Fatigue Micromechanism Characterization in Carbon Fibre Reinforced Polymers Using Synchrotron Radiation Computed Tomography.

摘要

Carbon fiber reinforced polymers (CFRPs) are well established as an important weight-reducing structural technology, particularly within the aerospace sector due to their high specific stiffness and strength. CFRPs are widely identified as being very fatigue resistant, but typically this advantage is not fully exploited in design. Understanding and predicting the durability of these materials is of great interest. The current work aimed to delineate the micro-mechanisms of fatigue damage in carbon fiber-epoxy laminated composites using in situ and ex situ synchrotron radiation computed tomography (SRCT). Several novel observations have been obtained for the micro-mechanisms of fatigue crack growth. Broadly similar micro-mechanisms of damage initiation have been identified in fatigue and quasi-static loading in a particle-toughened carbon fiber-epoxy composite system. Results showed that damage propagation is closely related to the local microstructure. Toughened systems exhibit different damage behavior in resin-rich regions and fiber-packed zones, which appears to exaggerate non-uniform crack growth. Zones of retarded crack growth correspond to resin rich regions, which contain bridging ligaments. There is evidence that the load cycling contributes to progressive failure of bridging ligaments in the crack wake, especially in the toughened particle system. The un-toughened system showed more uniform damage propagation across the crack front, due to the more uniform microstructure and showed a higher number of fiber breaks within the 0 plies with respect to the toughened systems, particularly within regions close to the 0 ply splits. It seems likely that a key mechanism of fatigue in the toughened-particle system on intralaminar loading is the degradation of bridging ligaments introduced by particles in the fatigue crack wake rather than due to processes at, or ahead of the crack tip.