An Energy Criterion for Adhesive Failure of a Composite Pipe under the Influence of External Pressure

Adhesive failure as a result of the development of delamination or splitting is one of the most common types of strength loss in composite structural materials. Delaminations of fiberglass panels, pipes, and pressure vessels can occur under the influence of bending and torsional moments, as well as compressive loads. In composite pipes, under the action of temperature stresses or external compressive pressure, the inner layer or liner may peel off with a simultaneous loss of stability. To analyze the critical stresses when adhesive failure occurs, an energy criterion is used, but, however not in a differential form, but in the form of a comparison of the difference between the initial and final elastic energy of the layer with the work of adhesive destruction proportional to the delamination area. The solution to the problem of large deflections of the layer after loss of stability is reduced to elliptic integrals of the first and second kind. The introduction of the parameter of specific work of adhesive destruction into the energy criterion with a dimension different from the dimension of stress makes it possible to describe the scale effect of strength—the dependence of critical stresses on the radius of the pipe and the characteristic thickness of the layer, the delamination of which is associated with the minimum critical stress. The given estimate of this thickness indicates the most dangerous depth of location of a technological defect, such as nongluing, and can serve as a justification for interpreting the results of nondestructive testing of composite pipes.