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Micromechanical Prediction of a Composite Failure Under Longitudinal Compression



A micromechanical approach is presented to predict strength of a composite under a longitudinal compression only in terms of the original properties of its constituent fiber and matrix materials. An initial fiber misalignment and further rotation due to matrix shear strain are taken into account in evaluating the internal stresses of the fiber and matrix through micromechanics Bridging Model. The thus obtained homogenized matrix stresses are converted into true values by means of the corresponding stress concentration factors (SCFs) of the matrix before a failure assessment against its original strength parameters is made. An efficient Mohr’s type criterion is established to determine a matrix failure and the failure orientation angle, which in turn has an influence on the fiber rotation. A fiber compressive failure is detected using the maximum normal stress failure criterion. Whichever of these two kinds of failures occurs first corresponds to the composite compressive failure. Our theory has been applied to predict the longitudinal compressive strengths of the UD (unidirectional) composites used in the worldwide failure exercises (WWFEs). The predictions correlate reasonably well with the available test data.


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