Strength of Miscanthus sinensis giganteus stems

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1 Annals of Warsaw University of Life Sciences SGGW Agriculture No 56 (Agricultural and Forest Engineering) 2010: (Ann. Warsaw Univ. Life Sci. SGGW, Agricult. 56, 2010) Strength of Miscanthus sinensis giganteus stems TOMASZ NOWAKOWSKI Department of Agricultural and Forest Machinery, Warsaw University of Life Sciences SGGW Abstract: Strength of Miscanthus sinensis giganteus stems. Baisng on carried out investigations on Miscanthus stems one can find that moisture content of investigated internodes varied from 26.27% to 11.15% and decreased with an increase in distance from the ground. The bending force values for the first three investigated zones did not differ statistically, since biometric parameters for these sections were similar. For sections VII and VIII a distinct force decrease to N was found. Average values of specific bending energy varied from 2.11 to 3.39 mj mm 2, while their course had the nature similar to changes in moisture content of Miscanthus stems. Key words: Miscanthus sinensis giganthean, bending specific energy. INTRODUCTION Miscanthus sinensis giganteus has been regarded as one of energetic plants of very high yield potential. Therefore, it is more and more frequently cultivated on energetic plantations, since it has majority of desirable features [Roszewski 1996; Tworkowski et al. 2010]. Irrespective of Miscanthus harvesting technology, on all its stages there occur a multiple interaction between the machine units and the crop. Learning of these phenomena would allow for selection of optimal machine operation parameters, leading to energy savings and selection of most favourable conditions of harvest [Frączek and Reguła 2009]. Therefore, the current works aim at determination of Miscanthus stem properties and its mechanical model. The analysis of Miscanthus stem geometry point out at a linear dependence between: length of internodes, their cross section area, cross section of node along the stem height; these changes have decreasing course from the lowest internode [Kolowca 2007]. The empirical mechanical model of the stem combines stresses, elasticity modulus and number of internode. The obtained results of Miscanthus stem model point out that elasticity modulus and bending strength along the stem height are positively correlated to each other [Kolowca et al. 2009]. Miscanthus is characterized by high values of elasticity modulus that exceed four times the values for basket willow and are dependent on the place of taking sample [Nowakowski et al. 2009]. One can find that elasticity modulus value increases from the lowest internode towards top, while carrying capacity decreases [Kolowca and Knapik 2008]. Considering the carried out works and the need for widening knowledge on mechanical properties of Miscanthus, the investigations were undertaken towards assessment of maximal force occurring during plant bending at various height, as well as corresponding specific energy values.

2 22 T. Nowakowski MATERIAL AND METHODS There were investigated the stems of Miscanthus sinensis giganthean obtained on April 2nd 2009 from experimental plantation of energetic plants of Agriculture and Biology Faculty WULS in Skierniewice. In investigations there were randomly selected 30 plants of biometric specification presented in Table 1. The TABLE 1. Specification of research material I, III, V, VII, VIII was determined by drying-and-weighing method. The sample mass was determined with accuracy 0.01 g with the use of RADWAG AG WPS 600/C scale. Determination of strength parameters of static bending was carried out for five height zones connected with natural structure of the plant, where division boundary was defined by the nodes. 10 Mean Min Max Median Kurtosis Skewness Standard deviation Variability coefficient [%] Mass of plant [g] Mass of leaves [g] Mass of stem [g] Length [mm] Stem diameter at height [mm] length was measured with a 3 m measuring tape, while the diameter with the use of numerical caliper VIS with accuracy of 0.01 mm. In the measurements on strength parameters 10 stems were used, that were divided at nodes into separate sections (internodes). The investigations were carried out four days after harvest, to simulate the biomass harvest into bunches, their transport and stationary breaking-up. There were investigated 5 stem sections counted from the butt end, obtaining five groups of samples. The moisture content of investigated sections measurements of force-deformation were executed for each zone, using the testing machine TIRAtest and PN-77/D Standard. The sample was freely placed on supports spaced by 0.06 m and loaded at half-length perpendicularly to radial section. The head motion speed was equal to 0.01 m min 1. The applied experimental conditions were coherent to that used for other plants [Skubisz 2001; Lisowski et al. 2009a, 2009b]. Basing on executed measurements the specific bending energy F jg was calculated as a quotient of total deformation

3 Strength of Miscanthus sinensis giganteus stems 23 Intermode Moisture content, % Moisture content FIGURE 1. Changes in moisture content depending on internode energy and section area calculated for ellipse section: E jg 1 S t F dx g where: E jg specific bending energy [mj mm 2 ], F g maximal bending force [N], S t cross section of sample at its bending place [mm 2 ], x deformation value for maximal force [mm]. In strength parameter calculations the force and deformation values were determined for the maximal force value on the force deformation diagram. RESULTS AND DISCUSSION The obtained results of plant biometric measurements point out at substantial homogeneity of the sample with respect to dimensions, since variability coefficient value does not exceed 14%. Small values of kurtosis point out at flattening of diagrams for investigated properties size and also at the distribution close to normal distribution. Only for diameter at height 2 m the kurtosis amounts to 4.83; it proves that the size curve is very slender and characterized by big concentration of investigated property around average [Jóźwiak and Podgórski 1995]. The skewness results point out at very weak and weak left-hand and right-hand asymmetry of distribution, with the exception of diameter at height 2 m. Figure 2 presents exemplary curves of force deformation dependence obtained during bending of Miscanthus stems for the internodes I, III, V, VII and VIII. One can find that with an increase in height, the value of force at which the material tissue bending strength is exceeded decreases. A decisive factor for these changes are differences in the stem cross-sections at particular heights (Tab. 1). As a results of variance analysis there was proved the effect of internode on the force and specific energy values (Tab. 2). The course of force F g and specific energy E jg along the stem height is presented

4 24 T. Nowakowski Force, N Deformation, mm FIGURE 2. Exemplary curves of force-deformation dependence obtained for internodes (I, II, III, V, VII and VIII) TABLE 2. Results of variance analysis on bending strength parameters of Miscanthus stems Parameter Maximal bending force, F g Specific bending energy E jg Descriptive features Sum of squares Degrees of freedom Mean square Femp Critical level of significance Internode < Residue Total Internode Residue Total in Figures 3 and 4. As distance from the field surface increases, the maximal force value decreases I the range from to N. However, for the first three investigated sections of stems only inconsiderable changes in the force values were found (6.2 N for average values). It was proved in detailed significance analysis for the groups of investigated sections, yielding three homogeneous groups: the first one for sections I, III., the second for sections III and V, and the third one for sections VII and VIII (Tab. 3). It resulted from the fact that the first group included the stem sections of lower plant segments of biggest geometric dimensions. One can find also that the biggest force values were obtained at three moisture content levels exceeding the average value; this certainly affected the obtained results. It was found quite different nature of specific energy changes during bending of Miscanthus (Fig. 4). At bottom stem section of naturally decreased moisture content due to postponed measurement date in relation to harvest date, the energy value amounted to 2.11 mj mm 2. The highest energy values were obtained for the stem sections III and V (3.39 mj mm 2 ). With the exception of lower stem section, the sections situated closer

5 Strength of Miscanthus sinensis giganteus stems 25 Force Fg, N Stem section (internode) FIGURE 3. Course of changes in force F g [N] along Miscanthus stem height Specific energy Ejg, mj mm 2 Stem section (intermode) FIGURE 4. Course of changes in specific energy E jg [mj mm 2 ] along Miscanthus stem height TABLE 3. Homogeneous groups of average strength parameters for Miscanthus internode bending Internode Maximal force F gmax Specific energy E jg Mean,. N Homogeneous groups Mean, mj mm 2 Homogeneous groups I III V VII VIII

6 26 T. Nowakowski to the plant top were characterized by smaller energy values. The lowest value (2.85 mj mm 2 ) was found for VIII internode. The obtained results were characterized by fairly moderate variability (variability coefficient equal to 22.65%). Since the energy values are related to the stem cross-section, the stem dimensions are decisive for the obtained results. The moisture content was one of factor determining the specific energy values, since one could find the similar changes in specific energy of investigated internodes and in moisture content. However, detailed analysis on the effect of internode on specific energy values allowed for isolation of two homogeneous groups: one for the lowest internode, and the second one for the remaining internodes (Tab. 3). Therefore, taking samples from higher parts of plant will not influence the changes in specific energy values. SUMMARY Analysis of the obtained results of investigations on moisture content of Miscanthus plants harvested in spring enabled to find that it changed distinctly along the stem height. For the investigated plants it ranged from 11.15% to 26.27% for stem sections I and III, respectively, while the maximal bending force decreased linearly from to N. Destruction of sample calls for proportionally lower bending force, when the cross-section of sample is decreased. These changes are small for internodes I, III and V, since the plants of that area are characterized by similar biometric and moisture parameters. The specific energy needed for bending plants ranged from 2.11 to 3.39 mj mm 2.The variance analysis proved the effect of internode on the force and specific energy values. The obtained information are useful in designing of machines related to harvesting of Miscanthus and justify the need for carrying out further investigations on mechanical properties of energetic plants. REFERENCES FRĄCZEK J., REGUŁA T. 2009: Wpływ wybranych czynników na wartość współczynnika tarcia rozdrobnionych pędów miskanta olbrzymiego. Inżynieria Rolnicza, nr 6(115), JÓŹWIAK J., PODGÓRSKI J. 1995: Statystyka od podstaw. Wyd. Państwowe Wydawnictwo Ekonomiczne, 384. KOLOWCA J. 2007: Analiza geometrii źdźbła miskanta olbrzymiego. Inżynieria Rolnicza, nr 7(95): KOLOWCA J., KNAPIK P. 2008: Właściwości mechaniczne źdźbła miskanta olbrzymiego. Inżynieria Rolnicza, nr 9(107): KOLOWCA J., WRÓBEL M., BARAN B. 2009: Model mechaniczny źdźbła trawy miscanthus giganteus. Inżynieria Rolnicza, nr 6(115): LISOWSKI A., NOWAKOWSKI T., KLO- NOWSKI J. 2009a: Właściwości mechaniczne ślazowca pensylwańskiego, [w:] Biomasa jako źródło energii, red. Jackowska I. Warszawa Wyd. Wieś Jutra, LISOWSKI A., NOWAKOWSKI T., KLO- NOWSKI J., SYPUŁA M., CHLEBOW- SKI J. 2009b: Naprężenia tnące i energia jednostkowa cięcia łodyg roślin energetycznych, [w:] Produkcja biomasy. Wybrane problemy, red. Skrobacki A. Warszawa Wyd. Wieś Jutra, NOWAKOWSKI T., LISOWSKI A., KLO- NOWSKI J., GENDEK A. 2009: Moduł sprężystości przy zginaniu łodyg wybranych roślin energetycznych. Zeszyty Pro-

7 Strength of Miscanthus sinensis giganteus stems 27 blemowe Postępów Nauk Rolniczych. Zeszyt 543, Warszawa 2009, PN-77/D Drewno. Oznaczenie wytrzymałości na zginanie statyczne. ROSZEWSKI R. 1996: Miskant olbrzymi Miscanthus sinensis giganteus. Nowe rośliny upraw-ne na cele spożywcze, przemysłowe i jako odnawialne źródła energii. Wydawnictwo SGGW, SKUBISZ G. 2001: Development of studies on the mechanical properties of winter rape stems. International Agrophysics 15: TWORKOWSKI J., KUŚ J., SZCZUKOW- SKI S., STOLARSKI M. 2010: Produkcyjność roślin uprawianych na cele energetyczne. [w:] Nowoczesne technologie pozyskiwania i energetycznego wykorzystania biomasy, (red.) Bocian P., Golec T., Rakowski J., Wydawca Instytut Energetyki, Warszawa: Streszczenie: Wytrzymałość łodyg miskanta olbrzymiego (Miscanthus sinensis giganteus). Wzrost zapotrzebowania na materiał biologiczny z przeznaczeniem na cele energetyczne spowodował zainteresowanie roślinami o dużym potencjale plonotwórczym. Do takich roślin zaliczamy miskanta olbrzymiego. Przy uprawie w sprzyjających warunkach po trzecim roku uprawy plon może osiągać 30 t s.m./ha i utrzymuje się do 8 9 roku prowadzenia plantacji. Na rozwój lub ograniczenie upraw niezwykle ważnym czynnikiem jest zapewnienie specjalistycznych maszyn do jej zbioru i obróbki. Dlatego pozyskanie informacji niezbędnych do projektowania maszyn związanych z procesem zbioru roślin miskanta stało się koniecznością. W pracy przedstawiono wyniki badań związanych z oceną maksymalnej siły występującej podczas zginania roślin na różnej wysokości jak również odpowiadającej jej energii jednostkowej. MS. received April 2010 Author s address: Katerdra Maszyn Rolniczych i Leśnych Warszawa ul. Nowoursynowska 164 Polska tomasz_nowakowski@sggw.pl