Almen Strip Quality

Author:  Prof. Dr. David Kirk, Coventry University, U.K.
Source:  The Shot Peener magazine, Vol 32, Issue 3, Summer 2018
Doc ID:  2018034
Year of Publication:  2018
Abstract:  
INTRODUCTION: Shot peeners are required to declare values of peening intensity derived at prescribed intervals. These values depend, to a significant extent, on the quality of the Almen strips that are being used. The primary factor defining “quality” of Almen strips is that they should be accurate. Accuracy is defined as a combination of bias and precision. Fig.1 illustrates the concept of bias. Imagine that there was some way in which we could know the “true value” of the arc height that should result from a fixed time of exposure to a fixed shot stream. If we then expose a batch of strips for the same time to the same shot stream, we may find that the mean value of the measured arc heights was different from the “true value”. This difference is called “bias”.