Compressive behavior of hemp fiber (Cannabis sativa L.) stalks

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1 The Cndin Society for ioengineering The Cndin society for engineering in griculturl, food, environmentl, nd iologicl systems. L Société Cndienne de Génie grolimentire et de ioingénierie L société cndienne de génie grolimentire, de l ioingénierie et de l environnement Pper No. CSE939 Compressive ehvior of hemp fier (Cnnis stiv L.) stlks Md. Mjiur Rhmn Khn, Ying Chen *, Clude Lguë 2, Huert Lndry 3, Qingjin Peng 4, Wen Zhong 5. Deprtment of iosystems Engineering, University of Mnito, Winnipeg, Mnito R3T 5V6, Cnd 2 Fculty of Engineering, University of Ottw, Ottw, Ontrio KN6N5, Cnd 3 Pririe griculturl Mchinery Institute, Humoldt, Ssktchewn SK 2, Cnd 4 Deprtment of Mechnicl nd Mnufcturing Engineering, University of Mnito, Winnipeg, M, R3T 5V6, Cnd 5 Deprtment of Textile Sciences, University of Mnito, Winnipeg, Mnito R3T 2N2, Cnd * Corresponding uthor. Tel: , Fx: Emil ddress: ying_chen@umnito.c Written for presenttion t the CSE/SCG 29 nnul Conference Rodd s rudenell River Resort, Prince Edwrd Islnd 2-5 July 29 strct. Compressive strength of hemp (Cnnis Stiv L.) stems is of gret importnce for the design of hemp hndling nd processing mchines. study ws crried out to evlute the compressive ehvior of hemp stlks. Two vrieties of hemp stlks produced for single purpose () nd dul purposes () in Mnito, Cnd were used in the study. Ech vriety of hemp stlk ws divided into three height regions of the stem: upper, middle nd lower. The hemp stem specimens were cut into 25.4 mm in length nd the physicl properties of hemp specimen were mesured efore the compression tests. The outer dimeter of hollow hemp stlk vried from 6 to 7 mm; the inner dimeter vried from 3 to 8 mm; the liner density vried from to 37 g m -. The dimeters nd liner density were greter t lower height regions of specimen. Specimens were compressed y computer-ided lortory scle compression pprtus oth in xil nd lterl directions of hemp stem. The force-displcement curve ws recorded. The imum compressive lod t stem filure, stem modulus nd energy requirement for compression were derived from the curve. The results showed the imum compressive strength, modulus nd energy requirements were significntly differ t different hemp height regions nd were incresed with incresing stlk dimeters. In generl, higher strength, modulus nd more energy required for compression of the lower height region of hemp stlk oth in xil nd lterl directions of stem. Keywords. modulus. hemp (Cnnis stiv L.), height region, dimeter, compression, lod, energy, Ppers presented efore CSE/SCG meetings re considered the property of the Society. In generl, the Society reserves the right of first puliction of such ppers, in complete form; however, CSE/SCG hs no ojections to puliction, in condensed form, with credit to the Society nd the uthor, in other pulictions prior to use in Society pulictions. Permission to pulish pper in full my e requested from the CSE/SCG Secretry, PO ox 23, RPO McGillivry, Winnipeg M R3T 5S3 or contct ioeng@shw.c. The Society is not responsile for sttements or opinions dvnced in ppers or discussions t its meetings.

2 . Introduction Hemp (Cnnis Stiv L.) is one of the ncient plnts with long cultivtion history tht cn e hrvested for single purpose (fier only) or for dul purposes (seed nd fier). The world production of hemp grew from 5, tonnes in 2 to lmost 9, tonnes in 25 (FO, 29). Hemp cultivtion ws stopped four decdes go due to the prohiition of the lternte use of hemp s drug. Due to the high demnd on nturl fier from composite nd textile industril, severl countries, including Cnd, reintroduced the industril hemp with low tetrhydrocnninol (THC) content. In Cnd, more thn producers re now growing industril hemp, following its legliztion in 998. The hemp crege in Cnd ws 48, cres in 26 nd the reported net profits were from $2 to $25 per cre (Hnsen, 28). Hemp hndling involves tremendous energy nd lour s hemp plnts itself hs lrge mount of iomss yield nd high percentge of cellulose nd lignin (ócs & Krus, 997), which mkes it one of the most chllenging crops to hndle nd process in opertions such s hrvesting, cutting, ling nd decorticting for fiers. In these opertions, one chllenge is deling with the high strength of the plnt stlks with suitle mchinery, nd nother chllenge is the high energy requirement to perform these opertions. Thus, the mechnicl properties of hemp stlks ought to e known in order to design nd develop efficient mchinery for hemp processing nd hndling. In recent yers, reserch hs een crried out to investigte some engineering perspectives of hemp plnts, such s mechnicl ehviors during cutting (Chen et l., 24). The results showed tht the vlues of the imum force nd the totl cutting energy required for cutting hemp stem were 243 N nd 2. J, respectively. The liner reltionship etween cutting energy nd specific mss of hemp stem hs een used to estimte the power required to cut hemp mteril in field condition. Mny other engineering properties of hemp stlks re still unknown, for exmple, compressive ehvior of hemp. Compressive ehvior is very importnt, since compression of stlk is involved in ll of hrvesting, ling, nd decorticting processes. The compression ehvior of plnt mterils depends on species, vriety, stlk structure, stlk dimeter, mturity, moisture content nd cellulr structure (Persson, 987). To develop rpe stlk hrvesting technology, reserch on compressive ehvior of rpe stlk ws crried out using computer-servo mteril testing system y Qingxi et l. (27). They found tht rpe stlk ws heterogeneous, non-liner nd nisotropic, nd tht physico-mechnicl properties were different in ll directions of the stem. The verge vlue of rpe stlk compression destruction stress mesured ws.9 MP nd the elsticity modulus of compression ws 72 MP. The mechnicl properties including compression strength of sorghum stlk specimens were studied y Oke et l. (984) who reported tht compressive ehvior of sorghum stlks remrkly vried in different height regions: upper, middle nd ottom levels of sorghum stlk. The sorghum stlk specimens were deformed in qusi-sttic process using flt knives with 3-7 o evel ngles t different loding rte y Chttopdhyy nd Pndey (999). They showed tht the compressive strength nd the energy 2

3 sored in compression incresed s the evel ngle ws incresed nd oth decresed s the rte of loding incresed from to mm min -. To know the influence of dimeter nd ge of moo fier on its physicl properties, the compressive strength ws evluted for two types of moo (Lo et l., 24). The results showed tht the compressive strength decresed with incresing the outer dimeter of moo nd the rnge of strength vlue ws N mm -. Study of compressive ehvior of sugr cne ws conducted for hrvester design nd development (hholyotin et l., 988). The compression force of sugrcne stlk vried in different height regions of stem, prticulrly etween the ottom nd top height portion. lhovec (988) studied the Young s modulus, compressive strength nd sher strength of severl griculturl products. They found tht the tensile compressive strength ( σ ) nd Young s modulus (E) of vegetle flesh nd.75 culturl plnt stlks hd n exponentil reltionship ( σ m =.2E ). m In summry, there hve een some studies on compressive ehviors of different plnt mterils. However, no dt hve een reported for compressive properties of hemp stlk. The gol of this study ws to understnd the compression ehvior of hemp stlk, which will led to the design of effective nd efficient mchinery for hemp hndling nd processing. The specific ojectives were to study the compressive strength, modulus, nd energy requirement of hemp stems s ffected y different vrieties of hemp, height regions of hemp stem, nd compression directions of hemp stem. 2. Mterils nd methods 2. Specimen preprtion () () Fig.. Two vrieties of hemp stem specimens efore compression: () ; (). Two hemp vrieties, nd, were used in the compression experiment. oth were grown in Mnito, Cnd in 28. ws cultivted for single purpose (fier only) nd 3

4 ws for dul purposes (seed nd fier), nd oth were unretted nd unled. efore the compression tests, the seed portion of hemp stlk ws removed. Then, the rest of the stem wsdivided eqully into three height regions s upper, middle nd lower. The hemp specimens were prepred ccording to STM stndrd method for compression test of plstic mterils (STM D- 695, 28). Stems were cut into short sections hving fixed length of 25.4 mm (Figs.,). s the hemp stem is hollow, specil ttention ws tken to ensure smooth cutting without ny rekge of the stem. 2.2 Testing pprtus Compression tests were performed using universl testing system. Fig. 2 shows the schemtic digrm of the min mchine frme of the system. The system cn e used for stretching, compression nd relxtion of different iomterils. The system ws composed of min test frme hrdwre, dt cquisition system nd computer. The cpcity of lod cell of the mchine ws - 89 N. The loding rte ws mm min -. Movele jw Motor drive Ger ctutor Computer r Mchine frme Lod cell Compression rod Hemp stlk Smple holder Dt cquisition Fig. 2. Schemtic digrm of the compression test mchine. 2.3 Experimentl design completely rndomized design ws used for ech of two vrieties: nd. The tretments were the comintions of two specimen compression directions: xil nd lterl, nd three height regions: upper, middle nd lower. Forty replictes were tested for ech tretment, nd 4

5 totl numer of test ws 48 (2 vrieties x 2 directions x 3 regions x 4 replictions). The tretments re summrized in Tle. Tle Summry of the experimentl tretments Tretment Description Hemp vriety Stem direction xil Lterl Height regio Lower Middle Upper Single purpose (fier only) Dul purpose (fier nd seed) Compressed in the xil direction of stem Compressed in the lterl direction of stem Lower height region of hemp stem Middle height region of hemp stem Tender height region of hemp stem 2.4 Mesurements 2.4. Physicl properties Prior to compression tests, the outer nd inner dimeters ( d & d 2 ) of ech specimen were mesured using micrometer. ecuse of the vrition of dimeter long hemp stem, the dimeters t two ends of specimen were mesured to get the men dimeter. The stem wll thickness (t) ws clculted y the difference of outer nd inner dimeters of specimen. The mss of ech specimen ws mesured, nd the liner density (μ) ws defined s the mss per unit length Compressive properties () () Fig. 3. Two vrieties of hemp specimens fter compression: () ; (). 5

6 During compression test, specimen shown in Figs., ws plced on the smple holder. The specimen ws compressed y the compression rod t constnt speed. fter some compression, the specimens roke, minly ecuse of the stem wll eing collpsed (Figs. 3,). The dt cquisition system recorded the lod nd the displcement utomticlly during the course of compression. The lod-displcement curves of the tested specimens were used to derive the compressive properties of hemp stem. The imum compressive lod, P i.e. lod ws defined s the pek of the lod-displcement curve. To elucidte the compressive strength of hemp stem t specific stem cross-sectionl re, imum stress (stress t which filure tkes plce) ws determined. Treting the hollow hemp stem s tuing, the imum lod ws trnsformed into the imum stress ccording to the following eqution (Qingxi et l., 27): P σ = () π 2 2 ( d d2 ) 4 where σ is the imum stress in MP; P is the imum lod in N, d nd d 2 is the outer nd inner dimeter of stem in mm. P nd σ respectively represent the imum compressive lod nd imum compressive stress of the hemp stem specimens. The vlue of the modulus of compression, M ws otined from the slope of the first liner prt of the lod-displcement curve up to the pek point y using stndrd method for plnt mterils (Mohsenin, 986). The compressive energy, E ws clculted s the re eneth the entire loddisplcement curve evluted y numericl integrtion (Chttopdhyy nd Pndey, 999; Chen et l., 24). 2.5 Dt nlysis nlysis of vrince (NOV) (Steel & Torrie, 98) ws performed to exmine the min effects of experimentl fctors nd their interctions using the sttisticl nlysis softwre V9. (SS/STT). No interctions of the experimentl fctors were detected. Thus the min effects re presented. Mens of tretments were compred using Duncn s multiple rnge tests. Regression nlysis ws mde on the dt to exmine the trends of compressive properties in reltion to stlk outer dimeter. significnce level of proility P <.5 ws used for ll nlyses. 3. Results nd discussion 3. Physicl properties The vriety hd n verge outer dimeter of 6.7, 8.5 nd 9.2 mm for the upper, middle nd lower height regions, respectively (Tle 2). Lrger vlues of outer dimeters were oserved for the specimens: 8.7, 2.7, nd 6.3 mm for the upper, middle nd lower height regions, 6

7 respectively. The dimeter results were consistent with recently reported hemp stem dimeter, rnging from 6 to 6 mm y Chen et l. (24) nd comprle with the dimeters of mize stlks ( mm) found y Prsd nd Gupt (975). The wll thickness of the stem in the upper, middle nd lower height regions were 2.5, 3.4 nd 6.6 mm (), nd 4., 5.3 nd 8.7 mm (), which gve cross-section re of 86.5, 47.8 nd 249. mm 2 (), nd 7.9, nd 676. mm 2 (), respectively. The wll thickness nd cross-sectionl re of hemp stems were much greter thn those of lflf stems found y Gledr et l. (28) nd whet strw reported y Skuisz (98) nd Huer (99). The verge liner density of the upper, middle nd lower height regions ws 4.9, 22.4 & 36.6 g m - for nd 9.8, 4.3 & 9.3 g m - for, respectively. The liner density result for ws consistent with the report of hemp stem y Chen et l. (24). The liner density of hemp ws much higher thn tht for 6 grss species (2. 4 g m - ) reported y McRndl nd McNulty (98). Tle 2 * Physicl properties of hemp for two different vrieties in different stem height regions Property d (mm) 6.7 c (.3) 8.5 (.2) 9.2 (.8) 8.7 C (.8) 2.7 (.25) 6.3 (.36) t (mm) 2.5 c (.7) 3.4 (.2) 6.6 (.9) 4. C (.4) 5.3 (.2) 8.7 (.22) (mm 2 ) 2.7 c (.85) 36.9 (.47) 62.3 (2.76) 43. C (.92) 85. (3.92) 68.9 (7.9) μ (g m - ) 9.8 c (.33) 4.3 (.46) 9.3 (.7) 4.9 C (.73) 22.9 (.6) 36.6 (.6) * Mens in the sme rw followed y the sme lowercse or uppercse letters re not significntly different (proility P<.5) ccording to Duncn s multiple rnge tests. Vlues in prentheses re stndrd errors of the men. d, t,, μ: outer dimeter, wll thickness, cross-section re, nd liner density of hemp stem. ll physicl properties mesured were significntly incresed towrds the lower height regions of stem. lso, the vlues of the physicl properties of were significntly lower thn those of. The results showed tht nd could e considered s two distinct hemp plnts, which were pproprite for investigting how the initil properties ffected tht of the mechnicl performnces during different hndling nd processing conditions, such s, compressions. 3.2 Compressive properties Typicl lod-displcement curves Fig. 4 illustrtes typicl lod-displcement curves recorded from the compression tests. The curves showed some fluctutions, ut minly hve two stges: pre-filure () nd post-filure (). In stge, the force incresed from zero t the moment of initil contct etween the compression rod nd the hemp specimen, nd reched pek when the specimen structure filed. In stge, fter the filure, some specimens were le to provide some resistnce to the continued displcement of the compression rod, while some specimens showed drsticlly decresed strength. This rupt drop in lod-crrying cpcity of stem is relted to the hollow structure of hemp stem. 7

8 8 6 P (N) Fig. 4. Typicl compressive lod-displcement curves of hemp stem Compressive strength The vlues of P incresed linerly with the upper height region to the lower height region for oth vrieties in the xil compression direction (Fig. 5). Differences in P mong three regions were ll significnt. For the upper, middle, nd lower height regions of stem, the corresponding vlues of the xil P ws 624, 93 & 9 N for. Much higher vlues (762, 233 & 425 N) were otined for. For the lterl compression direction, the vlues of P were 58, 8, & 73 N for ; gin, higher P (82, 59 & N) were the cse for (Fig. 5). Trends of vritions of P with the height region nd the mgnitudes of P for the lterl direction were different thn those for the xil compression direction. First, the vlues of P for the lterl compression direction were out one tenth of those for the xil compression direction. Secondly, c C 4 5 Stem height region Stem height region () () Fig. 5. Mximum compressive lod (P ) of two hemp plnts ( nd ) s function of different height regions of stem: () xil compression direction, nd () lterl compression direction. Mens followed y the sme lowercse or uppercse letters re not significntly different. 8

9 did not lwys hve higher lterl P thn. Thirdly, the upper nd middle height regions hd similr P tht ws significntly lower thn tht of the lower region for oth vrieties. The trends of hemp stem height region effects on the compression lod otined were consistent with the compression results of sorghum stlks (Oke et l., 984). They reported tht the compression lod of sorghum stlks decreses s the stlk tpers from ottom to upwrds. This my e explined y the following fcts. The lower height region of stem is the oldest prt of the plnt nd hs the highest lignin content. Lignifiction cuses the cell wlls to thicken, gretly incresing their rigidity nd consequently the compressive lod. Mens of σ vried from.7 to 27 MP, depending on the height region of stem nd the compression direction. Similr to the P, the xil σ ws much greter thn the lterl σ. However, it ws interesting tht the trends of the effects height region on σ (Figs. 6,) were completely reverse of those of P. tht hd lower P generlly hd greter σ in oth compression directions, when compred to c 2 Stem height region Stem height region () () Fig. 6. Mximum compressive stress (σ ) of two hemp vrieties ( nd ) s function of different stem height regions: () xil compression direction, nd () lterl compression direction. Mens followed y the sme lowercse or uppercse letters re not significntly different Modulus of compression The modulus of compression otined for the xil compression direction ws etween 55 nd 776 N mm -2 (Fig. 7). The xil modulus of compression t the lower height region ws greter for oth vrieties. Smller lterl moduli (85-9 N mm -2 ) were otined (Fig. 7). For, higher lterl modulus ws oserved t the lower region, while for, higher lterl modulus ws oserved t the upper region. The resons were unknown. 9

10 stem height region Stem height region () () Fig. 7. Modulus of compression (M) of two hemp vrieties ( nd ) s function of different stem height regions: () xil compression direction, nd () lterl compression direction. Mens followed y the sme lowercse or uppercse letters re not significntly different Energy requirement The effect of stem height region on the energy requirement followed the trends: upper<middle<lower for the xil compression nd upper=middle<lower for the lterl compression (Figs. 8,), regrdless of the hemp vrieties. For, the compressive energy ws 43, 822 & 65 mj in the xil compression direction nd 23, 35 & 84 mj in the lterl compression direction for the upper, middle nd lower height regions, respectively. For, the corresponding vlues were 593, 3 & 89 mj in the xil direction nd 36, 33 & 62 mj in the lterl direction E (mj) C c E (mj) Stem height region Stem height region () () Fig. 8. Mximum compressive energy (E) of two hemp vrieties ( nd ) s function of different stem height regions: () xil compression direction, nd () lterl compression direction. Mens followed y the sme lowercse or uppercse letters re not significntly different.

11 The results indicted tht more energy ws required to compress the lower region stem in the xil direction. These trends of E cn e explined y the similr trends of P shown in Figs. 5, Effects of hemp stem dimeters on compressive properties It would e lso interesting to know how dimeters of hemp stem ffected the compressive properties, regrdless of the height regions of the stem. In most hemp hndling nd processing opertions, stem dimeter my e more prcticl prmeter thn height region. Therefore, the dt were interpreted sed on effects of stem dimeter (outer dimeter) in the following discussion Compressive strength The imum lod, P, incresed with incresing stem outer dimeters, d in ll cses (Figs. 9,). The xil P for oth nd seemed to e non-linerly relted to d (Fig. 9). For the lterl compression direction, liner reltionship ws oserved etween P nd d for oth nd (Fig. 9). The regression equtions representing these reltionships nd their coefficients of determintion (R 2 ) re presented in Tle Power () Power () 4 3 Liner () Liner () () () Fig. 9. Vrition of imum lod (P ) with outer dimeters of hemp stem (d ) for two vrieties: nd : () xil compression direction, nd () lterl compression direction. The imum stress, σ, decresed with incresing d for ll cses (Figs.,). This trend lso pplies to other plnt mterils. Lo et l. (24) reported tht the compressive strength per unit re of cellulosic mterils, such s moo fier decresed significntly with the increse in its outer dimeter. The compressive strength lso depends on the wll thickness of the hollow rpe stlk (Qingxi et l., 27). For the xil compression direction, the reltionships of σ nd d followed the exponentil equtions (Fig. ), while for the lterl direction, the reltionships followed non-

12 liner power function (Fig. ). The regression equtions nd the R 2 vlues re presented in Tle Expon. () Power () Power () 3 Expon. () () () Fig.. Vrition of compressive stress (σ ) with outer dimeter (d ) of hemp stem for two vrieties ( nd ): () xil compression direction, nd () lterl compression direction Energy requirement With incresing stlk dimeters, more energy required for compression of hemp stlks (Figs.,). For the xil compression direction, the dt for oth nd could e descried y the non-liner power functions; wheres, for the lterl direction, followed non-liner power function nd followed liner function (Tle 3). 5 5 E (mj) Power () Power () E (mj) Power () Liner () () () Fig.. Vrition of compressive energy (E) with outer dimeter (d ) of hemp stem for two vrieties ( nd ): () xil compression direction, nd () lterl compression direction. 2

13 Tle 3 * Regression equtions of compressive properties of hemp stem s functions of the outer dimeters of stem. Property Compression direction Eqution R 2 Eqution R 2 P ( N) xil P =. 842d P = d.68 Lterl P = d P = d d σ ( MP) xil σ = e.22d.6 σ = e.57 Lterl. 832 σ = d σ = d.6 E (mj ) xil E =.6474d E = 2.535d.7 Lterl E =.73d.82 E = 5.66 d * P, σ, E, d : imum compressive lod, imum compressive stress, compressive energy, nd outer dimeter of hemp stem. 4. Conclusions Hemp stem dimeter nd liner density incresed towrds the lower height regions of stem. The dul purpose hemp stlk, hd greter dimeters nd liner density thn the single purpose hemp,. The verge outer dimeter of hemp stem in the upper, middle nd lower height regions were 8.7, 2.7, nd 6.3 mm for nd 6.7, 8.5 nd 9.2 mm for, respectively. The verge liner density t the upper, middle nd lower height region ws 4.9, 22.4 & 36.6 g m - for nd 9.8, 4.3 & 9.3 g m - for, respectively. In generl, higher imum compression lod nd more energy requirement for compressing the lower height region of hemp stem in oth xil nd lterl directions. The verge imum compression lod t the upper, middle nd lower height regions were 624, 93 & 9 N for & 762, 233 & 425 N for (in the xil direction) nd 58, 8, & 73 N for & 82, 59 & N for (in the lterl direction). The imum stress vried from to 27 MP nd.7 to 2.8 MP in the xil nd lterl directions, respectively. The modulus of compression ws higher in the lower height regions for nd for the xil compression direction. The modulus vried from 55 to 776 N mm -2 for two hemp vrieties in the xil direction. In the lterl direction, modulus in the middle height region ws similr for oth hemp vrieties, nd different vlues were oserved for the lower nd upper height regions. The compressive energy requirements were significntly ffected y the hemp height region. The verge energy requirement t the upper, middle nd lower height regions were 43, 822 & 65 mj for & 593, 3 & 89 N for (in the xil direction) nd 23, 34, & 85 N for & 36, 33 & 62 mj for (in the lterl direction). The imum compression lod incresed with incresing outer dimeters of hemp stem. The reltionship etween imum compression lod nd outer dimeter of hemp stem could e 3

14 descried y power function (in the xil direction) nd liner function (in the lterl direction). The imum stress ws exponentilly decresed (in the xil direction) nd followed power function (in the lterl direction) with incresing outer dimeter for oth vrieties. The energy requirements for compression incresed with incresing stem dimeters followed y power function for two hemp vrieties in oth compression directions except for in the lterl compression direction. cknowledgements The study ws funded y Nturl Sciences nd Engineering Reserch Council of Cnd (NSERC). The uthors wish to cknowledge Keith Wtson, Mnito griculture, Food & Rurl Inititives for providing hemp stlks. Thnks re given to Dr. Stefn Cenkowski for his technicl guidnce on the test pprtus. Thnks re lso given to Composites Innovtion Ctr Mnito Inc, Emerson Hemp Distriution Compny, nd Prklnd Industril Hemp Growers Co-op Ltd for their supports to the project. References STM stndrds (28). D-695: Stndrd test method for compressive properties., ( hholyotin ; Krdngn P; Ichito K; Gotoh Y (988). Study on some physicl properties of sugr cne for whole stlk hrvester design. Ksetsrt Journl (Nturl Science), 22, 88-9 lhovec J (988). Mechnicl properties of some plnt mterils. Journl of Mterils Science, 23, ócs I; Krus M (997). The Cultivtion of Hemp: otny, Vrieties, Cultivtion, nd Hrvesting, HempTech, Sestopol, C Chen Y; Grtton J; Liu J (24). Power requirements of (Cnnis Stiv) cutting nd conditioning. iosystems Engineering, 87(4), Chttopdhyy P S; Pndey K P (999). Mechnicl properties of sorghum stlk in reltion to qusi-sttic deformtion. Journl of griculturl Engineering Reserch, 73, FO (29). griculturl Production., ( Gledr M N; Jfri ; Mohtsei S S; Tteefr ; Shrifi ; O Dogherty M J; Rfiee S; Richrd G (28). Effects of moisture content nd level in the crop on the engineering properties of lflf stems. iosystems Engineering,, Huer J (99). study of the physicl properties of whet strw. M.Phil., Crnfield Institute of Technology, Silsoe College, Silsoe, UK 4

15 Hnsen R (28). Industril Hemp Profile. griculture Mrketing Resource Center, Iow Stte University, Iow, US. ( _profile.cfm) Lo T Y; Cui H Z; Leung H C (24). The effect of fier density on strength cpcity of moo. Mterils Letter, 58, McRndl D M; McNulty P (98). Mechnicl nd physicl properties of grsses. Trnsctions of the SE, 23(2), Mohsenin N N (986). Physicl properties of plnt nd niml mterils. Gordon nd rech, NY, US Oke O; Kul R N; Mittl J P (984). Physicl nd mechnicl properties of sorghum (Sorghum icolor) stlk hrvested t vrious intervls fter grin mturity. griculturl Wstes,, 3-45 Prsd J; Gupt C P (975). Mechnicl properties of mize stlk s relted to hrvesting. Journl of griculturl Engineering Reserch, 2(2), Persson S (987). Mechnics of cutting plnt mteril. SE pulictions, Michign, US Qingxi L; Yito L; Cixi S; oping T (27). Reserch on the physicl mechnics properties of the rpe stlk. n SE meeting presenttion pper No. 7636, SE, Minnepolis, Minne., US Skuisz G (98). The dependence of the Young modulus of winter whet stlk in vrious phenologicl phses. University of griculturl Science, vol 37, pp. 9, Godollo, Hungry Steel R G D; Torrie J (98). Principles nd Procedures of Sttistics, iometricl pproch, 2nd edition, McGrw-Hill Inc, Montrel, QC, Cnd 5