The effect of pneumatic shot peening (PSP) on the fatigue properties of K403 turbine blades has been investigated under the high and low cycle combined fatigue (CCF) load with two types of turbine blades: untreated blades and PSP treated blades. It is found that there is a threshold vibration stress for the blades in this study. The PSP has a positive effect on the CCF life of blades mainly due to the compressive residual stress resulting in the reduction of the number of crack sources and propagation rate, when vibration stresses are below the threshold vibration stress. However, the PSP treatment has no effect or a negative effect when vibration stresses are above the threshold value. The compressive residual stress is released along with the microstructure changes of K403 alloy. Meanwhile, the microstructure changes, reflected in the precipitation of the lamellar MC carbides and σ phases, can accelerate the processes of crack initiation and propagation.

In this study, a combined low‐ and high‐cycle fatigue (CCF) life prediction model, which considers the crack closure effect (CCE) of micro‐defects, is proposed based on the continuous damage mechanics. The model is decomposed into three submodels: the low‐cycle fatigue (LCF), high‐cycle fatigue (HCF) under the maximum stress of LCF (HCFML), and their coupled damage models. The experimental CCF data of K403 full‐scale turbine blades are used to verify the accuracy. The prediction life falls within the ±2.62 times of scatter band compared with the experimental results. Further, there are the different damage evolution forms at different vibration stresses. When the vibration stress is below 29 MPa, the CCF damage mainly is caused by the LCF. However, while the vibration stress is above 29 MPa, the HCFML damage plays a major role. The CCF damage of the first stage serration of K403 turbine blades is mainly from HCFML.

Turbine components (blades, guides and casing) of gas turbine engine usually suffer from fatigue load in company with a HTG environment in service. The corrosive substances in HTG can deposit on the surface of turbine components and induce accelerated damage known as hot corrosion. In this study, an experimental system is designed and built up to conduct LCF tests of superalloy in HTG environment. The influence of HTG on the LCF behavior of the nickel-base superalloy GH4169 at 650°C is studied. According to the test results, the average fatigue life of the specimens in HTG environment (22270 cycles) is about 31.5% less than that in air (32496 cycles). The protective oxide film on the surface of the specimen can be destroyed by the electrochemical reaction between HTG and oxide film. Compared with the specimen tested in air, there are more fatigue sources in the specimen tested in HTG environment, and the transgranular–intergranular transition occurs in the crack growth area.

Granular coal is a kind of multilayer and structured solid matter, which consists of a large assemblage of individual granular solids and has dual characters of coal and granular materials. Its crack propagation law can be studied using the coal mechanics and multi-scale characteristics. First of all, the linear elastic material may be damaged under compression; and the cause of crack propagation is explained from the viewpoint of energy that the dynamics of crack propagation is due to the release of strain energy. And then, further study on the granular coal crack propagation under uniaxial compression from macroscopic and microscopic raspects is carried out by physical experiment and numerical simulation. Results show that a cone is formed at the bottom of the heap, the crack propagation is slowed down with the decrease of coal particle size, mutation points in crack propagation will appear, and the crack will not be smooth after the granular coal is damaged completely. Besides, due to the influence of granular coal particle size, uniformity has an important effect on crack propagation. The greater the homogeneity coefficient, the later the fractures occur. The acoustic emission energy release becomes frequent and severe in the mild, moderate and deep stages of crack propagation. These results will be conducive to further study on the law of geotechnical granular materials crack propagation under compression.

The effect of pneumatic shot peening (PSP) on the fatigue properties of K403 turbine blades has been investigated under the high and low cycle combined fatigue (CCF) load with two types of blades: untreated blades and PSP treated blades. It is found that there is a threshold vibration stress which should be 194MPa. The PSP has a positive effect on the CCF life of blades mainly due to the compressive residual stress resulting in the reduction of the number of crack sources and propagation rate when vibration stresses are below the threshold vibration stress. However, the PSP treatment has no or negative effect when vibration stresses are above the threshold value. The compressive residual stress is released along with the microstructure changes of K403. Meanwhile, the microstructure changes, reflected in the precipitation of the lamellar MC carbides and σ phases, can accelerate the process of crack initiation and propagation.