Matrix Cracking in Impacted Glass/Epoxy Plates

In addition to delamination, which has been found to be the major failure mode in a fiber-reinforced laminated composite plate subjected to subperforation impact, matrix cracking and fiber breakage have also been observed. Each failure mode, however, does not generate independently. On the contrary, the different modes interact with one another. Therefore, in order to have an overview of the failure mechanism in an impacted com posite plate, it is necessary to find out the mechanism of every failure mode and the in teractions among them. Microscopic observations of the cross sections of impacted com posite materials have revealed the interaction between matrix cracking and delamination. In this study, however, several techniques have been used to present the matrix cracking patterns in impacted glass/epoxy plates with different thickness, geometries, boundary conditions, stacking sequences, and types of loading. The matrix cracking patterns on the surfaces of impacted plates have been enhanced by dye penetrant while those of the in ternal laminae have been investigated by edge replication. Results have shown that the delamination area on the second interface of a three-lamina glass/epoxy plate coincides with both the central matrix cracking zone of the impacted lamina and the middle crack- free zone of the non-impacted lamina. The matrix cracks in the internal lamina are also restricted by the projected delamination area. The association between delamination and matrix cracking has been discussed and also the effect on matrix cracking of the tensile stresses introduced by the flexural wave.