Development and experimental validation of strain rate-dependent failure criteria for unidirectional non-crimp fabric composites

In this study, two invariant-based failure criteria are proposed to predict failure of a unidirectional non-crimp fabric (UD-NCF) carbon fiber/epoxy composite. Three different failure modes, namely matrix failure, fiber tensile failure, and fiber compressive failure, are considered. The matrix failure functions are based on linear and quadratic transversely isotropic stress-invariants, while fiber failure is evaluated with a maximum stress criterion for tension and an adapted kinking criterion for compression. The main advantages of the invariant-based criteria are fewer required experiments for calibration and minimal computational effort in comparison with fracture plane-based criteria. Moreover, the chosen mathematical formulation ensures a non-negative Hessian and decoupled tensile and compressive behavior. Furthermore, the strain rate dependency of the investigated UD-NCF composite is incorporated using empirical relations defined in previous work by the authors. For validation purposes, off-axis tests are performed at quasi-static and high strain rates. Overall, the observed agreement with experimental data presented here as well as from literature is excellent, highlighting the feasibility of the proposed criteria for design of UD-NCF composite structures.