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Established the double cold expansion simulation model, and investigated the effects of surface micromorphology characteristics on the fatigue performance of double cold expanded holes. The double cold expansion process and fatigue life of the strengthened holes was simulated by using ABAQUS and MSC. Fatigue software. The hole wall element was selected, and the surface micro-profile of the hole wall was represented as the semi-ellips micro-notches. The S-N curve of the material is modified by effective stress concentration factor Kf, and investigated the effects of surface micro-profile on the fatigue performance of double cold expanded holes.The results show that there existed compressive residual stress layer on the hole wall after the double cold expansion process, and the fatigue life of the expanded sample was increased. With the increasing of the number of micro-notches in the hole wall, the stress concentration factor can be alleviated effectively, and stress concentration factor Kt is positively correlated with the depth-width ratio b/a and the distance-width ratio d/（2a）. The double cold expansion process can reduce the surface roughness of the hole wall by 21%～49%, which can effectively alleviate the notch stress concentration and improve the fatigue performance of the hole.

Zirconia is gradually used in manufacturing aerospace and other fields because of its excellent mechanical processing properties. Due to its hardness and brittleness, zirconia can easily cause excessive and unstable changes in grinding force during machining, resulting in extensive surface damage and poor surface quality. Therefore, it is important to establish an appropriate grinding force model and achieve accurate control and prediction of the grinding force. Ultrasonic-assisted grinding can reduce grinding forces, improve workpiece surface quality, and increase processing efficiency. However, the grinding force model for ultrasonic-assisted grinding is still not adequately investigated. In this study, a new method for predicting the axial force of ultrasonic-assisted grinding is proposed. Vickers hardness and indentation fracture theories combine two different methods: plastic removal and brittle fracture. Moreover, conventional and ultrasonic-assisted grinding tests are performed. Then, the relationship between grinding forces and process parameters is investigated using numerical statistical calculation methods. The grinding force data obtained from the test validate the theoretical model, with the average error between the theoretical and experimental values being 22.87%. The influence of machining variables on the grinding force is investigated, and experimental results of conventional al grinding and ultrasonic-assisted grinding are compared. It is found that the rotary ultrasonic-assisted grinding force can be reduced by up to 66.76%. [ABSTRACT FROM AUTHOR]

SiCf/SiC composites have promising applications in aerospace industries. SiCf/SiC composite micro-holes are important components, such as gas film holes on turbine blades. However, micro-hole machining in the SiCf/SiC composite is challenging because of its excellent mechanical and physical properties and poor machinability caused by micro-hole constraints. Therefore, a novel brazed diamond abrasive core drill was designed to achieve high self-sharpness by continuously losing blunt diamond grits and exposing sharp diamond grits. The wear and self-sharpness of the developed drill were investigated and compared with those of an electroplated diamond core drill during ultrasonic vibration-assisted drilling of SiCf/SiC composite micro-holes. The material removal behaviors of SiCf/SiC composites, including drilling forces, exit tearing, hole dimensions, hole wall quality, and the wear of core drills, were also studied. The developed core drill demonstrated reduced drilling force and a significantly prolonged lifetime. Further, it achieved superior drilling performance, drilling accuracy, and micro-hole quality. [ABSTRACT FROM AUTHOR]