Sensitivity analysis and structural modification techniques are used to investigate the structural modifications of a machine gun tripod which suffers from severe vibration during firing due to the resonance. The fini...
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Sensitivity analysis and structural modification techniques are used to investigate the structural modifications of a machine gun tripod which suffers from severe vibration during firing due to the resonance. The finite element analysis and modal test techniques are used to determine the natural frequencies of the machine gun. The sensitivities of natural frequencies with respect to the structural parameters of the tripod are obtained by the method of sensitivity analysis, and they can be used as an indication for the structural modification of the tripod so as to shift the natural frequencies effectively. By the structural modification techniques, finally, the optimal structural modifications of the tripod for desired natural frequencies are made to avoid the resonance, and this optimal structural modification is verified by re-analysis of the modified structure and the vibration contrast between original structure and modified structure. The research resulted in a successful structural modification for desired natural frequencies, which can avoid the resonance and thereby greatly improve the shooting precision of the machine gun during firing.
The deformation and failure of pressed polymer bonded explosives under different types of loads including tension, compression and low velocity impact are presented. Brazilian test is used to study the tensile propert...
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The deformation and failure of pressed polymer bonded explosives under different types of loads including tension, compression and low velocity impact are presented. Brazilian test is used to study the tensile properties. The microstructure of polymer bonded explosives and its evolution are studied by use of scanning electronic microscopy and polarized light microscopy. Polishing techniques have been developed to prepare samples for microscopic examination. The failure mechanisms of polymer bonded explosives under different loads are analyzed. The results show that interfacial debonding is the predominant failure mode in quasi-static tension, while extensive crystal fractures are induced in compression. With the increase of strain rate, more crystal fractures occur. Low velocity impact also induces extensive crystal fractures.
The damage properties of polymer bonded explosives under dynamic loading were studied by using ultrasonic evaluation. Explosive samples were damaged by a low-velocity gas gun at different impact velocities. Ultrasonic...
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The damage properties of polymer bonded explosives under dynamic loading were studied by using ultrasonic evaluation. Explosive samples were damaged by a low-velocity gas gun at different impact velocities. Ultrasonic examination was carried out with a pulse through-transmission method. Spectra analyses were carried out by using fast Fourier transform. Characteristic ultrasonic parameters, including ultrasonic velocities, attenuation coefficients, spectra area and master frequency, were obtained. The correlation between the impact damage and ultrasonic parameters was analyzed. A damage coefficient D was defined by considering a combination of ultrasonic velocity and amplitude. The results show that ultrasonic parameters can be used to quantitatively assess the damage extent in impacted plastic bonded explosives..
The dispersion of the fuel due to the center high explosive, including several different physical stages, is analyzed by means of experimental results observed with a high speed motion analysis system, and the effect ...
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The dispersion of the fuel due to the center high explosive, including several different physical stages, is analyzed by means of experimental results observed with a high speed motion analysis system, and the effect of center high explosive charge is suggested. The process of the fuel dispersion process can be divided into three main stages, acceleration, deceleration and turbulence. Within a certain scope, the radius of the final fuel cloud dispersed is independent of the center explosive charge mass in an FAE (fuel air explosive) device, while only dependent both on the duration of acceleration stage and on that of the deceleration. In these two stages, the dispersion of the fuel dust mainly occurs along the radial direction. There is a close relation between the fuel dispersion process and the center explosive charge mass. To describe the motion of fuel for different stages of dispersion, different mechanical models should be applied.
An experimental study on acceleration mechanism of flame propagation of propane-air mixture in ducts with obstacles was conducted. The acceleration mechanism of flame propagation is mainly due to the positive feedback...
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An experimental study on acceleration mechanism of flame propagation of propane-air mixture in ducts with obstacles was conducted. The acceleration mechanism of flame propagation is mainly due to the positive feedback of the turbulence region induced by obstacles for combustion process. It can be seen from the experimental results that the maximum explosion pressure can increase by 20%, the maximum rate of pressure rise can increase by 10 times and the flame propagation velocity can increase by 20 times when obstacles are present.
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