Cohesive technology applied to the modeling and simulation of fatigue failure

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Estimation of fatigue and fracture properties of materials is essential for the safe life estimation of aging structural components. Standard ASTM testing procedures being time consuming and costly, computational methods that can reliably predict fatigue properties of the material will be very useful. Toward this end, we present a computational model that can capture the entire Paris curve for a material. The model is based on a damage-dependent irreversible cohesive failure formulation. The model relies on a combination of a bilinear cohesive failure law and an evolution law relating the cohesive stiffness, the rate of crack opening displacement, and number of cycles since the onset of failure. Threshold behavior of the fatigue crack propagation is determined by the initial value of the damage parameter of the cohesive failure law, while the accelerated region is the natural outcome of the cohesive formulation. The Paris region can be readily calibrated with the two parameters of the proposed cohesive model. We compare the simulation results with the NASGRO material database, and show that the threshold region is adequately captured by the proposed model. We summarize a semi-implicit implementation of the proposed model into a cohesive-volumetric finite element framework, allowing for the simulation of a wide range of fatigue problems. © 2009 Springer-Verlag US.

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Virtual Testing and Predictive Modeling: For Fatigue and Fracture Mechanics Allowables