Advances in computational dynamics for inelastic continua with anisotropic material behavior: Formulation and numerical implementation of inelastic ductile behavior of spruce wood

Abstract

A new material model for wood is proposed and analyzed in this contribution. It is focused on anisotropic ductile failure at large strains and high strain-rates. The anisotropy of the ductile failure is represented by a multi-surface yield criterion coupled to anisotropic damage, which represents the anisotropic material behavior of wood due to its fibre orientation. The rate-dependency of the approach is modelled by visco-plasticity for large strain-rates in order to enable its application to the simulation of experiments at high loading velocities, e.g. impact and drop tests. To account for high strain-rates requires transient simulations of the nonlinear dynamic response of the structure. Moreover, a novel time integration method based on a three point backward Euler scheme is introduced. The localization of strain and mesh dependent results arising from simulations with softening formulations are overcome by gradient enhancement of the damage formulation. To this end, three nonlocal damage variables are introduced as additional degrees of freedom, which results in a coupled system of partial differential equations for displacement and damage variables. The material model is applied to the simulation of experiments on wood in a Split Hopkinson Pressure Bar experiment and in a drop weight test.