Compressive Failure due to Kinking of Fibrous Composites

A new approach to compressive strength modeling of fibrous composites, that bridges the micromechanics relevant to compressive failure due to fiber kinking with the global characteristics of a composite structure, is presented in this work. To analyze the mechanics of kinking and calculate the critical compressive stress, a steady state kink propagation model is utilized for the layers under compression in the fiber direction. The proposed model incorporates the influence of boundary conditions, laminate thickness and lay-up configuration, as well as the importance of the micro-geometry. The analysis results are used to gain a better understanding of the influence of the macro-geometry in addition to the micro-geometry and fiber and matrix material properties. The predictions of the model for unidirectional laminates under direct compression and cross-ply laminates under four-point bending are discussed and comparisons with some experimental results for carbon/thermoplastic composites are presented.