United States Department of Transportation
i
Evaluation of Parameters Used in Progressive Damage Models
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2022-09-01
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[PDF-2.79 MB]
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Edition:Final
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Abstract:Damage initiation and propagation in carbon fiber composites can be classified as corresponding to loading of the fibers in tension & compression, the matrix in tension & compression, and the matrix in shear. Matrix compression has been studied the least. The matrix- compression damage parameters needed for finite element simulations are not available. Matrix-tension values are typically used. While such estimates are sufficiently conservative (i.e., result in predictions of failure at lower loads than would occur and are thus “safe”) the difference from the correct matrix-compression values are unknown. Consequently, this approach may lead to overly conservative designs. The purpose of this project is to evaluate currently-used finite element methods to determine the extent to which the use of these incorrect matrix-compression damage parameters impacts simulation predictions and calculations. The method used was to determine accurate matrix-compression damage parameters, use them in simulations, and compare the outputs to those obtained from the current approach of using tensile values. Accurate matrix-compression damage parameters were determined through development of a suitable test specimen and experimental measurements. With these parameters simulations for several layups and loadings were performed with the commercial finite element package and compared to simulations using tensile values. Results showed that the appropriate matrix-compression damage material model was an energy release rate at the propagating tip of the damage region. The contribution of residual load-carrying ability in the wake of this tip (due to surface contact under compressive loading) was insignificant. Furthermore, the energy release rate was found to consist of Mode I and Mode II components of respective magnitudes of 3.42 times the currently-used tensile value and 11.88 times the currently-used tensile value. The extent to which the use of incorrect matrix-compression damage parameters impacts simulation predictions and calculations was evaluated using six layups and two loading configurations. Results showed the change in value did not significantly affect fiber-tension damage or fiber-compression damage for any layup or loading and only slightly affected Mises stress. However, the change in value did significantly affect matrix-tension damage, matrix-compression damage, and matrix-shear damage for all layups and both loadings. This report shows that the current method using a tensile value for matrix-compression damage can introduce significant errors in predictions of damage initiation and propagation in finite element simulations of carbon-fiber laminates.
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