Intensity and Coverage

Author:  Jack Champaigne
Source:  The Shot Peener magazine, Vol 03/Issue 4, Winter 1990
Doc ID:  1990151
Year of Publication:  1990
Abstract:  
Two critical factors in the shot peening process are intensity and coverage. These may be compared to time and temperature in the heat treating process. In both cases these parameters must be correctly specified. The survey conducted in the previous issue of The Shot Peener provided interesting study, a tabulation of the data appears in Table 1. One of the more surprising results was the large number of multiple responses where both intensity and coverage were used to determine peening exposure time. A description of terms should help the discussion. Intensity is the energy level of the shot stream as indicated by Almen strip deflection. The curvature of the Almen strip is plotted as a function of exposure time. The strip is at saturation when its curvature no longer increases upon additional exposure. In essence, the strip has absorbed all of the energy it is capable of holding by plastic deformation. The term coverage describes the denting of the surface caused by shot impacts. Complete coverage occurs when the entire surface is deformed by adjacent impact craters. (A purist would add that only the largest shot, striking at the highest velocity at the greatest angle contribute to effective peening and therefore coverage is not achieved by smaller impacts.)