Mode I Experimental and numerical analysis of the interlaminar fatigue behaviour of thermoplastic composites considering R-curve effects
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Through the application of innovative production processes, thermoplastic composites might help the aviation industry become more sustainable. However, there is currently not much experimental understanding on the fatigue behaviour, and validated analysis methodologies on thermoplastic composites are rather limited [1]. In this work, the fatigue onset and propagation interlaminar properties of AS4D/PEKK-FC thermoplastic composite were characterized under mode I loading and the effects of resistance curve (R-curve) due to ductile fracture and large-scale fibre bridging were analysed through a fatigue cohesive zone model (FCZM). It was concluded that the fatigue onset and propagation performance of AS4D/PEKK-FC thermoplastic is superior to a high performance thermoset [2] proportionally to the fracture toughness of the material. Regarding the R-curve effects such as plastic deformation and large-scale bridging, they seem to develop differently under monotonic or fatigue loading. The experimental findings remark the need of developing a simulation strategy to account for R-curve effects under fatigue loading. In this work, a simulation strategy for a FCZM fatigue damage accumulation model was developed. Multiple superposition of cohesive laws were used and fatigue model parameters were determined based on experimental fatigue onset and propagation data. It was concluded that fatigue parameters in the model must allow independent fatigue damage accumulation rates to the superposed cohesive laws.