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Sunghwan Jung(정성환),Prabhu Murugesan(프라부 무르해산),Hyungyil Lee(이형일) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4
The ultrasonic peening technique that we propose is to form cavitation bubbles inside a nozzle using ultrasound, peening the inner surface of the nozzle with the cavitation shock waves in static water induced by ultrasound. Recently, our ultrasonic peening technique generated a compressive stress of ~ 400 MPa at the inner surface of a very narrow pipe (with the inner diameter of 16 mm and made of SUS304), which is challenging to access. The peening stress at the inner surface, also, remained compressive until the depth of ~ 400 m from the surface, which well meets the requirement (-250m) of EPRI (Electric Power Research Institute). Our peening technique offers unique advantages as listed below. -The ultrasonic peening engages static water (as no water jet flow is involved), generating far less mechanical vibration in the engaged nozzle, which, therefore, ensures that the peening can be safely carried for the inner surface of the nozzle. -The ultrasonic peening solely uses an inexpensive and widely used an ultrasonic probe, making the system production cost exceptionally low. -Initial set-up at the nuclear site for the ultrasonic loading (mainly using an ultrasonic probe) is easy and simple, allowing the outage time for set-up and operation to be substantially reduced. -The power consumption for the ultrasonic loading (as no water jet flow is involved) is only in the range of 100W, which is far less than that of water jet peening reported to be 50-100 kW. The present ultrasonic peening technology is reliable, low production cost, simple and easy to operate with significantly reduced outage time, and high energy efficient.