The present paper deals with the analytical investigation of the mode-I debonding occurring in the double cantilever beam test (DCBT). Among the various modeling approaches, Cohesive Crack Model (CCM) and Finite Fracture Mechanics (FFM) are herein selected due to their ability to join the stress- and energy-based approaches. According to both approaches, the specimen is modelled as an assemblage of two beams partly bonded together by a weak interface, i.e. the interface is considered equivalent to a bed of springs acting along the direction normal to the interface. Concerning the cohesive interface approach, it is assumed that, ahead of the physical crack tip, there exists a cohesive zone where the relation between the normal stress and relative displacement between the adherents is described by the cohesive traction separation law, herein assumed to be of Dugdale type (constant stress) or with a linear softening. The interfacial stresses are determined in closed form, together with the global load-displacement response. The expressions of the maximum load and the corresponding process zone are given. The CCM predictions are compared to the Linear Elastic Fracture Mechanics (LEFM) ones. As expected, it is found that the LEFM overestimates the debonding load, thus justifying the need for a more refined modelling. A second approach is the one provided by the FFM, according to which the springs are simply linear-elastic up to their breakage. Thus, the FFM implementation is quite straightforward and in any case much simpler than the CCM. Since, for what concerns the debonding loads, the predictions provided by CCM and FFM are in very good agreement with each other, FFM can be seen as an excellent candidate for preliminary sizing of composite structures against debonding occurrence. Finally, the CCM approach is checked numerically with a FEA. The DCBT interface is discretized with zero-thickness generalized contact elements and implemented in the finite element code FEAP. Also in this case, a good agreement between the results obtained confirms the accuracy of the proposed approach and its feasibility in engineering practice.
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