Buckling, postbuckling and non-self-similar decohesion along the finite interface of unilaterally constrained delaminations in composite

This dissertation presents a study on the buckling and decohesion of unilaterally constrained delaminations. The buckling of unilaterally constrained plates was investigated in two different contexts. First, infinite rectangular plates were considered. The system was modeled as a plate resting on a tensionless elastic foundation. Assuming a periodic response, the governing equations were solved accordingly. Due to the constraint an increase in the buckling load of 22-36% was obtained for the cases considered.;The second context pertains to finite rectangular plates. Employing a nonlinear elastic foundation model, the governing equations were solved approximately for a wide range of parameters. As a verification of the validity of the results, the buckling loads obtained from the infinite plate and the finite plate (aspect ratio = 5) solutions were compared and showed a very close agreement. This demonstrated that using nonlinear elastic foundation models to model unilateral constraints is viable. Experimental investigation using shadow Moire technique showed clearly that unilaterally constrained mode shapes were periodic and the experimentally obtained buckling loads were found to be bounded by those obtained theoretically.;The non-self-similar decohesion of local delaminations was investigated by modeling the delamination as an elastic finite plate attached to an interphase layer which was modeled as a nonlinear elastic foundation exhibiting tension-softening and compression-stiffening constitutive law. The compression-stiffening was employed to simulate the presence of a rigid unilateral constraint. Such a model was found to closely characterize the decohesion process without resorting to any fracture mechanics concepts overcoming the limitations of the latter in predicting non-self-similar growth of delaminations. Further, during the formulation no distinction was made between the phenomena of buckling (and postbuckling) and non-self-similar growth. In other words, the same equations govern the entire behavior from beginning (starting to load/displace the structure) to end (complete delamination and/or loss of stiffness) without specification to certain regimes of validity. The simplicity and generality of such an approach proved to be viable for the delamination problem where buckling, postbuckling, non-self-similar growth and unilateral constraint are all present.