Stress-state and strain-rate dependency of fracture in SCFR-PEEK composites under biaxial loading

This study presents a hybrid experimental-modelling framework to investigate the anisotropic deformation, strain-rate sensitivity, and fracture behaviour of short carbon fibre reinforced polyether-ether-ketone (SCFR-PEEK) composites subjected to in-plane multiaxial loading. Quasi-static uniaxial and biaxial tensile responses were characterised using an electromechanical biaxial testing system, while dynamic uniaxial and biaxial tensile tests were conducted using an electromagnetic biaxial split Hopkinson bar (EBSHB) apparatus, enabling systematic assessment of material behaviour over a wide range of strain rates. The comprehensive experimental dataset formed the basis for the development of a phenomenological anisotropic elastoplastic constitutive model capable of reproducing rate-dependent deformation and fracture responses under diverse stress states. The proposed model integrates orthotropic elastic properties, an anisotropic yield function, a strain-rate dependent hardening law, and a stress-state dependent anisotropic fracture criterion. Model parameters were identified from uniaxial and biaxial tensile tests that explicitly account for fibre alignment and directional anisotropy, and were calibrated separately for quasi-static and dynamic regimes to ensure predictive consistency across loading rates. The coupled constitutive and fracture framework was implemented within a finite-element framework to enable high-fidelity simulation of anisotropic elastoplastic deformation and fracture under complex multiaxial loading paths. Model validation was performed through quasi-static Nakajima tests and dynamic drop-weight impact experiments involving biaxial stress states. The simulations show good agreement with experimental observations in terms of deformation evolution, strain localisation, and fracture initiation. The developed framework therefore provides a robust and versatile tool for predictive simulation of coupled deformation and fracture processes in SCFR-PEEK composites under realistic multiaxial and rate-dependent loading conditions.