As a surface peening technique, shot peening introduces residual compressive stresses to the surface of the part, which effectively increases the fatigue life of the structure and material. However, when structures are subjected to alternating loads, this can lead to stress relaxation on the material surface, weakening the effectiveness of the shot peening process. In addition, reasonable shot peening parameters are essential. In this paper, the effects of shot peening pressure and shot coverage on the fatigue life of materials during shot peening were investigated, followed by fatigue tests on 20CrMnTi specimens using a high-frequency fatigue testing machine to study the effects of shot peening and re-shot peening on the fatigue life of shot-peened materials after different load cycles. The results show that a reasonable shot peening pressure and coverage rate can significantly improve the fatigue life of the material, while a shot peening pressure higher than 0.4 MPa will reduce the fatigue life of the material 20CrMnTi. Coverage rates of 100% and 200% can both improve the fatigue life of the material, while a 200% coverage rate has a better strengthening effect. Re-shot peening removes the residual compressive stress relaxation on the surface of the material caused by cyclic loading and improves the fatigue life of the material. The maximum value of the residual compressive stress on the surface of the test material after shot peening is 443 MPa, and after a certain number of fatigue loads, the residual compressive stress on the surface is reduced to 203 MPa, which is subjected to secondary shot peening, and the residual compressive stress is restored to 415 MPa, and the fatigue life is significantly increased. When the second shot peening time is taken as 25% of the fatigue life of the initial shot blasting of the material, the shot peening effect is better.

Shot peening technology is used to improve the fatigue strength of materials and parts, and is one of the most effective surface engineering techniques to prolong fatigue life. In this paper, according to the finite element simulation analysis of shot peening, a randomly distributed multiple-shot finite element model was established. The superimposed effects of multiple projectile impact craters in shot peening are fully considered. The effects of shot velocity, shot peening angle and shot coverage on the residual stress field and surface roughness were studied. The alloy steel 20MnTiB, widely used in the automotive industry, was used as the raw material to process the specimens. The shot peening tests of different process parameters were carried out. The test results verified the correctness and accuracy of the random distribution model of multiple-shot. The shot-peening simulation model proposed in this paper allows a more accurate analysis of the effect of shot-peening parameters on the surface residual stress field and helps to quickly set the correct shot-peening process parameters. This paper further investigates the effect of shot peening parameters on fatigue life, providing a basis for the rational development of shot peening solutions.

Industrial robots are widely used in various industrial fields, such as handling and welding, due to their good repeat positioning accuracy. The motion error determines the absolute accuracy. For robot design, dimensional parameter errors and drive parameter errors, a mathematical model of a kinematic exponential product with error screws was proposed. The influence of different rod lengths and transmission errors on the accuracy of the end motion was analysed. A composite analysis method based on screw theory and vector method is proposed for the spatial deflection error of robot rotating joints with clearance. By using screw theory, a mathematical error model of the axial movement and spatial deflection of the joint gap was established. A mathematical model of joint space radial movement was established by using the three-dimensional vector method. Through numerical simulation, the position distribution law of the random error of the robot terminal in the workspace and the distribution of the plane projection density were obtained. By solving the attitude matrix, the distribution of each Euler angle error was obtained. A simulation test was carried out to verify the model's correctness. The calculation showed that the method is simple and correct, and the obtained error distribution characteristics are of great significance to improving robotic kinematic calibration accuracy and optimising the spatial position error distribution.

The harsh environmental loads may lead to strength failure in the turbine in an aero-engine. To accurately assess the strength reliability of the turbine under multiple loads, the stress distributions of 41 danger sites of a turbine under thermal, centrifugal, and pneumatic loads were determined by the flow-thermal-solid coupling analysis using ANSYS. Second, based on the flow-thermal-solid coupling analysis and response surface method, the probabilistic analysis model of stress at the danger site was established. And the probabilistic distribution of stress was determined by sampling and hypothesis testing. Finally, the reliability model of the turbine with multi-site damage and failure dependency was established, by which a reliability of 0.99802 was calculated. And the actual reliability of the turbine was 0.99626 determined by the Monte Carlo simulations, which verified the model in precision. The results indicated that the reliability model has a high efficiency and higher precision than the traditional reliability model with failure independence.

The clearance of a kinematic pair will lead to the contact collision between the joints of the mechanism, which will have a great influence on the dynamic characteristics of a mechanical system with clearance. In order to study the influence of a rotating motion pair with clearance on the dynamic characteristics of a tool changing robot, a contact wear dynamics model of a modular tool changing robot was established based on the three-state model of “free-contact-collision”. Different from analysis of a light linkage structure, this paper takes a solid structure with large mass as the analysis object. Based on the impact contact force model and the improved Coulomb friction model, the effects of clearance size, rotational speed and friction coefficient on the dynamic characteristics of the tool changing robot were analyzed. The Archard wear model was used to predict the wear between the motion pairs with clearance. The analysis results show that, with the increase of clearance size and actuating speed, the fluctuation range of velocity and acceleration increases, and the fluctuation frequency decreases. Under the action of friction, the contact force between components will be reduced due to energy loss so that the kinematic reliability of the mechanism is improved. The wear of the moving pair with clearance is non-uniform. Through the research of this paper, the motion characteristics of the tool-changing robot at low speed and heavy load are clarified. The results show that the established method can realize the dynamic characteristics analysis of low-speed heavy-duty mechanisms with joint gaps, which can be used to guide the design of tool-changing robots, and also has important reference significance for the design of mechanisms containing joint gaps in general.