Mechanical properties for spring design: Which material property is most essential for spring materials intended to store and release elastic energy repeatedly without permanent set?

Introduction / Context:
Springs are energy-storage elements that deflect elastically under load and return to their original shape upon unloading. Selecting the correct governing property helps in choosing alloys and heat treatments for coil springs, leaf springs, and torsion bars.

Given Data / Assumptions:

• Service involves cyclic loading within the elastic range.
• Permanent deformation (plastic set) is undesirable.
• Fatigue is a concern, but the question seeks the essential property enabling energy storage and release.

Concept / Approach:
Resilience is the capacity of a material to absorb elastic energy and release it upon unloading. The area under the stress–strain curve up to the elastic limit represents modulus of resilience. While stiffness (spring constant) dictates deflection per load, resilience governs how much energy can be stored safely without yielding.

Step-by-Step Solution:
Define resilience: elastic energy storage capability up to elastic limit.Relate to spring action: during loading, energy is stored; during unloading, it is released with minimal loss.Differentiate from stiffness: stiffness sets deflection, not energy capacity per se.Conclude resilience is the most essential property for springs.

Verification / Alternative check:
Design practice uses high-strength, high-resilience alloys (e.g., Si–Mn steels) and shot peening to improve fatigue while preserving elastic behavior.

Why Other Options Are Wrong:
Ductility and plasticity involve permanent deformation; creep resistance relates to long-term high-temperature loading; stiffness alone does not define safe energy storage capacity.

Common Pitfalls:
Equating maximum stiffness with optimal spring performance; ignoring the importance of elastic limit and energy density.

Final Answer:
resilience