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Shot peening has been used as a process to improve fatigue life and fatigue strength of metal for centuries. Modern applications began with General Motors Corporation in the 1920's, when they began shot peening valve springs to improve fatigue life. Over the years this process has been applied to a variety of metals to improve fatigue characteristics and with the advent of SEM (Scanning Electron Microscope) technology, failure mechanisms such as SCC (Stress Corrosion Cracking) and IGA (Intergranular Attack) have been identified. Shot Peening has been proven to retard SCC and eliminate IGA. Detailed shot peening specifications have been developed by major aircraft manufacturing companies and many of these practices have been incorporated in the repair and overhaul of operational aircraft. The integration of automated, controlled shot peening into these applications has placed shot peening in the REQUIRED SERVICES category.

Search peening can be defined as the use of controlled shot peening as a tool to expose subsurface corrosion. The stretching of the surface coupled with the compressive stress induced by the multiple impacts of the shot help to delaminate hidden layers, as is found in exfoliation corrosion. Recently, Boeing Airplane Company's Defense and Space Group, in association with the United States Air Force, funded a study to determine the application of using shot peening to identify exfoliation corrosion. Metal Improvement Company and British Airways have also developed a method to determine the extent of corrosion so that the removal of damage can be accomplished with a high degree of accuracy. This certifiable controlled process, “search peening,” allows a minimal amount of metal removal, so that engineers have the maximum acceptable material to work with, enabling them to keep tolerances within safe limits.

Advances in chemistry and parts design have extended the useful life of many engine, structural and landing gear components. Sufficient data has been collected and sunmarized to estimate length of service periods between inspection and overhaul, and even the number of times that components can be reconditioned and reused. Shot-peening has become an important element in obtaining improvements in fatigue life and as a preparatory process for many coatings. The purpose of this paper is to discuss typical applications of shot-peening used in the overhaul process. we will also identify process controls necessary to retain or restore the shot-peening benefit designed into parts by the original manufacturer.

New methods of measuring and controlling coverage and, in special situations, intensities, have been developed and are gaining recognition by concerned users of shot peening. For coverage control a fluorescent material accurately reflects degree of coverage attained. Techniques for the peening of very small holes to achieve a uniform beneficial compressive stress is shown as well as a method of measuring intensity in holes too small to be checked by conventional Alman strips. Shot Peen Precondition of Autofrettage for improved fatigue life are combined to show significantly increased fatigue life in parts treated solely by either of these two processes alone.