Cohesive Zone Material model in ANSYS: a sensitivity analysis on a DCB test case

The interlaminar failure of a composite structure, known as delamination, is of special interest because when such a structure is subjected to certain types of external loads, in particular compression loads, the failure process can continuously grows, resulting in a complete structural collapse of the damaged area. In order to design structures, which are damage-tolerant, analyses must be conducted to study the propagation of delaminations. Hence, the aim of this work is to investigate on the tools available in the commercial finite element code ANSYS®, which are able to simulate the delamination growth and other similar fracture phenomena. In particular, the cohesive bilinear constitutive model was applied to a simple test case (double cantilever beam) and the sensitivity of the model with respect to the number of time steps, artificial damping and mesh density was assessed. It was found that: 1. the cohesive model was very sensitive to the number of time steps used in the analysis. The user has to be chose appropriately such a number so that the constitutive model is correctly enforced and the solution time is kept acceptable; 2. simulations are not significantly sensitive to the mesh density, nevertheless, some oscillations in the reaction curve were obtained by using coarser mesh; 3. the artificial damping coefficient affects the solution as soon as the initial crack starts to grow. The value of 0.1t was found adequate to obtain reliable results by keeping low the computational time.