Finite element simulation of shot peening

Shot peening is a complex cold working process commonly used to improve the fatigue life of critical components.  The process involves a large number of spherical beads (with diameters in the order of a few mm) impacting surfaces at high speeds. The impacts lead to plastic deformation in the contact areas and consequently to residual surfaces on the surfaces. The residual stresses typically tend to be compressive and thereby, increase the fatigue life and aid in the prevention of crack propagation.  The Almen intensity is one of the main parameters used to quantify the intensity of a shot peeing process. It is related to the amount of energy transfer from shot stream to the workpiece and depends on various process parameters such as the shot size, velocity, and the angle of impact. Almen intensity is measured indirectly by shot peening a thin rectangular strip, also known as Almen strip, which is fixed onto a holder by using four bolts. When the bolts are removed, the stresses in the strip readjust leading to a bow in the direction of peeing. The Almen intensity is obtained from a plot of the height of the bow (arc-height) versus time. It is the arc-height corresponding to a critical time. The critical time is corresponding to the minimum T such that in the time interval T to 2T, the increase in the arc-height is less than 10% from its value at T. For optimizing the shot peening process, it is important to understand the effect of various shot peening parameters on the Almen intensity. The finite element method is the ideal tool for this purpose. At UNC Charlotte, we developed a fully integrated shot peening model using two step analysis in Abaqus/Explicit 6.13.4.   A combination of Matlab code and a python script were developed to model the impact of approximately 6000 randomly generated shots on an Almen strip. The Jonson-Cook model is used to characterize the mechanical response of the strip.  The Python script is also used to create shot-strip contact and set the boundary and initial conditions. The results obtained through the simulations, agree well with the experimental studies. At present we are doing a parametric study, to find the effects of these parameters on intensity and on the process in general.