High power ultrasonic generator for high cycle fatigue testing and surface hardening of metallic materials

An in-house built equipment which generates high intensity ultrasonic vibrations at about 22KHz frequency with displacement amplitude reaching upto 150μm has been described. This equipment is capable of performing a dual role viz. (a) fatigue testing metallic materials in the high cycle region to failure in just a few minutes under conditions of resonance, and (b) introducing very high compressive residual stresses in work-hardenable materials within a few minutes even under non-resonant conditions. In addition, it can also be used in quality control for rapid screening of good and bad welded joints (from the point of view of their fatigue resistance). A few fractographs of selected ultrasonic fatigue fractures are presented. Typical values of the compressive residual stresses obtained through this method are also reported. The ultrasonic generator is modular in design comprising of an oscillator. DC power supply, power inverter etc. and can deliver upto 750 W of power to the magnetostrictive transducer (made of nickel laminations.) A catenoidal concentrator brazed to the transducer has been used to generate large amplitude vibrations.