The Relation Between Structural Properties And Mechanical Behavior Of Bamboo

Bamboo as a substitute of wood has many advantages:fast-growing,short recycle,high productivity and high strength.To reveal the relation between its structure and mechanical properties,3-year-old Moso bamboo grown in Huoshan in Anhui Province were selected as experimental subjects.The major results are as follows:1.Structural properties of internodes and node of bambooAll cells in internodes are strictly aligned in longitudinal direction,the transverse ray cells don't exist.Vascular bundles bend when crossing nodes.Bamboo fiber volume fraction decreases gradually from outer to inner in radial direction of different heights in internodes.The average value of bamboo fiber volume fraction increases from bottom to top in longitudinal direction of a culm.Bamboo fiber volume fraction decreases gradually from outer to inner in radial direction of both internodes and node.The fiber length first increases,after reaching its maximum value then decreases in radial direction of both internodes and node.Double-wall thickness of thick-walled bamboo fiber first increases then decrease in radial direction of nodal part, but it doesn't change much in internodes.The diameter of bamboo fiber increases from outer to inner in radial direction of both internodes and node.The ratio of wall thickness and diameter of thick-walled bamboo fiber in node decreases from outer to inner in radial direction.But that of thin wall fiber in node doesn't show much varies.The ratio of wall thickness and diameter of bamboo fiber in internodes doesn't regularly.2.The basic density of bambooThe basic density of bamboo node which is 0.664 g/cm³ is larger than that of bamboo internodes which is 0.629 g/cm³.The variance analysis shows there is significant difference between them.3.The mechanical properties of bambooThe results of tensile experiment of samples which were divided in radial direction show that:the tensile strength and elastic modulus in longitudinal direction has direct proportion with bamboo fiber volume fraction.The equitation isσ=548.41A_f+6.5137(R²=0.9784);E=43.191A_f-1.8332(R²=0.9765) respectively.The tensile strength and elastic modulus of fiber sheath areσ_f=556.4433 MPa,E_f=43.6262 GPa respectively,calculated by mixture rule of composite material.It indicates bamboo fiber,whose tensile strength in longitudinal direction is higher than that of wood and even iron,is the major and important component which bears load.The results of tensile experiment of bamboo fiber sheath in longitudinal direction shows its tensile strength is 478.1913 MPa,smaller than that calculated by mixture rule.The reason is that bamboo fiber sheath doesn't have parenchyma ground tissue around it.The parenchyma ground tissue in bamboo can transfer loads between fibers,so it can enlarge the load bearing capacity of bamboo fiber.The results of contrastive tensile experiments of bamboo internodes and node in longitudinal direction show that:the tensile strength of the former is higher than that of the later.The variance analysis shows there is significant difference between them.The failure in internodes is of toughness type,while that of node is of crispness type.The results of contrastive bending experiments of bamboo internodes and node with epidermis and bamboo yellow in tangential direction show that:the maximum bending load of node is larger than that of internodes.The variance analysis shows there is significant difference between them.The results of the same contrastive bending experiments of bamboo without epidermis and bamboo yellow in longitudinal direction show that:there is no difference between their bending strength.It displays the nodal part doesn't cause any decrease in bending strength of bamboo.The results of contrastive bending experiments of crack and non-crack samples show that:there is no difference between their bending strength.The fracture stiffness of bamboo is 4847.305 KPam^1/2,which presents bamboo is the material with high toughness.The results of contrastive shearing experiments of bamboo internodes and node with epidermis and bamboo yellow in longitudinal direction show that:the shearing strength of the node is higher than that of the internodes.The variance analysis shows there is significant difference between them.The results of the same contrastive shearing experiments of bamboo without epidermis and bamboo yellow in longitudinal direction show that:the shearing strength of the node is little higher than that of the internodes.The variance analysis shows there is no difference between them.It implies the deciding factor of bamboo shearing strength in longitudinal direction is the strength of parenchyma ground tissue.The results of contrastive compressing experiments of bamboo internodes and node with epidermis and bamboo yellow in longitudinal direction show that:the compression strength of node is higher than that of internodes.The variance analysis shows there is significant difference between them.This is because the fiber volume fraction in node is larger than that in internodes.The results of contrastive compressing experiments of bamboo internodes and node without epidermis and bamboo yellow both in longitudinal and radial direction show that:the compression strength of node is higher than that of internodes.The variance analysis shows there is significant difference between them.These are due to the higher fiber volume fraction and the transverse fibers in nodal part.In a word,the node doesn't cause decrease in bamboo strength except the tensile strength in longitudinal direction but enhances it.This is a good example of function adapt in natural wood.