Progressive failure strain measurement of a compression loaded carbon fiber laminate

A new approach to measure the strain in compressive loaded laminates is discussed in this paper. Current state of the art testing standard like the DIN EN ISO 14126 is not able to measure the strain of the laminate after first ply failure. From tests it is known that strain gauge data is not valid after initial failure due to the fact that local strain of the delaminated layers is measured or because of strain gauge delamination. It is observed that multidirectional laminates can have a significant amount of residual strength after initial failure. In order to improve the knowledge of the material and understand the failure mechanisms it is necessary to be able to obtain reliable strain data after initial failure. This paper describes how digital image correlation (dic) can be used to obtain global and local strain data of laminates loaded in compression. The specimen geometry that is used for the dic test is similar to the one of the test standards in order to allow easy comparability. The test results that are obtained using dic measurements show good agreement with the one that are based on standard test methods.