Flow stress
Flow stress is defined as the instantaneous value of stress required to continue plastically deforming the material - to keep the metal flowing. It is the yield strength of the metal as a function of strain, which can be expressed:[1]
- Yf = Kεn
- Yf = Flow stress, MPa
- ε = True strain
- K = Strength Coefficient, MPa
- n = Strain hardening exponent
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 following properties have an effect on flow stress: chemical composition, purity, crystal structure, phase constitution, exit microstructure, grain size, and heat treatment.[2]
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.
References
- ↑ Mikell P. Groover, 2007, "Fundamentals of Modern Manufacturing; Materials, Processes, and Systems," Third Edition, John Wiley & Sons Inc.
- ↑ Flow Stress