Discussion Forum

Hi Comsol Users and Technicians,

I'm working on a soft thin film (subject to expansion) in adhesion to stiff substrate using cohesive zone model. The interface is thus in mode II cracking. I assumed elastic perfectly plastic relation for the film and an elastic relation for the substrate. I found that in some cases, depending on the relative value of interfacial strength (tau_c) and yield stress, the plastic flow begins while interfacial shear stress is well below tau_c until a certain displacement is reached and the damage occur. The interfacial normal stress is compressive and vertical displacement is negative (negative, meaning there's a small penetration, does not contribute to the effective gap distance). It seems that the dissipated energy would not the the area of the triangle for the bilinear relation since the stress is well below tau_c.

I also tried to decrease the interfacial shear strength (Tau_c) such that maxmum stress occur before yield. In this case, the interfacial shear stress overshoots shear strength by a factor of 1.4 and then stays at the high value (probably bounded by the yield stress).

My concern is whether CZM can work with plastic relation. Are they in contradiction in the sense that the material along the interface is subject to two constitutive equation?

Any comments would be highly appreciated.

Xiaokang