Shot peening is the most suitable treatment to improve mechanical fatigue resistance and enhance mechanical components’ life.

Shot peening effectiveness has been widely demonstrated by studies carried out by important entities such as NASA, Ford Motor Company, FIAT Research Center and many universities worldwide.

Shot peening is a technological process to be carried out under controlled conditions. Theoretical studies and, of course, field experience, show that there are many factors that can affect the result of shot peening. Each case is studied and resolved in a very specific way.

How Shot Peening works

The process

Shot peening, also known as controlled shot peening, is a mechanical treatment carried out at room temperature consisting on peening, under very controlled conditions, the surface of a metal part using a beam of metal beads projected at high speed.

The impact of the shot, causes the plastic deformation of the surface layers that tend to spread while the inner layers try to return to their original state. The resulting equilibrium causes the surface layers to undergo residual compressive stresses, thus increasing the resistance against mechanical fatigue of the treated component.


On April 28, 1988, a miraculous landing happened, saving 90 passengers and 4 crew members. The only victim was a flight attendant. The landing of an aircraft with such a significant loss of structural integrity was and continues to be an unprecedented event. The official report of the United States National Transportation Safety Board concluded that the accident was caused by load stress due to repeated compressions and decompressions of the cabin. It is estimated that 90% of the breaks in mechanical components are attributable to fatigue phenomena due to which the consequences are frequently catastrophic. Fatigue is a mechanism of accumulation and propagation of damage in a mechanical component undergoing variable stress over time. It is an extremely complex phenomenon that is cannot be always easily evaluated during the design phase.

The benefits

As a general rule, it can be said that shot peening increases the minimum fatigue resistance by 10-15% and can even reach surprising increases of up to 50% of the fatigue limit in cases of properly optimized treatments. Compressive surface stress, together with certain levels of lattice distortion, make it possible to increase the resistance to mechanical fatigue of a component subject to mono-axial or multi-axial loads in the case of high stress concentrations. It can also be successfully used in cases of contact fatigue such as pitting and fretting. The surface micro-roughness generated can be useful in solving problems related to noise or lack of lubrication.

The machinery

The shot peening machine is essential in the process. Shot peening belongs to the category of “special processes”. That is why the only way to control the process is to ensure that process parameters are kept within a tight tolerance range throughout the treatment. Compressed air installations are universally known as the most suitable for treatment. Our most modern and advanced facilities, which guarantee the best repeatability, are fully automated. Our machines are controlled by automatisms processing and feedbacking signals from various sensors to guarantee the most accurate possible peening conditions.

The principle and the effects

When the shot hits the surface of the component, a micro dimple is produced with a perimeter ring-like edge. The dimple and the ring are the result of two simultaneous events. On impact, the shot plasticizes the surface layers of the material, making them larger and compresses those that are on the sub-surface, according to the well-known Hertz theory. The superposition of these two events produces a residual stress profile with a high value on the surface and a peak on the subsurface that depend on the treatment conditions. The compressive surface tensions generated by shot peening are mainly responsible for the increase in the fatigue resistance of the treated components.

The technology

The technological history of shot peening is relatively recent and is still evolving. The process depends on three fundamental parameters: Shot, Intensity and Coverage. Shot is the “tool” by which the residual compression stresses are introduced. Its shape must be strictly spherical. Angular shaped grit particles can be the cause of breakage beginnings. Intensity is a parameter that is determined through the “Saturation Curve” and is directly related to the kinetic energy of the shot beam. It has nothing to do with the current consumption of the installation. The coverage is represented as the percentage relationship between the surface of the shot impacts with respect to that of the area to be treated. To obtain the best performance of the treatment, it is necessary to work both on the definition of the parameters and on their control during the processing of the parts.