Hysteresis loop area in rubber's stress-strain curve

Steps:

• Recognize the graph as a stress-strain curve for rubber, showing loading (extension) and unloading paths.
• Observe the paths form a closed loop due to viscoelastic behavior, not overlapping perfectly.
• Calculate that the loop's area equals the difference in work done during loading versus unloading.
• Conclude this difference represents energy lost, not recovered, as heat from internal friction.

Why C is correct:

• In viscoelastic materials like rubber, the hysteresis loop area quantifies energy dissipated as heat per cycle, per the definition of mechanical hysteresis.

Why the others are wrong:

• A: Elastic energy is the reversible area under the unloading curve, recoverable upon release.
• B: Rubber undergoes minimal plastic deformation; energy for that would show permanent strain, absent here.
• D: Work to extend is the total area under the loading curve alone, not the shaded loop.

Final answer: C