A model was developed for impacts of elastic perfectly plastic spherical particles with impact velocities up to 250 m/s. The model is based on the two master curves, for normalized pressure and projected contact area c (2), which both are functions of the representative strain I > at maximum impact. The model and its parameters were fitted to finite element results for elastic perfectly plastic and strain rate-independent materials. It was applied to a wide range of materials with different ratio between yield stress and elastic properties, different ball sizes and impact velocities. The impact model predicted the results from finite element method for contact radius, maximum impact depth in both target and ball as well as remaining impact depth in target and ball. The remaining impact depth was determined from elastic spring back with Hertzian and quadratic pressure at maximum impact. The rebound velocity was also estimated by following the load-deformation path during spring back. If the strain rate-compensated yield stress was used for the master curve parameters, then the model predicted the impact results also for the investigated strain rate-dependent materials.

Shot peening is a manufacturing process commonly used to increase fatigue life in components for the automotive and aircraft industry. In this paper the effect of shot peening is described for a case hardened gear steel. For gears there are three main factors from shot peening that influence fatigue life: residual stresses, microstructure and surface roughness. The paper describes an experimental series where these parameters were measured for common industrial shot peening settings. The aim was to show how several different measurement techniques and results correspond to each other for certain shot peening parameters. The aim was also to gather experimental results that can be used for verification of shot peening simulations. To simplify measurements and decrease variation, flat steel plates were used as targets. Residual stress, full width at half maximum (FWHM), retained austenite, surface roughness/topology, hardness and Barkhausen noise were measured and related to microstructural changes. The mean indentation diameter was measured for individual shots at low coverage of each intensity which was used to determine the average velocity of the media. The mean diameter and hardness of the shot peening media was also determined.

Shot peening is a manufacturing method that makes indentations on a components surface by impacting it with small steel balls (media). In a production environment the shot peening process is usually controlled by defining media size, coverage and Almen intensity. For simulating shot peening, the media velocity is needed and therefore it must be measured or correlated to the Almen intensity. This paper details a method to record indentations on a test plate and then compare them to single shot indentations with measured velocities. For small media sizes the results are in reasonable agreement with other published results but at larger sizes there is a larger spread in published results. It is therefore recommended that the media velocity is either measured directly or that the indents are analysed as presented in this paper.

A material model for predicting fatigue related changes due to shot peening is developed. The model includes plastic behaviour at large strains and transformation of retained austenite. The model is simplified to limit the amount of material parameters needed and an iterative approach is used to fit the parameters to experimental data in the form of uniaxial tests on through hardened specimens, single impacts of carbide balls on polished case hardened test plates and on shot peened, ground test plates. With good accuracy, reasonable computer resources and basic experimental techniques to fit the model parameters, the model can predict; residual stresses, retained austenite transformation and work hardening in form of Vickers hardness increase. The model is also adequate for parameter studies as exemplified by changing media hardness, coverage or media shape variations. For surface roughness predictions, the initial surface roughness of the target must be included and future work is needed there.