Optimization of CZM parameters of Norway spruce tested in mode I using multistart simplex method

Abstract

The paper addresses the advanced fracture analysis of the SEN-TPB test on Norway Spruce in three anatomical directions: tangential (T), radial (R) and tangential–radial (TR). It utilizes reverse engineering to obtain cohesive zone model (CZM) parameters, which are then compared to the experimental values obtained using the compliance-based beam method (CBBM) and additional standard material tensile tests perpendicular to the grain. The optimization employs force–displacement curves to find their optimal fit using the multistart simplex optimization method. Results indicate that CZM modeling can be relatively problematic when realistic values are used; however, the best agreement with experimental data is observed for the group of cracks in the TR direction. A fundamental issue with CZM modeling in the elastic part has been identified and discussed. The sensitivity of the problem to various parameters was assessed, and an energy balance in the CZM at $F_{max}$ was performed. This work contributes to knowledge about realistic modeling of the interface and a fundamental understanding of fracture in wood.