Question

Metals with high monotonic strain-hardening exponents ($n > 0.15$) and those with a low strain-hardening exponent ($n < 0.15$) respectively would undergo

• A. Ideal plastic, Ideal elastic
• B. Ideal elastic, Ideal plastic
• C. Cyclic hardening, cyclic softening
• D. Cyclic softening, cyclic hardening

Hint:

High strain-hardening exponent metals ($n > 0.15$) undergo cyclic hardening; low exponent metals ($n < 0.15$) show cyclic softening.

Answer 1

The Correct Option is C

Step 1: Understanding Strain-Hardening Exponent The strain-hardening exponent ($n$) characterizes how a metal strengthens as it is plastically deformed. A higher value of $n$ implies better capacity to strain-harden under repeated loading. - When $n > 0.15$: Materials tend to exhibit cyclic hardening due to increased resistance to deformation with repeated loading. - When $n < 0.15$: Materials tend to cyclically soften, as they cannot accumulate as much strain hardening, and internal stresses reduce their ability to resist deformation over time. Step 2: Linking to Cyclic Loading Behavior Under fatigue or cyclic loading, high $n$ metals harden, while low $n$ metals soften - this is the critical distinction that governs material selection in applications like springs or rotating machinery.