Crack bifurcation modes in composite plates under impact

Abstract

Cracked plates with bonded elastic circular inclusions inside a matrix were subjected to an impact tensile loading. The influence of the inclusion on the propagation of an initial edge-crack was discussed in this paper. Two types of specimens were tested, that is with hard or soft inclusions surrounded by soft or hard matrices respectively. It has been shown that bi-, or tri-furcations of the propagating crack have persistently occurred at the region of mesophase between matrix and circular inclusions. The phenomenon of splitting of the initial crack was common in both types of specimens, For the definition of the prevailing stress field, the dynamic stress intensity factors were evaluated at different positions of the crack, as well as the crack-velocities along the main crack or its branches during their propagation. It was observed that the crack initiation in soft plates with hard inclusions was followed by the emission of Rayleigh waves, which contributed to the mode of fracture of the composite. Isochromatic patterns were also used to simulate the stress-field of the propagating cracks against the inclusions at distinct time-instants where the propagating crack was frozen at this instant and static photoelastic analysis was applied. These approximations gave satisfactory results with the cracks advancing inside the composite plates.

Crack Propagation Modes in Particulates: A Study Approaching Reality

“…The occurrence of the Rayleigh waves coupled with those discovered in [3] has been established in the present study. To describe and interpret fracture phenomena, accompanied by emission of surface waves in SEN composite specimens, attention is focused on photos of Figure 6.…”

“…This is obvious even for the remote inclusions from the crack tip. On the other hand, the caustics of the inclusions approached by the propagating crack tip are progressively reduced in size, as may be observed from Figure 6 (3,5). The glass beads are rigid and impenetrable fillers and they act as &dquo;pins&dquo; thrusted in a flexible matrix, thus creating stresses around them due to external loading.…”

“…Finally, Rayleigh waves were observed in plates sensitive in surface deformations such as ductile and thin plates [18]. During the fracture of SEN-composite plates, consisting of a flexible matrix, which surrounded a rigid bonded inclusion, Theocaris and Demakos [3] have also observed emission of Rayleigh waves, travelling along the lips of a propagating crack.…”

“…Theocaris and Demakos [3] have already studied, in the microscale, the crack bifurcation modes, due to an enlarged inclusion in a composite plate under dynamic tension: In this paper the same authors have investigated the influence of the mesophase zone on the failure process of the composite plates. The mesophase extends from the inclusion towards the matrix with continuously varying elastic modulus E, (r) from the value Ef of the inclusion to the value E_ inside the matrix.…”

“…This is because to the insurmountable difficulties, that this problem encounters, arising from the complex interaction phenomena occurring during the crack propagation. Emission of Rayleigh and shear waves [3] from the free boundary of the specimen, as well as crack arrests and bifurcations at the interfaces between inclusions and matrix lead to a directional instability of the propagating crack. Furthermore, the existence of the mesophase zone provokes decelerations of the propagating cracks [3] close to the interfacial surfaces.…”