Question

The strain rate sensitivity of flow stress for occurrence of superplasticity is in the range of:

• A. 0.3--0.6
• B. 0.01--0.1
• C. 0.1--0.2
• D. 0

Hint:

Superplasticity requires high strain rate sensitivity — typically in the range of 0.3 to 0.6 — allowing materials to deform extensively without localized necking.

Answer 1

The Correct Option is A

Strain rate sensitivity (\( m \)) is a measure of how the flow stress of a material responds to changes in the rate of deformation (strain rate). It is defined by the relation: \[ \sigma = K \cdot \dot{\varepsilon}^m \] where \( \sigma \) is flow stress, \( \dot{\varepsilon} \) is the strain rate, and \( m \) is the strain rate sensitivity exponent.
Superplasticity is the capability of some materials to undergo extremely high elongations (typically over 200%) without necking, under specific conditions of fine grain size, elevated temperatures, and suitable strain rate sensitivity.
For superplastic behavior to occur:
- The value of \( m \) should typically lie between 0.3 to 0.6.
- Lower values (e.g., \( m<0.2 \)) correspond to normal deformation behavior.
Thus, option (1) is correct.