testing techniques are suitable to measure

certain parameters such as the modulus of elasticity which correlate to the

mechanical properties of wood. In forest products industry, the NDT methods are

frequently used normally for defect detection, products grading, in-situ wood

structure evaluation and health monitoring of living trees. Research by Bucur

et.al (1987) entitled "Elastic Constant of Wood By Ultrasonic Method' have used

pine, spruce, beech and tulip-tree. Whereby, the attainable ultrasonic velocity

has been used to estimate the elastic properties of selective wood.

2

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Later, in 1990, Sakai et.al established the research which, focus on the

correlation between propagated ultrasonic velocities and the moisture content of

wood. He found that the wave velocity decreases with the moisture content which

mean the elastic properties deteriorate by the 'wetness' of the sample. The

ultrasonic approached has yet comes to the end until in 1995 a group of

researcher leads by Sidek was carried out a study pertaining to the ultrasonic

method on the elastic properties of tropical trees.

Balazs et.al (2001) was focusing onto the method feasible to access the

integrity of built in wooden members by using ultrasonic non-destructive testing.

In 2001, Prof. Beall and his colleagues from Forest Products Laboratory,

University of California did some research which are based on the ultrasonic

method but more technical on the impact of usage the acoustic emission and

acousto-ultrasonic. He found that new technology of AU has changed

significantly from time-domain approach to the use of wideband receivers to

permit signal processing.

3

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CHAPTER 2

MECHANICAL PROPERTIES OF WOODS

2.1 Introduction

The subject of elasticity as a part of mechanical properties is concerned

with the determination of the stresses and displacements in wood structures.

When a solid is subjected to external forces, it undergoes a change in shape.

When the load is released the solid reverts to its original state. Sometimes under

certain circumstances, the shape may not return to what it was prior to the

application of the force. We say that the material has deformed permanently. If

the material returns to its original dimension when force is removed, the material

is said to have undergone elastic deformation. These are due to the less force

subjected that could cause permanent deformation.

A form of Hooke's law can represent the elastic behavior of many

materials like woods and wood products. Wood is technically said to undergo

elongation, which indicates that the extension of a sample is linearly related to

the exerted force, F. One should be considering the correlation of the stress, a

and strain, e. The relationship is given by proportional relating Young's modulus,

E or tensile modulus. Moreover, the linear elasticity represents the stretching

(compression or distortion) of atomic bonds and for this reason E is also a

4

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measure of a material's inherent bond strength. A material having a high value of

the tensile modulus is considered stiff. Linear elasticity of this kind is found in all

classes of solid materials at all temperature.

2.2 Definition of Wood Strength.

Strength may be defined as the ability to resist applied stress: the greater

the resistance the stronger the material (Anon,2001). Resistance in term of

stress which the material can endure before the "failure' occurs could be

measured. Strength of wood is often thought of in terms of bending material

strength.

2.2.1 Density

Density is an essential element in determining the toughness of wood. For

wood, density is given as kilogram per cubic meter. Density is the single most

important indicator of strength in wood, heavier wood will generally tend to be

stronger than the lighter one.

2.2.2 Stress

Stress is the amount of force for a given unit of area. It is typicaiiy

measured in kilogram per square meter (kgm"3).

2.2.3 Strain

Define as unit of deformation or movement per unit of original length. It is

typically expressed meters per meter.

5

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2.2.4 Elasticity

Elasticity is aproperty of wood in which strains or deformations are

recoverable after an applied stress is removed up to certain level of stress known

as the proportional limit. Below this point, each increment of stress will produce a

proportional increment of strain and the wood will return to its original position

once stress is removed. Beyond the proportional limit, each increment of stress

will increasingly larger increments of strain yet the removal of the stress will

result in a partially recovery of the strain.

2.2.5. Modulus of Elasticity

It is well known as Young's modulus is the ratio of stress to strain. For

wood, this ratio is constant within the elastic range below the proportional limit

thus making it useful in static bending tests for determining the relative stiffness

of a board. Normally been measured in kilogram per square meter and

abbreviated as MOE.

2.2.6. Modulus of Rupture

Modulus of rupture is the maximum load carrying capacity of a member. It

it generally used in tests of bending strength to quantify the stress required to

cause failure. It has also been reported in kilogram per square meter.

6

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CHAPTER 3

NON DESTRUCTIVE ULTRASONIC TESTING

3.1 Introduction

The ultrasonic measurement techniques are a non-destructive testing

which is not damaging the specimens when experiment is carried out. The

ultrasonic method has strong correlation with elastic constant. Whereby, under

the ultrasonic techniques, the propagated ultrasonic waves velocity could be

successively used to determine the elastic constant of the targeted samples.

Through a certain derivative formulae, we could estimate the elastic properties of

wood and their quality as well.

3.2 History of Ultrasonic.

The earliest experiment on ultrasonic was done at the close of 18th

century when Lazzaro Spallazani (1874) explain the ability of bats to avoid

obstacles while flying in the dark. He blinded a bat but still the bat was able to

find its way in the dark without hitting any obstacles. But when the bat ears were

made useless, the bat failed to avoid the obstacles while flying in the dark. This

means that bat are using sound wave, which are beyond the human hearing

perception. Bats can produce ultrasonic waves with the frequency 40-50 kHz.

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When the waves reach the objects, it will be reflected and received back by the

bats. Although the studies of inaudible acoustic waves started around 19th

century, but the modern ultrasonic only appeared about 1917 with investigation

on submarine detection methods. Since that time, the ultrasonic technology has

grown enormously, with the application found in science, industry, medicine and

military.

The earliest development in acoustic had been traced back to the ancient

times but nearly all the important foundation for modern 'discovery' and advance

of ultrasonic are found in the 20th century. The application of ultrasonic method

started during the World War 1 in August 1914 when Paul Langevin measured

the distance of two object underwater using the pulse echo technique at the

frequency of 40 kHz. The most important application was the Solokov method

(1934) in detecting solid deformation by the electronic instrument, time taken by

the echo pulse propagate from launcher to the material surface with different

physical content may allow distance between the two deform part of the material

be detected.

3.3 Propagation of Ultrasonic Waves in Woods.

Basically there are three modes of propagation, which are bulk waves, surface

waves and lamb waves.

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3.3.1 Bulk Waves

Bulk waves consists of longitudinal or compression wave and shear or

transverse wave. Compression wave propagates in the longitudinal direction in

which the oscillation of the particle is forward, compressing and depressing

(Figure 3.3a). It can transmit sound through liquid and solid bodies. However, the

propagation of shear wave occurs with the oscillation of particle in medium at

transverse direction or right angles to the direction of propagation (Figure 3.3b).

The excitation of shear wave can be seen as a motion of particles moving

sinusoidal up and down by a periodical shear force. It can only propagate

through solid and cannot propagate in liquid and gas.

3.3.2 Rayleigh Wave

These are waves, which travel on the surface of the solid materials (Figure

3.3). They are comprised of longitudinal and shear waves, in fact, ninety percent

of this wave is composed of shear wave. However, only wave with high

frequencies can generate this type of wave, i.e. 300 MHz.

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P: direction of propagation

Q: direction of polarization

Figure 3.3a: The propagation of compression wave

strecth

comoress

•*• P

* Q

P: direction of propagation

Q: direction of polarization

Figure 3.3b: Shear wave propagation

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Figure (3.5b): A asymmetrical Lamb wave

3.3.3 Lamb Wave

When the thickness of the material is smaller than the wavelength, only

two types of wave can propagate within the solid material, namely symmetrical

and asymmetrical Lamb waves. As shown in Figure 3.5a and 3.5b, symmetrical

wave is also called as quasi-longitudinal wave because the motion of particles

mostly longitudinal while asymmetrical wave is also called as bending wave

because the direction of propagation is perpendicular to the displacement of

particle which shows the presence of shear wave.

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3.4 The Correlation of Ultrasonic-Elastic Properties

The longitudinal and shear waves velocity obtained from the ultrasonic

measurements is used for the elasticity determination. The velocity of an elastic

wave in wood or wood product solely depends on the density of the sample and

the adiabatic elastic constant Cj,.. By combining the Newton's law in correlation

with the equation of harmonic waveform, it will lead to the Christoffel equation:

iU-Simpv2 | =0

where, Tm = CjkimNkNi & Nj - waves vector. From the Christoffel equation, three

mode of ultrasonic waves velocity namely as Second Order Elastic Constant

(SOEC) has been determined.

The equation of SOEC:

Cn=pv 2 (1) C44 = pv2 (2) Ci2 = Cn -2C44 (3)

whereas,

p - density VL- longitudinal velocity. vs- shear velocity

From this equation, the elastic modulus of the certain material such as Young's modulus E, bulk modulus, B and Poisson ratio, a could be identified.

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MEASUREMENT SCIENCE REVIEW, Volume 11, No. 5, 2011

160

Density and Ultrasonic Characterization of Oil Palm Trunk

Infected by Ganoderma Boninense Disease

M. M. K. Najmie, K. Khalid, A. A Sidek and M. A. Jusoh Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia,

[email protected]

Oil palm trunks infected by Ganoderma boninense disease have been studied using density and ultrasonic characterizations. The ultrasonic characterizations have been performed using a commercial ultrasonic instrument at the frequency of 54 kHz. The measurements have been done in 3 zones: inner zone, central zone and peripheral zone. It was found that the stem density of the oil palm infected by Ganoderma boninense disease was reduced by 50% in comparison to the original healthy trunk. From this effect the velocity of the ultrasonic wave propagated through the Longitudinal, Radial, and Tangential directions is lower for the trunk infected by Ganoderma boninense disease compared to a healthy trunk. For the 10 cm thickness of samples, the ultrasonic velocity for all transit directions was in range of 260 – 750 ms-1 for the infected sample, whereas for healthy samples was in the range of 460 – 900 ms-1. These results are very useful for the detection of the area which has been affected by the disease.

Keywords: Oil palm trunk, ultrasonic testing, elasticity constant, Ganoderma boninense

1. INTRODUCTION HE OIL PALM TREE Elaeis guineensis, which belongs to the Palma family, is one of the most versatile crops in tropical countries. Oil palm was the

major commodity inside the Malaysian agriculture sector. Commercial cultivation of the oil palm started in 1917 and has expanded tremendously in recent years because it is suitable to be planted in most lands in Malaysia. Malaysia is presently the world’s leading exporter of oil palm having a 60% market share and oil palm was second only to soybean as the major source of vegetable oil. It has spread throughout the tropics and is now grown in 16 or more countries. However, the major center of production is in South East Asia (SEA) with Malaysia and Indonesia together accounting for around 83 % of world oil palm production in 2001 [1]. The oil palm exportation reached about RM31 billion increased by 8.54% or RM2.44 billion in 2006 compared to 2005 [2]. Oil palm trunk can also be used to make furniture, as an additive in concrete, laminated oil palm veneer lumber and raw material for activated carbon. However, a soil fungus pathogen, Ganoderma boninense, which causes basal stem rot in oil palms trunk, ruins thousands of hectares of plantations in Southeast Asia every year. The disease causes infected palm trunks to fracture at the base, thus causing direct loss of oil palm trees.

The Ganoderma problems had been known for decades, but the search for solution was considerably hampered by a natural constraint. The disease does not cause external symptoms until it is too far advanced and at a stage when trees cannot respond to treatment anymore, as shown in Fig.1(a). Primary infection of palms by Ganoderma species has been considered to occur by contact of living palm roots with colonized debris within the soil [3]. Secondary spread of inoculums has been assumed to be by contact of living palm roots with each other [4]. Beside the very old palms, palms between 7 to 15 years old are also infected. This is the

prime age of fruit production and effort should be made to curb disease spread and loss of trees especially from this age group. Because the external symptoms become visible when the disease is too far advanced, very little information of the fungus, especially during its earliest point of entry, is known. So Ganoderma boninense disease is like a silent time bomb to oil palm trees.

Attempts to control this disease in the fields with fungicide have been made by various workers, but the results are inconclusive, though some systematic fungicides seem to be promising. The methods of fungicide application include soil drenching, trunk injection, or combination of these two methods [5]. However, management of chemical and biological control would be more effective if the disease could be detected before its external symptoms become evident. Ultrasonic testing is one of the non-destructive testing (NDT) methods which offer advantages due to the possibility of evaluating the structural integrity of an element without extracting test specimens, faster analysis of large populations, and versatility to adapt to standardized production line routines.

Another application of the non-destructive methods is the evaluation of structures that are in use, i.e., in situ evaluation, allowing for their maintenance or rehabilitation through a mapping of the deteriorated areas, which permits evaluations to be made of their structural integrity without the need to remove part of the structure [6]. Until now there was still no conclusive method for early detection of basal stem rot in order to stop the disease from spreading. The disease has now reached an alarming state as more and more palms become infected, and the target hosts are starting to shift towards even younger palms.

The objective of the present work is to study the ultrasonic transmission properties of the oil palm trunks through the healthy tissue and tissue infected by Ganoderma boninense.

T

10.2478/v10048-011-0026-x


161

(a)

(b)

Fig.1. (a) Oil palm tree infected by Ganoderma boninese disease. (b) A mature Ganoderma fructification at oil palm trunk.

2. SUBJECT & METHODS An oil palm tree was infected by Ganoderma boninense

disease obtained in Oil palm Farm, UPM. That oil palm tree reached the age of 30 years and showed Ganoderma boninense infection with the appearance of a mature Ganoderma fructification at stem. The lower fronds of the oil palm were dead and fractured as shown in Fig.1. Then, the oil palm trunk was cut from 20 cm above the ground to 100 cm height using a chainsaw. All samples were cut using Radial Arm Saw found at the Forest Research Institute Malaysia (FRIM). The trunk was cut to blocks of the size measuring 5 × 10 × 10 cm from stem center as shown in Fig. 2. The number of samples suitable to be used in this project was 27 and they were divided into 3 sections, namely: inner zone, central zone and peripheral zone. Then the samples were weighed using analytical balance to know the mass and density. The volumes of samples were also measured using digital veneer caliper. Density is the ratio of mass to volume of the sample with unit kgm-3, and it is written in equation form as:

vm=ρ ,

where ρ = density of wood, m = mass of wood and V = volume of wood.

As much as 10 readings were adopted for every sample and average value was calculated. Ultrasonic tester V-Meter Mark II with 54 kHz transmitter and receiver transducers typically used for wood measurement, and concrete, were used to measure transit time in three directions: tangential direction, radial direction and longitudinal direction, using direct transmission method based on fiber directions of oil palm trunk as shown in Fig.3.Transit time pulse, t propagate across material collected between two transducers, with known material length, l will give ultrasonic velocity, v. Velocity of ultrasonic wave was obtained through following equation and the unit is meter per second, ms-1:

tlv = .

(a)

(b)

Fig.2. (a) Cross section of sample for measurement from above. (b) Cross section of sample for measurement after being split in two and divided to 9 parts.

90 cm

90 cm

10 cm

10 cm

15 cm

Peripheral Zone

Central Zone

Inner Zone

90 cm

10 cm


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Fig.3. Ultrasonic measurement system used to measure oil palm trunk.

3. RESULTS AND DISCUSSION The relationship between density and height of the oil

palm trunk is shown in Fig.4. The graph shows that the density of infected area by Ganoderma boninense disease had lower density value compared to healthy area for every zone. There are discolorations between healthy areas and areas infected by Ganoderma boninense disease. Healthy areas were colored yellow white at parenchyma tissue while areas infected by Ganoderma boninense disease were

colored dark brown or blonde at parenchyma tissue. Generally, the dropping of the density in the infected area is about 50% from the original density. This means that the tree can easily fall down when it arrives at the critical stage. Oil palm wood is from monocotyledon type where distribution of vascular bundle is irregular and disarranged and it has no growth rings, while hardwood and softwood is dicotyledonous where distribution of vascular bundle is arranged and forms a circle spiral and also possesses growth rings. The density at the peripheral region was above the values of the inner region. Across the trunk the density is influenced largely by the number of vascular bundles per square unit which decreases towards the center. The area infected by Ganoderma boninense disease has lower density in comparison to the healthy area and this pattern applies for all directions. These characteristics show that the area infected by Ganoderma boninense disease can reduce the stem stiffness and weaken the building structure of the oil palm tree. It will also cause the oil palm tree to fall down, besides encouraging insect attacks such as ants, termites and tree worms.

Fig.4. Relationship between density and height of the oil palm trunk.

Fig.5. Relationship between ultrasonic velocity for tangential direction and height of the oil palm trunk (cut samples).


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Fig.5 indicates the graph of velocity for tangential direction at different height of oil palm trunk. The graph shows that those areas which are infected by Ganoderma boninense disease have lower velocity in comparison to healthy areas. Peripheral zone has higher velocity and is followed by central zone and inner zone for the same thickness of the samples. In the infected area the average velocity is 423.4 ms-1 at inner zone, 571.1 ms-1 at central zone and 615.5 ms-1 at peripheral zone, while in the healthy area the velocity is 507.5 ms-1 at inner zone followed by 732.6 ms-1 at central zone and peripheral zone, 873.3 ms-1. The graph of velocity in radial direction at different height

of oil palm trunk is shown in Fig.6. The results of radial direction follow the same pattern as tangential direction where at inner zone the average velocity of healthy areas is 489.2 ms-1 and average velocity of infected areas is 307.9 ms-1, while at central zone, average velocity of healthy area is 716.9 ms-1 and average velocity of infected area is 548.3 ms-1. Peripheral zone has higher average velocity at healthy areas, 828.8 ms-1 and velocity at infected areas is 657.0 ms-

1. Peripheral zone has a narrow layer of parenchyma and congested vascular bundles that transform into a sclerotic zone, which provides the main mechanical support for the palm trunk.

Fig.6. Relationship between ultrasonic velocity for radial direction and height of the oil palm trunk (cut samples).

Fig.7. Relationship between ultrasonic velocity for longitudinal direction and height of the oil palm trunk (cut samples).

The velocity for longitudinal direction is the highest

average velocity compared to radial direction and tangential direction. This is because ultrasonic wave can propagate faster when mechanical energy is parallel to grain direction. In Fig. 7, the results of average velocity for infected area are almost the same for all zones ranging from 275 to 625 ms-1. But in the healthy area, there is a significant difference in velocity between the zones. The velocity at inner zone is 1138 ms-1, at central zone is 1183.1 ms-1 and peripheral zone is 1565 ms-1.

4. CONCLUSION These results are very useful for the ultrasonic detection of

the areas which have been infected by the Ganoderma boninense disease. The Ganoderma boninense disease can reduce up to 50% of density compared to the original oil

palm density. Oil palm trunk fully infected by Ganoderma boninense disease showed mature Ganoderma fructification at stem. Ultrasonic velocity of infected area is lower than healthy area. Peripheral zone has lower ultrasonic velocity compared to central zone and inner zone at tangential direction and radial direction. In longitudinal direction, central zone shows higher transit time reading at infected areas. For future work we propose that the ultrasonic study should cover more oil palm trees that differ in age and maturity. Some parameters such as moisture content, density, fiber dimension, chemical content and mechanical qualities of oil palm trunk have different characteristics with respect to tree age. Follow-up study can also be done on different palm species such as coconut tree for comparative purposes. To overcome the problem of energy loss of ultrasonic wave, especially for big trees or young trees, a high power transducer should be considered.


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ACKNOWLEDGEMENT This project is supported by a research grant of Fundamental Research Grant Scheme (FRGS). Vote number: 55232133. The author would like to thank Taman Pertanian Univeristi (TPU), Universiti Putra Malaysia and Forest Research Institute Malaysia (FRIM) for providing access to their facilities.

REFERENCES [1] Turner, P.D. (1965). The incidence of Ganoderma

disease of oil palms in Malaya and its relation to previous crop. Annals of Applied Biology, 55, 417–23.

[2] Pilotti, C.A., Sanderson, F.R., Aitken, E.A.B., Bridge, P.D. (2000). Genetic variation in Ganoderma spp. from Papua New Guinea as revealed by molecular (PCR) methods. In Flood, J., Bridge, P.D., Holderness, M. (eds.) Ganoderma Diseases of Perennial Crops. Wallingford, UK: CABI Publishing, 195–204.

[3] Idris, A.S., Ismail, S., Arifin, D., Ahmad, H. (2002). Control of Ganoderma Infected Palm – Development of Pressure Injection and Field Applications. MPOB Information Series TT No. 131.

[4] De Oliveira, F.G.R., Candian, M., Lucchette, F.F. (2005). A technical note on the relationship between ultrasonic velocity and moisture content of Brazilian hardwood (Goupia glabra). Building and Environment, 40, 297–300.

[5] Erwinsyah. (2008). Improvement of Oil Palm Wood Properties Using Bioresin. PhD thesis, Dresden University of Technology, Institute of International Forestry and Forest Products.

[6] Basri, W.M., Akmar, S.N.A., Henson, I.E. (2004). Oil palm – achievements and potential. Proceedings of the 4th International Crop Science Congress, 26 Sep – 1 Oct 2004. Brisbane, Australia.

[7] ISTA Mielke GmbH. (2007). Oil World, Vol. 50, No. 7. Hamburg: ISTA Mielke, www.oilworld.biz.

Received August 3, 2011. Accepted October 21, 2011.

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