Estimate Compressed Layer Depth by Using Almen Peening Intensity

Author:  Dr. David Kirk | Coventry University
Source:  The Shot Peener magazine, Vol 39, Issue 3, Summer 2025
Doc ID:  2025018
Year of Publication:  2025
Abstract:  
INTRODUCTION Shot peening induces a surface layer that contains compressive residual stress. It is this compressed surface layer that is largely responsible for improved fatigue performance of components. The depth of the layer is therefore of pivotal importance to users. X-ray stress analysis, involving multiple layer removals, is the most accurate method of determining the depth of the compressed layer. Indirect methods, such as micro hardness profiles, also involve multiple layer removals. Both methods are tedious and expensive and are carried out after peening. Almen peening intensity is necessarily available for every peening operation. This article describes how Almen peening intensity can be used as an acceptable guide to the depth of the compressed surface layer. Most shot-peened components go directly into service. Occasionally, components are fine-finished after peening. This is done either to change the smoothness of the surface or to induce minor dimensional changes. Fine-finishing processes include polishing, lapping, honing and sanding. AMS 2432B provides some guidance as to the amount of material that can be removed without severely affecting the property enhancement provided by shot peening. This article describes the principles that lie behind the limitation of surface removal by fine-finishing. Essentially only a small fraction of the compressed surface layer should be removed. The thickness of the compressed surface layer is rarely measured, whereas the peening intensity is, of necessity, always available. AMS 2432B attempts to use peening intensity values as a guide to the amount of material that can be removed. To some extent the article is complementary to some sections of AMS 2342B.