Peen forming is commonly used in the aerospace industry to shape large and thin panels, such as wing skins. This manufacturing process uses shot peening to introduce unbalanced compressive stresses near the surface of the component. These stresses tend to bend the panel and, when optimized, lead to the desired contour. Sheet materials often exhibit both elastic and plastic anisotropy, which can alter the development of curvatures. Since peen forming relies on compressive stresses to upset equilibrium, resulting curvatures may also be affected by initial stresses in the part. In this work, the influence of the rolling direction orientation with respect to the sample was investigated experimentally and numerically for the first time for aluminium alloy 2024-T3 specimens. Although maximum deflections were only slightly dependent on the rolling direction orientation, it was found that radii of curvature varied by as much as 10% with respect to this parameter. Finite element simulations allowed quantification of the individual effects of non-equibiaxial initial stresses and elastic orthotropy. It was found that these factors can significantly influence curvature development. Comparison of experimental and numerical results suggested that plastic anisotropy should also be taken into account in future studies. The tools developed in this study show promises for the accurate prediction of peen forming process for large scale components.

Peen forming is a manufacturing process commonly used in the aerospace industry to shape large and thin panels such as wing and fuselage skins and rocket panels. Due to the large size of the components, this process is generally performed by moving the parts through a peening enclosure or by moving peening equipment following a trajectory on the parts. Previous research on peen forming simulation has rarely considered the influence of the peening pattern on the resulting deformed shape. The purpose of this work was therefore to evaluate experimentally and numerically this effect using small scale tests. A simple model was proposed to simulate incremental deflections as the shot stream traveled over the samples. Model parameters were calibrated experimentally and then applied to a different geometry for validation. Finite element analyses correctly predicted the complex radius distribution arising from the peening path and the constraints applied to the sample during peening.

Shot peening is a mechanical surface treatment that consists of projecting numerous small particles onto a ductile surface. Repeated and random hammering leads to compressive residual stresses as well as work-hardening near the surface resulting in a potentially significant improvement of the fatigue performance. On the other hand, shot peening also increases surface roughness and can produce surface damage which are detrimental to fatigue properties. Fatigue life prediction models have been proposed to predict the combined influence of these factors. Most of these models assume that shot peening leads to a uniform material state parallel to the surface. The current work investigated the heterogeneities present in peened aluminium alloy AA2024-T351 after repeated random impacts in terms of residual stresses, work-hardening, surface roughness, and damage while also considering the initial non-uniformities in the material. Experimental and numerical methods were combined to obtain a detailed description of the material state at various length scales. The implications of the heterogeneities in terms of fatigue performance as well as the potential contributions of numerical simulation were also discussed.

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.

Stress peening forming is widely used in the aeronautics industry to induce curvatures in wing skins. Most of the investigations of stress peen forming are empirical and experimental. In this paper, a three step numerical model that can simulate this process was developed. First, an implicit Finite Element Analysis (FEA) with ANSYS where a prebending moment along the spanwise direction of the component was performed. Then, an explicit FEA with LS-DYNA simulating shot impacts on the pre-stressed component was executed in order to obtain the resulting stresses inside the component. Finally, an implicit FEA with ANSYS was performed for calculating the arc heights and the curvature radii of the component in chordwise and spanwise directions. Numerical analysis of the process shows that the prebending moments have an influence not only on the residual stress profiles but also on the curvatures of the deformed component in chordwise and spanwise directions. This model was used to establish a relationship between the prebending moment and the resulting arc heights and residual stress profiles. The numerical strategies developed in this paper supply a useful tool for studying and optimizing the stress peening process.

Peen forming is commonly used on aluminium alloys in the aerospace industry for wing skin shaping. Numerous analytical, numerical, and experimental studies have been made to better understand the effects of various peening parameters on the final material state and to predict deformed shapes, but conclusions were often limited to trends. The purpose of this study is therefore to develop and verify experimentally quantitative numerical tools for peen forming applications by studying the simple case of peening an Almen-sized AA-2024 aluminium strip in an Almen holder. The first step consisted in improving an existing random dynamic model by determining optimal dimensions. The AA-2024 target mechanical behaviour was characterized experimentally and a combined isotropic-kinematic hardening law was selected to model the material behaviour. The dynamic impact model and material constitutive law provided good prediction of peening-induced stresses in thick AA-2024 for two shot velocities. The sequence-sensitive aspect of the forming process was also investigated and a new shell-based finite element model was proposed. Numerical and experimental results for three shot velocities were compared to evaluate the validity of this numerical simulation method and promising agreement was observed.

Shot peening is a cold working process widely used to improve fatigue life of aerospace and automobile components. Stress peen forming is widely used in the aeronautic industry to produce thin components with complex shapes, involving double curvatures, such as wing skins. In this paper, quantitative relationships between the saturation, surface coverage and roughness with respect to peening time have been established based on aluminum Al2024 test strips. The influences of peening velocity and peening time on the resulting residual stress profiles have been experimentally presented. The quantitative relationships between the prebending moment and the resulting arc heights of narrow strips and square strips have been experimentally investigated. Experimental results show that with the increases of the prebending moment, the resulting arc height following the prebending direction increases and the tendency is almost linear. Quantitative equations of the saturation, coverage and roughness as well as the relationship between the prebending moment and resulting arc height can be used for the optimization of shot peening and stress peen forming process.

Shot peening is widely used in the automotive and aerospace industries to improve the fatigue strength of metal components by introducing near-surface plastic strains and compressive residual stresses. This mechanical treatment is primarily controlled by monitoring Almen (peening) intensity, which corresponds to the arc height at saturation of standardized test strips exposed to the shot stream. However, the same Almen intensity may be obtained by using small shots impacting the surface at high velocity or by using large shots impacting the surface at low velocity. This paper describes a model for predicting Almen intensity based on an analytical model for shot peening residual stresses. Theoretical results for different sets of peening parameters were consistent with published experimental results and revealed that although different combinations of shot peening parameters can produce the same Almen intensity, each combination resulted in a different through thickness residual stress distribution.

Shot peening is a cold-working process that is used mainly to improve the fatigue life of metallic components. Experimental investigation of the mechanisms involved in shot peening is very expensive and complicated. Therefore, the Finite Element (FE) method has been recognized as an effective mean for characterizing the shot peening process and several types of FE models have been developed to evaluate the effects of shot peening parameters. However, in most of the existing FE models, the shot peening sequence and impact location were defined a priori. It is therefore the purpose of this study to consider the random property of the shot peening process. A novel 3D FE model with multiple randomly distributed shots was developed combining a Matlab program with the ANSYS preprocessor. The explicit solver LS-DYNA has been used to simulate the dynamic impingement process. Several potential applications of this novel model such as: the quantitative relationship of the peening intensity, coverage and roughness with respect to the number of shots have been presented. Moreover, simulations with multiple oblique impacts have been carried out in order to compare with results from normal impingements. Our work shows that such a computing strategy can help understanding and predicting the shot peening results better than conventional FE simulations.

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.

Shot peening is widely used to improve fatigue life of the metal component. It can also induce the distortion of thin component, which is called peen forming and is widely used for shaping aircraft wing skin. Shot peening surface coverage, intensity and saturation are important shot peening control parameters and have greatly influence on shot peening and peen forming results. Due to the insufficient investigation and control of these parameters, the design of peen forming for a specific shape has been based on experimental trial and error. The objective of this paper is to simulate the actual shot peening and peen forming process and relate the results with shot peening parameters. A newly developed 3D finite element model with multiple random distributed shots has been developed to simulate the shot peening process. An Implicit-Explicit sequence solution is applied to compare the results of conventional peen forming and stress peen forming.