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Received: 16.03.2016 Accepted: 25.05.2016 Published: 30.06.2018 This paper considers the subcritical elastic-plastic deformation of a three-layer composite and the layer separation accompanied by the fracture of an adhesive layer. The problem is reduced to the system of two variational equilibrium conditions with respect to the bonded layers' velocity fields by means of averaging a stress component in the adhesive layer across its thickness. When we solve an elastic-plastic problem in terms of subcritical deformation, the -area is distinguished where the fracture criterion is reached. The distribution of load (node forces) that affects a body from the -area is determined by resolving a pre-critical deformation problem with the known motion law of the -area boundary. As the next step, we consider changes in the body’s stressstrain state (SSS) during the fracture of the -area. We solve the elastic-plastic problem under simple unloading of the body’s -surface and remaining an external load that corresponds to the beginning of the fracture process. During the -unloading, the formation of new plastic areas, partial unloading and reaching the fracture criterion are possible. As a result, the body’s SSS at the moment when local unloading begins differs from its state when the -unloading ends. This constitutes a principal distinction from the common procedure of “killing the elements” when the element rigidity (after reaching the fracture criterion) is supposed to be close to null. Herewith the body state outside a removed element is considered to be unchangeable; and the generation of unloading and additional loading zones (after the element is excluded) is not considered. In case of linear elasticity, the solution of the problem with a removed area under fixed external load coincides with the -unloading solution by virtue of the solution uniqueness and the superposition principle. However, the solution of the elastic-plastic problem for the body with the removed area under simple loading will not coincide with the -unloading solution. The paper presents the solutions of composite delamination problems that illustrate the simple -unloading method both in linear elastic and in elastic-plastic formulations.

MODELLING THE GENERATION OF NEW MATERIAL SURFACES IN A COMPOSITE WITH AN ADHESION LAYER UNDER COHESIVE DESTRUCTION