Damage growth behavior and interlaminar fracture resistance of CFRP laminates under shear fracture mode

Interfacial failure problem of composite laminates was experimentally studied to know the dependence of interlaminar fracture resistance on various conditions as well as conditions of migration of the delamination into lamina to understand three-dimensional complex damage growths. A test method was proposed to realize a stable damage growth without influence of free edge under varying shear fracture mode in laminated composites. We could numerically evaluate critical energy release rate (ERR) for the delamination growth using a finite element method based on the measured shapes of the delamination and the applied load. Not only total ERR but also the ERR components in two directions parallel and normal to the fiber were calculated. The two components of the energy release were more appropriate to discuss the damage growth problem than the mode II and III components. When the normal component to the fiber was relatively small, the total ERR controlled the instability of the delamination. The delamination migrated into the lamina (that is, jumped to the other interface) where the ERR components normal to the fiber reached some level. The migration caused an anchoring effect on the delamination growth.