Investigation On Mechanical Sensitivity And Shock Initiation Characteristics Of Typical Fireworks And Crackers

Ignition happened under mechanical impact and friction is one of the important reasons that lead to accidental explosion of fireworks and crackers, and shock wave generated from the explosion is one of the main reasons for inducing sympathetic detonation and accident spread of the fireworks and crackers. The possibility of the explosion of the fireworks and crackers caused by impact and friction are called impact sensitivity and friction sensitivity, and the explosion of the fireworks and crackers induced by shock wave is called shock initiation. Therefore, it is important for safety investigate the initiation and sensitivity of fireworks and crackers. In this dissertation, impact sensitivity, friction sensitivity and shock initiation characteristics of typical fireworks and crackers and the main composition of smokeless firework propellants-expired single-base propellant was studied in terms of the theoretical, experimental, and numerical methods. The results will provide references for safe application of fireworks and crackers.The dynamic friction coefficient is a key parameter for determining the energy of fireworks and crackers obtained through friction, and the obtained energy is the basis for further researching of friction sensitivity. On the basis of the obtained energy, the relative strength of different experimental conditions in friction sensitivity tests was compared. A new method for determining the dynamic friction coefficient and the obtained energy was presented. The method combines the physical model of friction sensitivity device with theoretical analysis and numerical calculations. The dynamic friction coefficient of six fireworks and crackers and the obtained energy of three fireworks and crackers under different experimental conditions were measured with this method. The effects of different experiment conditions on obtained energy were discussed. The results show that the dynamic friction coefficients of six fireworks and crackers are range values. In the common test conditions, the obtained energy and its increasing rate follow the sequence:70°,1.23MPa<66°,2.45MPa<80°,2.5MPa<90°,3.92MPa<96°,4.9MPa. Meanwhile, it is found that the obtained energy of the fireworks and crackers increases with the increase of pressure and sliding velocity. Similarly, with the increase of the specific heat, the obtained energy increases, while the increase of the heat conductivity coefficient of steel causes the decrease of the obtained energy.The hazardous law of fireworks and crackers under impact and friction is very important and fundamental in safety studies. Systematic experimental researches of impact sensitivity and friction sensitivity were carried out for typical fireworks and crackers. The typical fireworks and crackers are mixtures of oxidant and combustible agent. On the basis of experimental research, dangerous compatibility principle of typical fireworks and crackers was established. It is found that the sensitivity of fireworks and crackers containing expired single-base prope Hants are at a high level. The impact sensitivity of the same oxidant and different combustible agents basically has the following sequence:expired single-base propellants> sulphur> carbon powder> aluminium powder>.magnesium alloy powder, and the friction sensitivity meets the following relation:expired single-base propellants> magnesium alloy powder> aluminium powder> sulphur> carbon powder. Meanwhile it is found during the experiment that the main characteristics of nonmetal combustible agents were blast marks, smoke and smell, while the sound and flare of metal combustible agents were very large.The shock initiation of expired single-base propellant is an important aspect in evaluating and analysing the safety problem of smokeless firework propellants. In order to investigate its shock initiation characteristics, the continuous detonation velocity test, shock wave sensitivity test and critical initiation pressure test were developed respectively with reference to GJB772A-97card gap test. The detonation formation process was studied, and the critical gap value and critical initiation pressure were obtained based on the tests. According to the experimental results, the parameters of reaction rate of ignition growth model for expired single-base propellant were preliminarily calibrated. Then the AUTODYN numerical simulation software was adopted to study the critical initiation characteristics of expired single-base propellant under shock wave. The building up process of reactive shock wave was observed at the PMMA50mm thick and it developed into a normal detonation at90mm. The critical gap value and critical initiation pressure are about50-52mm and1.35-1.49GPa respectively in term of the results of shock wave sensitivity test and critical initiation pressure test. The numerical simulation results show that the gap materials have a pronounced effect on critical gap thickness. With the increase of the thickness of confining wall, the critical gap thickness increases gradually. Among the three initiation modes, the critical gap thickness and energy influence under surface initiation are the largest ones.