Many structural members in service experience fluctuating loads and temperatures. Thermal stresses devlop on a contrained element if the temperature is cycled. Constraint exists in structural components due to temperature gradient, material anisotropy, and geometry effects. The equilibrium and compatibility equations determine the degree of constraint on the critcal component of the body. A two-bar structure is employed in this study to simulate different constraint conditions encountered in practice. The constraint types are termed (a) total, (b) partial, (c) over, and (d) notch constraint. Thermo-mechanical fatigue test results indicate that the fatigue lives decrease severely with increasing constraint, increasing temperature range and with the presence of notch or a defect.