Mixed-Mode Dynamic Crack Growth in Functionally Graded Glass-Filled Epoxy

Abstract

Compositionally graded glass-filled epoxy sheets with edge cracks initially along the gradient are studied under dynamic loading conditions. Specimens with monotonically varying volume fraction of reinforcement are subjected to mixed-mode loading by eccentric impact relative to the crack plane. The optical method of Coherent Gradient Sensing and high-speed photography are used to map transient crack tip deformations before and after crack initiation. Two configurations, one with a crack on the stiffer side of a graded sheet and the second with a crack on the compliant side, are examined experimentally. To elucidate the differences in fracture behavior due to functional grading, a homogeneous sample is also tested. The differences in both pre-and post-crack initiation behaviors are observed in terms of crack initiation time, crack path, crack speed and stress intensity factor histories. When a crack is situated on the compliant side of the sample, it kinks significantly less compared to when it is on the stiffer side. Crack tip mode mixity histories show small but positive values during crack growth from the stiffer side of the sample towards the compliant side whereas a small but negative mode mixity prevails for the opposite configuration.

Dynamic Crack Growth Normal to an Interface in Bi-Layered Materials: An Experimental Study Using Digital Gradient Sensing Technique

“…In case of mixed-mode crack propagation, the DGS contours show similarities with the mixedmode CGS contours reported in a few previous works [17,19]. Further, the availability of two orthogonal stress gradient fields in DGS offered additional ways of extracting fracture parameters relative to the ones previously demonstrated [19].…”

“…Further, Equations (9)-(10) can be modified for a dynamically propagating steady-state 1 crack as [19], …”

“…Previous studies have reported mixed-mode dynamic crack growth involving interfaces using photoelasticity [7,12,14,15] and/or high-speed photography [13]. Coherent Gradient Sensing (CGS) has also been used to study dynamically loaded stationary crack-tips [16] as well as propagating crack problems [17][18][19]. One of the earliest studies on dynamic interface crack growth was carried out by Tippur and Rosakis [17] using CGS wherein they reported unusually high crack velocities approaching the Rayleigh wave speed of the more compliant constituent of a bi-layered dissimilar material as the crack propagated along an interface.…”

Experimental Fracture Mechanics of Functionally Graded Materials: An Overview of Optical Investigations

“…Mixed-mode dynamic failure in FGMs was investigated by Kirugulige and Tippur [56], using material-system I. This problem was solved analytically by Chalivendra and Shukla [28] and can be implemented for use with CGS as follows.…”

“…This problem was solved analytically by Chalivendra and Shukla [28] and can be implemented for use with CGS as follows. Thus, CGS fringes representing surface slopes can be interpreted using [56],…”