Modelling Of Shot Peening Stresses And Simulation Of Integral Deforma- Tion Of Strip Peen Forming

Shot peening is widely used to strengthen the metallic components and to form the complex contour of large thin-walled components. The key processes and difficulties of the peen forming are the planning of peen firming parameters and the prediction of peen forming deformation. According to the deformation of peen forming, the sizes of machined flat components can be compensated to improve forming precision. Focusing on peen forming, aiming to reveal the mechanism of shot peening and to plan the peen forming parameters as well as to improve the peen forming precision, a series of analytical models and methods are proposed in this paper to guide the peen forming of large thin-walled components. The main methods and results are as follows:(1) An analytical model is established by introducing the Johnson Cook material model to the traditional expanding cavity model to obtain the peening stresses induced by a single-shot with a high initial velocity. For the peening stresses of multiple-shot impacts, the overlapping of stress fields is researched. It is revealed that the energy corresponding to the bending deformation of a plate introduced by multiple-shot impacts approximately obeys the normal distribution with the change of the distance of adjacent shots. From the normal distribution, a function involving peening coverage and single-shot impacting stress field is proposed. With the function, the peening stresses of any peening coverage can be calculated from the single-shot impact stresses and saturation peening stresses. The calculated results are verified by FE simulations and experiments.(2) Based on the expanding cavity model, the stress shot peening is analyzed to calculate stress peening stresses. The ellipsoid is used to represent the interface of impacting plastic defor-mation region and elastic deformation region. With the increase of prestress, the ellipsoidal interface is compressed in the prebending direction and stretched in the perpendicular di-rection of prebending. The influences of prestress on the peening stresses and resulting curvatures are further studied by FE impacting/indenting simulations and prestressed peen-ing/indenting experiments. It reveals that the impacting and indenting can erase the pre-stress and reproduce the same peening stresses in the surface layer as the conventional peening. Under the peening layer, the induced stresses are approximately equal to the pre-stresses. Larger magnitude of prestress results in larger resulting curvature and elongation in the prebending direction. The contribution of prebending on the resulting curvature in-creases with the increase of peening coverage. With the stress peen forming experiments, uniform indenting experiments are proposed to verify the simulation results.(3) The plate deformation under strip peening are analyzed. Within the peening strip, the dis-tribution of the peening stress is very complex since the plate peened by many discretely distributed shots. To achieve the planning of peening stress field, the actual peening stress field is approximatively represented with a stress field expressed with elementary functions by analyzing the characteristics of the average peening stresses. The approximate stress field has the same forming effects as the actual peening stress field. Then, the relationships between peening parameters and the approximate stress field are obtained by connecting the variables of the approximate stress field to the peening parameters. The relationships can be used to predict the plate deformation peened by usual peening parameters.(4) For the strip peen forming, a model that relating peening parameters to the strip peening coverage is established. The controllable peening parameters of peening coverage is shot dimple size and shot dimple distribution. The shot dimple distribution is related to shot type, shot flow, moving spreed of peening nozzle and the gaps of peening strips. In the perpendicular direction of peening strip, the shot dimples follow normal distribution. The standard deviation of the normal distribution can be determined by a experiment. With the normal distribution, the strip peening coverage can be calculated for any moving speed and moving trajectories of peening nozzle.(5) For the peen forming of a plate, an method is proposed to plan the peening stress field. The principles of the planning are minimizing the forming error and the peening elongation. In the planning, the actual constraints are transformed into the constraints on the variables of the approximate stress field to simplify the problem. To plan the peening parameters of a complex contour, an automatically performing method is established based on the software ABAQUS based platform. In order to compare the simulated contour and target contour, the simulated contour is monitored at a set of representative points. By comparing the simulated contour to the target, the peening induced stress field is adjusted. For a whole part, the automatic planning is carried out step by step on partitioned ares. By changing the eigenstrain in the simulation process, the induced stress is changed. The proposed methods are verified by the application on the peen forming of aircraft wing panel.(6) An equivalent simulation method is used to predicting the peen forming deformation of a large wing panel. The geometric data of the wing panel is obtained on the software CATIA based platform. With the isopleth of extreme curvatures, the locations of peening strips are determined. The peening induced stress are calculated with the planning method. Then, theFE model is built with composite shell element from the surfaces of developed flat panel model and designed panel model. To improve the convergence of the FE model, the induced stresses are introduced gradually. Final, the simulated contour are compared with the target contour to obtain the elongations along spanwise and comparing with experimental values.The planning of peen forming parameters and the prediction of peening deformation of large thin-walled component are performed in this paper. The researches were finally applied on the peen forming of the wing panel of aircraft C919. The planning of peen forming parameters and the compensation of the sizes of the machined flat panel according to the elongations improved the peen forming precision.