Evaluation of advanced composites using destructive testing techniques

Abstract

A very basic problem in manufacturing advanced composites is the occurrence of defects, such as voids, delamination, resin rich areas, distorted fibers and foreign material inclusions. Of these defects, voids are the unavoidable defects mostly coming from a variety of reasons, including resin type, poor vacuum source, air entrapment, leakage of vacuum bag and by-products formed during the curing cycle of laminates. These voids seriously affect the mechanical properties of composite panels, and cause severe damages during the service. In the present study, various destructive testing techniques, such as visual, burn-out or ignition loss of cured composites, image analysis and matrix digestion or acid digestive were used on advanced composite panels at various porosity levels (e.g., 0-2%, 3-6% and greater than 7%), and the obtained results were compared each other. Also, testing parameters were optimized using the standard samples to achieve maximum possible error free data of voids, fiber volume, fiber wash, inter laminar and trans laminar cracks, miss-oriented fibers, lay-up orders and latent defects. Optimization of parameters was performed using the design of experiments. We determined that the test results were significantly changed based on the test techniques, composite samples, as well as testing time, operator skill, cost of experimentation, initial equipment cost, pre and post treatments and lack of standardized testing patterns.