CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
2002 American Institute of Physics 0-7354-0068-7
DYNAMIC FRACTURE STUDIES USING SLEEVED TAYLOR
SPECIMENS
Martin R. Gilmore1, Joseph C. Foster, Jr2, and Leo L. Wilson3
1
Defence Science Technical Laboratory (DSTL - UK), Exchange Scientist at Air Force Research Laboratory,
Munitions Directorate (AFRL/MN), 101 WEglin Blvd, Ste 135, Eglin AFB, FL 32542,
2
AFRL/MN, 101 W Eglin Blvd, Ste 135, Eglin AFBt FL 32542.
3
SAIC at AFRL/MN, 101 W Eglin Blvd, Ste 135, Eglin AFB, FL 32542,
Abstract: The characterization of the inelastic response of materials to high rates of loading is a
challenging engineering problem. As the load rate increases, the interpretation of the data recovered from
the experiment become more difficult. At very high rates of loading, even the inertia of the test specimen
must be accounted for in the interpretation of the data [1]. The Taylor impact experiment is specifically
designed to exploit the inertia of the specimen to produce very high loading rates and has been used to
study the high strain (50%), high strain rate (103"4) behavior of materials for many years [2], Many highrate loading problems produce failure in the material. Continuum codes have been used to design sleeved
impact specimens to study the failure of materials under high rates of loading. Ductile core materials are
used as drivers to control rupture of more brittle sleeves of the material of interest. Annealed copper cores
are used to drive dynamic failure in AF1410 steel High rate plastic deformation data are presented for the
driver and the sleeve together with the fracture data.
a better understanding of the equation of motion of
the specimen - "at very high speeds a condition is
reached in which the inertia of the specimen itself
gives rise to changes of stress along its length,
which must be taken into account when seeking to
interpret experimental results" [2,4]. Preliminary
calculations were performed using an Eulerian
solver. Example results are presented in Figure 2.
INTRODUCTION
The high-rate load environment of the fragment
break-up problem drives the engineer to design
impact test techniques. A series of developmental
experiments using sleeved Taylor impact specimens
is presented. Two different heat treatments of a
formulation of AF-1410 steel were driven to highrate failure. The specimen design is illustrated in
Figure 1. A ductile copper core was used to drive the
steel sleeves. Plastic deformation and fracture are
observed. The test is based on the impact of a right
circular cylinder on an anvil, commonly called a
Taylor test after G.L Taylor [2]. Data in the 104"5 /sec
strain rate regime are presented.
Aermet-1 OO/ AF1410 Sleeve
0.499.0tW2
2.5004-0.005
Copper Core
NUMERICAL METHODS
Note: Press fit core into sleeve
A continuum mechanics code, cAst [3], was used
to aid in the design of the experiment and to provide
FIGURE 1. Sleeved Taylor test specimen configuration.
519
sleeved specimens; designed to provide controlled
high-rate fracture of materials. Two heat treatments
of AF1410 steel were used:
a) As Received (AR): Normalized and overaged.
Resulting in a RC hardness the range 36 - 40,
equivalent to a yield strength (0y) of ~ 130 KSI.
b) Heat Treatment (HT1): Normalized; 1650F 3hr.->
air cool to 400F. Austenized; 1575F 3 hr. -> oil
quench to 200F. Chill; 100F 2 hr. -> air warm to
room temperature. Tempered; 950F 5 hr. -> air cool
to room temperature, equivalent to a 0y - 250 KSI.
The code uses a Hull [5] constitutive model for
the material elastic/ plastic behavior. Tri/quad linear
fits for strength vs plastic strain and strength vs
internal energy are used. A Mie-Gruneisen [6]
equation of state model was used.
. Copper
150
0
+
*
*
4
>
A
V
* *a
^*
0
4*
*
*
4
t>
A
V
a
Cu- Expt half hardenned
Cu- Expt Annealed No Fracture Table 2 Cu- Calculation
Steel - Calculation
Sleeve- Expt AR No Fracture Table 2
Sleeve - Expt AR Fracture Table 2
Sleeve - Expt HT1 Fracture Table 2
Steeve- Expt HT1 No Fracture Table 2 *
Tayk>r[2]
*
D *
FIGURE 2. Plot of specimen velocity vs time during the
impact event
*
D
*
D
Figure 2 illustrates that the copper takes longer to
slow down than the steel (144 vs 77jxs) - and hence
can be used to drive the steel to failure. An analytical
1-D result relating particle speed through the
material (up = 0 / p c £ ) was (161 vs 71 fis), where
Up, 0, ps CL are the particle velocity, yield strength,
density and speed of sound. This calculation also
predicted a pressure exerted on the steel by the
copper core of approx l.SxlO9 Pa (-220 KSI). The
discrepancies in event time are due to the higher
frequency waves caused by reflections from the sides
of the specimen (0=0 boundary). That is, there are
waves traveling in both the transverse and radial
directions in the specimen.
The code appears to be modeling the interaction
adequately and will be used to evaluate the
specimen's equation of motion - required for
interpretation of the experimental data [2].
1.5
2
2.5
2
pV
70
r impact v y
3
FIGURE 3. Collation of all data
A velocity range of 130 to 300ms"1 (equivalent to a
strain rate of lO^V1) was examined. Figure 3 is a
collation of all the data L0/Lf (see Figure 5 for
definitions) vs p V2 \mpmt/<J is plotted.
Detailed post mortem measurements of the
specimens were made using an optical comparator.
Profile diameters (accuracy ~ 0.0005") were taken at
0.01" increments along the specimen.
0
-0.1
-0,2
-0.3
^0'4
-0.5
EXPERIMENTS
= 185ms'CUA-1
= 200ms"1 CUA-4
= 179ms"1 BMTE-2
= 198ms~1BMTE-3
= 140ms"1 BMTE-11
-0.6
Two sets of experiments were performed using a
.50 caliber gun launcher, firing specimens into a steel
anvil: Firstly, OFHC Copper specimens with a
Vickers hardness of 103 were tested in a caliber .50
L/D=5 configuration. These tests were used to
characterize the sleeved test core material. Details
provided by Foster et al [7] and figure 4. Secondly,
-0.7
0
0.5
1
1.5
FIGURE 4. Sample experimental results
520
2
Lagrangian Position (inches)
As with all experimental techniques, the central
problem is the interpretation of the data recovered
from the experiment Taylor's high load rate
experiments require the formulation of an approach
to account for the inertia of the specimen material in
the analysis of the data - hence the numerical
analysis.
Figure 4 is an illustration of the strain measured
along the specimen for copper and steel specimens.
The strain (ea =dU2/dZ) is plotted against the
Lagrangian position [7] normalized against L0.
Information in this plot can be used to characterize
the material behaviour for use in continuum
mechanics codes.
DISCUSSION
A summary of the experimental database is
presented in Table 1. A definition of the length scales
is provided in Figure 5.
Maximum engineering strains of 71% and 50%
are observed for the AR and HT1 specimens
respectively. For a classic Taylor (i.e. no copper
core) test fracture would have occurred at
approximately 14% strain.
TABLE 1: Summary of Experimental Results
Exptro
L0
R2F - 7,37
CUA-1
CUA-2
CUA-3
CUA-4
CUA-5
2.5
2.5
2.5
2.5
2.5
2.5
h
S
/
sd
Lr
H
Annealed Copper, OFHC. Note all Length scales are in inches. D0 = 0.499
Dsleeve
^copper
V-ms' 1
Fracture
1.768
1.783
1.888
1.956
1.741
2.111
1.17
1.19
1.256
1.259
1.168
1.224
0.598
0.593
0.632
0.697
0.573
0.887
0.732
0.717
0.612
0.544
0.759
0.389
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
0.97
0.909
0.866
0.818
0.986
0.717
191
185
172
161
200
130
small
No
No
1.81
2.217
2.159
1.9
2.11
1.737
1.321
1.822
1.787
1.102
1.457
1.469
0.489
0.395
0.372
0.798
0.653
0.268
0.313
0.283
0.341
0.6
0.39
0.763
0.101
0.093
0.097
0.94
0.883
.935
0.07
0.043
1.047
0.745
0.613
.668
.835
0.678
1.05
216
179
198
237
213
304
No
No
No
Yes
Yes
Yes
1.93
2.056
2.288
2.362
2.393
1.29
1.135
1.608
1.785
1.163
0.64
0.921
0.68
0.577
1.23
0.57
0.444
0.212
0.138
0.107
0.07
0.086
0.132
0.215
0.206
230
199
111
158
140
Yes
Yes
Yes
Yes
No
2.325
2.401
1.835
2.395
1.864
1.803
0.851
0.841
0.461
0.598
0.984
1.554
0.175
0.099
0.665
0.105
0.093
0.164
0.058
0.186
155
148
233
141
Yes
No
Yes
No
No
small
No
AF1410-2. Steel. As received
BMTE-1
BMTE-2
BMTE-3
BMTE-4
BMTE-5
BMTE-6
2.123
2.5
2.5
2.5
2.5
2.5
AF1410-2. Steel. Heat Treat 1
BMTE-7
BMTE-8
BMTE-9
BMTE-10
BMTE-1 1
2.5
2.5
2.5
2.5
2.5
.844
.623
0.925
0.686
0.518
0.701
0.549
0.522
0.680
0.512
AF1410-1. Steel. Heat Treat 1
BMTE-12
BMTE-13
BMTE-14
BMTE-15
2.5
2.5
2.5
2.5
Sample photographs of the specimens are
presented in Fig. 6. The fracture threshold for AR
and HT1 can be seen (from Table 1 and Fig 6) to be
between 198 and 213 msf1, and US-lSSms*1
respectively. The adiabatic shear bands are visible in
the middle image and fracture is observed to
propagate at 45° along one of these bands.
521
In the test the ductile copper core exerts a
significant pressure on the sleeve, and the specimen
acts like a thick-walled pressure vessel. The tests are
complimentary to the work on fracture under
hydrostatic pressure of Bridgman[9].
CONCLUSIONS
h'
I
A well-characterized, controlled experiment has
been designed that can be used to test material
performance at high strain rates. The test involved
propelling specimens at modest velocities (130 - 300
ms"1), strain rates of the order 104/5 s"1 are produced.
The pressure exerted on the sleeve by the core
dominates the experiment; modeling of this interface
by continuum mechanics code is challenging. Data
have been collected that characterized this process.
These data will be used to develop an analytical
model of the interaction and to support the models
embedded in the continuum mechanic codes.
S
FIGURE 5. Geometry of the test together with a basic
definition of parameters (see Table 1).
180ms*1
198mr1
ACKNOWLEDGMENTS
Many thanks to Denis Grady for his input to the
fundamental philosophy/ design of this experiment.
Thanks to the technical support of the advanced
warhead experimentation facility within AFRL/MN.
The US DOD and the UK MoD supported the
work.
REFERENCES
1.
2.
3.
4.
FIGURE 6. Top - AF14010 AR specimens.
Middle - close up of shear bands for AF14010 - AR at
198 ms'1 (Left) and 213ms'1 (Right).
Bottom-A¥14W HT1 specimens
5.
The type of failure observed varied with impact
velocity and material type. The higher strength, yet
more brittle, HT1 steel failed at lower velocities than
the lower strength, more ductile AR variant. As
velocity is increased the specimens failed in a 'petal5
pattern (Figure 6 top, bottom right hand side). With
HT1 this failure mode was more pronounced. In AR
the failure propagated along the shear bands and then
'ripped up' the side of the specimen.
6.
7.
8.
522
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pp.486,1945.
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DER "cAst V2,6\ FEA Tool, Defence Evaluation and
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Foster Jr. , J.C., 'The Modernized Taylor Anvil
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Bridgman, P.W., 'Fracture and Hydrostatic Pressure',
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