Coupled longitudinal and transverse damage modeling of fiber-reinforced polymers using a smeared crack approach

• Incorporation of damage evolution for fiber kinking using a Smeared Crack Model. • Introduction of an interaction scheme for transverse damage and longitudinal damage based on the effective damaged area. • Extension of the transverse stress failure initiation criteria to predict failure initiation under non-monotonic loading. • Implementation of the longitudinal damage model in an implicit solver scheme. Longitudinal damage, or fiber-dominated failures, is the principal contributor to the stiffness loss in multidirectional composite laminates. In this work, the 3D smeared crack model, previously developed for transverse damage in unidirectional fiber-reinforced polymer composites, is extended for the first time to include longitudinal tensile and compressive failure, considering fiber kinking using a continuum damage approach. This formulation is developed to facilitate the implementation in an implicit solver, increasing solution robustness and computational efficiency in quasi-static and long duration analyses. The smeared crack formulation is incorporated into the fiber kinking model and seamless coupled with the transverse damage evolution model to address combined loading modes and mixed mode loading. The performance of the model is evaluated using monotonic and non-monotonic damage evolution and verified with single element tests to demonstrate the consistency of the proposed formulation. Additional benchmark examples include open-hole tension and compression tests in multidirectional laminates, validated with experimental results, obtaining a good agreement in the predicted failure load, and correctly capturing the size effect.