In a typical stress–strain curve for mild (low-carbon) steel, which material point is commonly labeled “A”? Assume the standard sequence: proportional/elastic limit, yield point, ultimate stress, fracture.

Introduction / Context:
The stress–strain curve of mild steel shows distinct regions: linear elasticity, yield plateau, strain hardening, ultimate stress, and fracture. Correctly identifying these points is essential for design limits and material selection.

Given Data / Assumptions:

• Mild steel specimen under tensile test.
• Conventional labeling where “A” typically denotes the end of proportionality (elastic limit), followed by upper/lower yield.
• No diagram provided—use standard convention.

Concept / Approach:
The initial straight segment obeys Hooke’s law. The end of this linear behavior is the proportional (elastic) limit. Beyond this, yielding begins, often marked by an upper yield point, then a lower yield region. After plastic deformation and strain hardening, the curve reaches an ultimate maximum, then necks to fracture.

Step-by-Step Solution:
Identify the first key point at the end of straight-line elasticity → “A”.Subsequent points include yield point(s), ultimate stress, then fracture.Therefore “A” corresponds to the elastic (proportional) limit.

Verification / Alternative check:
Standard materials texts label the end of linearity as the proportional limit, sometimes coincident with the elastic limit for design purposes.

Why Other Options Are Wrong:
(b) and (a) occur much later; (d) comes after elastic limit; (e) is an offset proof stress definition, not the early “A” marker.

Common Pitfalls:
Confusing yield point with the end of proportionality; overlooking the difference between proportional and elastic limits in precise terms.

Final Answer:
Elastic limit (proportional limit)