Sugi (Cryptomeria japonica D.Don) wood generally has the so-called black heartwood, which contains the extremely high moisture content. Although subjected to the drying process, it is difficult to be dried up completely so that Sugi wood does nol have the sufficient strength for use. The reason is that during drying process, the bordered pit membrane on traicheids closes faster near the heartwood in Sugi wood so that the in|-ernal moisture is not easily come out to the outside. At the mean time, it also makes very difficult to saturate the rotten--proof chemicals into the dried Sugi wood to have it become an additionally v',duable wood. In this paper, we will develop an underwater shock wave technique to treat the pre-dried wood for the improvement of the drying property as well as the permeability and strength of Sugi wood by selectively fracturing the bordered pit membrane. The result indicates a very remarkable improvement on the drying time. The mechanism of the fracture of the bordered pit by underwater shock wave will be further studied in the fi~ture.
Explosive forming is one of the unconventional techniques, in which, most commonly, the water is used as the pressure transmission medium. The explosive is set at the top of the pressure vessel filled with water, and is detonated by an electric detonator. The underwater shock wave propagates through the water medium and impinges on the metal plate, which in turn, deforms. There is another pressure pulse acting on the metal plate as the secondary by product of the expansion of the gas generated by detonation of explosive. The secondary pressure pulse duration is longer and the peak pressure is lower than the primary shock pressure. However, the intensity of these pressure pulse is based also on the conditions of a pressure vessel. In order to understand the influence of the configuration of the pressure vessel on the deformation of a metal plate, numerical analysis was performed. This paper reports those results.
Explosives can easily generate the high energy and the ultra-high pressure. The performance of explosive depends on its own chemical property, the detonation wave usually propagates with the stable value of pressure behind it, the pressure is so called "Chapman-Jouguet (C-J) pressure" . If the higher pressure over C-J pressure can be expected to occur, it is very effective for a development of new materials. We take notice of Overdriven Detonation (following ODD.) phenomenon that expects to bring out higher detonation pressures than C-J pressure of explosive. This phenomenon can be occurred when the flyer plate of high velocity impacts the explosive, or the explosive compressed by the advance detonates, or converging detonation of the explosive.
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