The effects of edge quality on the measured compression strength of quasi-isoptropic composite specimens and its practical implication to the development of allowables

Abstract

This manuscript presents results from an experimental study that examined the effect of quality of edge finish of test coupons on the measured compression strength of quasi-isotropic carbon fiber laminates using test standard ASTM D6641. Different cutting and grinding tools were used to machine specimens to get them within the required dimensional tolerances, all of which caused microscopic damage to the specimen edge, mainly in the form of fiber pull-out. Results of compression strength testing showed that the fiber pull-out, despite being only on the order of 0.008 mm in depth, caused a significant reduction in measured compression strength. Upon polishing of the specimen edges to remove the microscopic “gouges” of fiber pull-out, the measured compression strength of the specimens increased. It was also found that open hole compression (OHC) and compression after impact (CAI) strength test results were not affected by fiber pull-out on the edges of specimens. The implications of these results on the development of pristine strength allowables is discussed and a more practical starting point at which to develop allowables is presented.