Computational modeling of material failure for parallel-aligned strand based wood composites

摘要

A three-dimensional nonlinear stochastic finite element model with size effect adjustment procedures has been developed to simulate the probabilistic distribution of tension strength of parallel-aligned strand based wood assemblies. An experimental database on the tensile modulus of elasticity (MOE) and tension strength of single and multiple ply parallel-aligned Douglas-fir strands has been developed. Based on the test data of single 2.5 * 17 mm veneer strands of varying lengths, input parameters for the model have been established. These parameters include the statistic geometric dimensions, the correlated single strand tensile MOE and strength distributions following a bivariate standard normal model. Based on nonlinear least square regression with constraints minimization, the tension strength distribution of each one of the multiple ply veneer strands (0.46 m long) has been used to establish a calibration factor, α, to account for the effects of resin, pressing and other factors on the strength of veneer assemblies and size effect. A failure criterion has also been set up within the nonlinear finite element frame with a stress update algorithm. A formula of strength modification factor α_f(n) is proposed to predict the probabilistic distribution of the tension strength of multiple ply veneer assemblies with various sizes of finite element meshes and different number of layers.