Overcoming Limitations of the Conventional Strain-Life Fatigue Damage Model

Abstract

The strain-based approach to fatigue life prediction usually relies on the conventional strain-life equation which correlates the elastic and plastic strain to the life. The correlation is based on separate log-linear curve fits of the elastic and plastic components of the strain data versus the life. It is well known, however, that these linear relationships may be valid only within a specific interval of stress or strain. When material behavior approaches elastic-perfectly plastic, for instance, it is not uncommon for the test data to deviate from linearity at both very high and very low strains. For such materials a separate fit of each curve is likely to give material constants significantly inconsistent with the fit of the cyclic stress-strain curve, especially if a good local fit over a restricted interval is obtained. In this work, some of the errors that arise as a result of this inconsistency are described, and recommended methods are developed for treating these errors. Numerical concerns are also addressed, and sample results are included.

Life Prediction of Two Rotor Steels under Creep-Fatigue Interaction at Elevated Temperature

“…With respect to stress relaxation creep damage occurs under the condition of the varied stress condition. Dealing with cyclic hold time effect Manson-Coffin Equation can be corrected into the following form [10]:…”