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This technique is part of the High Frequency Mechanical Impact (HFMI) processes. Other acronyms are also equivalent: Ultrasonic Needle Peening (UNP), Ultrasonic Peening (UP). Ultrasonic impact treatment can result in controlled residual compressive stress, grain refinement and grain size reduction.
In metallurgy, peening is the process of working a metal's surface to improve its material properties, usually by mechanical means, such as hammer blows, by blasting with shot (shot peening), focusing light (laser peening), or in recent years, with water column impacts (water jet peening) and cavitation jets (cavitation peening). [1]
The thermal method involves changing the temperature of the entire part uniformly, either through heating or cooling. When parts are heated for stress relief, the process may also be known as stress relief bake. [13] Cooling parts for stress relief is known as cryogenic stress relief and is relatively uncommon. [citation needed]
Induce residual stresses Peening a surface can reduce such tensile stresses and create compressive residual stress, which prevents crack initiation. Forms of peening include: shot peening , using high-speed projectiles, high-frequency impact treatment (also called high-frequency mechanical impact) using a mechanical hammer, [ 47 ] [ 48 ] and ...
Shot peening is a cold working process used to produce a compressive residual stress layer and modify the mechanical properties of metals and composites. It entails striking a surface with shot (round metallic, glass, or ceramic particles) with force sufficient to create plastic deformation .
The stress relief treatment resulted in 47% growth of the original, large peak, while it shifted to the left 28-RPM (less than 0.75%). Figure 5: Vibratory Stress Relief was performed on this mild steel weldment weighing almost 12 tons. Overall size was 17' × 15' × 2' (≈ 5.2 × 5.6 × 0.6 meters).
Laser peening (LP), or laser shock peening (LSP), is a surface engineering process used to impart beneficial residual stresses in materials. The deep, high-magnitude compressive residual stresses induced by laser peening increase the resistance of materials to surface-related failures, such as fatigue, fretting fatigue, and stress corrosion cracking.
During the welding process, residual stresses can present themselves in the area of the weld, either in the heat affected zone or fusion zone. The mean stress a welded joint may see in application, can be altered due to the welding processes implementing residual stresses, changing the fatigue life and can render S-N laboratory testing results. [2]