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A NATURAL COMPOSITE MATERIAL──BAMBOO

LI Shihong;FU Shaoyun;ZHOU Benlian(Institute of Metal Research, Chinese Academy Of Sciences,International Centre for Materials Physic, Chinese Academy of Sciences)ZENG Qiyun(Instilule of APPlied Ecology, Chinese Academy of Sciences)  
Natural biomaterial--bamboo--is investigated as a compostie matenial on macro,meso- and micro-scale. The macrostructre of bamboo can be treated as one-end-fixed column, the relationbetween its external ne-cural moment and the cross sectional fie-cural modulus reveals that its macrostructureis found to be satisfied with the equal-strength design principle of the mechanics of materials.The changingtrends of macro mechanical properties of bamboo and its fiber volume fraction(FVF)are very similar alongradial direction, and there exists typical lineal correlation between the longitudinal fie-cural strength, tensilestrength,tensile modulus and its fiber volume fraction. This can be explained with bamboo's mesostructureand the "Principle of Mixture" of fiber-reinforced composite materials. The constituents of bamboo can beclassfied as follows: 1. reinforcement--bast fiber in vascular bundles, i.e. fiber strand and sclerenchymasheath;2. matrix--thin-walled cells around vascular bundles, vessels and sieve tubes in vascular bundles.The tensile strength of bamboo bast fiber is much higher than that of thin-walled cells,thus bamboo's mechanical properties are dominated by the fraction of bast fibers. The influence of bamboo nodes to its structural stiffness and strength were determined, these nodes play an extremely important role in preventingbamboo culm from local bulking and in enhancing structural stability. On micro scale, bamboo fiber is investigated as a belieal, multi-layered hollow cylinder. The stiffness properties of such a fiber structure were calculated and compared with those of a model of Plain uniform fiber bundle like in common laminates. Thestiffness coefficient Q(66),which is in fact shear modulus, is increased greatly at a little loss of longitudinalstiffness Q(11). Therefore, such a complicated fiber structure of plant fiber have bulge on a uniform one, therationale of its complex microstructure was demonstrated in the case of stiffness.
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