Steel fatigue occurs when a metal structure or component is subjected to repeated loading and unloading of stress on a specific part (similar to bending a paper clip or staple back and forth repetitively until it breaks). When this process, also known as cyclic loading, exceeds a specific limit, tensile cracks form on the surface and alters microscopic grains within the metal which ultimately lead to fatigue failure if left untreated. Outside of replacing the metal, Ultrasonic Impact Treatment from Applied Ultrasonics has emerged as the most effective method of combating steel fatigue due to its ability to improve surface quality, force detrimental tensile stresses deep within the material, and reform the grains that comprise the structure of the metal.
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| *Example of cyclic loading and its effect on steel fatigue. |
The Impact of Surface Quality on Steel Fatigue
Because steel fatigue failure nearly always starts at the surface, the quality of the surface is one of the most important factors to consider when treating fatigue. High-stress fibers, as well as corrosive elements, such as oxidation or fretting that lead to tension failure in metal are most commonly found at the surface. Applied Ultrasonics patented Ultrasonic Impact Treatment alleviates these precursors to failure by introducing therapeutic compressive stresses near the surface, which creates a stronger, more corrosion-resistant area. These compressive stresses replace the damaging tensile stresses, which are driven deep within the metal.
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| Cross Section Highlighting Surface Corrosion in Metal |
Increasing Steel Fatigue Life through Stress Relief
By removing tensile stresses from the surface where they are most detrimental, UIT not only increases fatigue life, but also reduces the need for costly repetitive maintenance to the afflicted area. The tensile stresses formed during fatigue load cycles, or processes such as welding, cutting and casting, lead to deterioration of the surface and create cracks and notches in the metal. If left untreated, these cracks and notches widen and deepen to a dangerous level where the material must be repaired or replaced before fatigue failure occurs. By forcing these damaging tensile stresses to an industry-best depth of 12mm, Applied Ultrasonics’ ultrasonic impact technology is able to fortify the surface and the grains of which it is comprised.
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| *Onset of steel fatigue via formation of tensile cracks from cyclic loading |
Resisting Steel Fatigue on a Granular Level
Changes and flaws to grains near the metal’s surface, which occur during cyclic loads, substantially promote the onset of steel fatigue Throughout fatigue load cycles, grains in the metal undergo deformations that greatly impact the integrity of the material. Ultrasonic Impact Treatment (UIT) employs targeted ultrasonic frequencies to alleviate these flaws and changes by restructuring the size, shape and orientation of the grains to their strongest composition.
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| *Steel fatigue crack exacerbated by flaws in grain structure |
Effective Treatment Leads to Lasting Benefits
By increasing intergranular metal strength, improving resistance to corrosion, and extending steel fatigue life more quickly, effectively and cost efficiently than other treatment methods, Ultrasonic Impact Treatment from Applied Ultrasonics reduces the expense and downtime associated with constant maintenance, or replacement stemming from the factors of steel fatigue.
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