Research On Dynamic Deformation In Porcess Of Jet Formation And Penetration

It's very important to have research on jet formation and penetration because it involves the problem of superplastic deformation of metal. The analysis of jet microstructure has always been the weak point of jet research, and it's a very important way to reveal the dynamic superplastic fluid of jet. Two experiments were designed to recover jet and slug respectively. Combining with theory analysis and numerical simulation, we can know how stress wave and dynamic superplastic deformation influence macroscopic mechanical properties and microstructure of metal in the process of penetration. The change of temperature and grain size caused by superplastic deformation in jet formation can be gotten.Firstly, sand was used to recover slug in order to analyze its microstructure. Then with result of temperature rise caused by stress wave and strain in the collapse process of shaped charge, the conclusion that shaped charge can have superplastic deformation before jet forming can be achieved.Secondly, in order to resolve the problem of steel target hardening caused by jet, numerical simulation was used to gain the pressure of stress wave which is propagate in target in the process of penetration. Base on it, stress of target influence by two types of stress wave--shock wave and quasi-isentropic wave can be calculated, and compared with hardness tested by experiment, we know the target is harden by quasi-isentropic waveinstead of shock wave.Thirdly. SEM was used to observe steel target penetrated by jet. The results show that the width of area next to perforation which has equiaxed ferrite grain(typical characteristic of dynamic recrystallization) is about 0.2mm, the target next to it has normal deformation. The test of microhardness of target also proves the observation. Accroding to the measured width of ferrite, strains of different locations of target can be calculated, and then the target can be divided into superplastic deformation zone, large deformation zone, small deformation zone and original zone.Finally, an experiment was designed to recover jet in this paper. Jet with low speed can be produced by spherical segment Liner, and it's speed can be reduced fast when it penetrates steel target, then it can adhere on penetration channel wall. Because the following cooling process is very fast(<0.7s), the microstructure of jet layer adhering to perforation has the characteristics of dynamic superplastic deformation. SEM images show that equiaxed grains in jet layer are of the same size, and some twins are observed in the microstructure of jet layer. The change of macroscopic mechanical properties (hardness) and microstructure evolution (grain size) caused by superplastic deformation, and it lays the foundation to further research on mechanism of superplastic deformation.