Kunihisa Katsuyama

Experimental study on the channel effect in emulsion explosives

Abstract The precursor air shock wave (PAS), which propagates ahead of the detonation front in an air channel, precompresses and desensitizes the unreacted explosive charges. Under some conditions, the PAS causes detonation failure. This phenomenon is known as the channel effect. To investigate the mechanism of the channel effect in emulsion explosives, some experimental work has been carried out using a high-speed framing camera. The results of photographic observation demonstrated that the difference between PAS velocity and detonation velocity was the primary factor for the channel effect. It is assumed that a decrease in the PAS velocity can prevent the channel effect. The ability of increased surface roughness of the inner wall to decrease the PAS velocity was tested. Some experiments were conducted to investigate the effects of surface roughness on the PAS velocity and the detonation propagation. The experimental results indicate that increased surface roughness can reduce the PAS velocity and prevent detonation failure.

Photographic measurement of the detonation velocity of explosives by high-speed camera and its comparison with other methods

It is important to measure the detonation velocity of the explosives for considering the detonation performance of explosives. In this paper the Dautriche test method and the resistance wire method were carried out to measure the detonation velocity of explosives and observed these measuring method by high-speed camera at the same time. The results by two measuring methods were compared with each other. In the Dautriche test method the propagation and the collision of detonation of detonating fuse on the lead plate can be observed with high-speed camera. In the resistance wire method the detonation velocity of explosives was measured continuously. But there was delay time caused by the short circuit between the resistance wire and the stainless tube. The delay time was compared with the observation results of high-speed camera. It took a few microsecond(s) to generate the short circuit between the stainless tube and the resistance wire. The sample explosives which were measures with three kinds of methods was same kind of emulsion slurry explosives. The detonation velocity indicated same value on all kinds of methods.

Laboratory study on channel effect in emulsion explosives

Abstract The precursor air shock wave (PAS), which propagates ahead of the detonation front in an air channel, precompresses and desensitizes the unreacted explosive charges. Under some conditions, the PAS causes detonation failure. This phenomenon is known as the channel effect. To investigate the mechanism of this effect in emulsion explosives, some experimental works have been carried out using a high-speed framing camera. The results of photographic observation demonstrated that the difference between PAS velocity and detonation velocity was the dominate factor for the channel effect. It is assumed that a decrease in the PAS velocity can prevent the channel effect.

Photographic study of channel effect in emulsion explosives using a high-speed framing camera

The precursor air shock wave (PAS), which is propagating ahead of the detonation front in air channel, precompresses and desensitizes the unreacted explosive charges. In some conditions, the PAS causes detonation failure. This phenomenon is known as the channel effect. To investigate the mechanism of the channel effect in emulsion explosives, some experimental works have been carried out using high-speed framing camera. The results of photographic observation at the first experiments demonstrated that the difference between PAS velocity and detonation velocity was the primary factor for the channel effect. It is assumed that the decrease of the PAS velocity can prevent the channel effect. The increase of surface roughness of inner wall was adopted to decrease the PAS velocity. Some experiments were conducted to investigate the effects of surface roughness on the PAS velocity and the detonation propagation. Photographic observations were performed using rectangular tubes with sandpaper on inner ceiling wall to simulate surface roughness under various conditions. The experimental results indicate that the increase of surface roughness reduces the PAS velocity and prevents detonation failure. It is concluded that the surface roughness of wall has a great influence on detonation propagation in emulsion explosive.

Observation of the dynamic movement of fragmentations by high-speed camera and high-speed video

The experiments of blastings using mortal concrete blocks and model concrete columns were carried out in order to obtain technical information on fragmentation caused by the blasting demolition. The dimensions of mortal concrete blocks were 1,000 X 1,000 X 1,000 mm. Six kinds of experimental blastings were carried out using mortal concrete blocks. In these experiments precision detonators and No. 6 electric detonators with 10 cm detonating fuse were used and discussed the control of fragmentation. As the results of experiment it was clear that the flying distance of fragmentation can be controlled using a precise blasting system. The reinforced concrete model columns for typical apartment houses in Japan were applied to the experiments. The dimension of concrete test column was 800 X 800 X 2400 mm and buried 400 mm in the ground. The specified design strength of the concrete was 210 kgf/cm2. These columns were exploded by the blasting with internal loading of dynamite. The fragmentation were observed by two kinds of high speed camera with 500 and 2000 FPS and a high speed video with 400 FPS. As one of the results in the experiments, the velocity of fragmentation, blasted 330 g of explosive with the minimum resisting length of 0.32 m, was measured as much as about 40 m/s.

High-speed photography of dynamic photoelastic experiment with a highly accurate blasting machine

A high accurate blasting machine which could control 1 microsecond(s) was developed. At first, explosion of a bridge wire in an electric detonator was observed and next the detonations of caps were observed with a high speed camera. It is well known that a compressed stress wave reflects at the free face, it propagates to the backward as a tensile stress wave, and cracks grow when the tensile stress becomes the dynamic tensile strength. The behavior of these cracks has been discussed through the observation of the dynamic photoelastic high speed photography and the three dimensional dynamic stress analysis.