A. Gariépy

Residual stress near single shot peening impingements determined by nanoindentation and numerical simulations

The near-surface hardness and residual stresses resulting from a single shot peening impingement on aluminum alloy 2024-T351 were assessed by nanoindentation with spatial mapping of mechanical properties on cross sections through an impingement. For residual stress, a procedure was developed to couple nanoindentation experiments with numerical simulations for better understanding and predicting the effects of shot peening. A surface preparation method was developed that exposes the cross section of a single shot impingement for nanoindentation tests, while at the same time obtaining accurate measurements of the impingement dimensions. Starting parameters for the numerical simulation in terms of shot diameter and the shot velocity were selected to best match measurements of the impingement depth and diameter. The experimental results indicated that the greatest hardness was located at the nearest indent to the peened surface, whereas the maximum compressive residual stress was located sub-surface. When comparing experimental and numerical residual stresses, the experimental results showed a greater maximum compressive residual stress that was in closer proximity to the peened surface. Overall, residual stress fields compared between experimental and numerical results were similar, and differences could be explained in terms of the effect of strain hardening. The current work demonstrated the usefulness of coupling nanoindentation experiments with numerical simulations for evaluating the surface modifications resulting from a single shot peening impingement.

Potential applications of peen forming finite element modelling

Peen forming is a versatile and flexible manufacturing process commonly used in the aerospace industry to shape wing skins and rockets panels. Development of peening parameters needed to obtain a specific component shape can be both costly and challenging due to the use of empirical methods which involve large quantities of physical experiments coupled with trial and error processing of prototype components. Many iterations are often required to get the desired shape with no guarantee that a specific component geometry can be achieved. Reliable numerical simulations could substantially reduce the time, cost and risk associated with process development. The purpose of this study is to further investigate the use of numerical tools to model the peen forming process. This work combines static and dynamic simulation techniques to predict the development of curvature on representative wing skin panels that include features such as integral stiffeners. This work illustrates the considerable potential of finite element simulations to determine the process parameters needed to produce a component design, and substantially reduce the dependence upon physical testing.

Simulation of the shot peening process with variable shot diameters and impacting velocities

Abstract Shot peening is a surface treatment widely used to improve the fatigue performance of automotive and aerospace components. Beneficial compressive surface residual stress are introduced by projecting small, hard particles at high velocity onto a metallic part to plastically deform the surface. Shot types follow standardized size ranges and, in typical treatments, non-uniform impact velocities may also be encountered. In the current work, shot size and impact velocity distributions were evaluated and modelled for a specific industrial peening treatment with a sparse shot stream, using experimental data on shot and impact dimple sizes combined with finite element modelling and Monte Carlo simulations. The potential influence of impact velocity variability was assessed in terms of the residual stress state and surface roughness. For the process under study, depth of compressive residual stress was found to increase by 10% when accounting for non-uniform velocities, while the maximum compressive residual stress did not vary significantly. Furthermore, the advantages and limitations of omitting the lower-energy impacts to reduce the computational cost were evaluated.

3.12 – Peen Forming

Peen forming is a manufacturing method commonly used in the aerospace industry to shape large, relatively thin parts to complex contours. This process is a derivative of shot peening and uses peening-induced compressive stresses to upset the mechanical equilibrium and achieve the required curvatures. This chapter introduces the basic principle of peen forming and presents the equipment, procedures, and advantages of the method using examples of applications to wing and fuselage skins, rocket tank panels, and distortion correction. A summary of research works in the field as well as an analytical formulation of the process are also included.

Finite Element Simulation of Shot Peening: Prediction of Residual Stresses and Surface Roughness

Shot peening is a surface treatment that consists of bombarding a ductile surface with numerous small and hard particles. Each impact creates localized plastic strains that permanently stretch the surface. Since the underlying material constrains this stretching, compressive residual stresses are generated near the surface. This process is commonly used in the automotive and aerospace industries to improve fatigue life. Finite element analyses can be used to predict residual stress profiles and surface roughness created by shot peening. This study investigates further the parameters and capabilities of a random impact model by evaluating the representative volume element and the calculated stress distribution. Using an isotropic-kinematic hardening constitutive law to describe the behaviour of AA2024-T351 aluminium alloy, promising results were achieved in terms of residual stresses.

Finite Element Peen Forming Simulation

Shot peening consists of projecting multiple small particles onto a ductile part in order to induce compressive residual stresses near the surface. Peen forming, a derivative of shot peening, is a process that creates an unbalanced stress state which in turn leads to a deformation to shape thin parts. This versatile and cost-effective process is commonly used to manufacture aluminum wing skins and rocket panels. This paper presents the finite element modelling approach that was developed by the authors to simulate the process. The method relies on shell elements and calculated stress profiles and uses an approximation equation to take into account the incremental nature of the process. Finite element predictions were in good agreement with experimental results for small-scale tests. The method was extended to a hypothetical wing skin model to show its potential applications.