Tei Saburi

Observation of Shock Initiation Process in Gap Test

We have conducted the experiments for shock sensitivity of high energetic materials by gap test. The set up of gap test have been improved to observe the shock initiation phenomena in acceptor charge by high‐speed video. The length of gap material was varied to observe the reaction process under various situations. The luminescence at the surface of acceptor holder was used Go/Nogo decision. The distance from the gap end to the luminescence area increases with increasing in gap length. In the critical gap length in which the sympathetic detonation does not occur, the remarkable decomposition of acceptor charge was observed as gas expansion.

Numerical simulation of detonation propagation in PETN at arbitrary intitial density by simple model

Since the characteristic values of detonation such as the detonation velocity and pressure are dependent on the initial density of high explosive, the parameters of the equation of state (EOS) for detonation products or unreacted explosive are also dependent to the initial density. In general, the parameter set for each initial density has to be obtained to compute detonation phenomena. For simulation of arbitrary initial densities cases, we try to construct a new simulation procedure that only employs the information of theoretical maximum density (TMD). The well known linear relationship between detonation velocity and initial density for high explosive has been employed for this study. Two types of simulation were carried out. The Gruneisen parameter as function of specific volume was calculated by solving the ordinary differential equation, and was employed as unified form EOS to simulate detonation phenomena. To obtain the information of the EOS for arbitrary initial density, the simulation of anothe...

Pressure Measurement of Non-Ideal Detonation in Ammonium Nitrate Based High Energetic Material

In order to know accurate information on the non-ideal detonation pressure, steel tube test was carried out on ammonium nitrate (AN) and activated carbon (AC) mixtures. In this test, detonation velocity and pressure were measured simultaneously by varying thickness of PMMA placed between AN/AC and pressure gauge. The length and the diameter of the steel tube were 350 mm and 35.5 mm. The results showed that shock pressure attenuation in PMMA was not observed for this experimental condition (PMMA gap; 3-5 mm). The averaged measured peak pressure and detonation velocity were 3.4 GPa and 3.2 km/s.

Detonation Velocity Measurement and Numerical Simulation for the System Consisting of Pellet Explosives and Air Gaps

The purpose of this study is to reconstruct the equation of state (EOS) whose parameters can be applied for high energetic material of arbitrary initial density without any modification. The simulation for detonation propagation in arbitrary initial density was proposed as the new method for obtaining the information of the EOS for detonation products of arbitrary initial density. At the same time, to collect the experimental data which verify the applicability of the numerical simulation, the detonation velocity for the system consisting of the pellet explosives and air gaps were conducted. The thickness of the 20 mm diameter pellet explosive was 10 mm, and air gaps were varied 0.5 mm to 2.0 mm. The relationship between detonation velocity and experimental condition was clarified for composition A5. The proposed one dimensional simulation was also conducted. The relationships between the pressure and the specific volume for detonation products were extracted from the proposed simulation

Design and Experiment of Compact Projectile Accelerator Driven by Explosives

This paper presents the design of a compact size projectile accelerator, and its application. To meet the various needs such as a compact body size to use under various experimental conditions, an easy maintenance for repetitive experiments during a certain period, and a capability of the velocity control, the compact accelerators were newly designed with a direct explosive drive method. Two different types of accelerator were designed: a PMMA accelerator and a metal accelerator. The pictures of the projectile shoot using the designed accelerators were recorded by SHIMADZU HyperVision HPV-1 high-speed video camera. As a result, it was recognized that the PMMA accelerator was failed to accelerate the projectile, while the metal accelerator succeeded to accelerate it effectively. The accelerating performance of the metal accelerator was further investigated. The explosives for projectile acceleration were Emulsion explosive and Composition C4 explosive weighing 5 to 35g. It was found that the metal accelerator has the capability to control the projectile velocity adjusting the weight of the explosives, and there is an approximate linear correlation between them in our experimental range. A series of impact tests on 5052S aluminum alloy targets was examined using the accelerator.

Behaviors of High Explosive near the Critical Conditions for Shock Initiation of Detonation

The behaviors of the high explosive near the critical conditions for shock initiation of detonation are investigated by high speed photography and pressure measurements in gap tests. The sample is RDX base explosive, and the inner diameter of donor and acceptor charges is 26 mm. Gap material is PMMA. Near the critical condition, the results under the following conditions have been discussed. 1) Shock to detonation transition (SDT) take place in acceptor, 2) The SDT does not occur, but the reaction wave affects the leading shock front in acceptor, and 3) The gap length in which the effect of the reaction wave to shock front almost disappears. These results are very useful to construct the initiation model for solid explosive.

Dynamic Response Analysis of Mortar Block under Blast Loading Using Digital Image Correlation

The dynamic strain distribution behavior of a mortar block blasting was experimentally investigated. A small-scale blasting experiment using a mortar block with well-defined property was conducted and the dynamic strain distribution on the mortal block surface was analyzed using a Digital Image Correlation (DIC) method to establish the effective method for investigating the relationship between blast design and fracture mechanism. The block was blasted by simultaneous detonation of Composition C4 explosive charges with an electric detonator in two boreholes. The behavior of the block surface was observed by two high-speed cameras for three-dimensional DIC analysis and it was also measured by a strain-gauge for comparison. The three-dimensional displacements of the free surface of the block were obtained and dynamic strain distributions were computed. A point strain profile extracted from the analyzed strain distribution data was compared with a directly observed strain profile by the strain gauge.

Self-ignition and flame development of high-pressure hydrogen flow in a rectangular tube by simultaneous shadowgraph and direct photograph

The flame observed during the sudden release of high-pressure hydrogen into a tube filled with air, in the absence of an igniter, has not yet been investigated. In this study, the self-ignition and flame development behavior of high-pressure hydrogen flow in a tube is investigated to obtain fundamental knowledge for safety engineering. Two high-speed cameras are used simultaneously to obtain density gradient data from the shadowgraph image and flame dynamics from the direct image. Self-ignition occurs at the point near the sidewall in the region where cold hydrogen and preheated air are mixed by the precursor shock wave. After ignition, the flame propagates along the wall surface and spreads throughout the mixing region.

Dynamic strain distribution of FRP plate under blast loading

The dynamic strain distribution of a fiber re-enforced plastic (FRP) plate under blast loading was investigated using a Digital Image Correlation (DIC) image analysis method. The testing FRP plates were mounted in parallel to each other on a steel frame. 50 g of composition C4 explosive was used as a blast loading source and set in the center of the FRP plates. The dynamic behavior of the FRP plate under blast loading were observed by two high-speed video cameras. The set of two high-speed video image sequences were used to analyze the FRP three-dimensional strain distribution by means of DIC method. A point strain profile extracted from the analyzed strain distribution data was compared with a directly observed strain profile using a strain gauge and it was shown that the strain profile under the blast loading by DIC method is quantitatively accurate.

Experiments and numerical simulations of plate gap model for high energetic materials

Experimental and numerical study for detonation propagation was conducted using the system in which the high energy materials and air gaps alternately stacked. The aim of this simulation is an extraction of information of the EOS for detonation product at arbitrary initial density from the numerical simulation with EOS at TMD (theoretical maximum density). In this report, we described the numerical procedure and an example of the calculation result. On the other hand, the experiment was designed for confirmation of the validity of our reactive flow simulation. The experimental system for this study consists of the pellet explosives and PMMA rings, PMMA pipe and booster explosive part. The pellets and the rings were alternately stacked in the PMMA pipe to make the system. The diameter of the pellet was 20 mm and the thicknesses were 10 or 5 mm. The thickness of the ring was varied to adjust the size of the air gaps between the pellets. The sample explosive was a composition A5 (RDX 98.8 wt%). The relationship between the bulk density which was estimated by the thicknesses of the pellets and the air gaps and the average detonation velocity was compared with the data for RDX. The slopes of those relationships differed mutually. Although the experimental results can be used for confirmation of the validity of the numerical procedure, it does not simulate the detonation wave in the powdered explosive. It may show the interesting process that consists of the shock wave in air, shock to detonation transition and steady detonation.