Numerical and experimental study on deformation and failure of trees under high-velocity impact loads

The multiphase and orthotropic nature of trees lead to their complex mechanical properties. In this paper, experiments and numerical simulation were conducted to investigate the deformation and failure processes of trees under impact loads. Gas gun system was applied for impact tests and high-speed camera was used to capture the impact failure process. An anisotropic constitutive model combined with strain hardening coefficients was applied to describe the dynamic response of wood materials. The presented numerical model was developed in commercial finite element software LS-DYNA to simulate failure process of a birch tree under impact of aluminum sabots at various velocities. The strain hardening coefficients were determined through correlation with the experimental measured energy absorption values under different impact speeds. The model was then further applied to study the impact resistance and energy absorption capability of the birch tree. The presented material model and modeling framework could be used for numerical investigation of various impact problems, e.g. vehicles' impact with electrical pole and aircraft crashing into forest.