Simulation of failure in timber with structural inhomogeneities using an automated FE analysis

In this contribution, approaches to analyse timber characterized by structural inhomogeneities are introduced using the Finite Element Method (FEM). In an automatable procedure, the structural behaviour of timber containing knots is simulated on the basis of a few geometrical data obtained by surface scans. To generate FE models automatically, two meshing procedures are introduced. The fibre course is determined numerically using a flow-grain analogy. Elastic, plastic and fracture mechanically based macroscopic material models are used to represent the mechanical properties of homogeneous wood, free of inhomogeneities. The procedure is used to compute global material parameters, as the global longitudinal elasticity modulus and tensile strength similar to EN 338 and therefore can be used for numerical timber grading. For comparison, experiments are considered where the global elasticity modulus and the ultimate load have been determined in tensile tests. The tests are simulated for selected boards. Possible failure zones are identified by the application of plasticity models. To determine the ultimate load at tensile loading numerically, cohesive elements are applied.