Modelling the double cantilever beam test with bending moments by using bilinear discontinuous cohesive laws

A theoretical model of the double cantilever beam tests with bending moments (DCB-UBM) is presented. The specimen is modelled as the assemblage of two laminated beams connected by a cohesive interface. It is assumed that the traction-separation laws – i.e. the relationships between the interfacial stresses and relative displacements – are described by bilinear discontinuous functions. An analytical solution for pure modes I and II is determined by solving the related differential problem. Furthermore, analysis based on the path-independent J integral is carried out. Formulas are given to determine the cohesive law parameters from experiments. Experimental tests have been conducted on glass fibre reinforced specimens under pure mode I and II loading conditions. The predictions of the theoretical model turn out to be in very good agreement with the experimental results.