Notched fatigue strength of single crystals at high temperature

The high temperature notched fatigue strength of the CMSX-4 single crystal superalloy has been experimentally investigated. Notched specimens with orientation <001> have been tested at 950°C in load control in the LCF life regime. SEM observations of the failed specimens has been made in order to associate the actual crack initiation location in the notch to the crystallographic orientation and to the critical location in the notch as given by suitable multiaxial fatigue parameters. In order to model the material behavior in the notch, stress-strain analysis of the notched specimens was performed by an elastic-plastic FEM procedure; the parameters describing the material behavior of the single crystal superalloy have been identified by comparison with experimentally determined stress- strain fatigue behavior of smooth specimens. A suitable model for the assessment of the fatigue life of single crystal materials is proposed for the purpose of application to the design of turbine engines components.