An analytical approach to predicting tensile pseudo-ductility and multi-stage failure process of multidirectional thin-ply CFRP laminates

Abstract

This paper presents an analytical model for predicting the nonlinear tensile response and progressive failure modes of multidirectional laminates. The proposed method extends the unidirectional pseudo-ductility model to multidirectional laminates and captures the complete failure process by taking accounts of various failure modes, including fiber breakage, matrix transverse failure, free-edge delamination, and potential intermediate layer fragmentation and delamination. Combining the matrix nonlinearity with fiber fracture and delamination in the intermediate layer, the [±θ_n/0°_m/±θ_n] configuration theoretically exhibits the highest uniaxial tensile pseudo-ductility, which is influenced by factors such as ply thickness, ply angle, and proportion of plies. Tensile testing on specimens with various thin-ply [±θ_n/0°₂/±θ_n] configurations were conducted to validate the accuracy of the prediction model. The results showed a good agreement in the stress–strain responses. Furthermore, the [±30°₆/0°₂/±30°₆] configuration exhibited intermediate ply fragmentation with a pseudo-ductile strain of 4.04 %, while other configurations with higher 0° ply proportions experienced catastrophic delamination or fracture. The Digital Image Correlation (DIC) results illustrated the strain evolution process, showing progressive delamination for the [±30°₆/0°₂/±30°₆] configuration and catastrophic delamination for the [±30°₄/0°₂/±30°₄] configuration. The analytical approach offers a straightforward method for capturing failure modes and stress–strain responses, facilitating pseudo-ductility design in multidirectional laminates.