Since engineering materials are exposed to dwell-times in service, it is important to understand the effects of dwell times on the fatigue life. The mechanisms controlling deformation and failure under dwell conditions are in terms of metallographic damage namely; transgranular fracture, intergranular fracture, mixed intergranular transgranular fracture modes, surface striated damage, creep damage and oxidation. These mechanisms are very difficult to include in a quantitative model to predict the dwell sensitivity behavior of high temperature materials. Published creep-fatigue data were compiled from various sources for a number of materials such as copper alloys (NARloy-Z, AMZ1RC), steel alloys (9Cr-lMo), and nickel based alloys(lN 100, Rene 95, Waspaloy). In general, dwell-times were found to be detrimental to the fatigue life of materials, but the exact extent of the effect varies depending on the material, duration of the dwell, and the direction in which a dwell was applied. In this research an attempt has been made to further develop the models of the senior author and include such concepts as stress relaxation with respect to a particular dwell time. Very limited data sets are available in the literature showing all the test details needed for developing a model for this research. However, the initial trials show stress relaxation as a result of a dwell cycle may exhibit an effect that may describe dwell. A dwell sensitivity damage mechanistic map and a new dwell sensitivity damage parameter were developed.
& Goswami, T.
(2002). Dwell Sensitivity Behavior and Modeling. Journal of the Mechanical Behavior of Materials, 13 (5-6), 373-385.