Introduction

Currently, two parameters are used to characterize the effect of shot peening: coverage and intensity. Coverage is a visual two-dimensional parameter that is easily defined (the percentage of the dimpled area relative to the total area) and can be directly measured. In contrast, shot peening intensity is a non-visual three-dimensional parameter that is difficult to define and can only be indirectly measured.

The indirect measurement method for shot peening intensity involves peening Almen strips for different durations (time, number of passes, or speed) and then plotting a saturation curve. When one side of an Almen strip is peened, it bends convexly toward the peened surface. The arc height value hh of this bending deformation can be measured using an Almen gauge. Different peening times tt yield different arc height values, allowing the shot peening intensity curve (commonly referred to as the "saturation curve") to be plotted. The "saturation intensity" is a specific arc height value on the saturation curve, defined as the point where a doubling of the peening time results in a 10% increase in arc height. Saturation intensity is used to quantitatively differentiate between different saturation curves and has become an industry-standard method for quantifying the energy strength of the shot stream.

Each impact from a shot media particle creates a dimple, resulting in a certain amount of plastic elongation deformation parallel to the surface of the test strip. This plastic elongation deformation causes the Almen strip to bend by δhδh. Since the deformation is elongational, the Almen strip bends convexly toward the peened surface. In this regard, peening an Almen strip is very similar to shot peen forming.

Gauge Measurement

Each measured arc height value hh is the cumulative result of numerous individual δhδh contributions, similar to how a rain gauge operates. After a collection time tt, the height of the rainwater is hh, with each raindrop contributing δhδh to the height. The height of the rainwater is also influenced by the rate at which raindrops enter the gauge. Thus, the following formula can be derived:

h=r⋅δh⋅th=r⋅δh⋅t