SEDL / STP / STP868-EB / STP34252S

A Model for Creep/Fatigue Interactions in Alloy 718

Nicholas, T
Materials Research Engineer, Air Force Wright Aeronautical Laboratories (MLLN), Wright-Patterson AFB, OH

Weerasooriya, T
Research Engineer, University of Dayton Research Institute, Dayton, OH

Ashbaugh, NE
Research Engineer, University of Dayton Research Institute, Dayton, OH

Pages: 14    Published: Jan 1985

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Abstract

An experimental investigation was conducted to evaluate the crack growth rates in Inconel 718 at 649°C under symmetric and unsymmetric triangular waveshapes and triangular waves with hold times at maximum load. Data are presented as crack growth rate per cycle as a function of total cycle time. An analytical model is developed which predicts crack growth rate from an integration of the sustained load crack growth rates over the cycle when time-dependent behavior is dominant. The data show that the loading portion of a cycle is the major contributor to the time-dependent crack growth behavior. At low unloading frequencies or high load ratios, however, the unloading portion of the cycle is found to become increasingly important. The model utilizes minimum baseline data and is proposed for predictions of crack growth rate over a variety of loading cycle types.