Understanding Peening Intensity and Saturation Curves

Peening intensity is a key parameter in the shot peening process. It represents the energy transferred to a component’s surface through repeated impacts from high-velocity media (such as steel shot or cut wire). This mechanical action generates residual compressive stresses that enhance fatigue strength and delay crack formation.

More technically, peening intensity is defined as the arc height of a standard Almen strip at saturation, a point at which additional exposure produces minimal additional deformation.

If intensity is too low, the induced compressive stress may not reach the depth required for effective fatigue protection. If too high, it can lead to:

• surface roughening,
• micro-cracks,
• or even loss of ductility.

In other words, controlling intensity is essential to maximize the life of components while preserving their integrity.

Common specifications for intensity come from standards such as:

• SAE J443 (procedures)
• AMS 2430 / AMS 2432 (aerospace components)

An Almen strip is a standardized piece of steel, placed in the shot stream. As it is peened on one side, it bends into an arc due to surface expansion. The height of this arc, measured with an Almen gauge, gives a direct indication of the process intensity.

Product tip:
Use laser-measured PA Almen Strips (A, N, or C type), which offer printed flatness values, improved traceability, and are available with different certifications (J442, AMS 2432).

A single strip doesn't define intensity, we need a saturation curve, constructed by:

• Exposing 4 or more strips to increasing peening durations (e.g. 10s, 20s, 40s, 80s)
• Measuring arc height after each exposure
• Plotting the curve (arc height vs exposure time)

Intensity is the arc height at time T, where increasing the exposure to 2T results in less than 10% arc height increase. This is known as the 10% rule.

Let’s say your arc heights for 10, 20, 40, and 80 seconds are:

• 6.0
• 7.2
• 8.1
• 8.9 (mm × 1000)

If the increase from 40s to 80s is only ~10%, then 40s = T and intensity = 8.1A (Almen A-strip, 0.0081").

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Product tip:
Use PA FlowMaster with Ultimate or PASV Valves for closed-loop flow control, allowing precise intensity regulation. Recipes can be saved and switched via digital inputs.

In production, you don’t build a full curve every time. Instead, you can:

• Peen a verification strip at time T and check its arc height is within acceptable range (e.g. 0.006–0.010")
• Occasionally verify again at 2T to confirm stability
• Rebuild a full saturation curve:
  • after media change,
  • nozzle replacement,
  • or machine relocation.

Note: Intensity is not cumulative : more exposure time increases coverage, not intensity.

• Using strips with poor flatness ➜ false readings
• Incorrect holder assembly (e.g. burrs, debris)
• Over-torquing screws ➜ strip warping
• Misinterpreting arc height as intensity

Tip: Use Industrial PLUS Almen Gage by PA with digital readout (0.0001”) and no magnetic interference.

Controlling and verifying shot peening intensity is not just a formality, it directly impacts fatigue performance, component life, and regulatory compliance. Understanding how to construct and interpret saturation curves ensures that each component is processed consistently and correctly.

With the right tools, media, and measurement methods, manufacturers can ensure their shot peening process delivers maximum performance and reliability. 

If you have any doubt or need advice, don’t hesitate to reach our technical experts