Numerical simulation tool for wooden boards with a physically based approach to identify structural failure

Knots and the resulting fiber deviations are the main influencing parameters of the effective stiffness and strength behavior of wooden boards on a structural scale. Depending on the size, shape and arrangement of knots/knot groups, certain effective mechanical properties can remain unaffected or change significantly. For this reason, a reliable prediction of the mechanical behavior of wooden boards is a basic requirement for efficiently designed wood products and timber structures. Within this work, a Finite-Element simulation tool was developed, which is able to consider a realistic three-dimensional fiber course in the vicinity of knots and also accounts for density and moisture dependent strength and stiffness properties. The estimation of effective strength values within this tool is done by examining the qualitative stress changes in predefined volumes, and is based on the formation of failure zones predominantly caused by perpendicular-to-grain tension in the vicinity of knots. Comprehensive test series, comprising tensile and four-point bending tests were carried out and used for validation. In general, a very good correlation between numerical and experimental results was obtained.