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Manufacturing techniques using shock waves generated by underwater explosion have been developed and studied for many years. The major advantages of these techniques are that the pressure acts for a relatively long duration, and there are no thermal effects on the materials. We have been approaching the utilization of the underwater shock wave for various metal processing methods such as in metal forming, explosive welding and shock compacting of difficult-to- consolidate powder. It is necessary to control the underwater shock waves with regard to the processing objectives. In many cases, the underwater shock waves have been used quite close to the explosives. The properties of the underwater shock wave in the region far from the origin of the explosion (more than 1000 mm) have been investigated since long time, but those near the explosive are not yet known. In this paper, we have tried to make clear the properties of shock waves near the explosive. The pressure of the underwater shock wave generated by a detonation cord was measured by a pressure transducer, which was made by a tungsten bar with semiconductor gauges. We found that the pressure of the underwater shock waves decreased almost exponentially. We also investigated the properties of the underwater shock waves by high speed photography. Two kinds of high speed photography were used in experiments. One was the streak photograph and the other was the shadow graph. The propagating of the underwater shock waves was made to clear by framing photographs with an image converter camera. The Profiles of the underwater shock waves were also obtained from high speed photography using a pulses laser as an optical source. Using these profiles of the underwater shock wave, we could obtain the velocity of the shock wave front, and finally we could obtain the pressure across the underwater shock waves by using the Rankine-Hugoniot condition. The pressure obtained by optical measurement agreed with the results obtained by the transducer. As a result of these experiments, the attenuating processes of underwater shock waves, even those near the explosives, were understood.
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