A combined critical distance and energy density model to predict high temperature fatigue life in notched single crystal superalloy members

• An anomalous CGR regime is observed on notched tubular specimens.
• The short CG regime is shown to correspond to plastic zone size ahead of the notch.
• A damage model is used to describe short CG and fatigue life of smooth specimens.
• CGR is computed at critical distance within factor of two of experimental results.
• Good predictions of initiation period are achieved.

The formation of short cracks at notched members of superalloy single crystals under high temperature low cycle fatigue is analysed. AM1 superalloy at 950 °C is studied for [0 0 1] and [1 1 1] loading axis under fully reversed strain loading. An anomalous crack growth rate regime is observed that depends upon test frequency. Local strain gradient is computed using a finite element model and crystal viscoplasticity constitutive equations. A damage model based on viscoplastic strain energy density and dilation energy density is used to describe short crack growth and fatigue life of smooth specimens. Finite element results are used to identify a critical distance model for notched specimens. A good correlation between experimental results and model predictions is achieved for all test orientations and frequencies.