B D Jenrette

L M Lee

M J Forrestal

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M. J. Forrestal 
Sandia National Laboratories, 
Albuquerque, N. Mex. 87185 
Mem. ASME 
L. M. Lee 
B. D. Jenrette 
Ktech Corporation, 
Albuquerque, N. Mex. 87110 
Laboratory-Scale Penetration 
Experiments into Geological 
Targets to Impact Velocities of 
2.1 km/s 
We obtained forces on 3.0 and 6.0 CRH, ogival-nosed projectiles penetrating a 
simulated geological target. A gas gun and a powder gun accelerated foundry core 
targets (a simulated soft sandstone) to steady velocities between 0.6-2.1 km/s, and 
the targets subsequently impacted 20.6 mm diameter penetrators. Rigid-body mo-
tions of the penetrators were obtained with laser interferometry and piezoelectric ac-
celerometers. At a penetration velocity of about 1.5 km/s, the 6.0 CRH nose shape 
exhibited severe, permanent deformation; whereas, the 3.0 CRH nose shape re-
mained undeformed for penetration velocities up to 2.1 km/s. 
Introduction 
Backman and Goldsmith (1978) and Zukas (1982) discuss 
many recently developed analytical and experimental methods 
used to study penetration mechanics. For metal perforation 
and penetration, laboratory-scale experiments play a domi-
nant role in the research required to understand penetration 
phenomena. However, experimental work on penetration into 
geological targets seems to be dominated by full-scale, field 
tests. Over the last two decades, Young (1969, 1971) and Pat-
terson (see Forrestal, Longcope, and Norwood, 1981) con-
ducted hundreds of instrumented, full-scale, field tests into 
soil, rock, and sea-ice targets. These penetrators usually con-
tained on-board recording systems and measured deceleration 
during the penetration event. To complement these full-scale 
test programs, we have recently devised some laboratory-scale 
experiments. Forrestal et al. (1984) used gas guns to perform 
reverse-ballistic experiments with simulated, geological 
targets. Piezoelectric accelerometers measured the rigid-body 
acceleration of several nose shapes for impact velocities be-
tween 0.2-1.2 km/s. Since current field data are limited to im-
pact velocities less than 0.6 km/s, laboratory-scale ex-
periments can provide time-resolved data for much higher im-
pact velocities. 
For the present study, we measured rigid-body penetrator 
motions with laser interferometry and accelerometers for im-
pact velocities from 0.6 to 2.1 km/s. As in our previous paper 
(Forrestal et al. 1984), the targets were foundry core samples 
made at the Sandia foundry. These targets had nominal densi-
ty 1.8 Mg/m3 and simulated many of the properties of the 
Contributed by the Applied Mechanics Division and presented at the Sym-
posium on Mechanics of Impact Fracture—Part II, Winter Annual Meeting, 
Miami, Fla., November 17-21, 1985, of the AMERICAN SOCIETY OF MECHANICAL 
ENGINEERS. 
Discussion on this paper should be addressed to the Editorial Department, 
ASME, United Engineering Center, 345 East 47th Street, New York, N.Y. 
10017, and will be accepted until two months after final publication of the paper 
itself in the JOURNAL OF APPLIED MECHANICS. Manuscript received by ASME 
Applied Mechanics Division, February 12, 1985. 
3.43 mm 
20.6 mm 
12.8 mm 
20.6 mm 
(c) (d) 
Fig. 1 Penetrator nose shapes: (a) 6.0 CRH; (b) tip-modified 6.0 CRH; (c) 
3.0 CRH; (d) overlay of (b) and (c) 
natural targets at the Sandia Tonopah Test Range, Nevada. 
For impact velocities less than 1.2 km/s, we used the Air Force 
Weapons Laboratory 102 mm bore (4.0 in.) gas gun; and for 
impact velocities between 1.2-2.1 km/s, we used the Sandia 
National Laboratories 89 mm bore (3.5 in.) powder gun. For 
impact velocities above 1.2 km/s, the penetrator accelerations 
approached the accelerometer capability (105 g); and for these 
Journal of Applied Mechanics JUNE 1986, Vol. 53/317 
Copyright © 1986 by ASME
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1.26 1.41 1.47
1.15 1.46 1.75 2.11
1.25 1.46 1.54 1.65 1.77 2.07
Fig.4 Post·test nose shapes: (a) top, 6.0 CRH; (b) middle, tip·modifled
6.0 CRH; (c) bottom, 3.0 CRH
STEEL TUBE
PENETRATOR NOSE
L1NEN·PHENOLIC
POLYURETHANE
HOLDER
Fig. 2 Schematic for the powder·gun, reverse-ballistic experiments
-l/l......
E
.:.:
- 0.08
>....
o
o
...I
~ 0.04
0.12 ~-----r-----r----r-------r-----,
0.00 ~=--_---L .L-__---'- -'----__...J
o 20 40 60 80 100
TIME (P.s)
Fig.3 Rigid-body, velocity-time responses for the 6.0 CRH nose shape.
Impact velocities V = 1.25 and 1.77 km/s.
higher impact velocity experiments, rigid-body motions were
measured with laser interferometry (VISAR).
In our previous paper (Forrestal et a!., 1984), we performed
experiments to impact velocities of 1.2 km/s with two conical
nose shapes and a 6.0 CRH ogival nose shape made from a
tungsten alloy. For this study, we performed experiments on
the same nose material to impact velocities of 2.1 km/s on 3.0
and 6.0 CRH ogival nose shapes. At a penetration velocity of
about 1.5 km/s, the 6.0 CRH nose shape exhibited severe, per-
manent deformation. Brooks (1974) observed this same effect
in his study on penetration into metal targets and termed this
phenomenon the hydrodynamic transition velocity. By con-
trast, the 3.0 CRH no~e shape remained undeformed for
penetration velocities up to 2.1 km/s. In addition, we con-
ducted a few experiments with the nose shape shown in Fig.
lb. This nose has a 6.0 CRH shape except its tip has a blunted,
conical shape. The overlay in Fig. 1d shows that this tip-
modified 6.0 CRH nose shape has nearly the same geometry as
the 3.0 CRH nose shape. We hoped this design modification
would avoid the hydrodynamic transition that occurred with
the 6.0 CRH nose shape. However, several experiments in-
dicated negligible differences in the motion responses and the
hydrodynamic transition velocities for the 6.0 CRH nose
shape and the tip-modified 6.0 CRH nose shape.
Experiments
Reverse-Ballistic Experiments. Figure 2 illustrates the
reverse-ballistic experimental arrangement. Foundry core
samples, contained within hollow projectiles, were accelerated
to steady velocities, and the targets subsequently impacted
20.6 mm diameter (0.81 in.) penetrators. The Sandia Foundry
made the targets with nearly the same process as that used for
making molds for metal castings. This material is a mixture of
silica sand (90 percent by weight) and binder ingredients. After
the mixture is oven fired, the material resembles a low-density
cemented sandstone with nominal density 1.85 Mg/m3 and
porosity 30 percent. Triaxial material tests data for this
material are published (Forrestal et a!., 1984). As typical for
dry geologic materials, shear resistance increases significantly
with increasing confining pressure.
As shown in Fig. 2, polyurethane holders, designed to en-
sure normal impact and offer negligible axial constraint, sup-
ported the penetrators. Thin (0.25 mm, 0.01 in.) steel tubes
held the nose shapes forward of the polyurethane holders to
permit full-length' penetration of the foundry core targets
before the projectile struck the back of the holders. These
tubes were 246 mm (6.25 in.) long and were about nine percent
of the total penetrator masses.
For the powder-gun experiments (impact velocity greater
than 1.2 km/s), 69 mm diameter (2.7 in.), 121 mm length (4.75
in.) foundry core samples were contained in linen-phenolic
projectiles with aluminum base plates. The gas-gun ex-
periments used aluminum projectiles and 89 mm diameter, 89
mm length foundry core samples. At both facilities, impact
velocities were measured to within 0.2 percent accuracy with a
series of electrical contact pins.
Penetrators. The nose shapes shown in Fig. 1 were made
from a dense (18.7 Mg/m3) tungsten alloy.l These shapes con-
sisted of a 6.0 CRH, a tip-modified 6.0 CRH, or a 3.0 CRH
section and a stepped-cylindrical section. As illustrated in Fig.
2, the thin (0.25 mm) supporting tubes were shrunk fit to the
nose shapes. All penetrators had 20.6 mm diameter after-
bodies and masses of about 0.22 kg. Figure 2 illustrates the
set-up for experiments that used laser interferometry to
measure nose responses. As previously mentioned, some ex-
periments were also conducted with piezoelectric ac-
~nnertium W-2, Kennametal Inc., Latrobe, Pa. 15650.
318/ Vol. 53, JUNE 1986 Transactions of the ASME
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600 
400 
•z. 
UJ 
O 
ce 
o 
U. 200 
@ VISAR 
A ACCELEROMETER 
- DATA FITS 
6.0 CRH 
0 " V 
1.0 1.4 1.8 
IMPACT VELOCITY (km/s) 
Fig. 5 Peak force versus impact velocity 
2.2 
600 
400 
$ 2 0 0 
DC 
o 
100 
©VISAR 
A ACCELEROMETER 
— DATA FITS 
oLv-
0.6 0.8 1.0 1.2 1.4 1.8 2.2 
IMPACT VELOCITY (km/s) 
Fig. 6 Measurements and data fits for the 3.0 CRH nose shape 
celerometers.2 For these experiments the accelerometers were 
screwed into the back of the nose shapes (Forrestal et al., 
1984). 
Measurements. Rigid-body velocity and acceleration were 
measured with laser interferometry (VISAR) and ac-
celerometers, respectively. Laser interferometry' (VISAR, 
Barker and Hollenbach, 1972) was developed to measure time-
resolved motion of the back surface of shocked specimen. 
VISAR is a widely used precision tool for shock profile 
measurements. However, our experiments were concerned 
with rigid-body motions and the back surface velocity 
magnitudes were much lower than those for typical shock 
2PCB Model 305A, PCB Piezotronics Inc., Depew, N.Y. 14043. 
Table 1 Data summary for the 3.0 CRH ogival-nosed penetrators with 
cylindrical diameter 20.6 mm (0.810 in.); (GG = gas gun, PG = powder 
gun, A = accelerometer, V = VISAR) 
Impact 
Velocity 
(km/s) 
0.608 
0.704 
0.785 
0.895 
1.01 
1.14 
1.15 
1.46 
1.75 
2.11 
Target: 
Density 
(Mg/ra3) 
1.83 
1.83 
1.86 
1.85 
1.86 
1.84 
1-77 
1.35 
1.86 
1.84 
Facil ity, 
Measurement 
GG, 
GG, 
GG, 
CC, 
CG, 
CC, 
GG, 
PG, 
PG, 
PG, 
A 
A 
A 
A 
A 
A 
V 
V 
V 
V 
Penetrator 
Mass 
(kO 
228 
229 
229 
229 
228 
228 
217 
210 
220 
223 
Peak 
Acceleration 
(R) 
37,000 
44,000 
50,000 
57,000 
70,000 
73,000 
85,000 
138,000 
203,000 
256,000 
Peak 
Force 
(kN) 
82 
99 
113 
128 
158 
165 
181 
283 
440 
560 
Table 2 Data summary for the 6.0 CRH ogival-nosed penetrators with 
cylindrical diameter 20.6 mm (0.810 in.); (GG = gas gun, PG = powder 
gun, V = VISAR, O = ogival tip, C = conical tip) 
Impact 
Velocity 
(km/s) 
1.10 
1.25 
1.26 
1.41 
1.46 
1.46 
Target 
Density 
(Mg/m3) 
1.84 
1.85 
1.80 
1.81 
1.85 
1.84 
Facility, 
Measurement, 
Nose Tip 
CC, V, 0 
PG, V, 0 
PG, V, C 
PC, V, C 
PG, V, 0 
PC, V, 0 
Penetrator 
Mass 
<ks) 
214 
218 
219 
218 
223 
220 
Peak 
Acceleration 
(K) 
60,000 
72,000 
73,000 
83,000 
87,000 
92,000 
Peak 
Force 
(kN) 
127 
153 
156 
178 
190 
198 
wave studies. Therefore, for these relatively low-velocity 
measurements, we used an air-delay-leg VISAR (Amery, 1976, 
and Kusher et al., 1981) that was about five times more sen-
sitive than VISARs used for shock wave studies and provided 
3-5 fringes. Briefly, the interferometer provided a fringe 
signal with a fringe count proportional to the back surface 
velocity of the nosepiece. For the Argon-Ion laser and the 
delay length used for these experiments, each fringe cor-
responded to 0.031 km/s velocity change. Typical velocity-
time data are presented in Fig. 3. Details on the acceleration 
measurement are contained in our previous paper (Forrestal et 
al., 1984). 
Experimental Results 
Figures 4-6 and Tables 1 and 2 summarize the results of this 
study. The post-test photographs3 shown in Fig. 4 indicate 
clearly that the 6.0 CRH and tip-modified 6.0 CRH nose 
shapes exhibit severe, permanent deformations for impact 
velocities larger than 1.5 km/s. Brooks (1974) observed this 
same effect when he conducted experiments with 6.0 CRH, 
tungsten-alloy penetrators and AISI 4340 steel targets. That is, 
3We were not able to provide a soft catch for the penetrators. After impact, 
the penetrators interacted with a series of baffel plates. 
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in excess of a particular impact velocity the nose shape 
changed from essentially nondeforming to one that exhibited 
plastic flow. Brooks (1974) called this impact velocity, the 
hydrodynamic transition velocity. By contrast, the 3.0 CRH 
nose shape remained undeformed for impact velocities to 2.1 
km/s. 
We first conducted experiments with the 3.0 and 6.0 CRH 
shapes shown in Figs, la and lc. The tip-modified, 6.0 CRH 
shape shown in Fig. lb was designed with the intent of increas-
ing the hydrodynamic transition velocity. However, subse-
quent experiments showed that this tip modification had no 
measurable effect. Figure Id compares profiles of the 3.0 
CRH and tip-modified 6.0 CRH nose shapes. The close 
similarity of these shapes indicates that the hydrodynamic 
transition velocity is sensitive to small geometry changes in 
nose shape. 
Velocity-time profiles shown in Fig. 3 for the 6.0 CRH nose 
shapes provide additional information about the 
hydrodynamic transition velocity. The 1.25 km/s impact 
velocity was below the transition velocity, and velocity time 
was nearly linear after nose entry and before the end of travel 
through the foundry core target. However, the 1.77 km/s im-
pact velocity was above the hydrodynamic transition velocity, 
and the velocity-time profile exhibited a monotonic slope in-
crease after 40 LIS. This velocity-time profile suggests that the 
onset time for the transition from a nondeformable nose to a 
plastically deformed nose shape was 40 us. 
As previously discussed, rigid-body velocity and accelera-
tion of the nose shapes were measured with laser in-
terferometry (VISAR) and accelerometers, respectively. Most 
of the experiments were conducted at impacts below the 
hydrodynamic transition velocity. For these experiments, 
velocity response was a smooth rise for about the time of nose 
entry followed by a nearly constant slope. This slope was 
measured to obtain peak acceleration and used to calculate 
peak force. Details of the acceleration measurements are 
discussed in our previous paper (Forrestal et al., 1984). Brief-
ly, the rigid-body acceleration data show a smooth monotonic 
rise for about the time of nose entry followed by a nearly flat 
plateau. The magnitudes of the measured plateaus were used 
to calculate peak force. Tables 1 and 2 summarize the penetra-
tion data below the hydrodynamic transition velocity. 
Penetrator masses included the masses of the nose shape, sup-
porting shell (0.02 kg), and accelerometer (0.005 kg, when 
applicable). 
Peak force versus impact velocity data and quadratic fits to 
the data are shown in Fig. 5 for both the 3.0 and 6.0 CRH4 
nose shapes. The curve for the 6.0 CRH shape stops at V = 
1.5 km/s, the hydrodynamic transition velocity. Data for the 
tip-modified, 6.0 CRH nose shape (Fig. lb) are presented in 
Table 1, and these data show no measurable differences be-
tween the tip-modified 6.0 CRH and the 6.0 CRH nose 
shapes. It should also be pointed out that at V = 1.5 km/s (the 
Accelerometer data for the 6.0 CRH nose shape were taken from our 
previous paper (Forrestal et al., 1984). 
transition velocity for the 6.0 CRH nose shape), the force on 
the 3.0 CRH nose shape was 50 percent larger than that on the 
6.0 CRH nose shape. We have, at this time, no explanation for 
this observation. 
Data and linear fits to the data for the 3.0 CRH nose shape 
are also presented on a log-log plot in Fig. 6. Empirical models 
are widely used as predictive tools (Sliter, 1980), and these 
data can be described conveniently in the form 
F=KV" 
and AT = 148 and n = 1.18 for 0.61 < V < 1.14, A" = 134 and 
n = 1.98 for 1.14 < V < 2.11, andF, Vhave the units of kN, 
km/s. 
Discussion 
Over the last two decades, hundreds of instrumented, full-
scale, field tests into geological targets have been conducted. 
To complement these full-scale test programs, we have devised 
some laboratory-scale experiments that measure penetrator 
motion for impact velocities to 2.1 km/s. Since data for in-
strumented, field tests are currently limited to impact 
velocities of about 0.6 km/s, only laboratory-scale ex-
periments can currently provide time-resolved, velocity, and 
acceleration data for higher impact velocities. 
Acknowledgment 
This work was supported by the US Department of Energy. 
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Laboratory-Scale Penetration Experiments into Geological Targets to Impact Velocities of 2.1 km/s

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Laboratory-Scale Penetration Experiments into Geological Targets to Impact Velocities of 2.1 km/s

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