Dynamic Delamination Crack Propagation in a Graphite/Epoxy Laminate

Abstract

Ballistic impact tests of [90/0]5s T-300/934 graphite/epoxy laminates of beam-like dimension with embedded delamination cracks were conducted. High speed photography (16 000 frames/second) was used to record the impact response and subsequent crack propagation. From the photographic data, impact characteristics such as the contact duration and the dynamic response of the impact specimen were measured. In addition, the time of initiation of delamination propagation and measurements of the subsequent delamination length versus time were obtained. By changing the location of the embedded delamination in the specimens relative to the impact point, additional results were obtained on the variation of the threshold impact velocity necessary to cause crack propagation in the different specimen configurations. These data, together with the photographic results, suggest that the mode of crack propagation is dependent on the specimen geometry as well as the loading condition. The time dependent nature of the crack velocity and its variation with impact conditions was investigated. A finite element program was used to calculate the dynamic strain energy release rate before the onset of crack propagation. This strain energy release rate was used to gage the instability of the delamination crack during impact.

A novel technique for time-resolved detection and tracking of interfacial and matrix fracture in layered materials

“…This failure mechanism is conÿrmed by Salpekar (1993) who showed that a signiÿcant mode-I component of the strain energy release rate is present at delamination initiation. Others also studied the mode of propagation for delamination (Choi et al, 1991b;Grady and Sun, 1986;Liu et al, 1993;Sun and Manoharan, 1989;Tao and Sun, 1997). These studies clariÿed the mode of delamination propagation under di erent loading conditions.…”

Vibration testing of impact-damaged composite laminates

“…Allowing for some scatter in the data, the amount of delamination crack extension that occurs seems (ref. 7) to vary linearly with the impact energy. After the postimpact crack length in each specimen was measured as previously described, the specimens were again vibration tested.…”

Initial Impact Damage of Composites

“…In the local (r,s,q) coordinate system, the geometric shape function is given by 8 g(r,s,q) -Z NI gi (16) where the components of [NJi are given by…”

“…Using the geometrical shape functions given in (16), and the chain rule, the transformation from global to local variables is given by The computational effort required for this special case is significantly reduced relative to that required for the general element. As with the two-dimensional element, consistant mass matrices are generated for both three-dimensional elements.…”