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Integrated Computational Materials Engineering (ICME) for Metals: Using Multiscale Modeling to Invigorate Engineering Design with Science by Mark F. Horstemeyer

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2.5 MULTISTAGE FATIGUE (MSF) MODELING

In the framework of a multiscale predictive fatigue model, the macroscale form should start from an elastic–plastic fracture mechanic (EPFM) perspective (e.g., crack tip opening displacement) that can account for the subscale heterogeneities and plasticity; to develop the framework for this analysis, one must then define the different stages of the fatigue life and the associated microstructures that affect each stage of the life of the component. In this sense, this case study focuses on the MSF approach [151] that decomposes fatigue life into three consecutive stages based on the MS details of fatigue crack growth, similar to the approach summarized by Suresh [152], that is,

c02e069 (2.69)

where NTotal is the total fatigue life, NInc is the number of cycles to incubate a crack at a micronotch that includes the nucleation of crack-like damage and earlier crack propagation through the region of the micronotch root influence, and NMSC is the number of cycles required for the propagation of a microstructurally small crack (MSC) with the crack length, ai < a < k MS, with MS defined as a characteristic length scale of interaction with MS features and k as a multiplier in the range between one and three. Also NLC is the LC linear elastic fracture mechanic (LEFM)-based solution. Each stage in the MSF model will have different lives for different types of ...

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