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Glossary

Cyclic Stress-Strain Curve

The materials deformation during a fatigue test is measured in the form of a hysteresis loop. After some initial transient behavior the material stabilizes and the same hysteresis loop is obtained for every loading cycle. Each strain range tested will have a corresponding stress range that is measured. The cyclic stress strain curve is a plot of all of this data.

The curve describes the behavior of the material after it has been plastically deformed. This behavior is usually different than the initial behavior that is measured in a traditional tensile test. A simple power function is fit to this curve to obtain three material properties; cyclic strength coefficient, K' , cyclic strain hardening exponent, n' , and elastic modulus, E.