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Glossary

Goodman Diagram

Tension mean stresses reduce the fatigue life from that observed with completely reversed loading. The Goodman diagram, originally proposed in 1890, is a graphical representation of this effect.

The alternating stress is plotted on one axis and the mean stress on the other. The allowable alternating stress with no mean stress is the fatigue limit. The maximum mean stress, with zero alternating stress, is the ultimate strength. A straight line is then drawn between the two points. Any combination of mean and alternating stress on this line will have the same fatigue life. Mathematically this may be expressed as: