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One of the most essential tasks in probabilistic damage tolerance assessment is to describe the scatter in crack growth accurately. This study proposes a stochastic model of the crack growth rate, which calculates the critical parameters of a random distribution accurately by combining the Markov chain and data fitting algorithms. The proposed method is validated by the crack growth test data of Ni‐based superalloy GH4710Li at 550°C. The validation results show that the proposed method is a robust and efficient stochastic model for the crack growth rate. [ABSTRACT FROM AUTHOR]

• A dislocation-based damage-coupled constitutive model for SX superalloys is developed. • The incorporation of structure-induced GND can improve the simulation accuracy. • A heat-resistant speckle pattern that is suitable for long-term applications is developed. • Secondary orientation can significantly influence the creep life of circular hole. • An empirical model for rapid evaluation of creep life is proposed based on high throughput simulations. Circular holes in single crystal (SX) turbine blades are susceptible to creep failure at high temperatures, due to the stress concentrations near the holes. In this study, a dislocation-based damage-coupled constitutive model for SX superalloys is developed, validated, and applied to unveil the effect of secondary orientation on the creep life of circular holes. The structure-induced geometrically necessary dislocations (GND) density resulting from the macroscopic strain gradient is incorporated. The dissipated energy is employed as the indicator to predict crack nucleation. Initially, the specimens without a hole are employed to calibrate the parameters and validate the model in the absence of structure-induced GND. Creep experiments incorporating the digital image correlation technique are conducted on the specimens with a hole under different secondary orientations, which aims to validate the simulated strain distribution, crack nucleation location, and creep life under the influence of structure-induced GND. The results indicate that the incorporation of structure-induced GND contributes to mitigating the conservatism in the creep life prediction of circular holes. Because, the GND can enhance dislocation hardening near the hole, extending the predicted life and improving the accuracy of life prediction. Meanwhile, both experiments and simulations indicate that the secondary orientation influences the crack nucleation locations at the hole edge. The variation in the creep life at different secondary orientations is attributed to the changes in both the maximum value and uniformity of resolved shear stresses distributed across slip systems. Finally, the model is applied to simulate the creep behavior of a circular hole under various secondary orientations, stresses, and temperatures. An empirical model is developed to rapidly evaluate the creep life of a circular hole in the SX superalloy, which facilitates the engineering application of the proposed model. [Display omitted] [ABSTRACT FROM AUTHOR]

• An in-situ test system combined with DIC is developed under SEM, which can capture the SB evolution and microcrack nucleation. • For circular hole on SX superalloy, effects of secondary orientation and temperature on tensile behavior and SB evolution are revealed. • A SB evolution model is proposed, which uses different CRSSs as the plasticity criteria and internal state variables inside and outside SB. • The proposed model can simulate the SB evolution, SB direction, SB-induced strain concentration, and microcrack nucleation. Circular holes on single crystal (SX) superalloys are widely utilized as film cooling structures on SX turbine blades, while their failure is a persistent issue. This study presents in-situ tests using digital image correlation (DIC) to reveal the slip band (SB) evolution behavior near the circular hole on SX superalloy, and proposes a mechanism-based model to capture the SB-associated evolutions of stress, strain, and damage fields. In the experiment part, high-temperature in-situ tensile tests are carried out under scanning electron microscope on plate-like SX specimens with circular hole, which can achieve the in-situ measurement and observation for the SB-induced strain concentration and microcrack nucleation. Experimental results reveal the effects of secondary orientation and temperature on stress-strain curve, SB evolution and SB direction. Besides, the microstructure observation shows that the γ´ phase shear is the primary cause of strain concentration inside SB. In the simulation part, a physics-based SB evolution model is proposed under the framework of crystal plasticity. For the regions inside and outside SB, different critical resolved shear stresses are utilized as the plasticity criteria, and different slip resistances are used as internal state variables in the flow rule to simulate the SB-induced strain concentration. A damage evolution rule is developed based on the plastic work density in slip systems to simulate the microcrack nucleation near the hole edge. Finally, the proposed model is validated through the experiments. The model can effectively simulate the SB initiation/evolution, SB direction, SB-induced strain concentration, and the microcrack nucleation near circular hole on SX superalloy. [ABSTRACT FROM AUTHOR]

In this study, a physics-based model is proposed to predict the γ/γ′ microstructure evolution of single crystal (SC) superalloy at medium temperature and high stress level. Considering multiple hardening mechanisms, the crystal plasticity (CP) model accounting for γ/γ′ microstructure evolution is developed to predict the creep strain. Creep fracture and interrupted tests are conducted for a kind of Nickel-based SC superalloy firstly. Based on the microscopic observation of the tested specimens, the γ/γ′ microstructure evolutions including dissolution and rafting behaviors of γ/γ′ phases are observed. Besides, the hardening mechanisms during plasticity accumulation can be revealed as the coupling of dislocation bypassing, dislocation hardening and γ′ phases shear. Based on the unit cell model (UCM), the dimensional parameters evolution of γ/γ′ phases is modeled. The Fick's law is employed to describe the dissolution of γ′ phase, and the rafting behavior is modeled based on the release of elastic-plastic energy. The diffusion coefficient is derived to consider the effects of both temperature and stress. Applying the γ/γ′ microstructure evolution as the input, the CP-based constitutive model accounting for the multiple hardening mechanisms is developed. The Orowan stress denoting the resistance of dislocation bypassing is modified to account for both horizontal and vertical channel width. Finally, the proposed model is validated by the test results. The γ/γ′ microstructure evolution model is verified by the statistical data including fraction, length and width of γ′ phases within the temperature range of 850–900 °C and stress range of 550–660 MPa. Further, the modified CP model is validated using creep strain curves within the temperature range of 760–900 °C and stress range of 500–660 MPa. The predicted results are in good agreement with the test data. • The γ/γ′ microstructure evolution behaviors and hardening mechanisms are revealed for single crystal (SC) superalloy at medium temperature (850–900 °C) and high stress (600–660 MPa) level. • A physics-based microstructure evolution model considering the coupling of dissolution and rafting is proposed. • A multi-scale constitutive model considering multiple hardening mechanisms is developed. • The Orowan stress is modified to account for both vertical and horizontal matrix channels of SC. [ABSTRACT FROM AUTHOR]