Thermal stresses exist when temperature gradients in a material produce expansions or contractions.

Thermal stresses exist when temperature gradients in a material produce expansions or contractions.

• A. Thermal stress
• B. Residual stress
• C. Flow stress
• D. Fatigue stress

Answer: (A)

When temperature differences inside a material cause different regions to try to expand or contract by different amounts, and those regions are bound together so they can’t move freely, internal forces develop to keep the parts connected. Those internal forces are thermal stresses. The situation described—temperature gradients leading to unequal expansion or contraction and the resulting internal stress—directly defines thermal stress. Residual stress is related but broader: it’s stress that remains in a material after the original cause (like cooling or forming) is removed. Flow stress and fatigue stress describe how a material responds to mechanical loading—resistance to deformation and damage from repeated loading, respectively—not the stresses caused by temperature-induced differential expansion.

When temperature differences inside a material cause different regions to try to expand or contract by different amounts, and those regions are bound together so they can’t move freely, internal forces develop to keep the parts connected. Those internal forces are thermal stresses. The situation described—temperature gradients leading to unequal expansion or contraction and the resulting internal stress—directly defines thermal stress.

Residual stress is related but broader: it’s stress that remains in a material after the original cause (like cooling or forming) is removed. Flow stress and fatigue stress describe how a material responds to mechanical loading—resistance to deformation and damage from repeated loading, respectively—not the stresses caused by temperature-induced differential expansion.