Meaning, Measurement Philosophy and Verification of

Author:  Dr. David Kirk, Visiting Prof , Coventry University
Source:  The Shot Peener magazine, Vol 24 / Issue 1, Winter 2010
Doc ID:  2010006
Year of Publication:  2010
Abstract:  
“Peening intensity” is the depth-inducing capability of a shot stream. Shot peening causes plastic deformation of component surfaces - inducing compressive residual stress in the deformed surface layer. The depth of the plastically-deformed layer needs to be controlled. Shot streams have several properties that allow us to control the depth. Consider, by way of analogy, a stream of bullets fired by a machine gun. That stream has the ability to surface damage a target. This ability depends on the size, velocity and hardness of the bullets. Large, hard-nosed, bullets fired at high velocity will generate much deeper surface damage than will small, soft-nosed bullets fired at low velocity. A clear parallel can be drawn with the depth-inducing capability (peening intensity) of a shot stream. “Peening intensity” is the parameter used to define and regulate the depth-inducing capability of a shot stream. When shot peening was in its infancy, J. O. Almen recognized the need for quantification of this capability. He conceived the brilliant idea of measuring the depth-inducing capability indirectly - by measuring the deflection induced in a set of steel strips peened for increasing periods. The term “Saturation Curve” was coined to describe the increase in peened strip deflection that occurs with increased peening time. A particular point on that curve, “Peening Intensity,” is used to quantify a shot stream’s depth-inducing capability. The greater the strip deflection at that point the greater is the shot stream’s capability. The equipment and procedures needed to estimate peening intensity are detailed in standard specifications J442 and J443. This article addresses three major problems associated with “peening intensity” – attempting to provide at least partial solutions. These problems concern the actual meaning, measurement philosophy and verification of peening intensity.