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JP Journal of Solids and Structures

JP Journal of Solids and Structures
Volume 5, Issue 1, Pages 31 - 47 (March 2011)

MICROSTRUCTURE-DEPENDENT FATIGUE DAMAGE PROCESS ZONE AND NOTCH SENSITIVITY INDEX
Gbadebo Owolabi, Benedict Egboiyi, Li Shi and Horace Whitworth

Abstract:
The development of simulation methods for calculating notch root parameters for the purposes of estimating fatigue life is a critical aspect of designing against fatigue failures in notched components. At present, however, treatment of the notch root stress and plastic strain field gradients, coupled with intrinsic length scales of grains or other material attributes, are yet to be developed; ultimately, the approach will be necessary to form a predictive basis for notch size effects in forming and propagating microstructurally small cracks in real structural materials and components. In this study, computational micromechanics is used to clarify and distinguish process zone for crack formation and microstructurally small crack growth, relative to scale of notch root radius and spatial extent of stress concentration at the notch. A new nonlocal criterion for fatigue damage process zone based on the distribution of a shear-based fatigue indicator parameter is proposed and used along with a statistical method to obtain a new microstructure-sensitive fatigue notch factor and associated notch sensitivity index, thereby extending notch sensitivity to explicitly incorporate microstructure sensitivity and attendant size effects via probabilistic arguments. The notch sensitivity values, obtained for a range of notch root radii using the new statistical approach presented in this study, follow the general trends obtained from experimental results available in literature.

Keywords and phrases: crystal plasticity, fatigue damage process zone, micromechanics, crack formation and growth.

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