Study On Pit Formation Of Granite Targets By Heavy Metal Long Rod Projections Under Hypervelocity Impact

From the last century to the present,a large number of national defense fortifications in the world have changed from the surface to the underground.Most of these fortifications are buried deep underground or protected by natural mountains.It is very difficult to use traditional weapons to damage such targets.Therefore,the ultra-high speed ground attack weapons have attracted the attention of weapon design departments.Because of the limitation of experimental cost and technology,the experimental data of hypervelocity impact on the ground medium target is very few,and the characteristics of crater formation and the factors affecting the crater formation under hypervelocity impact are lack of regular knowledge.Therefore,in order to systematically study the problem of hypervelocity impact on the ground medium target,the following work is carried out in this paper:(1)Nonuniformity and discontinuity are the natural defects of natural rocks.In order to ensure that the hypervelocity impact test can form an analyzable law of pit formation and provide reliable parameter support for the numerical simulation later,this paper carries out various material tests on the granite selected in the test according to the national specifications,including sound velocity test,uniaxial compression test,split test and separate type According to the Hopkinson bar test,many mechanical properties of granite are obtained,and the homogeneity and continuity of the sample meet the test requirements;(2)The long rod tungsten alloy projectile with a length to diameter ratio of 10 was used to impact the granite target at an ultra-high speed of 1.5-3.5km/s.The crateringcharacteristics were obtained and compared with the concrete target under the same conditions.It is found that in the range of projectile target combination and velocity,the crater formation of the target body is in the form of "crater + bullet hole";in the range of projectile target combination and velocity,the crater diameter does not increase with the increase of penetration speed,but first increases linearly,and then reaches a platform with the maximum crater diameter;compared with the crater formation characteristics of concrete,the same type of projectile body is found At the same speed,the damage to concrete is higher than granite,that is to say,granite has stronger protective performance than concrete.(3)The nonlinear dynamic analysis software AUTODYN was used to simulate the hypervelocity impact of tungsten alloy long rod on granite.The JH-2 damage constitutive model is coupled with the tensile fracture softening model to simulate the shear and compression failure effects of materials in the high stress area of the granite target and the crack growth and damage in the low stress area of the target under the main tensile stress.In this paper,the Euler method is used to describe the compression failure and the crack formed by shear and tensile fracture by defining the damage.The penetration depth obtained by simulation is in good agreement with the experimental results,and the damage development of the target in the penetration process and the influence of some parameters of the target on the penetration depth are obtained.