Shiro Kubota

An investigation on underwater explosive bonding process

In this paper, we propose a new explosive bonding method for bonding materials by using the underwater shock wave from the explosion of explosives in water. This method is especially suitable to bond the materials with thin thickness and largely dissimilar property. In bonding those materials, the shock pressure and the moving velocity of shock wave on the flyer plate should be precisely managed to achieve an optimum bonding conditions. In this method, the bonding conditions can be controlled by varying of the space distance between the explosive and the flyer plate or by inclining the explosive charge with the flyer plate. We made the experiment of this technique bond the amorphous film with the steel plate. A satisfactory result was gained. At the same time, numerical analysis was performed to investigate the bonding conditions. The calculated deformation of the flyer plate by the action of underwater shock wave was compared with the experimental recordings by high-speed camera under the same conditions. The comparison shows that the numerical analysis is of good reliability on the prediction of the experimental result. Furthermore, the numerical simulation also gives the deformations of the flyer and the base plate, and the pressure and its variation during the collision process.

On Generation of Ultra-High Pressure by Converging of Underwater Shock Waves

The characteristics of a new assembly for the shock consolidation of difficult-to-consolidate powders, such as inter-metallic compounds or ceramic materials, were investigated by both the experimental method and numerical simulation method. The assembly consists of an explosive container, a water chamber, and a powder container. Once the explosive is detonated, a detonation wave occurs and propagates, and then impinges on the water surface of the water chamber. After that, there occurs immediately an underwater shock wave in the water chamber. The underwater shock wave interacts with the wall of the chamber during its propagation so that its strength is increased by the converging effect. We used the usual shadow graph system to photograph the interaction process between detonation wave and water. We also used a Manganin piezoresistance gage to measure the converged pressure of the conical water chamber. Finally, we numerically investigated, in detail, the converging effects of the various conical water chambers on the underwater shock waves. The experimental results and the correspondingly numerical results agree quite well with each other.

Equation of state for detonation product gases

A thermodynamic analysis procedure of the detonation product equation of state (EOS) together with the experimental data set of the detonation velocity as a function of initial density has been formulated. The Chapman–Jouguet (CJ) state [W. Ficket and W. C. Davis, Detonation: Theory and Experiment (University of California Press, Berkeley 1979)] on the p-ν plane is found to be well approximated by the envelope function formed by the collection of Rayleigh lines with many different initial density states. The Jones–Stanyukovich–Manson relation [W. Ficket and W. C. Davis, Detonation: Theory and Experiment (University of California Press, Berkeley, 1979)] is used to estimate the error included in this approximation. Based on this analysis, a simplified integration method to calculate the Gruneisen parameter along the CJ state curve with different initial densities utilizing the cylinder expansion data has been presented. The procedure gives a simple way of obtaining the EOS function, compatible with the deto...

Homeothermal Adjustment in the Immediate Postdelivered Infant Monitored by Continuous and Simultaneous Measurement of Core and Peripheral Body Temperatures

To investigate the process of homeothermal acclimation to extrauterine environment, core and peripheral body temperatures in the human neonate were continuously and simultaneously recorded. Twenty-one term-delivered babies were divided into two groups. In group I, 10 babies were kept at 32-34 degrees C for the first 2 h of extrauterine life and at 24-26 degrees C for the succeeding 6 h. In group II, II were kept at 24-26 degrees C for the first 8 h after delivery. Three thermisters were used: one catheter-type placed in the rectum and two involving the zero-heat flow method placed at the sternum and footsole. Because of technical limitations, rectal temperature (Tre) was monitored until temperature in the sternum (Tst) stabilized, after which this transition from Tre to Tst was noted as Tre-st. Changes in resulting temperatures were quantitatively analyzed using Students t test, for both intra- and intergroup comparisons. Tre-st significantly decreased during the first 28 and 42 min for groups I and II, respectively, after which time this temperature rose and stabilized. In group I, the Tre-st reached the homeothermal stage at 2 h 49 min, while 4 h 27 min were required for group II. In group I, the footsole temperature (Tsf) reached a plateau after 2 h 10 min. In group II, Tsf showed a large decrease followed by a slow rise, with no stability achieved during the 8-hour observation period. Intergroup comparisons revealed that the mean Tsf reached conditions not significantly different from those of group I at 6 h 57 min.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Estimation of the dynamic fracture process of rock material utilizing high speed photography

The experimental study is conducted to estimate fracture process of the cylindrical rock specimen. In this experiment, an explosive is used as the explosion source, and a pipe filled with water is arranged between the explosive and the cylindrical rock specimen. The main purpose of this fracture test is to collect the experimental data on the behaviors of the dynamic fracture of the rock. In addition, one of the aims of this test is to estimate the dynamic tensile strength of the rock in wide range of strain rate utilizing Hopkinsons effect. Therefore, during the fracture process of the rock, the free surface velocity and the fracture part near the free surface were observed by a laser vibration meter and high speed camera. The precise detonator was used to control the initiation time of the explosive by using an accuratley controlled blasting machine. The results of the fracture test for Kimachi sandstone and the validity of this test are discussed. In order to understand the relationship above fracture condition and the incident underwater shock wave into the rock specimen, the numerical simulation is carried out. The 2D hydrodynamic code based on ALE finite difference scheme is employed. In the case of the fracture test with 50 mm water pipe, the incident underwater shock wave into the cylindrical rock specimen has irregular pressure distribution near the shock front.

Optimal Thermal Control with Sufficient Nutrition May Reduce the Incidence of Neonatal Jaundice by Preventing Body-Weight Loss Among Non-Low Birth Weight Infants Not Admitted to Neonatal Intensive Care Unit

Background: Neonatal jaundice is strongly attributable to excess body-weight loss as a result of insufficient calorific intake. Objectives: To examine the incidence of neonatal jaundice (defined by use of phototherapy) and body-weight loss, as well as their association, among neonates under optimal thermal control with sufficient nutrition, a local protocol for temperature and nutritional regulation. Methods: We retrospectively identified a cohort of 10,544 neonates (birth weight ≥2,500 g) placed in thermo-controlled incubators for 2 h immediately after birth. Neonates were fed with 5% glucose solution 1 h after birth and breastfed every 3 h (with supplementary formula milk if applicable) according to basal maintenance expenditure. Total serum bilirubin levels at day 4 (peak level) were assessed. Phototherapy was performed on the basis of total serum bilirubin level ≥18 mg/dL. Risk ratio (RR) and 95% CI for the use of phototherapy against maximum body-weight loss were estimated using Poisson regression with robust variance. Results: Incidence of phototherapy use was low (0.3%) and the mean total serum bilirubin level was 8.5 mg/dL (SD 2.7 mg/dL), with a low mean maximum body-weight loss (1.9%) and low incidence of excess body-weight loss ≥7% (0.4%). Maximum body-weight loss was associated with risk of neonatal jaundice (RR 1.27; 95% CI 1.04–1.54), and became significant at approximately 4% of maximum body-weight loss. Conclusion: Optimal thermal control and sufficient nutrition may greatly reduce the incidence of neonatal jaundice by preventing neonatal body-weight loss.

Pulse Laser Ignition of Preheated PETN

Nd:YAG pulse laser was used to ignite powdered and preheated PETN. To enhance efficiency of laser absorption by PETN, it was mixed with a small amount of carbon black powder. In this study, we will propose two‐pulse laser ignition method, the first pulse is a long pulse to heat up PETN up to melting point, then second laser to ignite the heated PETN. By adopting this procedure, second short pulse laser energy can be reduced to ensure that the energy can be transferred by relatively slender plastic optical fiber. To simulate the slow laser heating process by long pulse laser, high‐power cw YAG laser up to 30W was used. While two ns‐YAG laser of about 200 mJ/pulse with 4 ns and 12 ns were used for ignition. Higher peak power with donut‐like profile laser beam of 4 ns duration gives damage to fibers, while lower peak power with relatively flat profile laser beam of 12 ns duration can safely pass through optical fiber of 1 mm diameter. We performed a series of melting experiments of PETN under normal optical ...

Numerical Simulation on Laser Initiation of Thin Explosive

The processes of the laser initiation of pentaerythritol tetranitrate (PETN: density 1.0g/cc) are calculated using one‐dimensional hydrodynamic code to study the effects of the initiation methods on the initiation process. The simplified assumptions for the initial condition are used to model the three types of the initiation method, utilizing direct absorption of laser energy, impact of the laser driven‐flyer plate and ablation of the metal film. The governing equations are Lagrangian conservation equations and are solved by a finite difference method. The reaction rate law is used the ignition and growth model.

Optical measurements of flyer plate acceleration by emulsion explosive

This paper presents the study on the application of explosive welding technique to the field of the urgent repair of the gas and water pipe networks. The essential parameters related to the explosive welding are scrutinized from the point of view of the minimizing the damage to the steel pipe after welded explosively with a flyer plate. The emulsion explosive is contained in a rectangular hard-paper box whose bottom is the flyer plate with 100 mm length, 25 mm width and 1.5 mm thickness. The flyer motions of the flyer plates accelerated by emulsion explosive are observed by high-speed photography from the side and front view of the flyer plate. The damage to the pipe by the flyer plate is discussed with the results of the observation of flyer motion and explosive welding test under various experimental conditions. Moreover, one way to control the motion of the flyer plate is proposed. We put a PMMA buffer block into the explosive. The flying process of flyer plate is calculated by the finite different scheme based on the ALE method. The effectiveness of this method is demonstrated by the experimental and numerical studies.