Practical Examples and Implications of Almen Strip Physics

Author:  David R. Johnson and Mark F. Gruninger | Purdue University School of Materials Engineering
Source:  The Shot Peener magazine, Vol 38, Issue 4, Fall 2024
Doc ID:  2024031
Year of Publication:  2024
Abstract:  
Introduction For several decades, Almen strips have been valuable tools to provide shot peeners insights and expectations pertaining to the peening conditions they are employing. During the same time period, several excellent models have been proposed and developed which provide physical and mathematical bases for the interactions between the impinging media and the strip. Since one of the guiding principles at Purdue’s School of Materials Engineering (MSE) is to “intersect” industrially relevant research with “real world” engineering education, multiple studies have been undertaken to examine the relationships between fundamentally developed models with conventional shot peening practice. An appropriate place to start is Kirk’s discussion of the physics that lead to the bending of shot peened Almen strips [1,2] which involves the plastic deformation of a peened Almen strip surface and the subsequent formation of a compressive residual stress. The imparted peening intensity is proportional to the depth of this compressive residual stress region. Thus, if the residual stress versus depth curve is known, then the corresponding arc-height (H) can be estimated from a simple elastic bending analysis. For this case, the estimate arc-height (H) for bending along the length of the strip is [1]: