Spring terminology: The load (force) required to produce a unit deflection of a spring is termed as what?
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AFlexural rigidity
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BTorsional rigidity
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CSpring stiffness
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DYoung's modulus
Answer
Correct Answer: Spring stiffness
Explanation
Introduction / Context:Springs are characterized by how much they deflect under load. The direct proportionality constant between load and deflection in the elastic range is the spring stiffness, a critical parameter for designing suspensions, valves, and vibration isolators.
Given Data / Assumptions:
- Small deflections in the elastic range (Hooke’s law holds).
- Deflection measured along the spring’s working direction.
- Material and geometry fixed.
Concept / Approach:For linear springs, F = k * x, where F is load, x is deflection, and k is spring stiffness (spring rate). Therefore, the load required for unit deflection is simply k. Other listed terms are stiffness-related but apply to beams or torsional members, not directly to overall spring response in translation.
Step-by-Step Solution:
Define spring law: F = k * x.Set x = 1 (unit deflection): F_unit = k.Hence, the required term is spring stiffness.For helical compression springs, k = G * d^4 / (8 * D^3 * N) (for reference), where d = wire diameter, D = mean coil diameter, N = active coils, and G = shear modulus.Verification / Alternative check:Dimensionally, k has units of force per unit displacement (e.g., N/mm), matching “load per unit deflection.”
Why Other Options Are Wrong:
- Flexural rigidity (E * I) applies to beam bending stiffness, not directly to a spring’s axial rate.
- Torsional rigidity (G * J) is a torsional stiffness measure of a shaft or rod.
- Young’s modulus is a material constant, not the overall element stiffness.
Common Pitfalls:Confusing material modulus with system stiffness; stiffness depends on geometry and boundary conditions in addition to material properties.
Final Answer:Spring stiffness