Shadow Moire Monitoring of Damaged Graphite/Epoxy Specimens.

Graphiteepoxy composites are prone to a wide range of defects and damage, which can significantly reduce the residual strength. Of the various types of defects, delaminations i.e. single or multiple internal cracks whose planes are parallel to the surface of the component arising in service are probably the most insidious, because they cause serious reductions in compression strength and are difficult to detect. In-service delamination damage can occur from a variety of events. The most important source because the probability of occurrence is high is impact, i.e. from dropped tools or from stones thrown up from the runway. It is highly desirable that procedures are available to monitor delamination damage and estimate its severity by analytical means. Compression tests to failure were performed on six graphiteepoxy specimens. Three of the specimens contained an inclusion and the other three had impact damage. During the tests, the out-of-plane deflections of the specimen surface were monitored, using the shadow moire technique. Initially, this report describes the performance of the shadow moire technique for this application, in order to generate interest in more widespread use of the technique. It is shown that the inclusion specimens behaved differently from the impacted specimens and in order to analyse the inclusion specimens, large deformation theory must be used.