Fatigue Life Improvement — Shot Peening

Overview

Unlike other applications, shot peening is not used to "clean" a surface — it is used to improve a material's fatigue life and performance by inducing compressive stress on the surface through controlled ball-blasting impact. It is a common process in the aerospace, defense, and energy/turbine sectors for critical parts subject to high mechanical loads (such as turbine disks, springs, and gears). Unlike other applications, this process serves a materials-engineering purpose rather than a cleaning purpose.

What Is Shot Peening? Shot peening is a cold working process in which spherical media (steel shot, ceramic beads, glass beads) are bombarded onto a metal surface at a controlled velocity. The goal is not to clean the surface — each media impact creates a small plastic deformation (dimple) that induces a layer of compressive residual stress in the surface layer of the material.

How It Works: This compressive stress layer acts as a "preload" against the part's tensile stresses; since fatigue cracks typically initiate and propagate under tensile stress, the pre-existing compressive layer at the surface delays crack initiation and propagation. As a result, the part's fatigue life, resistance to stress corrosion cracking, and overall fatigue strength increase significantly.

Shot Peening vs. Standard Blasting: Standard blasting (for cleaning/roughening) is typically done with angular media that cuts the surface to remove rust/scale/coatings; shot peening uses spherical media with no sharp edges, and the goal is not material removal but controlled peening of the surface. Using angular media can create notches/micro-cracks that reduce fatigue resistance rather than improving it.

Critical Process Parameters: For a repeatable, correct result, the following parameters are controlled to tight tolerances: media sphericity and hardness, media size, blasting velocity/pressure, coverage (at least 98–100% of the surface must be processed), and Almen intensity (the intensity of applied energy, measured by the deflection of a standard test strip). These parameters are typically documented per aerospace/automotive standards such as SAE J442/J443 and AMS 2430.

Typical Applications: Aircraft and turbine engine components (blades, landing gear parts, airframe structures), springs and gears, crankshafts and connecting rods, and automotive components subject to high-cycle fatigue loading, and in general any metal component where fatigue-driven failure is a critical failure mode.