Question

A cast iron beam shows a brittle fracture on the stress-strain diagram. What does this indicate about its elongation at break?

• A. It is very high.
• B. It is moderate.
• C. It is very low.
• D. It increases with temperature

Hint:

Ductile vs. Brittle Fracture. Ductile: Significant plastic deformation, large elongation before fracture. Brittle: Little or no plastic deformation, small elongation before fracture. Cast iron is a brittle material.

Answer 1

The Correct Option is C

Materials are classified as ductile or brittle based on their behavior under tensile stress, particularly after yielding.
- Ductile materials (like mild steel, copper) undergo significant plastic deformation (elongation) after yielding and before fracturing.
Their stress-strain diagrams show a large strain at fracture.
- Brittle materials (like cast iron, glass, ceramics) exhibit very little or no plastic deformation before they fracture suddenly.
Their stress-strain diagrams show fracture occurring shortly after the elastic limit, with very small elongation (strain) at break.
Since the cast iron beam shows a brittle fracture, it indicates that it underwent very little plastic deformation before breaking.
Therefore, its elongation (or strain) at break is very low.