Question

Considering the stress-strain diagram, the material would be best suited for an application requiring high toughness is:

• A. Mild steel, due to its extensive plastic deformation and toughness
• B. Cast iron, because of its high brittleness
• C. Aluminum alloy, as it has the highest modulus of elasticity
• D. Cast iron, due to its high strength

Hint:

Tough materials bend, not break — and mild steel does exactly that. Great for absorbing impact and resisting fracture!

Answer 1

The Correct Option is A

Toughness is defined as the ability of a material to absorb energy and plastically deform without fracturing. It is represented by the total area under the stress-strain curve.
Why Mild Steel is Best for High Toughness:

• Mild steel has a combination of moderate strength and very good ductility.
• This enables it to undergo significant plastic deformation before failure.
• The large area under its stress-strain curve indicates high toughness.
• It is commonly used in structures and applications where energy absorption and damage tolerance are important.

Why the Other Options Are Incorrect:

• (B) Cast iron: Very brittle and fractures easily with little plastic deformation.
• (C) Aluminum alloy: Has lower modulus than cast iron and limited plastic deformation compared to mild steel.
• (D) Cast iron: Though strong, its brittleness limits its toughness.

Thus, the material best suited for high toughness is mild steel, because of its excellent ability to deform plastically and absorb energy.