A model for fatigue crack initiation from notches

Document Type

Conference Proceeding

Date of Original Version



A model is developed to predict the number of cycles for fatigue crack initiation from a notch. It is based on the concept that the initiation of a fatigue crack occurs when the accumulated plastic shear deformation in the notch root reaches a critical limit which is defined in terms of the threshold stress intensity factor of the material under consideration. A viscoplastic analysis using unified constitutive equations is employed in order to describe the evolution of the notch plastic zone size as well as the stress and plastic strain distributions within this zone on cycle by cycle basis. This analysis takes into consideration the material s time- and cyclic-dependent characteristics. Experimental verification of the model was carried out using specimens made of AM350, an austenitic steel alloy. A series of crack growth measurements were performed in order to calculate the threshold stress intensity factor which is then used to determine the plastic deformation limit of this alloy. The model is used to calculate the number of cycles to crack initiation which is compared to that obtained experimentally under various loading parameters. The correlation between the model prediction and the experimental results are reported and discussed.

Publication Title, e.g., Journal

American Society of Mechanical Engineers (Publication) NDE



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