Springs – limiting capacity: What is the term for the greatest load a spring can sustain without suffering any permanent set (permanent distortion)?

Introduction / Context:
Design of helical and leaf springs requires specifying a safe maximum load so that, after unloading, the spring returns to its original dimensions. The engineering term for the limiting service load that does not cause permanent set is essential for specifying acceptance tests and service ratings.

Given Data / Assumptions:

• Spring is used in the elastic range during service.
• Permanent set corresponds to plastic deformation.
• We need the correct terminology used in spring design and testing standards.

Concept / Approach:
Springs are commonly tested up to a specified maximum force and then unloaded to verify that no permanent deformation remains. That maximum force is called the proof load. It establishes a pass/fail criterion for elastic performance under service conditions.

Step-by-Step Solution:
Identify the physical requirement: no permanent set after removing the load.Relate to terminology: the greatest load meeting this requirement is the proof load.Differentiate from related terms: proof stress is a stress level; stiffness is a rate of load vs. deflection; proof resilience is energy, not load.Conclude that the correct choice is 'proof load'.

Verification / Alternative check:
Manufacturing specifications often state: 'Spring shall withstand the specified proof load and recover to within tolerance of free length,' confirming the definition.

Why Other Options Are Wrong:

• Proof stress: a stress value (commonly at a specified offset), not a load.
• Stiffness: spring rate (force per unit deflection), not a limiting load.
• Proof resilience: energy stored at the elastic limit, not the force itself.
• Elastic limit load: descriptive phrase but the standard accepted term in spring testing is 'proof load.'

Common Pitfalls:
Confusing energy and load terminology; assuming 'stiffness' relates to strength rather than deflection rate; mixing 'proof stress' (material property) with spring system limits.

Final Answer:
proof load