Interface plasticity and delamination onset prediction

The authors carry out tensile tests on composite multi-layers that display a sliding at the interfaces between layers before delamination detection. At delamination onset, the sliding value at the free edges is almost the same for all of the tested laminates. A delamination criterion involving the measured critical sliding value is then adopted for predicting delamination onset in the tested laminates. A multi-particle model which takes into account the interface sliding is used for evaluating the interfacial stresses. The model equations are determined by means of the Hellinger-Reissner variational formulation in which the sliding is supposed to be a state variable of the system. For a given tensile load, the sliding is then determined by using a plasticity criterion (herein two criteria are studied) and a normal flow rule. The comparison of the theoretical calculations with the experimental data proves that delamination is predicted accurately and that the interface sliding is evaluated correctly.