条形装药土中爆炸冲击波及空腔的数值模拟

NUMERICAL SIMULATION OF THE SHOCK WAVE AND CAVITY OF A STRIP-SHAPED EXPLOSIVE CHARGE EXPLODING IN SOIL

本文用拉格朗日坐标有限差分法对条形装药土中爆炸的冲击波和空腔参数进行了一维轴对称数值模拟。计算中取爆破介质为弹-理想塑性体。计算得到的冲击波,爆炸空腔的参数与X光摄影数据的比较,结果表明计算与实测结果基本一致。

Recently, cylindrical charges have been widely used as a kind of special charge structures in engineering and military blasting and attention has been paid to its further theoretical studies. This paper studies the parameters of the explosion cavity :n soil and its generated shock waves by using the finite difference method and the elastic-perfect-plas-tic model proposed by P.Chetuvik et al; An artificial viscosity is used to smooth discontinuities in calculation. Comparing the results of calculation with those obtained by the X ray photographic experiment, good agreement is obtained.A. Hypothesis and preliminary conditions:1. Cylindrical charge explosion in soil is considered as a transient detonation.2. The powdered RDX explosive is used with a diameter of 5.6 103 m. length/diameter 21 .8. and charge density 1. 0× 103kg/m4. The ordinary black and yellow top-surface clay arc used as the media, its cohesive coefficient is 2. 45×104Pa, angle of internal friction 23°28'. density 1.8×103kg/m3 and water content 15-16%.3. The media densities are regarded as functions of the Lagrangian coordinates, independent upon the time.B. Explosion model and constitutional relations:1. Effects of detonation products under high temperature and pressure in the media are described with the elastic-perfect-plastic model as in Fig.l.When the medium is under high pressure, the loading stress is far beyond its elastic limit in to a plastic state. So a reasonable function is selected to describe the plastic flow. In addition, the elastic precursor is considered simultaneousely.2. Constitutional relationsThe Mohr-coulomb friction failure relation:|τ|=C-σtgφwhere τ= maximum shear stress,σ= normal stress at tangential plane. φ=angle of internal friction. C=cohesion. is used to describe the yielding properties of the soil. Therefore, the yielding relation isf=|τ|-C+σtgφC. Results and conclusions:1.The particle velocity decreases exponentially with the increase of distance.2.The shock wave form passing fixed-point and the spatial distributions of the shock wave at various times all reflect the propagation characteristics of the shock wave. Besides, the decay behavior of the peak pressure is in accord with that of the experiment.3.The final dimension of the explosion cavity depends on the soil strength. When the cavity pressure is less than the soil strength, the expansion of the cavity stops immediately.4. The shock wave parameters and explosion cavity generated by the cylindrical charge explosion can be calculated rather correctly for some soils using the elastic-perfect-plastic model, but some factors, for example, free surface, charge shape, and the distribution of the charge weight and so on, are not considerd. There are some differences among the results of calculation and those obtained by the experiments.