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Glossary

Strain Life Curve

The strain life curve is determined by testing materials in strain control. The strain range is controlled and the corresponding stress range and fatigue life are determined. It is convenient to consider the elastic and plastic strain amplitudes separately when curve fitting the test data. Two data points are plotted for each test, one for the elastic strain amplitude vs life and another one for the plastic strain amplitude vs life.

Test data is then fit to a simple power function to obtain the material constants; fatigue ductility coefficient,ε'_f, fatigue ductility exponent, c , fatigue strength coefficient, σ'_f , and fatigue strength exponent, b ,

The total strain is then obtained by adding the elastic and plastic portions of the strain.