Geometry and Loading Effects on the Compressive Strength of Fibrous Composites

This work addresses the important engineering problem of the com pressive strength of fibrous laminated composites, bridging the micromechanics relevant to compressive failure due to fiber kinking with the global characteristics of a composite structure Simple modeling incorporates the influence of boundary conditions, laminate thickness and layup configuration, as well as the importance of the microgeometry. The mechanism of failure under compression is assumed to be microbuckling of fibers that localizes at points with the maximum initial imperfection and leads to the formation and, under critical conditions, propagation of kink bands. To analyze the mechanics of kinking and to calculate the critical compressive stress, a steady state kink propagation model is utilized for the layers under compression in the fiber direction. The analysis results are used to gain a better understanding of the influence of the macrogeometry (laminate thick ness and gauge length) in addition to the microgeometry (fiber diameter and fiber volume fraction), and the fiber and matrix material properties The predictions of the model are compared with experimental results for carbon/thermoplastic unidirectional laminates under direct compression and cross-ply laminates under four-point bending.