Papers by Author: Yuji Ogata

Abstract: 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.

Abstract: The crater on the reinforced concrete wall generated by the explosion of a few grams of Composition C4 explosive was investigated. A series of the single-shot blast experiment were conducted. The structural specimens for the reinforced concrete wall (750 mm × 750 mm × 250 mm) were used for estimation of the crater size. The diameter of the borehole was fixed 16 mm, and the length of borehole was varied to generate the various size of crater. The amount of explosive was also varied from 3.0 to 8.0 g. The effect of the length of the borehole to the crater depth was examined. High-speed photography was used to observe the fracture process of the crater. As the results, in the difference of the side where the crater was generated, the situation of crushing was different. The strain measurements were also conducted.

Abstract: The relationship between the initial temperature dependence of the detonation velocity and the initial density is examined using a proposed unified form of the EOS for pentaerythritol tetranitrate (PETN). First, the derivatives of the variables at Chapman-Jouguet (C-J) points are calculated. These derivatives are used to investigate the initial state dependence of the detonation velocity using the relationship between the detonation velocity and the initial state variables. As a result, the contributions of the coefficient of thermal expansion and the increment of the initial internal energy to the detonation velocity are clarified. We found that the initial temperature derivative of the detonation velocity can be estimated from the initial density derivative of the detonation velocity.

Abstract: The crack on the reinforced concrete wall generated by the explosion of several grams of Composition C4 explosive was investigated. A series of the single-shot blast experiment were conducted. The structural specimens for the reinforced concrete wall () were used for estimation of the crater size. The diameter of the borehole was fixed 16 mm, and the depth was varied to generate the various size of crater. The amount of explosive was also varied from 2.0 to 3.5 g. The effect of the depth of the borehole to the crater depth was examined, and the optimum charge condition for making the large crater at borehole side was clarified. For the case in which the fragmentation at the back side was allowed, the optimum charge condition was also found. High-speed photography was used to observe the growth process of the surface cracks. As the results, it was predicted that the crater was generated at 2 ms after explosion at least. The strain measurements were also conducted.

Abstract: 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

Abstract: In order to investigate the hazard of the fragments caused by the explosion damage, the simply-simulated explosion experiment and numerical simulation were conducted. In this study, the behavior of the disk supposing the fragment driven by an explosive was investigated. In the experiment, the optical observation using a high-speed camera was performed to obtain the basic data about a disk, such as flying velocity. Moreover, numerical simulation was performed using analysis software LS-DYNA. Comparison and examination for experimental results and numerical results were reported.

Abstract: The development study of blast containment vessels for anti-terrorism has been conducted. The goal of this study is to develop safe disposal vessel for 10 kg of explosives. Considering of the use at the airport or railroad stations, it needs to be more compact compared with the conventional explosion chamber. By introducing both the internal structure and attenuation technology in the vessel, sufficient blast proof ability to contain internal explosion is realized. The blast containment vessel can be used repeatedly by exchanging the internal structure. To realize these concepts, model experiments were carried out using high speed photography, strain and pressure measurements. By introducing these technologies, the vessel for the 1 kg of explosive materials has been made, and the experiments employing 1 kg C4 explosive have been conducted. Finally, the compact blast containment vessel for 10 kg explosives was made, and its blast proof ability was shown by the internal blast test.

Abstract: To obtain a better understanding of detonation properties of ammonium nitrate (AN) and activated carbon (AC) mixtures, steel tube test was carried out for stoichiometric composition of powdered AN and AC mixtures and the detonation velocity and the pressure profile were measured. Based on the results obtained the relation between the detonation velocity and the peak pressure was discussed with the theoretically predicted values which were obtained by the thermohydrodynamic CHEETAH code with the BKWC equation of state. The measured detonation velocity and peak pressure were far below the theoretically predicted values and the non-ideal detonation behaviour was confirmed.

Abstract: To obtain a better understanding of detonation properties of ammonium nitrate (AN) and activated carbon (AC) mixtures, steel tube test with several diameters was carried out for various compositions of powdered AN and AC mixtures and the influence of the charge diameter on the detonation velocity was investigated. The results of test indicated that the detonation velocity increased with the increase of the charge diameter. The experimentally observed values were far below the theoretically predicted values made by the thermohydrodynamic CHEETAH code and they showed so-called non-ideal detonation. The extrapolated detonation velocity of stoichiometric composition to the infinite diameter showed a good agreement with the theoretical value.

Abstract: 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.