Surface compression. Fatigue life 2–5× better. AMS 2430.

Fatigue cracks initiate at surface tensile stresses. When cyclic loading creates a surface tensile stress, a crack can start. Peening creates a compressive layer at the surface — before cyclic loading creates tensile stress, the surface is already in compression. Fatigue cracks cannot initiate until the compressive preload is overcome. Effect: 2–5× fatigue life improvement depending on part geometry and loading.

Almen intensity measures peening effect via a standardized test strip. An Almen strip is thin hardened steel that bends measurably when peened (the strip curves because peened side has compressive stress). Strip curvature measured on Almen gauge. Designations: A-strip for standard intensity (0.004–0.020 range), C-strip for higher intensity, N-strip for lower. Example spec: "Peen per AMS 2430 to Almen intensity 0.010–0.015 A, 200% coverage."

Shot blasting: surface cleaning, removes scale/rust, uses coarse media at high velocity, leaves rough texture. No engineering purpose beyond cleaning. Shot peening: controlled process with specific shot size, velocity, coverage, and Almen intensity. Engineering purpose: residual stress management for fatigue life. Same basic equipment but dramatically different process control and engineering intent.

Minimally. Peening may cause 0.005–0.05 mm growth on the peened surface due to plastic deformation. For precision parts, this should be accounted for in the machining sequence: peen first, then finish-machine critical surfaces if tight tolerance required. For parts where ±0.05 mm dimensional change is acceptable, peening doesn't compromise fit.

Shot peening cost: $10–40 per part for small parts, up to $100+ for large complex peening. Significant cost adder, but usually justified by fatigue life improvement. For safety-critical aerospace: peening is mandatory per specification — not optional. For commercial applications where fatigue isn't limiting, peening may be overkill. Cost-benefit analysis typically favors peening for any fatigue-loaded part.

Shot peening typically adds 3–7 business days to overall lead time. Specific peening services routed through our AMS 2430-qualified partner for aerospace work. Documentation package (shot media records, Almen strip results, traceability) included. For non-aerospace peening (general automotive, industrial), in-house peening with standard documentation.