Physics · Mechanical Properties Of Solids · NEET
When you slowly increase the load on a material, stress and strain trace one path (the loading curve). When you slowly remove the load, they trace a different path back to zero (the unloading curve). If these two paths do not coincide, the gap between them is elastic hysteresis. The material 'remembers' being stretched and returns along a lower-stress path.
Work done per unit volume equals the area under a stress-strain curve. During loading you do work on the material (area under loading curve). During unloading the material returns work to you (area under unloading curve). Because the loading area is bigger, the difference — the enclosed loop area — is the net energy per unit volume that was NOT returned. It leaves as heat, so the material warms up.
No, but they are related. Elastic after-effect is the delay in returning to original shape after the load is removed. Elastic fatigue is the weakening of a material after repeated stress cycles. Elastic hysteresis is specifically the loop between the loading and unloading curves and the heat lost each cycle. Repeated hysteresis cycles are one cause of elastic fatigue.
Rubber is an elastomer with long, tangled polymer chains. Stretching untangles them and releasing lets them re-tangle, but this internal friction dissipates a lot of energy, giving a wide loop. Steel has a rigid crystal lattice with tiny reversible strain, so its loading and unloading curves almost overlap — a very thin loop and little heat lost.
Car tyres and shock absorbers use materials with high hysteresis on purpose: the loop area absorbs bumps and vibrations as heat, giving a smooth ride. A material with low hysteresis (like a good spring or a bell) returns almost all energy, so it bounces or rings for a long time.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the lag between the loading and unloading stress-strain curves of a material, forming a loop whose area equals the energy lost as heat per cycle.
It represents the energy dissipated as heat per unit volume of the material during one complete loading-unloading cycle.
Rubber shows a much larger hysteresis loop than steel because its polymer chains lose more energy to internal friction; steel's loop is very thin.
Yes. High-hysteresis materials are chosen for tyres and shock absorbers to soak up vibration as heat, while low-hysteresis materials are used for springs and bells.
No. The energy not returned as mechanical work is converted to heat, so total energy is fully conserved.
