What is shot-peening?
Shot-peening is a cold working process used to impart compressive residual stresses in the exposed surface layers. Also, it is used mainly to improve the fatigue life of metallic components.
Results are accomplished by bombarding the surface of the component with small spherical shots made of hardened cast-steel, conditioned cut-wire, and glass or ceramic beads at a relatively high velocity (40±70 m/s). After contact between the target and the shot has ceased, a small plastic indentation is formed causing stretching of the top layers of the exposed surface.
Upon unloading, the elastically stressed sub-surface layers tend to recover their original dimensions, but the continuity of the material in both zones, the elastic and the plastic, do not allow this to occur. Consequently, a compressive residual stress field followed by tensile is trapped in the treated component. This surface compressive residual stress field is highly effective in preventing premature failure under conditions of cyclic loading. Fatigue failure generally propagates from the upper-most surface of the component and usually starts in a region that is subjected to high tensile stresses.
Finite element modeling using Abaqus/CAE
Despite its importance to the aerospace and automobile industries, little or no attention has been devoted to the accurate modeling of the process. Shot peening is a very complex process to model numerically, involving dynamic analysis of fast-moving shot impacting on a metallic component which can often have complex geometry. There are a significant number of parameters involved in shot peening that need to be controlled and regulated in order to produce a more beneficial compressive residual stress distribution within the component.
These parameters can be categorized into three groups relating to the shot, the component, and the process. The shot parameters include size, density, shape, impact velocity, rotary inertia, incident angle, and hardness. The component parameters include geometry, initial yield stress, work-hardening characteristics, and hardness.
The process parameters include mass flow rate, air pressure, angle of attack, the distance between nozzle and component, and percentage coverage. In order to control the resulting residual stress pattern in peened components, it would be highly beneficial to establish quantitative relationships between these parameters and residual stress characteristics.
This package describes a three-dimensional dynamic finite element (FE) study of single-shot impacting on a metallic component using Abaqus/CAE software. The prediction is validated by comparison with results from the published literature by Meguid et al. (1999).