Abstract: Conclusion:

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Dale Hicks
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1 Chian, S.C., Tan, V.B.C. & Sarma, A. (2017). Projectile Penetration into Sand: Relative Density of Sand and Projectile Nose Shape and Mass, International Journal of Impact Engineering, 103, pp Abstract: Compacted granular materials, like sand, have a tendency to dilate and expand under shear loading. Such tendency of dilation is beneficial to inhibit projectile penetration. Furthermore, the higher the striking velocity of a given projectile, the higher is the peak strength of the sand sample. Different nose shapes (spherical, flat, hemispherical, conical and ogival) and mass (7g, 15g and 20g) of projectiles were fired into sand samples of relative densities ranging from medium dense to very dense state (60%, 75% and 90%). Results showed that the pointed ogival head projectile had the lowest ballistic limit, whereas the blunt flat head projectile required the highest ballistic energy to defeat the sand block. Despite visible effect of nose shape, the mass of projectile has a larger influence on the amount of absorbed energy. On the other hand, initial compaction of the sand alters the depth of penetration marginally. This is attributed to the projectile impact which compacts the sand as the projectile penetrates through the sand sample. A strong linear correlation between projectile nose shape, mass and ballistic impact energy was established in this study, which allows protective engineers to easily design sand barriers to defeat a range of projectiles. Furthermore, it was found that the energy absorption of sand remains high even when subjected to striking velocities way beyond its ballistic limit. This opens up avenues for sand barriers to be used as sacrificial layer of a composite lightweight protective barrier. Conclusion: Ballistic tests were conducted on a range of relative densities of sand with different shape and mass of projectiles. The following are the observations: (a) The pointed conical head projectile had the lowest ballistic limit, whereas the blunt flat head projectile required the highest ballistic energy to defeat the sand block. The order of ballistic velocity limit from the lowest to highest values are: 20g conical head, 20 g ogival head, 20g hemispherical, 15g conical head, 15g hemispherical, 20g flat head, 15g flat head and 7g spherical head projectiles. (b) The mass of projectile has a significant influence on the amount of absorbed energy for all nose shapes (flat, conical and spherical/hemispherical heads). The effect is more dominant than the nose shape of the projectile. (c) A strong linear correlation between projectile nose shape, mass and ballistic impact energy was established, which allows quick estimates of the requirements in designing sand barriers to defeat a range of predetermined projectiles at impact energy. (d) The average penetration resistance of the projectiles follows a linear correlation with the square of striking velocity. A heavier mass projectile produces a steeper slope due to the fact that heavier mass projectiles have higher average velocity inside the target. (e) The back-calculated drag coefficients of the projectiles are within the range of conventional values. Although some projectiles have different nose shapes, the extended length of the body could have alter the flow pattern, leading to similar drag coefficients. In addition, drag coefficients do not appear to be influenced by projectile mass. (f) Sand has shown to possess good absorption of impact energy with unique mild reduction in absorption effectiveness over a wide range of velocities. This was proven with various shape and mass of projectiles. Tests with 20g conical head has the lowest threshold energy absorption ratio.

which have yet to be explored thoroughly in modern armour systems. Fig.

2 Given the above findings, it is therefore postulated that armours overlaid by a layer of sand on the exterior may likely produce a superior resisting composite which have yet to be explored thoroughly in modern armour systems. Fig. 1: Nose shapes of projectiles (from left to right: sphere, flat, hemispherical, conical and ogival heads)

3 Fig. 2: Ballistic limits of sand block for different type of projectiles

4 Fig. 3: Striking velocity vs absorbed energy plots for different projectile nose shapes

5 Fig. 4: Striking velocity vs absorbed energy plots for different projectile mass

6 Fig. 5: Relationship of ballistic energy and shape factor of projectile Fig. 6: Drag coefficient of projectiles against numerator of Reynolds number

7 Fig. 7: Ballistic effectiveness based on energy absorption ratio