Research On Shot Peening Residual Stress Of Orthotropic Material And Its Finite Element Simulation

This article studied the process by different shot peening treatment, the nickel-base single crystal superalloy DD3 material residual stress distribution and changes in internal structure, and the residual stress under high temperature stress relaxation behavior. On this basis, the article carried out further use of ANSYS/LS-DYNA finite element software and made comparison with experimental model of the corresponding shot peening process, established the homogeneous model using local coordinate system to load, and adjusted the different parameters of shot peening process to analyze the residual stress field on the DD3 influence by different parameters and the distribution of residual stress, for further discussion of the nature of shot peening residual stress for single crystal.The Nickel-base single crystal superalloy DD3's shot peening treatment results showed that, after shot peening treatment of DD3 sample, residual stress gradually increased with the layer depth increased, indicating that the increase of shot peening intensity within a certain range will help to improve the parameters of residual stress. DD3 single crystal alloy had obvious characteristics of the surface residual stress distribution along the different orientation since DD3 was orthotropic. Different peening coverage and different orientations of the sample surface resulted in different residual stress.The initial orientation of single crystal structure of the shot peened DD3'surface residual stress distribution was relatively significant. Shot peening could promote crystallization of nickel base single crystal and more, made layer crystal block more fragment. With increasing of surface coverage, ODF maximum orientation density and orientation line strength decreases, the sample showed different shot peening layer texture characteristics. Coverage of 80% and 200% samples of different orientation texture shot diversified. With 400% coverage, different texture orientation distribution of the sample was quite similar.Using ANSYS / LS-DYNA software based on the actual process of shot peening experiment to establish a uniform shot peening model, set the local coordinate system to load, consistent with the experimental results of DD3 residual stress distribution curve with the layer depth and different orientations surface residual stress. Adjusted different shot peening parameters with the finite element analysis, we could see the 4 parameters of shot peening have different influence on the residual stress field, including the coverage of the main parameters, shot velocity, shot material and size with different influence on residual stress field. Shot peening coverage has such direct impact on the maximum residual compressive stress and compressive stress layer depth that in a certain range, increased coverage will result in the increase of the maximum residual stress and layer depth. The major impact of the projectile is related to projectile material density. High-density projectiles hit by the spray material will result in deeper compressive residual stress layer and larger compressive residual stress. Projectile with smaller diameter balls used for shot peening will lead to a high residual compressive stress, but the shallower layer of depth. High speed shot has larger kinetic energy, so deeper residual compressive stress field occurs.Finite element simulation model results for DD3 shot peening also show that, due to the spray material DD3 belongs to orthotropic material, the three mutually perpendicular orientations are anisotropic, so researches on one of the orientation distribution are carried out, thus inferring the other two orientation regulation. Simulation test selected (001) surface for analysis, from which can see, with the testing angle increases, the sample surface by spraying DD3 residual compressive stress appeared in the trend of increasing first and then decreasing. Through the 4 shot peening parameter adjustment we can find that change of these parameters will affect the value of stress, but the angle of minimum stress appears remains unchanged. It can be inferred that crystal orientation can affect the distribution of residual stress, but the minimum residual stress must only appear to the lowest dislocation on the slip systems.