Three-dimensional nonlinear orthotropic finite element material model for wood

The presented study concentrates on the development of three dimensional (3D) constitutive equations for wood materials. The developed material model is implemented in a nonlinear finite element simulation code. Wood is a very complex and highly anisotropic material with lots of inhomogeneities. The nonlinear characteristics of the material complicate the utilization of numerical simulations for structural safety prediction. A realistic description of nonlinear material behavior of wood could aid considerably in numerical accuracy and predictability. The presented model uses incremental-loading and curve-fitting techniques to trace the nonlinear behavior of wood material. User-defined nonlinear parameters are introduced to control the stiffness change based on the stiffness of previous iteration or initial stiffness. A modified Johnson rate dependent model is employed to account for the influence of strain rate. The presented 3D nonlinear model is implemented in the FE explicit code DYNA3D. The model is validated through comparison with experimental tests reported in the literature. The model efficiently captured the nonlinear characteristics of wood, and therefore provides a new 3D material modeling approach for wood materials.