Proportionality limit/ elastic limit: Which statement is correct?

Proportionality limit/ elastic limit: Which statement is correct?

• A. It is the maximum load before fracture
• B. It marks the end of the plastic deformation region
• C. It is the linear region where Hooke's law holds
• D. It is where plastic deformation begins and all loads are recoverable

Answer: (C)

The essential idea is that the proportionality (elastic) limit marks the portion of the stress–strain curve where Hooke’s law applies, so stress is proportional to strain. Within this region, deformation is elastic: if the load is removed, the material returns to its original shape. Beyond this limit, the relation becomes non-linear and plastic deformation begins, meaning some permanent change remains after unloading. The statement describing the linear region where Hooke’s law holds correctly matches this concept. The other options mix up what happens at different points on the curve: the maximum load before fracture is the fracture point, not the elastic limit; saying it marks the end of the plastic region is inaccurate since plastic deformation is the permanent, non-recoverable part; and claiming all loads are recoverable when plastic deformation begins is incorrect because plastic deformation is not recoverable.

The essential idea is that the proportionality (elastic) limit marks the portion of the stress–strain curve where Hooke’s law applies, so stress is proportional to strain. Within this region, deformation is elastic: if the load is removed, the material returns to its original shape.

Beyond this limit, the relation becomes non-linear and plastic deformation begins, meaning some permanent change remains after unloading. The statement describing the linear region where Hooke’s law holds correctly matches this concept.

The other options mix up what happens at different points on the curve: the maximum load before fracture is the fracture point, not the elastic limit; saying it marks the end of the plastic region is inaccurate since plastic deformation is the permanent, non-recoverable part; and claiming all loads are recoverable when plastic deformation begins is incorrect because plastic deformation is not recoverable.