Strain rate effect of mode II interlaminar fracture toughness on the impact response of a thermoplastic PEEK composite

International audienceRecent advancements in composite production and processing are making thermoplastics a viable option in a wider array of aerospace applications. In particular, Carbon Fibre Reinforced Plastics (CFRP) with thermoplastic resin are believed to have better damage tolerance properties than thermosets. However, few studies have been conducted regarding the numerical modelling of the behaviour of such materials submitted to low energy impacts. Here the Discrete Ply Model (DPM), that predicts the failure of laminated composites with the help of cohesive elements, is used to compare thermosetting and thermoplastics impact damage tolerances. The DPM is improved to take into account the strain rate effect of the fracture toughness (FT) in mode II of interlaminar interfaces. First, the End Notched Flexure (ENF) test that induces unstable crack growth is used both to experimentally measure the value of FT in mode II for high speed crack growth and to identify the strain rate effect used in the model. Second, the DPM is then used to simulate impact tests for various stacking sequences ([45 2 , − 45 2 , 0 2 , 90 2 ] 2S , [0 2 , 45 2 , 90 2 , − 45 2 ] 2S , [0 2 , 30 2 , 90 2 , − 30 2 ] 2S and [90 2 , − 45 2 , 0 2 , 45 2 ] 2S ) and impact energy levels (10, 20 and 30 J). Good correlations with experiment are observed in terms of force/displacement curves and delaminated areas. The numerical model correctly describes the asymmetry of the delaminated interfaces and the propagation of groups of interfaces located near the mid-thickness of the laminated plates. Finally, the damage associated with a 30 J impact is compared for the carbon/PEEK of this study and classical carbon/epoxy plates using numerical simulations (DPM). No significant difference has been found. The results corroborate those obtained in previous studies showing the relatively low value of FT in mode II, using an ENF test and infrared thermography (IRT). This article therefore questions the apparent superiority of carbon/PEEK laminated composites over carbon/epoxy laminated composites in terms of impact damage tolerance