Dynamic delamination and fracture in thick fiber reinforced composites

In this paper we describe some results of optical experiments performed on dynamically deforming thick polymeric composite laminate plates. The composites used for the first part of this study, investigating dynamic delamination, were graphite/epoxy fiber reinforced composite plates, consisting of 48 plies (6 mm in thickness) in either a quasi-isotropic or a unidirectional arrangement. In the dynamic delamination study plates were impact loaded in an out-of-plane configuration using a gas gun. Impact velocities used ranged from 1 m/s to 30 m/s. The lateral shearing interferometer of Coherent Gradient Sensing (CGS), in conjunction with high speed photography was used to obtain real time interferograms of the out-of-plane deformation of the laminate surface. From a quantitative analysis of the interferograms quantities such as the speed of delamination are measured and presented. In the second part of this paper, we present some preliminary results from optical (CGS) experiments performed on impact loaded one point bend pre-cracked composite plates. The plates used were again graphite/epoxy fiber reinforced composite plates, consisting of 48 plies in a unidirectional configuration and containing an edge pre-notch. In-plane impact loading was provided by a drop weight tower device. An impact speed of 4 m/s was used. From the resulting interferograms crack tip speeds of the order of 1000 m/s were measured.