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Relating Paris Law Fatigue Crack Growth in Composites with a Physics-Based Fatigue Model

RAY S. FERTIG, III

Abstract


The focus of this paper is to explore potential connections between the kinetic theory of fracture (KTF), a physics-based fatigue life prediction methodology, and the traditional Paris Law approach to prediction of fatigue crack propagation in composites. In previous research, KTF has been used primarily as a predictor of fatigue initiation. In this work, linear elastic fracture mechanics assumptions are used to advance a crack through a polymer material that is nominally epoxy. The results show that KTF-based crack propagation is compatible with the Paris Law description of fatigue life propagation. Furthermore, the KTF approach is shown to correctly predict crack growth trends with changing frequency, temperature, and R-ratio. These parameters directly influence the Paris Law coefficient. The Paris Law exponent is shown to depend entirely on the nature of the crack tip singularity.

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