Structural plastics subjected to continuous, sustained loads over a long period are highly susceptible to a phenomenon where deformation increases steadily over time, even if the applied stress remains constant. This property is known as
- AFatigue
- BRelaxation
- CCreepCorrect
- DElastic Hysteresis
Solution
Concept
Creep deformation in structural polymers
Formula
Total Strain(t) = Elastic Strain + Creep Strain(t)
Step-by-step solution
1. Structural plastics and polymers exhibit viscoelastic behavior under mechanical stress. 2. When subjected to continuous sustained load, polymeric chains gradually slip, disentangle, and rearrange over time. 3. This progressive, time-dependent increase in strain under constant stress is defined as creep. 4. Hence, the phenomenon described is creep. Answer: C
Explanation
When polymeric and plastic materials are subjected to prolonged constant stress, molecular polymer chains slowly untangle and slip over time. This continuous, progressive deformation occurring under sustained load is defined as creep. Creep deformation can lead to excessive sag and structural failure if not accounted for in long-term load-bearing designs.
Why the other options are wrong
A) Fatigue is structural damage and fracture caused by cyclic or fluctuating stress. B) Relaxation is the decrease of stress over time under constant strain. D) Elastic hysteresis is the energy dissipated between loading and unloading cycles within the elastic range.
Shortcut
Deformation increasing over time under constant stress = Creep.
Common mistake
Confusing creep (strain increase at constant stress) with stress relaxation (stress decrease at constant strain).
Correct answer: C) Creep