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.
The pressure occured by an explosive is limited by its own property and its own performance. This pressure is called “C-J pressure”. If the pressure that is higher than C-J pressure can occur, it is very effective for a development field of new materials. So, Overdriven Detonation phenomenon in explosive is considered, that brings out higher detonation pressures than C-J pressure of an explosive. In this study, the flying metal plate accelerated by driver explosive impact against driven explosive, and Overdriven Detonation phenomenon occurs, the relation between driver explosive and driven explosive and the work on the front of the explosive is reported.
Reversed plane bending fatigue tests were carried out on two kinds of forged Al-25Si P/M (Powder Metallurgy) aluminum alloys having different sizes and distributions of Si particles. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. It was found that the crack initiation strength of the material with fine Si particles was higher than that with coarse Si particles. Although little difference in strength was observed between the forged and transverse directions in the former material, some difference was found depending on the specimen orientations in the latter material. When the stress intensity range was calculated by considering the difference of the projected area of Si particles to the plane perpendicular to the loading axis, the difference in fatigue strength among the specimens oriented differently could be explained. The macroscopic crack growth rate, da/dn, could be expressed by the Paris equation in terms of the maximum stress intensity factor, Kmax, irrespective of stress level and specimen orientation. The fatigue crack growth rate was found faster in the coarse grained material than that in the fine grained material, and as the crack propagated along the Si particles, more deflective behavior of crack growth was observed in the material with fine Si particles, which was thought to result in the increase in crack growth resistance.
It is economically that we actually examine with the condition, which was chosen by numerical analysis. Therefore, the necessity for numerical analysis has been increasing and more realistic numerical analysis is called for. In this paper, in order to perform more realistic numerical analysis for explosion in a pipe, sliding boundary condition of Mark L.Wilkins was applied to the treatment of the boundary which different materials, such as an explosive and its container. Applying this sliding boundary condition is able to prevent cell destructions. And this leads the successful simulation and more realistic numerical analysis. The feature of the explosive applications is to obtain the high energy, super-high pressure and extreme temperature that are difficult to obtain by the static methods. In this paper, the numerical simulation for powder compaction was carried out in order to evaluate the performance of a numerical analysis and the characteristic of the device. This device was so called cylindrical method, and the powder, which filled up into the cylindrical container, was compressed toward the central part from the outer wall side of a pipe by the super-high pressure generated by the detonation of the surrounding explosive. In this devise, water is set between the explosive part and powder part to change the pressure that acts on the powder part, and paraffin is set at the central part of this device in preventing the extreme pressure raise. Additionally, many boundaries were formed with the explosive, water, powder, and paraffin part and each container in this device. Therefore, sliding boundary condition was very important to apply for all boundaries. From numerical analysis results, it was found that pressure which acts on the powder part does not change so much if the radial direction thickness of the explosive part is 20mm or more. Moreover, it was also confirmed that the pressure of the powder part was made high by setting the water part, and that the extreme pressure raise was prevented by setting the paraffin part.
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