Fatigue micromechanism characterisation in carbon fibre reinforced polymers using synchrotron radiation computed tomography

In situ synchrotron radiation computed tomography (SRCT) has been used to evaluate fatigue damage micromechanisms in [90/0]s carbon fibre reinforced epoxy double-edge notched specimens. Interactions between cracks and toughening particles have been identified within the epoxy, particularly: particles de-bonding ahead of the main crack tip, creating a preferential damage path, and the bridging of cracks by un-failed ligaments. The critical mechanism of fatigue crack growth appears to be the degradation of bridging ligaments in the crack wake. Damage has been quantified in terms of crack opening and shear displacements, and the results have been compared with corresponding damage occurring due to quasi-static loading of the same materials. The removal of bridging ligaments in fatigue loading results in higher, more uniform crack opening (and shear) displacements and less serrated crack fronts. These observations have potential implications for material development, damage resistant and damage tolerant structural design approaches.