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Progressive damage modeling of composite materials under compressive loads Zobeiry, Navid

Abstract

The in-plane compressive strength of fibre reinforced composite materials is known to be less than their corresponding tensile strength. There are a multitude of compression damage mechanisms that occur in composites, the form of which depends on the properties of the constituents and fibre lay-up. These mechanisms primarily consist of a combination of matrix cracking (yielding), localized buckling of fibres or kinking, and delamination. Whether the interest is to assess the structural integrity of composite materials in-service or to quantify their energy absorption capability under axial crushing, it is crucial to have predictive analysis tools that capture the physics of the damage mechanisms and their propagation under compressive loads. In this study, a constitutive model is formulated for the complete in-plane response of composite materials within the framework of a previously developed continuum damage mechanics model CODAM (Williams, 1998; Williams et al., 2003; Floyd, 2004). While the previous CODAM formulation was limited to simulating the progression of damage under tensile loading, the current formulation accounts for the initiation and propagation of damage under compression, tension and load reversals in each mode of loading. The model is implemented in the commercial finite element code, LS-DYNA, and combined with a modified crack band model originally developed by Bazant (Bazant and Planas, 1998) to overcome the mesh sensitivity problems that plague all strain-softening type constitutive models. The new model is validated against two sets of experimental data available in the literature, namely, eccentric compression loading of notched sandwich panels of various sizes (Bayldon, 2003a, 2003b), and axial compression of composite panels with central open holes of various panel and hole sizes (Soutis et al., 1993, 2002). It is shown that for these loading applications the predictions of the compressive strengths and the degree of size effect are in good agreement with the measured experimental results. Since the formulation of the model and its calibration are based entirely on the fundamental physics of the damage mechanisms, these successful validations instil confidence in exercising the model for predicting the response of composite structures of various sizes under a variety of in-plane loading applications involving compression, tension and load reversals.

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