EFFECTS OF MATRIX DUCTILITY AND PROGRESSIVE DAMAGE ON FATIGUE STRENGTHS OF UNNOTCHED AND NOTCHED CARBON-FIBER PLAIN WOVEN ROVING FABRIC LAMINATES

The influence of matrix resin systems with much different ductility-a thermosetting epoxy and a thermoplastic nylon 6-on the fatigue strengt h and fatigue damage mechanisms of carbon fibre plain woven roving fab ric laminates under tension-tension cycling has been studied. The fati gue tests were performed at room temperature on unnotched and notched parallel-sided plate specimens. The carbon/nylon unnotched laminates e xhibit a higher relative fatigue strength than the carbon/epoxy unnotc hed laminates. Different fracture modes appear for the carbon/epoxy un notched laminates, and the development of progressive and extensive de lamination leads to a longer fatigue life and a larger reduction in te nsile modulus. Such a fracture mode dependence is not observed for the carbon/nylon unnotched laminates. Regarding the notched specimens, th e failure mechanism of the carbon/epoxy laminates is exclusively gover ned by the progressive delamination from the notch tips, while no appr eciable effects of the notches are observed on the notch tip fracture of the carbon/nylon laminates. This much different notch sensitivity r esults in a slightly higher relative fatigue strength for the carbon/e poxy notched laminates.