Effect of Pre- and Post-Processing upon Shot-Peening Residual Stresses

Abstract

The process of shot-peening finds extended use in industry to combat fatigue fracture in engineering components. The introduction of compressive residual stresses increases the fatigue life considerably and forms an integral part of the design process. Although the benefits of the shot-peening process are well established, all investigations overlook the history of the component being treated. This increases the scatter in the results and makes them unreliable. Also, although researchers are aware that post-processes performed on treated components reduce and redistribute the peening compressive residual stresses, no experimental confirmation exists.

The following work is the result of an extended investigation into the effect of pre- and post-processing upon shot-peening residual stresses.

Specimens were subjected to controlled turning to produce four different surfaces roughnesses, and the residual stress fields for each were established by a modified centre hole drilling technique. The different specimens were then exposed to the same shot-peening parameters and the resulting residual stress distribution again investigated. A comparison of the two revealed that rough turned surfaces had lower compressive residual stresses after shot-peening and the reason was the initially higher tensile residual stress associated with the rougher surfaces. It was also shown that the maximum amount of residual stress was induced when the surface roughness before and after shot-peening were similar.

For the post-processing effect controlled grinding was studied and the results indicated a straight line reduction in the maximum compressive residual stress as well as a redistribution of the stress field. It was also shown that even after a layer removal equivalent to 50% of the arc-height, the compressive stress still remained compressive. The material investigated was an aircraft alloy 817M40.