Two-parameter model of the failure of adhesive joints
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The proposed two-parameter model of adhesive failure makes it possible to study the limiting states of a composites with delaminations by constructing criterional relations of the type (4.5), (4.6). Within the framework of the above-stated hypotheses and results, the process of the adhesive failure of composites with delaminations can be represented as follows. The application of an external load results in the formation of zones of interfacial shear prefracture near the ends of the delaminations. The dimensions of these zones depend both on the geometry of the delaminations and on the external load. With a further increase in the load, microscopic interfacial defects accumulate in the region Ses(0), which leads to an increase in the size of this region in accordance with a relation of the type (4.3). Avalanche shear failure occurs when the external loads reach the limiting values established in accordance with criterion (1.2).
The results obtained here are based on the assumption that the strength conditions for the constituent phases are satisfied. It should be noted that the proposed approach can be used to construct a model which will embrace the process of adhesive-cohesive failure of composites. To do this, it is necessary to also employ the corresponding strength hypotheses of the phases, which in turn increases the number of phenomenological constants (such as the critical stress intensity factors KIc, the yield point σy, the fracture stress σf, etc.) In the last case, it is possible to qualitatively describe a range of composite failure processes with allowance for the interaction of brittle microcracks within the phases and delaminations of different types. It should also be noted that the results obtained here -particularly the model of failure of adhesive joints with allowance for finiteness of the interfacial stresses — justify the use of the methods of plate and shell theory  and other methods in the analysis of laminated composites.
KeywordsStress Intensity Factor External Load Laminate Composite Interfacial Shear Adhesive Joint
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