Fatigue fracture behavior of a new aligned short-carbon-fiber reinforced thermoplastic prepreg

Short-fiber composites have become increasingly important because of their advantage in manufacturing complex structural parts; this advantage is due to their superior strain capability over long-fiber composites. Unfortunately, in the past, this advantage was always accompanied by a significant loss in mechanical properties. Therefore, a new aligned short-fiber reinforced thermoplastic prepreg (HTA7/PEI) has been developed to minimize this drawback. It has already been shown that the unidirectional mechanical properties of this new composite are only slightly less than those of a similar long-fiber material [1 ]. This paper will focus on the fatigue behavior of aligned short-fiber tensile specimens with a center hole. The various fatigue crack forms around the hole, such as inter-fiber splits and delaminations, are investigated and compared to those of long-fiber specimens. Then, the dependence of crack propagation on fatigue time and the response to residual stiffness was studied in detail. A linear relationship between split length and residual stiffness was found and used to predict residual stiffness as a function of split length and fatigue time. The predicted residual stiffness showed good agreement with the measured values.