Effect of stiffness matrices terms on delamination front shape in laminates with elastic couplings

Analytical modeling and fractographic analysis were led on carbon fiber reinforced polymer (CFRP) laminates subjected to double cantilever beam (DCB) tests. Specimens with delamination interfaces θ//−θ, θ//θ and 0°//θ were investigated. Analysis was conducted according to classical laminate theory (CLT) toward the deformative behavior of laminates and possible presence of elastic couplings. Components of matrices A, B, and D, as well as the parameters Dc and Bt were obtained using the Matlab software environment. Fractographic analysis was performed after the DCB tests in order to evaluate the shape of delamination fronts in specimens with different interfaces. The results showed that couplings between the bending moment and twisting curvature, as well as between the twisting moment and mid-plane normal strains, were strongly dependent on specimen plies orientation at delamination plane. The presence of elastic couplings caused the development of non-straight delamination fronts, which may produce inaccuracies in fracture toughness determination. Moreover, additional analysis was performed on the influence of θ layers on the B16 and the D16 terms responsible for the mid-plane shear deformation and twisting curvature. The results indicated that a greater number of same orientation layers significantly amplifies the undesirable effects of elastic couplings.