Effect of Temperature on Toughness — General Trend for Metals As the temperature of a metallic material is increased (within typical service ranges), its toughness generally:

Introduction / Context:
Toughness is the ability of a material to absorb energy up to fracture, often measured by impact tests like Charpy V-notch. Understanding how temperature affects toughness is crucial for selecting materials for cold climates or cryogenic service.

Given Data / Assumptions:

• Metallic materials in the range from subzero to elevated but sub-melting temperatures.
• Body-centered cubic (BCC) alloys exhibit ductile-to-brittle transitions; face-centered cubic (FCC) alloys remain generally tough.

Concept / Approach:
As temperature increases, atomic mobility and slip increase, which reduces the tendency for brittle fracture and raises ductility. Consequently, the area under the stress–strain curve (a measure of toughness) generally increases with temperature for most metals in normal service ranges.

Step-by-Step Solution:
At low temperature, dislocation motion is hindered → brittle behavior → low impact energy.Raise temperature → more slip systems operate → higher elongation and impact energy.Therefore, toughness tends to increase with temperature.

Verification / Alternative check:
Charpy impact curves for carbon steels show higher absorbed energy at higher test temperatures, especially past the ductile-to-brittle transition region.

Why Other Options Are Wrong:

• Remains same: ignores clear temperature dependence.
• Decreases: opposite to the general trend in the non-cryogenic range.
• Always drops to zero or becomes infinite: physically meaningless statements.

Common Pitfalls:
Forgetting special cases: some precipitation-hardening alloys may lose toughness at very high temperatures; the question addresses the general trend over typical ranges.

Final Answer:
increases