Strain is a gradual, continuing irreversible deformation due to constant stress level below yield stress.

• A. False
• B. True
• C. Not defined
• D. Both

Answer: (A)

Strain is the measure of how much a material deforms under load, and the type of deformation depends on the stress level and time. When the applied stress is below the yield strength, the typical response is elastic deformation: the material stretches or compresses but returns to its original shape when the load is removed. Permanent deformation occurs only after yielding, which leads to plastic (permanent) strain. There is also creep, a time-dependent irreversible deformation that can happen under sustained load, usually at elevated temperatures or over long periods, but it is not the normal behavior described by “constant stress below yield.” So the statement is not correct because strain under below-yield stress is not inherently gradual irreversible deformation; it is predominantly elastic, with permanent changes only arising from plastic deformation after yielding or from creep under special conditions.