5. Experimental results

Two types of concrete targets were made for penetration testing, i.e., the frusta of either a pyramid or a cone (Figure 11). The pyramid and cone shapes were intended to save materials in the rear end of the samples. The larger-area side was subjected to the projectile penetration. The frustum of pyramid had dimensions of <sup>12</sup>″ <sup>12</sup>″ in the larger-end side and 13″ in depth, while the cylinders were 6″ and 11″ in diameter and 11″ in height. Both types of concrete targets were cast in 5000 psi and 8000 psi uniaxial compressive strengths. For verification purposes of the gas operated facility the first two shots were on two 2500 psi concrete cylinders (6″ <sup>12</sup>″). Limestone aggregate (#67) was used for the 5000 psi samples while (#78) was used for the 8000 psi samples.

Figure 11. Types of concrete targets used for penetration testing.

Projectiles of three different diameters (12, 20, and 30 mm) were used for penetration into the concrete targets and were launched using the same pressures (1200 psi) to assess their speeds, penetration depths, and target damage.

Figure 12 shows an example of the projectile after impacting the concrete targets, the damaged concrete targets and location of projectiles after the impact. Some target specimens were shattered by the projectile and the penetration of the projectile were not observed. This was primarily due to the size of concrete specimen relative to that of the projectile. However, as projectile size decreases (or concrete specimen size increases), the phenomena of projectile penetrating through concrete target become more likely to occur.

4.2 Normal and shear strength calibration for parallel bond

Figure 9.

Figure 10.

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Projectile model created in DEM.

Compressive Strength of Concrete

compressive strength and microstrength is shown in the Figure 10.

Relation between macro-compressive strength and micro-strength.

Normal strength and shear strength (σ<sup>c</sup> and τc) for parallel bond are the two major micro-parameters contributing to the material's compressive strength. Three typical calibration tests were carried out: varying normal strength, varying shear strength, and varying both with a constant relative ratio. The relationship between

Figure 12. 8000 psi cylinder impacted by 30 mm diameter and 218 g projectile at v = 360 m/s.
