Which statement is true?

Asked in SSC JE 27/01/2018 (Evening)

Detailed Explanation

The limit of proportionality is the stress up to which stress is proportional to strain. Being a stress, it is independent of the size of the specimen.

Why “Limit of proportionality depends on type of material” Is Correct

It is a material property: mild steel, aluminium and copper each have their own value. A bigger cross-section needs a bigger load to reach it, but the stress at the limit is the same. So it depends on the type of material.

Stress–strain curve of mild steel in tension. O–A: straight line, Hooke's law holds up to the limit of proportionality A. B: elastic limit. C and D: upper and lower yield points. D–E: yielding at nearly constant stress. E–F: strain hardening up to the ultimate stress F. G: fracture.

Why the Other Options Are Wrong

A. Limit of proportionality depends on area of cross-section: Area changes the load at which the limit is reached, not the stress value.
B. Limit of proportionality depends on type of loading: For the same material, the proportional limit stress is a constant.
D. All options are correct: Only (c) is correct.

Key Point

Limit of proportionality, yield stress and ultimate stress are material properties.

Key Concepts for Students

Mild steel limit of proportionality ≈ 200–250 N/mm².
Heat treatment and alloying change these values.
Tests use standard specimens to measure them.

Practice more: this is question 25 in Stress and Strain MCQs – Part 2. Try the whole set and check every answer instantly.