The coated inclusion effect on the mode of fracture of encapsulated particulates

The fracture toughness of hard plates, reinforced with brittle inclusions, can be altered by introducing in these composites an intermediate thin layer made of a deformable phase. This was proved in this study, where cracked PMMA plates including bonded rubbery encapsulations inside their matrices were subjected to static or dynamic tensile loadings. The improved toughness of these composite plates at high strain rates, comparative to the respective toughness of homogeneous plates, indicated the beneficial role of the rubber encapsulation in the failure of these composite plates. While studying the fracture behavior of the plates at different strain rates, it was observed that the propagating crack, when approaching the inclusion, follows an interfacial path along either the external or the internal surface of the soft coating or propagates and stops inside the core inclusion, depending on the applied strain rate. Throughout the experimental analysis the method of dynamic caustics was used for the evaluation of the stress intensity factor and crack velocity. Interesting results were obtained by studying the failure characteristics of these composite plates, as well as the variation of fracture toughness and the stress intensity factors depending on crack velocities. By considering that the plates examined constitute a satisfactory model for the representative element of the particulate material, the results found are useful because they provide an insight into the behavior of such particulates.