Impact Fatigue Behaviour of Flapper Valve Steel

The purpose of this study is to discuss the impact fatigue failure mechanism of a suction valve that involves the fracture with fragments torn off from the edge or surface. The shape and dimensions of the test specimen and stopper were made the same as those of the suction valve and stopper in an actual compressor. The specimen was operated by short-duration compressed air pulses, and struck against the stopper and seat alternately. The impact velocities of the specimen against the stopper and seat were controlled by the pressure of the compressed air. The short-duration compressed air pulses were generated by air shutters. Impact fatigue tests were performed under several impact velocities of the specimen against the stopper. The cracked surface and fatigue failure surface were observed at each certain number of impact cycles with an optical microscope and a scanning electrbn microscope. The crack feature, crack propagation, and crack origin were examined. From those results, impact fatigue failure mechanism of the suction valve is clarified.