FAILURE MECHANISM AND STRAIN FIELDS ON A CARBON/EPOXY COMPOSITE SUBJECTED TO COMPRESSION AFTER IMPACT

Abstract eng:
Polymer composite panels are widely used in aeronautic and aerospace structures due to their high strength vs. weight ratio. The objective of this study is to determine mechanisms of the failure of impacted composite laminates when subjected to compression. The other aim is to investigate using an optical strain measurement to detect impact damage in laminates subjected to loading. For this purpose a series of impact and compression after impact (CAI) tests were carried out on composites made of carbon fibre-reinforced epoxy resin matrix. First, impacted specimens were analyzed by an ultrasonic probe to assess delamination area around the impact site. Second, digital image correlation (DIC) measurement was performed to investigate the strain fields and the surface shape before and during loading. The fullfield strain measurements showed a concentration band of a compressive strain near the impact where buckling occurred. The shear strain visualisation around the impact showed an area of heterogeneous deformation which was compared to the detected delamination area acquired by an ultrasonic technique. The results showed that the shear strain fields are able to identify the extension of impact damage and that the strain concentration factor can be a failure criterion to consider an ultimate load.

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