A universal kinking-based strength model for unidirectional composite laminates under multiaxial loading

The high-accuracy and efficient prediction of unidirectional composite materials under multi-load interactive loading conditions has long been a challenge. However, existing failure criteria for single-load conditions fail to account for load coupling effects, leading to reduced accuracy and efficiency along with limited applicability in multi-load scenarios. In this work, we propose the closed-form kinking-based (CFK) model as a universal multiaxial strength model by considering kinking-band instability. The CFK model combines biaxial tensile strength with uniaxial parameters derived from the torsion model, significantly improving the prediction of failure modes under multi-axial loading. Meanwhile, the model incorporates shear-driven kinking instability, enabling precise representation of the stress state. Critically, the closed-form solution replaces traditional search algorithm, achieving a balance between accuracy and efficiency. The model requires only input of readily measurable material parameters and demonstrates universal applicability to diverse composite material systems. Finite element simulations and experimental validation demonstrate that the model enhances computational efficiency by 41.4% relative to traditional algorithms, while significantly outperforming existing models in prediction accuracy. These findings establish an effective framework for multiaxial strength prediction of composites, while providing important theoretical basis for related fields.