A Non-linear Mean-Field Debonding Model at Large Strains for the Analysis of Fibre Kinking in UD Composites

Fibre kinking is the most prevalent failure mode observed in UD composites. The accurate prediction of kinking failure is of paramount importance in industrial applications. To address this challenge, we develop a non-linear mean-field debonding model (NMFDM) based on our previous work, which efficiently captures the non-linear material behaviour of UD composites under longitudinal compression leading to kinking failure. Building upon the foundation of our earlier mean-field model, this enhanced NMFDM incorporates geometric non-linearity due to fibre rotation under longitudinal compression and the non-linear elasticity of fibres in the fibre direction. These additions address crucial aspects in kink band formation and the typically non-linear elastic behaviour of carbon fibres, which were not considered in our previous work. Additionally, we introduce a fibre kinking model (FKM) to predefine initial fibre misalignments in the geometries, allowing us to study the formation of kink bands. The FKM considers the effects of initial misalignments and fibre rotations during kinking by proposing a transformation law for off-axis cases. As a representative example, we investigate the initiation and evolution of kink band formation in an AS4/8552 UD composite by predefining various initial misalignments. The results demonstrate that our newly proposed NMFDM yields reliable predictions of kink band formation in UD composites, outperforming other existing models and even comparing favorably to micrograph observations of kink bands. Compared to our previous work, this enhanced model offers a more comprehensive understanding of kink band formation, particularly under large strains, by incorporating the non-linear elasticity of fibres in the fibre direction. This advancement opens up potential applications in designing composite structures with improved resistance to compressive failure, paving the way for broader applications in aerospace, automotive, and other industries where high-performance composite components are crucial.