In situ synchrotron tomographic evaluation of the effect of toughening strategies on fatigue micromechanisms in carbon fibre reinforced polymers

Micromechanisms of fatigue failure in double-notch cross-ply carbon/epoxy coupons have been investigated using synchrotron radiation computed tomography (SRCT). The fatigue behaviour of toughened and untoughened matrices has been compared, highlighting similarities and differences of damage modes in terms of fatigue initiation and propagation. Results show that damage does not propagate evenly for the toughened systems: the presence of resin rich regions constrains crack propagation, which is shown to suppress damage growth. In contrast, untoughened material is characterized by more uniform crack progression. The presence of toughening particles in the resin system favours complex local crack geometries, such as crack deflection and the formation of bridging ligaments along the crack wake due to particle debonding events. A distinctive aspect of fatigue loading is identified in the degradation of crack bridging ligaments associated with increasing number of cycles.