The effect of the impact velocity and shape of the head of a rigid shell of caliber 20 mm on the depth of its penetration into a thick obstacle made of mild low-carbon steel for impact velocities of up to 600 m/sec is studied experimentally. Experimental relations between the penetration depth and the impact velocity are obtained for shells with conical and semispherical heads. It is found that for a penetration depth equal to 1 or 2 calibers, the penetration resistance does not depend on the head shape and is characterized by an average stress equal to 2.98 GPa.The impact and penetration of shells into various obstacles are extensively studied by experimental and numerical methods [1]. However, in view of the great diversity of situations, some particular questions require further investigation or refinement. The goal of this paper is to study the effect of the impact velocity and head shape of a rigid shell of caliber 20 mm on the penetration into a thick steel obstacle for relatively low velocities (up to 600 m/sec).The obstacles examined were massive disks of diameter 160 mm and thickness 70 mm made from low-carbon steel St. 3 in the supply state. A square grid with a 5-mm step was scribed on the front surface of the obstacles by rolling. The control determination of the standard mechanical properties gave the following average values: yield point a0,2 --203 MPa, ultimate strength atemp = 458 MPa, and elongation at rupture 55 ----24.5 %. The average value of the Brinell hardness HB was found to be 1.26 GPa.The obstacles were loaded by the impact of shells with conical (90 ~ opening of the cone) and semispherical head shapes. The shells of length 80 mm and diameter 20 mm (r = 10 mm) were made of ShKh15 steel and had Rockwell hardness HRc ----60-64 kg/mm 2. The shells were accelerated by a powder gun of the corresponding caliber. Variable-induction pickups (chronographs) were used to determine the velocities of the shells.No distortion of the shells was observed in the tests. Figure 1 shows photographs of the shells with semispherical and conical heads after impacts at velocities of 425 m/sec (Fig. 1, at the left) and 410 m/sec (Fig. 1, at the right). The surface fragments of two obstacles with the formed craters are shown in Fig. 2. Figure 2a refers to the impact from a shell with a conical head (v --410 m/sec) and Fig. 2b to that with a semispherical head (v -= 425 m/sec). The experiments show that, for almost equal impact velocities, a greater part of the material is involved in the formation of the bead in the case of the conically headed shell. Its edge diameter and height are greater than those for the semispherically headed shell. Radial cracks appear around the crater. Cracking is more significant the higher the impact velocity, and this process is more pronounced for the semispherical head. Deformation of the obstacle front surface, which is determined by the distortion of the measuring grid, is noticeable at a distance of one caliber from the bead edge. One can observe traces of the measuring grid at ...

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