Crack propagation in layered plates—an experimental study

The effects of the layer height and the material properties of a layered medium on the propagation mode of a crack are discussed. Crack-propagation velocities and dynamic stress-intensity factors were evaluated during fracture and the corresponding curves were plotted. The medium consisted of two identical external layers and a middle layer of softer or harder material. This layer contained an initial crack which ran parallel to the interfaces of the layers. All phases of the specimens were fabricated from epoxy polymers. After the preparation of the middle layer, the surrounding layers were successively cast along the middle layer's straight boundaries without applying any kind of adhesive. High-speed photography and dynamic caustics were utilized to establish the changes in crack speeds and intensities of the stress field. The influence of geometry and especially of the height of the middle layer and the mechanical properties of the layered material was studied; interesting results were derived.