Application suitability — is cast iron preferred for components subjected to shock loading? Evaluate the statement: “Cast iron is used for those parts which are subjected to shocks.” Indicate whether it is correct or incorrect, considering cast iron's brittleness and impact response.

Introduction / Context:
Material selection for components exposed to impact or shock requires understanding of toughness, ductility, and notch sensitivity. Traditional gray and white cast irons are economical and possess good compressive strength and damping, but their response to shock differs significantly from that of steels and ductile irons.

Given Data / Assumptions:

• “Cast iron” refers to gray and white cast irons unless otherwise specified.
• Shock loading implies high strain rate and stress concentration risk.
• Operating at room temperature.

Concept / Approach:
Gray cast iron contains flake graphite that acts as crack initiators, yielding low impact strength and brittle fracture under shock. White cast iron contains continuous carbides and is even more brittle. Therefore, ordinary cast irons are not preferred for shock-laden parts. If ductile (spheroidal graphite) iron is considered, impact properties improve due to nodular graphite morphology, but the blanket statement “cast iron is used for shocks” remains incorrect without that qualification.

Step-by-Step Solution:

Verification / Alternative check:
Impact test data show steels and SG irons outperform gray/white irons in absorbed energy; design manuals recommend steels for shock and fluctuating load cases.

Why Other Options Are Wrong:

• Correct / white cast iron versions: contradict material behavior; white iron is the most brittle.
• Thickness-based justification: section size does not eliminate notch sensitivity.
• SG iron caveat: while SG iron is better, the original statement lacks that qualification.

Common Pitfalls:
Choosing cast iron solely for cost and damping without checking impact toughness; overlooking notch effects at keyways or fillets.

Final Answer: