Delamination initiation in fully clamped rectangular CFRP laminates subjected to out-of-plane quasi-static indentation loading

To further investigate the effects of in-plane and out-of-plane stresses on the delamination initiation for composite laminates under out-of-plane loading, this paper reports a joint experimental and numerical study, in which the fully clamped rectangular CFRP composite laminates were subjected to out-of-plane quasi-static indentations. The results show that the combination of the out-of-plane shear and in-plane tensile stresses together determined the initiation of delamination, whereas the influences of the out-of-plane compressive stress on the delamination initiation can be neglected. For the purpose of understanding the effects of deformations on the out-of-plane shear and compressive stress distributions, a concise analytical model was developed, which was validated against the numerical and experimental results. As a key take-away, this study reveals that the common impact tests at the geometric centre of the panel may not resemble sufficient similitude with stiffened panels where panel flexure is suppressed by various geometrical stiffening concepts.