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To assess the contribution of residual stress to the improvement of high‐cycle fatigue (HCF) properties, HCF tests are performed on Ti‐6Al‐4V specimens with different residual stress levels but no other evident surface state modification induced by machining. Results indicate that compressive residual stress induced by machining significantly improves the HCF performance of Ti‐6Al‐4V specimens. Of all the specimens, the fatigue strength of specimens with a surface residual stress level of −400 MPa is increased by approximately 16.4%. Furthermore, to accurately predict the fatigue life based on three mean stress correction equations (e.g., Walker, Goodman, and Smith–Watson–Topper), the method of reducing surface residual stress by a reduction factor and then adding to the mean stress is proposed. A reduction factor of 0.55 is found to be appropriate for the alloy under the test condition, with majority of the predicted data falling within a factor of three scatter band. Highlights: Isolate residual stress from other surface integrity parameters by machining.Compressive residual stress improves both the fatigue life and strength.Effect of residual stress is considered by introducing a reduction factor in mean stress.Develop a life prediction method based on mean stress correction model. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) material has excellent high-temperature resistance and heat insulation performance, which plays a vital role in improving the working efficiency and running life of the engine. During the flight, the engine will inhale dust particles in the air. These particles are mostly from siliceous debris, which are usually called calcium magnesium aluminum silicate (CMAS). At present, CMAS corrosion has become one of the important problems affecting the service life of thermal barrier coatings. In this study, conventional yttrium oxide stabilized zirconia (YSZ) coatings and ytterbium oxide and yttrium oxide co-stabilized zirconia (YbYSZ) coatings were prepared by atmospheric plasma spraying. The two coatings were examined under thermal cycling-CMAS coupling conditions and divided into six life stages. The failure modes, CMAS permeation behavior, crack characteristics and mechanical properties of the two coatings at different life stages were evaluated systematically. The experimental results show that the YbYSZ coating has a longer life than YSZ coating under the thermal cycling and CMAS coupling condition, which increases by about 83% compared with the conventional YSZ coating. In the whole life stage, the porosity of YbYSZ coating is always higher than that of YSZ coating. The phase transition is not the reason for the failure and spalling of the coatings. The crack length of the two coatings showed an increasing trend, but the crack length of the YSZ coating was higher than that of the YbYSZ coating, and the crack density of the two coatings showed a "saddle shape", which was more obvious for the YSZ coating. The YbYSZ coating shows better mechanical properties under the thermal cycling-CMAS coupling condition with the evolution of life. [ABSTRACT FROM AUTHOR]

In this work, the correlation between ductile fracture toughness and a new unified constraint parameter Ad* for bi‐material interfaces with different mechanical mismatches (strength and hardening mismatches) has been investigated based on finite element analysis and experimental data validation. The results show that with increasing crack depth (geometric constraint) and mechanical mismatch level (increasing undermatch or overmatch level), the J–R curves and fracture toughness JC of bi‐material interfaces decrease. The constraint parameter Ad* values of bi‐material interface cracks are basically independent of the strength and hardening mismatches. A general correlation equation between fracture toughness JC and constraint parameter Ad* has been obtained, which may be applied to prediction of fracture toughness of any specimens or components with different geometric constraints and material properties mismatches (including homogeneous materials). The prediction capability of the correlation equation has been validated by experimental fracture toughness data of cracks with different strength and hardening mismatches in dissimilar metal welded joints. Highlights: Correlation between fracture toughness and constraint of bi‐material interfaces is studied.The constraint parameter Ad* of bi‐material interface is independent of the mismatches.A general correlation equation between fracture toughness and parameter Ad* is obtained.Prediction capability of the equation for fracture toughness is validated by experimental data. [ABSTRACT FROM AUTHOR]

In order to predict and assess creep life for plate structures with semi‐elliptic surface cracks under high temperature condition, the accurate calculation of the creep fracture mechanics parameter C* is a critical step. In this paper, the effects of crack sizes, plate geometries, and material creep properties on the parameter C* have been investigated under tensile and bending loads by extensive finite element analyses. Based on the results, the creep influence functions Hc for calculating C* values were obtained and fitted into equations for surface cracks in plates under both loads. The equations have been verified by finite element calculations. The C* solutions were obtained through these equations which are suitable for wide ranges of crack sizes, plate geometries, and materials. [ABSTRACT FROM AUTHOR]

In this work, the two‐parameter J‐Ad approach was applied to predict thefracture toughness of test single‐edge‐notched‐bend (SEN(B)) specimens with different in‐plane and out‐of‐plane constraints for two materials with different mechanical properties. The results show that for most SEN(B) specimens, the predicted fracture toughness agrees with the experimental data; thus, the capability and applicability of the two‐parameter J‐Ad approach are validated. The approach correctly predicts that the fracture toughness decreases with increasing in‐plane and out‐of‐plane constraints. Compared with the prediction results of the three‐parameter J‐Q‐Tz approach in the literature, the J‐Ad approach has better prediction accuracy and wider application ranges. The calculation procedure of the J‐Ad approach is also simple and convenient for engineering application. [ABSTRACT FROM AUTHOR]