Development of a Wood Material Model For Roadside Safety Applications

A computationally efficient wood material model is being developed and validated for performing LS-DYNA simulations of vehicle collisions into wooden guardrail posts. Typically, the failure modes and stress-strain relationships of wood depend on the direction of the load relative to the grain and the type of load (tension, compression, or shear). The model includes transversely isotropic constitutive equations and yield surfaces to simulate different stiffnesses and strengths parallel and perpendicular to the grain. Hardening and softening formulations simulate stress-strain relationships that are linear to brittle failure in tension and shear, and nonlinear and ductile in compression. A rate effects formulation increases strength with strain rate. For easy use, default material properties for Southern yellow pine and Douglas fir are provided as a function of moisture content, temperature, and grade. Correlations with static bending and bogie impact tests are being used to validate the model.