Using Shaded Almen Strips for Internal and Confined Area Peening

Validating peening intensity in confined or complex geometries, such as dovetail slots, holes, or pockets, poses a serious challenge. Conventional Almen strips cannot physically fit into these areas. And without validation, you risk being out of specification on critical surfaces, especially in aerospace or turbine components.

To solve this, a specific technique is used: the shaded Almen strip method.

A shaded Almen strip is a standard A or N type strip, but only a portion of its surface is exposed to the peening stream, usually through a machined mask, tape, or fixture. By restricting exposure to a precisely defined area, the shaded section simulates the behavior of surfaces inside the component.

The goal is not to measure arc height in that area directly, but to correlate it with a real strip placed inside the part or cavity.

1. Step 1: Prepare a Confined Test Strip
   A small Almen strip or custom test coupon is placed inside the cavity and peened under normal process parameters.
2. Step 2: Peen a Shaded Strip in Open Area
   A full Almen strip is placed outside, with only a segment exposed to simulate the internal area.
3. Step 3: Compare Arc Heights
   The arc height of the shaded area (on the full strip) is matched to the arc height of the internal strip.
4. Step 4: Calibrate Fixture or Time
   Once a correlation is established (e.g., 0.006" internal = 0.008" shaded), future peening can be validated only with shaded strips, eliminating the need to access the cavity again.

• Aerospace turbine blades with root slots
• Peening internal bores of engine parts
• Non-visual surfaces where strip extraction is difficult
• Qualification or Nadcap validation of blind zones

Important: The shaded strip technique is not a direct replacement for regular intensity validation, it is a controlled workaround, requiring initial correlation testing.

A manufacturer needs to verify peening intensity inside a root slot of a turbine blade. Standard strips cannot be inserted or removed safely.

• Engineers mount a shaded Almen strip on a flat plate
• The shading fixture replicates the geometry of the slot
• Once correlation is confirmed, future batches are validated with this shaded setup

Result: Repeatable, compliant process control without having to destructively extract strips from real parts.

Visual Suggestion

[insert graphic/icons from intensity level 2 – slide 32 to 37]

• Shaded Almen strips help validate intensity where access is impossible
• They require initial calibration with a direct test strip
• Once validated, they offer a practical and compliant solution for recurring verification

If your part has complex geometries or you're preparing for a Nadcap audit, contact a shot peening expert. They can help design valid shaded strip fixtures, run correlation testing and document compliance procedures. Don’t leave critical surfaces unverified, consult a specialist to make sure every peened surface is truly within spec.