Coverage: Development, Measurement, Control & Significance

Author:  Dr. David Kirk | Coventry University
Source:  The Shot Peener magazine, Vol 40, Issue 3, Summer 2026
Doc ID:  2026055
Year of Publication:  2026
Abstract:  
INTRODUCTION The prime objective with shot peening is to induce a ‘skin’ of compressively-stressed material that will improve the service performance of components. A necessary corollary of peening is that the surface is work-hardened by the impacting shot particles. This work-hardening normally improves service performance. On the other hand, excessive work-hardening exhausts the ductility of the surface material, leading to micro-crack formation and a reduction in service performance. As the particles impact the surface, they produce indentations that comprise a proportion of the surface area of the component. The term “coverage” is used to define the proportion of the shot peened surface that has been indented by the impacting shot particles. Hence expressions such as “99% coverage” are meant to indicate that 99% of the surface area has been indented at least once, whilst 1% of the area has not received any impacts at all. Central questions include: “How does coverage develop?” “How can coverage be measured and controlled?” “How does coverage vary?” “What is the optimum coverage” and “How does coverage relate to the required compressive surface residual stress?”