Duoqi Shi

A physically based methodology for predicting anisotropic creep properties of Ni-based superalloys

This paper is focused on developing suitable methodology for predicting creep characteristics (i.e., the minimum creep strain rate, stress rupture life and time to a specified creep strain) of typical Ni-based directionally solidified (DS) and single-crystal (SC) superalloys. A modern method with high accuracy on simulating wide ranging creep properties was fully validated by a sufficient amount of experimental data, which was then developed to model anisotropic creep characteristics by introducing a simple orientation factor defined by the ultimate tensile strength (UTS). Physical confidence on this methodology is provided by the well-predicted transitions of creep deformation mechanisms. Meanwhile, this method was further adopted to innovatively evaluate the creep properties of different materials from a relative perspective.

Constitutive modeling of a directionally solidified nickel-based superalloy DZ125 subjected to thermal mechanical creep fatigue loadings

A transversely isotropic continuum elasto-viscoplasticity model, which was developed from Chaboche’s unified constitutive model, was formulated to capture the thermal mechanical creep fatigue deformation behavior of a directionally solidified nickel-based superalloy. A fourth-order tensor was introduced to model material anisotropy. In order to model the tertiary creep behavior, the Kachanov damage evolution equation was coupled into the stress tensor. Based on the test results of uniaxial tensile, fatigue, and creep loadings at isothermal temperature conditions, the material parameters are obtained. Thermal mechanical fatigue (TMF) and creep–fatigue interaction test results were used to verify the robustness of the model. Additionally, strain–temperature-dependent stress–strain responses under TMF loadings were analyzed using the present model. Under strain-controlled conditions, both of the stress ranges and mean stresses are strongly influenced by the strain–temperature phases, a key parameter for TMF tests.

A simple unified critical plane damage parameter for high-temperature LCF life prediction of a Ni-based DS superalloy

A simple unified critical plane damage parameter (i.e., the modified resolved shear strain range ∆γmod) based on a slip mechanism-related critical plane concept was proposed in this paper, integrating life prediction of low cycle fatigue (LCF) behavior affected by anisotropy, load ratio and stress concentration into one framework, where the critical plane is determined as the slip plane on which the damage parameter is the maximum during the cycle. For notched specimens, this procedure was specially carried out at the fatigue initiation sites located on the notch surface, which were well predicted by the distribution of Von-Mises stress range ∆σMises. The applications of this damage parameter in a directionally solidified superalloy at high temperatures showed that the LCF lives resulting from complicated loading conditions (i.e., variable material orientation, temperature, loading ratio and notch feature) were well simulated consistently, and the predicted fatigue life is within a scatter band of ±3.