A study of the quasi-static and low-velocity impact behavior of laminated CFRP composites

The applications of composite materials have been increasing significantly in recent decades due to their superior mechanical properties and versatility. The major effect limiting the use of composite materials is the lack of understanding of their response and their structural integrity under dynamic loads. Among the prominent damage mechanisms, the debonding under dynamic loading is a well-recognized failure mode for laminated composites. Up to date, the impact of the significant parameters on the delamination is thoroughly examined in this study with primary focus on the hemispheric indenter diameter and the characteristics of the exerted load applied at constant energy levels. The damage morphology has been carefully investigated using X-ray computed tomography, quantifying the shape and size variation of delamination areas across plies. The experimental observations have been incorporated into the finite element modeling, carried out in ABAQUS, by means of cohesive elements, which allow for the setting of a failure criterion. The main delamination area has been confirmed to be localized on the tension side of the laminate, where the most bending stress is sustained. Moreover, the angular difference between adjacent plies that articulates the distribution of the interlaminar stresses has to be taken into consideration, since it has a great impact on the extent of delamination. It is concluded that the initiation of delamination can be detected using a delamination threshold load based on the quasi-static load-displacement curve. These results illustrate the importance of the indenter radius to thickness ratio as a governing parameter in the structural response of composite plates, aiding in the development of more accurate predictive models for damage assessment.