In the linear (elastic) region of the stress–strain curve, deformation is...

• A. Elastic and reversible
• B. Plastic and permanent
• C. Creep occurs
• D. Fracture occurs

Answer: (A)

In the linear elastic region, deformation is elastic and reversible. The stress–strain relationship is proportional (Hooke’s law): strain increases linearly with stress, with the slope given by Young’s modulus. When the load is removed, the material snaps back to its original shape because the atomic bonds return to their initial positions and no permanent rearrangement has occurred. This is the defining feature of elastic behavior: all deformation is recoverable and no residual strain remains.

If you push beyond this region, the material enters plastic behavior where permanent, non-recoverable deformation occurs due to dislocation movement and other microstructural changes. Creep refers to time-dependent deformation under a sustained load, typically at higher temperatures, which is not the immediate elastic response. Fracture is the final failure where the material breaks, which again is outside the linear elastic region.