Flow stress is defined as the instantaneous value of stress required to continue plastically deforming the material - to keep the metal flowing. The flow stress for a given material in continuum mechanics is dependent upon the temperature, , true strain, , and strain rate, . Therefore, it can be written a some function of those properties:
The exact equation to represent flow stress is dependent upon the particular material and the plasticity model being used. Other models may also include the effects of strain gradients.
- Yf = Kεn
Hence, Flow stress can also be defined as the stress required to sustain plastic deformation at a particular strain.
The flow stress is a function of plastic strain.
The flow stress is an important parameter in the fatigue failure of ductile materials. Fatigue failure is caused by crack propagation in materials under a varying load, typically a cyclically varying load. The rate of crack propagation is inversely proportional to the flow stress of the material.
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