Modelling the generation of new material surfaces in a composite with an adhesion layer under cohesive destruction

The paper is concerned with the subcritical elastoplastic deformation of the trilaminar composite and the delamination accompanied by the fracture of the adhesive layer. The problem is reduced to the system of two variational equilibrium conditions with respect to the velocity fields of the bonded layers by means of averaging the stress components in the adhesive layer thought its thickness. When we solve the elastoplastic problem in terms of subcritical deformation, the δ-area is distinguished where the fracture criterion is reached. The distribution of load (node forces) which affects the body from the δ-area is determined by resolving the pre-critical deformation problem with the known motion law of the δ-area boundary. As the next step, we consider the changes in the body’s stress-strain state during the fracture of the δ-area. We solve the elastoplastic problem under simple unloading of the body’s δ-surface and remaining the external load which correspond to the beginning of the destruction process. During the δ-unloading, the formation of new plastic areas, partial unloading and reaching the destruction criterion are possible. As a result, the body’s stress-strain state in the moment when the local unloading begins differs from its state when the δ-unloading ends. This constitutes the principal distinction from the common procedure of “killing the element” when the element rigidity (after reaching the fracture criterion) is supposed to be close to . Herewith the body state outside the deleted element is considered to be unchangeable; and the generation of the unloading zones and additional loading zones (after the element is excluded) is not considered. In case of linear plasticity, the solution of the problem with the ruptured area under the fixed external load coincides with the δ-unloading solution by virtue of the solution uniqueness and the principle of superposition. However, the solution of the elastoplastic problem for the body with the ruptured area under simple loading will not coincide with the δ-unloading solution. The paper presents the solutions of the composite delamination problems which illustrate the simple δ-unloading method both in the linear elastic as well as in the elastoplastic formulations.