performance. Data in the SNL database were obtained from weapon-sized penetrators instrumented to measure axial and lateral penetrator acceleration, strain in the EP case, and the structural response of internal components. Based on these data, Box 3.1 lists and defines physical properties of an EPW and impact conditions that are important in the design of an EPW. Figure 3.1 shows a typical EPW case configuration.

The ogive nose shown in Figure 3.1 is a ballistic shape that is formed by rotating an arc of radius Ro, tangent to the cylindrical body around the centerline of the body. A 6 caliber radius head (CRH) ogive nose is generally used on an EPW that is designed for the penetration of hard material at velocities of less than 900 meters per second. For higher velocities, a 3 CRH (blunter) is recommended in order to maintain penetrator stability. For impact velocities less than 300 meters per second into hard or frozen soil, a 9.25 CRH nose or a length-to-diameter ratio of 2 for cone-shaped-nose penetrators (sharper noses) can be used, since nose tip heating is not a problem at lower velocities. The flare on the rear of the penetrator in Figure 3.1 is important for penetrator stability if the length-to-diameter ratio of the EPW is less than 6.

BOX 3.1
Important Earth-Penetrator Weapon Parameters

Physical Characteristics

  • N: nose shape

  • d: body diameter, m

  • L: total penetrator length, m

  • m: total penetrator weight, kg

  • A: cross-sectional area, m2

  • m/A: cross-sectional density, kg/m2

Impact Conditions

  • V: impact velocity, m/s

  • θ: impact angle between velocity vector (trajectory angle) and target surface

  • α: angle of attack, angle between velocity vector (trajectory angle) and earth-penetration axis

FIGURE 3.1 Typical earth-penetrator weapon case.

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