Assessment of residual strength of repaired solid laminate composite materials through mechanical testing

Robust residual strength test methods are critical for assessing the validity of new repair techniques for restoring strength to damaged composite laminates. In this study, the strength of pristine, damaged and repaired solid laminate composite material has been investigated by performing four different mechanical tests. Impact damage was imparted to carbon fibre epoxy resin specimens using a drop tower instrument. Specimens were repaired using a novel resin injection technique employing a low viscosity adhesive as the repair resin. The compressive strength of specimens was determined using compression after impact (CAI) and large-scale CAI test methods. Tensile tests were performed to obtain tensile strength. Flexural strength was evaluated by four-point bend tests. The thoroughness of each test method in determining the success of the repair was investigated. This study demonstrates that the strength restoring capacity of a repair method is subject to the test method used to assess the residual strength. The four-point bend test was shown to be the best preliminary test method for screening repair techniques as it is not affected by loading anomalies. However, design criteria should always be considered when choosing a residual strength test method for assessing repair validity.