Materials testing — ductility index by percentage elongation: A tensile test shows 30% elongation for material A and 40% elongation for material B (same gauge length and cross-section). Conclude whether B is more ductile than A.

Introduction / Context:
Ductility quantifies the extent of plastic deformation a material can sustain before fracture. Common indices are percentage elongation and percentage reduction in area, both measured on standard tensile specimens.

Given Data / Assumptions:

• Two specimens of identical dimensions are tested to fracture.
• Percentage elongation for A = 30%, for B = 40%.
• Standard test conditions assumed identical (strain rate, temperature).

Concept / Approach:
Greater percentage elongation indicates higher ductility because the specimen undergoes more permanent extension prior to fracture. Therefore, with all else equal, material B is more ductile than A.

Step-by-Step Solution:

Verification / Alternative check:
For many metals, higher % reduction in area accompanies higher % elongation; both indices generally correlate with ductility. Even if %RA differs, the given elongation already supports the conclusion under identical conditions.

Why Other Options Are Wrong:

• “Incorrect” contradicts the definition of the ductility index used.
• Requiring %RA or limiting to brittle materials is unnecessary; elongation alone is a valid ductility measure.

Common Pitfalls:
Comparing elongations from different gauge lengths or non-standard specimens; always compare like with like.

Final Answer:
Correct