Comparison of two material models 58 and 143 in LS Dyna for modelling solid birch wood

Sustainability plays an increasingly important role in the automotive industry. In order to reduce the
ecological footprint, the suitability of alternative bio-based materials like wood is investigated within the
project WoodC.A.R. In order for wood to be used as an engineering material for structural components
or even crash relevant structures, it has to fulfill high mechanical demands. The material behavior has
to be predictable and describable in a numerical simulation. Therefore, two material models *Mat_58
(*Mat_Laminated_Composite_Fabric) and *Mat_143 (*Mat_Wood) were compared and
validated against quasi-static tension and compression tests in all its six anatomical directions but also
against three-point bending tests with the wood fibers oriented parallel to the beam’s axis. So called
“clear wood” samples, i.e. specimens without any growing features, were tested covering the different
load levels: linear elasticity, strain-hardening, strain-softening and rupture. While *Mat_58 is an
orthotropic material model, *Mat_143 is transversally isotropic which means there is no possibility to
distinguish between the radial and the tangential direction of the material. Therefore, a trade-off for
both directions has to be found. On the other hand, the material law *Mat_143 is able to consider
influences like temperature, moisture content or even the quality respectively sorting degree of the
wood. Both material models show that some simplifications considering the hardening and softening
behavior, especially in compression have to be taken into account in multi-element specimens. While
wood shows softening at longitudinal compression, there is a pronounced hardening in perpendicular
direction. The strengths and weaknesses of both material models are discussed.