Effects of Implanted Delaminations on the Tensile Strength of Graphite/Epoxy Laminates

摘要

The fracture of graphite/epoxy laminates implanted with materials to cause local delaminations was investigated both experimentally and analytically to assess the effects of the implants on the stress-strain behavior and ultimate tensile strength. Two different stacking sequences were examined: (+ or - 45/0)s and (0/ + or - 45)s with a majority of the tests conducted on the first stacking sequence. Implant thickness, shape, size and configuration, which describes the number and location of the implants, were varied. All implants were centered in the specimen. All these variables except implant shape were discovered to affect the fracture strength of the laminate. Implants with thickness below 0.0127 mm will not reduce the fracture stress as observed for the thin implant utilized. Reductions in strength for thickness greater than this are a result of the stress redistribution in the plies due, in part, to an induced bending moment as each ply is forced to bend around the implant. Significant stress redistributions predicted by the model occur when more than one implant is embedded in a laminate. Multiple implants which isolate plies prevent a path for three-dimensional load transfer within the delaminated region. Thus, cracks which form in this region will grow quickly into splits until arrested by the laminated plies. These cracks reduce the bending stiffness and strength of the delaminated plies. This will cause the laminate to fail at a reduced stress level than it would otherwise. Implant width was also found to reduce strength. The model could adequately simulate all these effects except for that due to the width. (Author)