Finite Element Modelling of Shot Peening and Peen Forming Processes and Characterisation of Peened AA2024-T351 Aluminium Alloy

» : Shot peening is a surface treatment commonly used to improve the fatigue performance of various metallic parts. This process consists of projecting a large number or tiny particles at high velocity onto the surface of a component. Each impact plastically deforms the material and repeated impacts lead do a beneficial compressive residual stress state near the surface. In addition, shot peening alters both the local mechanical properties and microstructure. On the other hand, it also generates increased surface roughness and possible damage. Its influence on fatigue life (or strength) therefore arises from a combination of multiple effects. Peen forming is a manufacturing method derived from shot peening. The compressive stress field induced by peening alters the mechanical balance and is used to shape thin components. This process has been used in the aerospace industry since the 1950s to contour large panels with gentle curvatures such as wing skins and rocket panels. It is a cost-effective alternative to conventional forming techniques since it does not require a specific set of dies for each target shape. In addition, peen forming can achieve various target contours by simply altering the shot peening treatments applied on different regions on the parts. This versatility may however not be used to its full potential since current peen forming procedures are commonly developed through empirical knowledge and trial-and-error. The main purpose of this thesis was to develop and validate finite element (FE) simulation tools for shot peening and peen forming. The specific aim was to achieve quantitatively accurate predictions for both processes and demonstrate the potential of reliable FE modelling for scientific investigation and industrial applications. First, an improved dynamic impact model that takes into account the stochastic nature of shot peening was proposed by carefully studying its dimensions, introducing a dispersion of shot sizes and significantly reducing its computational cost. In addition, cyclic mechanical testing was conducted to define a suitable material constitutive theory for aluminium alloy (AA) 2024-T3/T351 subjected to shot peeinng. By combining a realistic shot peening model with an appropriate material law, fairly good residual stress predictions were achieved for three different sets of shot peening parameters. Second, an experimental and numerical characterization of AA2024-T351 shot peened with parameters representative of fatigue life improvement applications was conducted. Multiple techniques, such as micro-indentation, residual stress determination and electron backscatter diffraction, were combined to gain a better understanding of the influence of shot peening on the material. The potential uses of finite element simulation to complement experimental data were also studied.