3. 2. EFFECT OF ATTACK ANGLE

Figure 11 shows a cross sectional view of the penetrator which came to rest in the sand box for three cases of different attack angle, . Considering that the penetrator mass, nose shape, and impact velocity are about the same among the three experimental runs, this figure clearly shows the influence of attack angle on penetration characteristics. In cases of the normal impact with zero attack angle, the body axis of penetrator model which came to rest coincides nearly with the impact direction within 1 5^° . But Figure 11 indicates that the existence of only a few degrees attack angle results in the deflection of penetration trajectory and in the large inclined stop angle from the normal. Also, it can be seen that the depth of emplacement becomes shallower with increasing in the attack angle.

As illustrated in Figure 11 , the penetration path-length is also affected by the attack angle. Figures 12a to 12d show how the penetration path length changes with the attack angle. The results in cases that the projectiles impacted at the velocities of 100 to 120 m/s are presented in Figures 12a and 12 b, while the data at the velocities of 140 m/s to 160 m/s are presented in Figures 12c and 12d. For the projectiles of all types, the penetration path length decreases as the attack angle increases. However, even if a projectile impacts at non-zero attack angle, the ogive-nose penetrators penetrate deeper than the cone-nose penetrators under the same velocity range.

The variation of the inflection angle with attack angle is shown in Figures 13a and 13b, including the results of normal impacts with zero attack angle. As expected, an increase in attack angle enhances the deflection from the impact direction. There is a linear correlation between the attack angle and the inflection angle for all models. The slope for each of penetrator's nose shapes by the least square fitting from experimental data is as follows;

The inflection angle for STD = 0.3 is the smallest of all. This indicates that the truncation of the nose tip is efficient to stabilize the penetration orientation. But the degree of the differences observed in the relationship between the inflection angle and the impact velocity for various nose-shapes is not very significant. Considering the behavior shown in Figures 12a and 12b, i. e., deeper penetration for an ogive nose than that of the cone-shape nose, the penetrator with the ogive nose may be preferred to the penetrator with the cone-shape nose.