6.3 Test Results
177
6.3.5 Damage of Aluminum Plate
Commonly, a piece of thin metallic plate was set behind the target to qualitatively
evaluate the residual kinetic energy and trajectory of the perforated projectile. For
instance, Bludau et al. (2006) considered that the perforation of 1.5 mm steel sheets
is equivalent to a fatal hit of the human body. In Table 6.2, 6 of 8 perforated bullets
impacted and perforated the aluminum plate.
In the present test, the fight trajectories of the steel core after perforating the
concrete slab were examined. Since the poor visibility of the field testing site,
the legible perforated steel core was not recorded from the high-speed camera.
Figure 6.13a shows the locations of the steel cores impacted on the rear aluminum
plate. It can be seen that, the ballistic trajectory of the steel cores after perforating the
concrete slab were deviated off the center obviously. Additionally, the gestures of the
perforated steel core were rotated obviously, e.g. Shot 1-5 in Fig. 6.13a. Figure 6.13b
shows the high-speed photograph of the bullet steel core after perforating UHP-SFRC
panel, obtained by Sovják et al. (2015). It indicates that, although the trajectory of the
steel core was also deviated to some extent, the gesture of perforated hard core was
maintained well and the steel core still had high penetration ability. Therefore, we
can derive that, adding the high strength basalt aggregates into UHP-SFRC material
can both deviate the ballistic trajectory and the gesture of the perforated core of API
bullet, and correspondingly decrease the penetration efficiency obviously.
Besides, for the present test, under the impact of the small caliber arms, the ejected
concrete fragments did not perforate the metallic plate arranged 0.6 m behind the
concrete panels. However, the ejected coarse aggregates and steel fibers might be
threatening in terms of the human safety. Therefore, attaching the fabric on the rear
face of concrete panels to prevent the majority of ejected fragments is an efficient
approach.
6.4 Discussions
6.4.1 Crater Dimensions
For the frontal impact craters, Wu et al. (2015a) proposed that the frontal crater
depths are reduced with the decreasing of the target thickness. In the present test,
due to the existence of the coarse aggregate with the average size nearly equal to the
diameter of the bullet, the definite influential laws of target thickness and rear fabric
on the frontal cratering dimensions, depth and volume were difficult to be derived.
For the rear impact craters, Fig. 6.14 shows the dimensionless rear crater area
(the ratio of the actual crater area to the cross section area of the hard steel core)
and rear crater volumes of three types targets, respectively. Since the rear craters
of panels with rear CFRP fabric were very slight, some small values are given in
Fig. 6.14b for the convenience of comparison. It can be seen from Fig. 6.14 that,
177
6.3.5 Damage of Aluminum Plate
Commonly, a piece of thin metallic plate was set behind the target to qualitatively
evaluate the residual kinetic energy and trajectory of the perforated projectile. For
instance, Bludau et al. (2006) considered that the perforation of 1.5 mm steel sheets
is equivalent to a fatal hit of the human body. In Table 6.2, 6 of 8 perforated bullets
impacted and perforated the aluminum plate.
In the present test, the fight trajectories of the steel core after perforating the
concrete slab were examined. Since the poor visibility of the field testing site,
the legible perforated steel core was not recorded from the high-speed camera.
Figure 6.13a shows the locations of the steel cores impacted on the rear aluminum
plate. It can be seen that, the ballistic trajectory of the steel cores after perforating the
concrete slab were deviated off the center obviously. Additionally, the gestures of the
perforated steel core were rotated obviously, e.g. Shot 1-5 in Fig. 6.13a. Figure 6.13b
shows the high-speed photograph of the bullet steel core after perforating UHP-SFRC
panel, obtained by Sovják et al. (2015). It indicates that, although the trajectory of the
steel core was also deviated to some extent, the gesture of perforated hard core was
maintained well and the steel core still had high penetration ability. Therefore, we
can derive that, adding the high strength basalt aggregates into UHP-SFRC material
can both deviate the ballistic trajectory and the gesture of the perforated core of API
bullet, and correspondingly decrease the penetration efficiency obviously.
Besides, for the present test, under the impact of the small caliber arms, the ejected
concrete fragments did not perforate the metallic plate arranged 0.6 m behind the
concrete panels. However, the ejected coarse aggregates and steel fibers might be
threatening in terms of the human safety. Therefore, attaching the fabric on the rear
face of concrete panels to prevent the majority of ejected fragments is an efficient
approach.
6.4 Discussions
6.4.1 Crater Dimensions
For the frontal impact craters, Wu et al. (2015a) proposed that the frontal crater
depths are reduced with the decreasing of the target thickness. In the present test,
due to the existence of the coarse aggregate with the average size nearly equal to the
diameter of the bullet, the definite influential laws of target thickness and rear fabric
on the frontal cratering dimensions, depth and volume were difficult to be derived.
For the rear impact craters, Fig. 6.14 shows the dimensionless rear crater area
(the ratio of the actual crater area to the cross section area of the hard steel core)
and rear crater volumes of three types targets, respectively. Since the rear craters
of panels with rear CFRP fabric were very slight, some small values are given in
Fig. 6.14b for the convenience of comparison. It can be seen from Fig. 6.14 that,