Determination of Shot Peening Coefficient of Restitution

Abstract

To characterise an impact between two solids, a coefficient of restitution is generally used er equal to 1 when the impact is perfectly elastic, 0 when the impact is totally plastic and between 0 and 1 when the impact is elastic - plastic. For the shot peening surface treatment process, this coefficient, which is linked to the shot hardness/ material hardness ratio, is of interest for two reasons. First, to characterise the distribution of the stream energy produced by an impact (stream energy = energy of the induced plastic deformations in the used shot and in the treated material + elastic energy + dissipated energy into vibrations etc.). Two, to compare the efficiency of different types (material, hardness, size and shape) of shot. The coefficient of restitution er can be introduced to an existing shot peening model. The present paper gives a theoretical analysis of the distribution of the different energies during the shot peening process and describes an experimental investigation to determine the values of the coefficient of restitution for four principal types of shot; three in cast steel: cut wire Fil Coupé (F.C.) 0.6 mm and WS280 with two hardness values: 48 and 58 HRC, and one in low carbon cast steel:F16. The target was 13% manganese steel sheet with a hardness of 60 HRC. Results of the different coefficients of restitution were noted for each type of shot and the values obtained were presented and discussed. They show reasonable agreement with the theoretical analysis. It has been observed that the coefficient of restitution is principally linked to the shot hardness, material hardness ratio and the shot shape.