Numerical and theoretical study of shot peening and stress peen forming process

Shot peening is a cold working process widely used to improve the fatigue life of metallic components in the aerospace and automobile industries. The performance and repeatability of this improvement depend greatly on the shot peening parameters, such as Almen intensity, surface coverage, peening time, etc. Finite Element Analysis (FEA) has been adopted to simulate the shot peening process based on the development of computer resources and numerical methods. Most of the existing Finite Element (FE) models, however, such as 2D models and one shot impact models, cannot describe numerous randomly distributed shot flow. Therefore, one goal of this study was to establish a 3D shot peening model that can simulate a random shot peening process and to study the quantitative relationship between peening parameters and peening results.;A novel 3D FE model that describes randomly distributed shots was developed in order to simulate the dynamic shot peening process. Using this 3D random FE model, a quantitative relationship was established between peening intensity, surface coverage and roughness, with respect to the number of shots, based on the same target component, aluminum 2024. The simulated results show that the novel FE model can help us to understand and predict shot peening results better than the existing conventional FE models.;An experimental study of shot peening and stress peen forming was carried out in order to validate the novel FE model. In shot peening experiments, the quantitative relationships between saturation, surface coverage and roughness, with respect to peening time, were established for aluminum 2024 test strips. A pre-stressing device was designed to apply prebending moments on the strip in order to perform stress peen forming. The principal conclusion was that with increasing prebending moment, the deformed arc height following the prebending direction increases.;A three-step implicit-explicit-implicit FE model was developed to simulate the stress peen forming process. Firstly, an implicit FE calculation was performed to acquire the initial stress distribution resulting from the prebending moment. Secondly, an explicit FE calculation was carried out to obtain the induced stress after shot peening. Finally, an implicit FE model was built to calculate the deformed arc height and radius of curvature of the deformed component. The three-step FE model is the first model that simulates the stress peen forming process. It provides a useful tool to predict the results of stress peen forming.;Stress peen forming is a special application of shot peening that deals with thin target components. Stress peen forming has been widely used in the aeronautics industry to produce thin components with complex shapes, such as wing skins. Most studies of the stress peen forming process have been based on trial and error experiments. Therefore, another objective of this study was to develop a numerical model in order to simulate this process, and to investigate the quantitative relationship between the prebending conditions (prebending moment or pre-stress) and the forming results (resulting arc height or radius of curvature).;An analytical model was also developed to study the shot peening process and to predict Almen intensity with reduced use of calculation resources. The study of this analytical model showed that although different combinations of shot peening parameters (shot size and velocity) can produce the same Almen intensity, each combination resulted in a different through thickness residual stress distribution. Therefore, it is important to choose different combinations of shot peening parameters, and to investigate their influence on the shot peening results.;Numerical, experimental and analytical methods were employed to study the shot peening and stress peen forming processes. With the help of the newly developed FE model for the simulation of the shot peening process, the shot peening intensity, saturation, surface coverage, and surface roughness can be studied in detail. Therefore, the new FE model provides a useful tool for designers, to guide their choice of the optimal shot peening parameters. In addition, the newly established FE model of stress peen forming provides a useful tool for prediction and optimization of the stress peen forming process. Finally, the analytical model for calculation of the shot peening process offers a simple tool to predict Almen intensity with respect to shot peening parameters.