Modeling delamination in composite laminates

Plate theory in conjunction with fracture mechanics approach is used to model delamination in composite laminates. Laminated structure with multiple delamination at one or two thickness locations is modeled by two or three separate Mindlin plates, respectively, with appropriate constraint conditions imposed between adjacent plates. On the base of the modified crack closure method, a general expression for the strain energy release rate at delamination front is derived for the plate model. The plate model for delamination is then used to analyze the DCB and ENF specimens. Delamination characteristics on these specimens are identified and a design recommendation for these specimens is made to improve fracture toughness test involving interface of different ply orientations. The curved delamination front in DCB specimen is measured experimentally and compared with plate model prediction. Low velocity impact tests are performed to characterize delamination growth. A delamination growth model is then established. Experimental data of impact-induced delamination compares well with plate model prediction. Based on experimental observation, a progressive delamination growth model is proposed, which co-relates delamination growth at different load levels. The validity of this progressive delamination model is also investigated by using the plate model