Metal Fatigue Solution

How Does Shot Peening Improve Fatigue Life?

Shot Peening is a surface enhancement process used to impart compressive residual stresses into fatigue-prone metals. This process increases fatigue strength by delaying the initiation of cracking. So how does laser peening compare to shot peening when it comes to fatigue improvement?

What is Metal Fatigue

Metal fatigue is a failure mode when a material is weakened in machines, transportation vessels, or structures due to repeated stresses and high-cycle operations. First micro-cracks begin to form at the surface of a component. Then due to continued stress, the micro-cracks begin to increase in size and severity. Finally, the micro-cracks have grown and the continuous cycle loading on the part causes the crack to propagate and succumb to metal failure requiring repair or total replacement.

Fatigue strength of metals can be weakened due to operational processes in a wide-range of industries including manufacturing, aerospace, automotive, and more. Metal fatigue can be costly and cause undesired downtime for an important industrial process. Shot peening is one way to counter the dreaded fatigue that occurs at the surface of critical metal components.

Image result for metal fatigue in engineering

How Shot Peening Improves Fatigue Life of Metals

metal fatigue failure
Closeup with focus on the surface of a fracture in a car spring due to metal fatigue.

When shot media is accelerated toward the surface of a metal part, it acts like a small hammer and creates indentations in the part. Those plastically formed indentations are the source for creating compressive residual stress.

Shot peening replaces tensile stress with compressive stress. The compressive stress minimizes the cracking damage. Since the cracking damage is minimized, the lifetime of the part is increased and fatigue failure is reduced. The compressive stress from shot peening can only reach a depth of about 0.25 mm but that’s enough to have a fatigue-reducing effect.

Laser Peening - Superior Fatigue Improvement

While shot peening provides an effective way to improve fatigue life, laser peening has demonstrated the ability to exceed the performance of shot peening when it comes to improving fatigue life of critical components. In fact, laser peening can provide over 10X life increases for components that have only previously been shot peened.

Laser Peening has a unique ability to achieve deeper depths of compressive residual stress compared to shot peening. The high-energy impact from the laser shot at the surface of the part combined with precision control are part of what enables laser peening to reach depths in a component that are unrivaled. Our engineers have the ability to control the depth of magnitude of compressive residual stresses by increasing the power and coverage of the laser pulse.  Laser peening can achieve compressive stress at a depth of 12mm depending on processing conditions, material, and geometry of the part.

Because laser peening uses less than 5% cold work, compressive residual stresses are also retained at much higher temperatures. Laser peening has an advantage for imparting compressive stress in parts that have hard-to-reach surfaces or complex geometries due to the optimization possible at precise locations on a part.

In the graph to the right, the shot peening (green and blue) curves show compressive residual stress values that quickly fall towards zero as depth increases. The laser peening (pink and orange) fall off more gradually and maintain compressive stress up to a milimeter beneath the surface.

 

 

Ready for a Superior Fatigue

Enhancement Improvement?

Shot peening can improve fatigue life in a component at a depth of 0.25mm. But laser peening goes well beyond that .

Laser peening is the leading technology for improving the fatigue life of critical components for industries like aerospace, power generation, automotive, maritime, and more. Due to the unmatched depth and controlled process of laser peening, our technology is relied upon as the best solution.

Don’t let metal fatigue continue to disrupt operations. Let’s discuss the best solution to help your parts last.