Study On The Damage And Fracture Of Reconstituted Bamboo

Bamboo is a kind of natural renewable resources,characterized by fast-growing,wide geographical distribution,high yield etc,having great development potential in the field of construction.Reconstituted bamboo is a new type of composite material which will be reorganized and strengthened,after cutting wire,crushing,washing,drying,dipping,hot rolled into plate,beam,column and other structures.In this paper,the composition of the reorganization of bamboo,the proportion of the relationship between the factors and the production process are summarized.The test piece was made by the recombinant bamboo,and then the test was put in different temperature and humidity environment.Tensile,compression and three point bending tests were carried out to obtain the properties of the material.Tensile curve shows that the linear rise and the vertical drop is brittle failure,and the peak value of elasticity is equal to 68.5Mpa,and the compression curve shows that the linear rise,the elastic and plastic rise,the yield stability is plastic failure,and the limit strength is equal to 53.1Mpa.The compressive modulus is about 2.5 times of the compression modulus,the Poisson's ratio is 0.3,and the critical condition load is 5660.571 Mpa.A large number of micro cracks and voids are distributed in the structure of the bamboo,and the initial damage is through the formation of macroscopic cracks which are visible to the naked eye.Delamination is the most typical failure mode.The criterion of linear superposition engineering is chosen as the fracture criterion,and the maximum circumferential stress theory is extended.Based on test results finite element simulation of three point bending test is carried out and the calculation of I type fracture toughness is 76.545Mpa·mm^1/2.By American Standard E399-72 the calculation is 83.9Mpa·mm^1/2 and Chinese research institute 24.1Mpa·mm^1/2.Numerical solution is in good agreement with the analytical solution.The stress factor of I and II in two dimensional environment can be transformed by the formula.The final linear superposition is obtained by engineering criteria 138.586Mpa·mm^1/2.In this paper,the theory of fracture damage field of composite materials is summarized,and the calculation principle and command program of finite element method are summarized.With the aid of the large-scale general finite element software Ansys,the change of the two-dimensional mixed mode and the stability,crack and expansion of the initial damage are analyzed.Numerical model based on the test results should be stress-strain curve by multi linear kinematic hardening constitutive model,and considering the large strain geometric nonlinear effect.Continuous trial selection suitable iterative load step to ensure the calculation accuracy and good convergence.The calculated crack load is 7.8KN,and the extension direction is-7.43.Stress field factor is I type,with positive and negative changes in a small range of II type,so the crack shape tends to be a straight line with the irregular up and down.In DCB tensile splitting test,the geometric size of the specimen is consistent with the finite element model.The first expansion of the load is 4.72 KN,and the final shape and analysis results are in good agreement,proved that the method is reasonable and accurate.The two-dimensional crack analysis case is written into APDL parametric language,in order to further deepen the study.