Comparison of continuum damage models for nonlinear finite element analysis of timber under tension in parallel and perpendicular to grain directions

Abstract

A reliable and efficient numerical modelling technique is essential to investigate the behaviour of timber and engineered timber products to promote their widespread use in construction. Wood is an anisotropic material and hence its mechanical properties largely depend on grain direction and type of loading i.e., material behaves differently under compression and tension. Material responses under tension parallel and perpendicular to the grain directions have been reported in the literature but the relevant progressive fracture behaviour has been ignored in typical numerical simulations, due to the complexities and uncertainties around modelling as well as lack of reliable test data. Fracture characteristics play a significant role in analysing crack initiation, propagation, and failure modes of timber so that its full potential can be utilised by knowing the post-elastic behaviour. This paper applies and compares four continuum damage mechanics based constitutive material models (MAT-22, MAT54/55, MAT-143 and MAT-261) available in the commercial finite element software LS-DYNA for simulating the post-elastic behaviour of general timber lamella products. Timber was modelled as both orthotropic and transversely isotropic material to simulate the fracture behaviour in tensile load cases. It is shown that the predicted fracture properties correlate well with experimental data. It was observed that all considered built-in continuum damage models in LS-DYNA are able to simulate the elastic response, but MAT-261, which was originally developed for modelling fibre reinforced composite materials, provides a simple yet reliable option for simulating fracture behaviour of timber.