The influence of cyclic fatigue damage on the fracture toughness of carbon-carbon composites

The influence of cyclic loads on the fracture toughness of a tightly woven carbon-carbon composite was investigated as a function of stress levels. Results of fracture toughness tests were correlated with microstructural examination using scanning electron microscopy (SEM). Values for the stress intensity factor, K-Ic, were determined using the ASTM single-edge notched bend test. Results were discussed in terms of the effects of applied cyclic stress levels and the relationship of the load-displacement curves. The fracture toughness of the composite remained unaffected when the maximum tensile load in the fatigue cycle was up to 80% of the static tensile strength. However, a decrease in the fracture toughness was determined when it was exposed to cyclic loads above this threshold stress level. Changes in texture associated with cyclic fatigue were determined in the matrix of this composite. Copyright (C) 1996 Elsevier Science Limited