Zhi-Yue Liu

An Investigation on the Properties of Underwater Shock Waves Generated in Underwater Explosions of High Explosives

A cylinder expansion test for high explosives was carried out to determine JWL parameters. Using the JWL parameters, we carried out numerical simulations of the underwater shock waves generated by the underwater explosion of the high explosives. Our results showed that the behavior of the underwater shock waves at the vicinity of the explosives differs greatly from that far from the explosives. Especially, the strength of the underwater shock wave nearby the explosive rapidly decreases due to the effect of the expansion of the gas products.

Overdriven detonation phenomenon in high explosive

The term “overdriven detonation” refers to detonation process in which the main detonation parameters, such as detonation pressure and propagating velocity, exceed the corresponding Chapman-Jouguet (C-J) values. This kind of detonation state can be realized by the impingement of a high velocity object upon the explosive. This paper presents our initial survey on the occurrence of overdriven detonation in high explosive. The HMX-based PBX is used to accelerate the metal plate being used as the impactor. The target explosive is the so-called SEP, simplified from the term of the ‘safety explosive,’ with the composition of PETN wt.65% and paraffin 35 wt.%. By changing the thickness of the metal plate under an unvaried amount of donor explosive, the different impinging velocities are yielded. The propagation of the detonation wave grown from the impingement of metal plate is recorded by the high-speed streak camera owing to the self-luminosity of detonation. The higher detonation velocity is found from the exp...

High-speed photographic study on overdriven detonation of high explosive

On the common circumstances the detonation of explosives has a steady propagation rate and can be satisfactorily explained by Chapman-Jouguets theory on this phenomenon. Hence, this type of detonation is more frequently called the Chapman- Jouguet (C-J) detonation. The detonation properties such as pressure, density, and temperature, of the detonation products are often characterized as the C-J values of the explosive that represent the corresponding maximums of the variables in the detonation products. However, when an explosive is initiated in some special ways, for instance, high velocity impact of a flyer plate, a strong detonation with properties higher than C-J values will be induced in the explosive. This strong detonation is what we called the overdriven detonation of explosive. The use of overdriven detonation expects to provide much more work to the surrounding matter than does the common C-J detonation. In order to have a basic knowledge of this detonation phenomenon, we designate an experimental set- up for the purpose of acquiring the overdriven detonation in high explosive. The set-up uses a circular metal plate accelerated by a piece of cylinder explosive (donor) to impact another cylinder explosive (acceptor), inducing a detonation wave in the acceptor explosive. The donor explosive used is PBX (85%wt HMX and 15%wt binder) explosive cylinder that has the detonation velocity of 7.84 km/s and the detonation pressure of 25.24 GPa and the acceptor explosive cylinder is SEP (65%wt PETN and 35%wt paraffin) with the detonation velocity of 6.97 km/s and the detonation pressure of 15.9 GPa. The impactor is the copper disc with the same diameter of the donor explosive and 1 mm and 2 mm thicknesses respectively. The detonations occurred in the acceptor explosive from the impact of copper flyer were recorded by the high-speed camera (IMACON 790). The photographs make us possible to estimate the detonation velocities from the distance and time data on them. In addition, we also make a numerical visualization on this phenomenon using a 2-D Lagrangian hydrodynamic code. The calculation, to somewhat extent, reproduces the consequences of the current experimental results.

A Method for Producing Extra-High Dynamic Pressure Due to the Efficient Use of High Explosive

In the material processing such as shock synthesis and powder consolidation by shock waves the method for generating dynamic pressure is a vital factor for the quality of the final recovered materials. A general and convenient way for producing shock wave demanded in such applications is to take advantage of the explosion effect from high explosive. Under normal conditions, a given high explosive can only provide some kind of magnitude of dynamic pressure after its explosion. Therefore, it is whether possible to obtain the higher dynamic pressure by adequately changing the form of the explosion of high explosive. Starting from this motivation, we put forward a new method for producing high dynamic pressure from the use of the overdriven detonation of high explosive. The proposed device consists of the following configurations. A metal flyer accelerated by the high explosive is used to impact another layer of high explosive to incur an overdriven detonation in this layer of explosive. The overdriven detonation of high explosive acts on the powder materials, bringing out high dynamic pressures to the materials studied. To examine the efficiency of this combination on the improvement of dynamic pressure, a numerical computation is performed on this system. The details on the illustration of this method as well as the results of numerical investigation will be given.

Deformation of Metal Pipe due to Underwater Shock Wave

The deformation process of the metal pipes, accelerated by underwater shock wave resulting from the underwater detonation of explosive inside the metal pipe, was investigated by means of both the optical observation experiment and the numerical calculation. The expanding deformation of metal pipes was experimentally viewed by both framing and streak photographic means. A computer code based on the arbitrary Lagrangian and Eulerian (ALE) method was used to perform the numerical simulation on this problem. It has confirmed that the deformations of the metal pipes obtained from the streak photographs agree quite well with those obtained by the numerical calculation. The experimental and numerical results both show that the expanding velocity along the radial direction in aluminum pipe is larger than that in copper pipe, under the same loading conditions: and also, the time needed to reach the maximum radial velocity is shorter in aluminum pipe than in copper pipe. The calculations clearly indicate that the metal pipes are able to acquire a maximum expanding velocity along the radial direction in a very short time after the beginning of the action of underwater shock wave, and also this maximum velocity value only decreases a little in the later time period.

Von Neumann reflection of underwater shock wave

Abstract This paper is devoted to studying the phenomenon of von Neumann reflection of underwater shock waves. The underwater shock wave was produced by means of underwater detonation of high explosive. The study includes three aspects: experimental observation, numerical simulation and theoretical analysis.

On direct transformation from hBN to cBN

Abstract A new apparatus was devised for direct phase transformation from hBN to cBN using the cylindrical explosion technique. The apparatus consisted of multiple thin-metal foils in a metal tube, surrounded by a high efficiency explosive. The space between the multiple thin-metal foils was filled with hBN powder. This apparatus was expected to produce higher pressure and temperature than the ordinary cylindrical method. These high pressures and temperatures have proven to be satisfactory in the direct phase transformation from hBN into cBN.

On von Neumann reflection of shock wave in condensed matter

In the irregular reflection of shock waves in gaseous media, a kind of reflection pattern, termed as von Neumann reflection(vNR), has been being studied by experimental, numerical and theoretical techniques. In condensed matter, such as liquid, metal and polymer, this kind of reflection pattern has not yet been noticed. This paper will present the studies on von Neumann reflection of shock waves in water and polymethylmethacrylate (PMMA). The basic characteristics of von Neumann reflection would be given.

A new apparatus for direct transformation from hBN to cBN

A new apparatus was devised for direct phase transformation from hBN to cBN by using the cylindrical explosion. The apparatus consisted of multiple thin-metal foils in a metal tube surrounded by a high efficiency explosive and the spaces between the multiple thin-metal foils were filled with hBN containing a small amount of copper powder. This apparatus was expected to produce higher pressure and temperature than the ordinary cylindrical method. These high pressure and temperature has been proved to be satisfactory to result in the direct phase transformation from hBN into cBN.

The irregular reflection from the symmetrical collision of two plane detonation waves in high explosive

The obliquely symmetrical collision of the plane detonation wave in high explosive was observed by means of a high-speed camera in framing mode. The plane detonation wave is generated by two kinds of devices: one using the plane wave generators; the other being the newly devised set-up. The collision angle is set to values greatly larger than the critical angle for irregular reflection of detonation wave from the theoretical prediction. The experimental results show that Mach reflection of detonation wave indeed occurs, but the length of Mach stem is short and the stem shape is smoothly curved. At the same time, the results also illustrate that the collision of detonation wave in high explosive indicates somewhat more complexity than shock reflection in gases and solids.