1) The frequency of cyclic loading has only a small effect on the fatigue strength.

2) The form of stress cycle such as square, triangular, or sinusoidal wave has no effect on the fatigue life.

3) The environment in which the component undergoes stress reversals has a marked effect on fatigue life. The fatigue life in vacuum could be some 10 times more than that in moist air. Also note the effect of corrosion fatigue.

4) The thickness of the test specimen has an effect on the fatigue properties. Thin­ner samples show a decrease in the crack growth rate.

5) Stress concentrators such as key ways with sharp corners promote crack initia­tion, thereby decreasing the number of cycles to failure.

6) Surface smoothness (or roughness) has strong effect on fatigue life and polished surfaces will have improved fatigue life.