Tensile Strength And Size Effect In Transverse Quasi-brittle Fracture Of Bamboo Scrimber

As a renewable and green composite with unidirectional fiber,bamboo scrimber has the advantages of densified and uniform micro-structure,high strength,variable size and shape,and high utilization rate of raw materials.Therefore,this material has a broad prospect in civil engineering.For the bamboo scrimber,size effect usually occurs in the longitudinal tensile strength calculated by mechanics of materials,so the fracture mechanics method should be used to analyze.In order to research the tensile strength and size effect of bamboo scrimber,the three-point-bending(3-p-b)tests in transverse I-type fracture were carried out on varisized un-notched and single-edge-notch(SEN)bamboo scrimber samples with geometric similarity and dissimilarity.Through the load-displacement curve,it is concluded that the transverse quasi-brittle fracture process of bamboo scrimber can be divided into three stages:linear elastic stage,softening stage and failure stage.Based on the boundary effect model(BEM)in fracture mechanics,a quantified relation between the micro-structure and the fracture properties of bamboo scrimber was acquired by introducing an important micro-structure parameter—average diameter G.And a tensile strength model was established to calculate the fracture parameters of bamboo scrimber.Three common mathematical statistics,namely normal distribution,Weibull distribution and lognormal distribution were adopted and compared to analyze the test data,and normal distribution was suggested for its high accuracy and effective reliability.And the tensile strength and fracture toughness of bamboo scrimber with 96%reliability were obtained.The calculation results of the tensile strength model indicate that the tensile strength of both geometric similarity and dissimilarity samples are within the reliability range of 96%.Moreover.f_t was in good agreement with the idea tensile strength obtained by the tensile strength and volume fraction of fiber bundles.Therefore,tensile strength model can be unacted on size effect,and the tensile strength calculated by this method was the intrinsic material property.And the tensile strength of the large-size members can be predicted by the general-size samples in the laboratory(50mm in height)through this method.And the maximum relative error was only 7.68%.In addition,in order to research the influence of moisture content on tensile strength of bamboo scrimber,3-p-b tests were conducted on SEN samples with different moisture content ranged from 5%to 25%.The test results showed that with the increase of moisture content,the tensile strength first increased and then decreased linearly.In summary,the research results of this paper improve the solid mechanics system of bamboo scrimber,and a nonlinear fracture mechanics method called tensile strength model is provided to determine the tensile strength of bamboo scrimber.And it provide a theoretical reference for the practical engineering application and industrial design of bamboo scrimber.