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概要

This paper describes shot peening treatment of modified 9Cr steel and 316FR austenitic stainless steel, candidate structural materials for FBR by using YAG laser. A laser peening system has been developed and used to provide laser peening treatment for plate s pecimens of the two types of the steels dipped in water. A high speed digital camera revealed that many small bubbles were initiated along the path of laser light, moved along the path and coalesced with one another to produce a few large bubbles. The large bu bbles imploded approximately 300 usec after each laser pulse emission. The high speed video implied that water jets were induced by the bubble implosion and impacted the surfaces of specimens to provide peening treatment for the specimens. The X-ray analyses w ere made around the peened portions of the specimen surfaces and revealed that the residual stress was tensile near the center of the peened portions and gradually decreased away from the center. The residual stress was compressive away from the peened sites.

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