What Is Flow Stress?

The distribution and density of dislocations in the crystal are related to the history of the crystal. In an unprocessed crystal, the movable dislocations will be arranged into a mechanically stable configuration. From this configuration to another low-energy configuration, In the meantime, at least one configuration with a large energy must be crossed, so the dislocation can only move when it is subjected to external stress. The so-called flow stress is the minimum stress required for dislocations to continuously pass through the crystal. ^[1]

In all calculations, the stress _f necessary to maintain plastic deformation during the process must be considered more important than temperature, strain, and strain rate. Our interest is not just initiating but also maintaining plastic flow.

Get enough attention. Thus, the yield strength found in many manuals is seldom applied; the flow stress across the real stress-true strain curve is between the strain limit and the terminal strain determined by the raw material.

In cold working, it can be assumed that the power-law formula is valid. Always use the available K and n values (see the table below for some data).

For hot working, the appropriate C and m values can be used to calculate the flow stress from the power function formula. If these values cannot be used for individual strains, one must assume that the flow stress remains constant throughout the deformation. If c and m data are not available, one has to perform compression tests. The thermal strength values determined in conventional slow tensile tests cannot be used, as they often represent only the high values obtained during deformation A much smaller fraction of the prevailing flow stress at much higher strain rates (typically 1-1000 s ^-1 ). Inferring high strain rates from low strain rates is dangerous because the value of m also varies with strain rate. ^[3]