XFEM study of crack propagation in logs after growth stress relaxation and drying stress accumulation

There are crack-prevention mechanisms in living trees. However, in the felled logs, relaxation of growth stress and accumulation of drying stress may cause crack propagation. To investigate the crack propagation behavior and crack patterns in log cross sections, theoretical and simulation models are developed in this paper. In the theoretical model, global stability and local instability of cracks are considered in logs. In the simulation models, energy release rate is calculated based on FEA J-integral calculation models; crack patterns on log cross sections are investigated by the XFEM and fracture mechanics simulation models. Simulation results suggest that various crack patterns may develop in log cross sections, and there are several representative patterns. The existence of the simulated crack patterns can also be verified in real logs. The results of parameterization indicate that the crack bifurcation has a close relationship with energy storage and release modes. The pattern of main cracks is related to the damage initiation–evolution parameters. These phenomena can be explained by the energy principle of crack propagation and the stability principle of energy storage systems.