Effect of initial overload on the low cycle fatigue life of GH4169 alloy at different temperatures.

• The LCF tests of notched specimens under three temperatures after different degrees of initial overload treatment was conducted. • The initial overloads could significantly improve the crack initiation life, but could also introduce damage near the notch surface, especially for large overload situations. • The LCF life model considering the sensitivity of overload induced residual stress can give a more accurate prediction. • A recommendation to improve the fatigue life of GH4169 alloy by initial overload was given through comprehensive experimental results and finite element model analysis. In this paper, the effect of initial overload on the low cycle fatigue life of GH4169 alloy at different temperatures was studied. The plate specimen with a central hole was designed to perform low cycle fatigue tests at 20 °C, 500 °C and 650 °C with variable initial overloads. Results showed that the subsequent crack propagation rate depended on both overload ratio and following test temperature, and excessive overload treatment would also damage the surface or internal grains of the specimens through fracture characteristics under SEM. A finite element model was adopted to analyze the residual stress and stress-strain field at the edge of the central hole. Then, the stress and strain data were input to three strain-based model to predict the fatigue life of GH4169 alloy considering residual and mean stresses. Based on the combination of the experimental results and model prediction, the suggestion to improve the fatigue life of GH4169 alloy by initial overload can be put forward as following: a single initial overload makes the maximum local stress reach 90 %–93.5 % of the true ultimate stress of the material, so as to maximize its fatigue life. [ABSTRACT FROM AUTHOR]