A New Method to Quantify the Heterogeneity of a Shot Stream – Coverage and Indent Distribution

Author:  J. Badreddine, C. Ernould, E. Guenier, Q. Puydt, A. Hazotte
Source:  ICSP-13
Doc ID:  2017035
Year of Publication:  2017
Introduction: Mechanical surface treatments, such as conventional shot peening (CSP), are commonly used in the industry to enhance the mechanical properties [1], [2], the fatigue life span [3]–[6] and the resistance to stress corrosion cracking [7]–[9] of metallic components. From the component point of view, the surface receives thousands of shot impacts with different impact speeds and angles. CSP being stochastic process, means of controlling their repeatability and homogeneity have to be developed, such as the measurement of Almen intensity [10], [11] and surface coverage. The latter is defined as the ratio of the area of impacted surface over the area of total surface to be treated. It is generally evaluated visually, as recommended by the SAE J2277 standard [12], by an operator with a magnification from x1 to x30. In the industry, "full coverage" is usually defined as 98%, while it is common to specify coverages higher than 100%, for instance 200%. In the field of shot peening, industrial tools have been developed along the years to try helping operator to better determine the surface coverage, such as special dies [13], [14], topography analysis [15]–[18], or image analysis [19]–[22] of the peened surface. It is worth noting that so far, these approaches only focus on the mean surface coverage, but fail to conduct more detailed analysis of the indented surface, from which precious information about the shot stream can be gathered. As an example, taking into account heterogeneities in the shot stream is essential to guarantee a homogeneous treatment, especially when shot peening is applied to large and complex surfaces.

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