CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
BALLISTIC TESTING AND HIGH-STRAIN-RATE PROPERTIES OF
HOT ISOSTATICALLY PRESSED T1-6A1-4V
YaBei Gu, Vital! F. Nesterenko and Sastry S. Indrakanti
Department of MAE, University of California, San Diego, CA 92093-0411
Hot isostatically pressed (HIPed) T1-6A1-4V powder based targets (including composites) have a
good ballistic performance against long rod, conical and flat projectiles impact (velocity range ~ 0.4
- Ikm/s). Compared to baseline material (MIL-T-9047G), new features such as different shape of
craters in long rod penetration tests were observed. The results of compression Hopkinson bar tests,
cut from tested targets (final strain controlled tests and hat-shaped specimen tests) are presented
with a goal to establish relations between ballistic performance and high strain rate properties of
HIPed materials.
INTRODUCTION
dense and porous (7.6% porosity) Ti-6Al-4V was
also investigated using a combination of standard
testing machines and compression and torsional
Kolskybars[7].
There is no data on the relation between ballistic
performance and high strain rate properties of Ti6A1-4V made from powder. The main goal of this
research is to investigate the ballistic performance
of Ti-6Al-4V based homogeneous materials
obtained by hot isostatic pressing against flat
ended, conical and long rod penetration impact.
Extensive experiment data were obtained about
high-strain-rate
properties
and
ballistic
performance for Ti-6Al-4V alloy with various
microstructures (e.g. equiaxed, acicular and
Widmanstatten
structures
produced
by
conventional processing methods) [1-4].
The high-strain-rate properties of Ti-6Al-4V are
most crucial in the design of components subjected
to impact or shock loading. Follansbee and Gray
[5] investigated the deformation behavior of Ti6A1-4V at temperatures 76 and 495 K, strain rates
between 0.001 and 3000 s"1, and compressive
strains up to 3.0. A deformation model based on
the kinetics of dislocation/obstacle interaction and
structure evolution was successfully applied. Lee
and Lin [6] investigated plastic deformation and
fracture behavior of Ti-6Al-4V alloy under high
strain rate at various temperatures. The results
show that the flow stress of TJ-6A1-4V is sensitive
to both temperature and strain rate. It was found
that adiabatic shear bands are the major fracture
mode at large plastic deformations under high
temperature and high strain rate. The ratedependent deformation and localization of fully
COMPARISON OF BALLISTIC
PERFORMANCE OF HIPed AND BASELINE
MATERIAL
Three types of ballistic experiments including
flat-ended projectile, conical projectile and long
rod projectile tests were conducted to evaluate the
ballistic properties of HIPed TJ-6A1-4V material.
Flat-ended and conical projectile penetration tests
were performed at U.C. Berkeley [8]. Long rod
penetration tests were conducted at the UDRI
[9,10]. The details about the preparation of targets
and testing can be found in papers [8-11].
Relatively large spread of data in plug velocities
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shear bands developed from the crater or within
the grains. The bifurcation and interaction found
frequently in the tested HIPed targets are an
example of complex shear bands patterns.
Twinning was also observed in tested HIPed target
inside grains close to the crater. Many of the
secondary shear bands is over 100 pm long and
over 10 pm thick [11].
Dimple structures on surface of plugs collected
after flat-ended penetration tests were evaluated
under SEM. Dimples with similar shape and size
distribution were found both in baseline and in
HIPed material even though the overall shape of
the plug appears significantly different [11].
Fig. 1 Different shape of craters after long rod projectile
penetration tests. (On the left is baseline material and on
the right is HIPed PREP nonmilled material). Arrows
show localized shear.
were found after flat-ended projectile penetration
tests. For example, one test from PREP nonmilled
HIPed Ti-6Al-4V shows only 80 m/s plug velocity
while another two similar tests result in 176.8 m/s
and 187.2 m/s velocities. This phenomenon also
happens in PREP milled HIPed and in PREP ELInonmilled HIPed material. Practically in all cases
plug velocities in baseline material were higher.
The bottoms of craters in HIPed and baseline
materials after long rod projectile penetration tests
at 1 km/s are presented in Fig. 1 [9,10]. The crater
shapes are quite different. In baseline material, the
penetration depth is about 18 mm and additionally
shear bands propagated forward to a distance of 6
~ 8 mm. In the case of HIPed samples, the
penetration depth is about 14-15 mm which is
smaller than in baseline material. The bottom part
of the craters is relatively flat for HIPed samples
and has a few dents left by the projectile (diameter
4.75mm).
Shear bands patterns were found to be quite
different in the baseline and HIPed targets after
ballistic tests with flat projectile. The shear bands
in baseline material exhibit systematic pattern
where a dominant shear band runs along the
penetration direction and pattern of secondary
shear bands develops at 45° to penetration path.
The secondary shear bands have a length of 40 ~
100 jam and width of 2 ~ 5 ^m.
Shear bands pattern in HIPed material does not
show "systematic" behavior. The dominant shear
band also runs along the penetration direction, but
the secondary shear bands propagated into the
target with angles 30°- 90° and interact with other
HIGH-STRAIN-RATE DATA
High-strain-rate constitutive relations were
obtained using split Hopkinson bar tests for
standard baseline material taken from the 50-mm
rod (MIL-T-9047G) and from the tested targets
made from HIPed material with different velocities
of plug. The sample is 4-mm by 4-mm cylinder
and the top and bottom surfaces were polished
before testing. Samples from baseline material
were prepared with axis parallel and normal to the
axis of 50-mm rod to examine the texture effect.
The results of the stress-strain curves are shown in
Fig. 2.
Ductility of PREP nonmilled HIPed material is
comparable with the ductility of baseline material
in perpendicular direction. PREP nonmilled HIPed
material has a comparable strength as baseline
material in the parallel direction, but lower than
that of the baseline material in the perpendicular
direction. The baseline material in the
perpendicular direction has low ductility compared
to the ductility in the parallel direction. Baseline
material has a larger spread of data for ductility
than HIPed samples. Phase analysis shows that
there is more p -phase in HIPed material (45%)
compared with the standard baseline material
(39%). This may contribute to the observed lower
ductility for HIPed material.
The strain controlled specimen tests also
validate that the ductility of PREP nonmilled
HIPed material is comparable with the ductility in
baseline material in perpendicular direction.
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1.8-
s
1.6
1.412-
0.604 .
020
0.05
0.1
0.15
02
Engineering Strain
025
0.05
0.1
0.15
02
0.25
Engineering Strain
Engineering Stnun
Fig. 2 Constitutive relations in different tests for baseline material at parallel direction (a), baseline material at
perpendicular direction (b) and HIPed PREP nonmilled material (c), (samples 6n, 7n and 8n; see Table 2 in [11]).
higher flow stress and similar energy dissipation
compare to HIPed material. The area of forced
shear localization has the similar thickness in all
three cases.
It is also found that larger amount of material is
involved into the shear flow in baseline material
sheared at perpendicular direction to forging. Only
material inside the shear band is heavily deformed
at shear direction parallel to forging at the same
level of strain (Fig. 5).
They both have a failure strain 0.12-0.17. Failure
strain is ~ 0.24 for baseline material in parallel
direction. The spontaneous shear bands were
initiated inside particular grains and represent the
dominant failure mechanism for plastic
deformation in HIPed material (Fig. 3).
Hat-shaped specimen tests were used to
evaluate shear deformation and failure of the
material by forced shear localization in the
postcritical region. The main advantage of this test
is that the flow stress vs. displacement can be
measured and subsequent microstructures can be
investigated.
The results presented in Fig. 4 show that PREP
nonmilled HIPed material has a relatively lower
flow stress compare to baseline material. Baseline
material in perpendicular direction has a relatively
50
100
150
200
250
300
350
400
Displacement (pm)
Fig. 4 Shear stress vs. displacement for baseline material
at parallel (squares) and perpendicular direction to
forging (stars) and HIPed PREP nonmilled material
(triangles).
CONCLUSION
HIPed material has a better ballistic
performance in comparison with baseline material
for three types of ballistic tests. Samples made
from ELI powder did not demonstrated better
performance in comparison with PREP powders.
Fig. 3 Nuclei of Spontaneous shear band in HIPed PREP
nonmilled material.
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Fig. 5 Forced shear bands developed in baseline material at parallel direction (a) and at perpendicular direction
(b) at strain rate ~ 103.
3.
Burkins, M., and Love, W., "Effect of Annealing
Temperature on the Ballistic Limit Velocity of Ti6A1-4V ELI", in Proceedings of 16-th International
Symposium on Ballistics, San Fransisco, CA, 23-27
September (1996).
4. Weerasooriya, T., Magness, L. and Burkins, M.,
"High Strain-Rate Behavior of Two Ti-6Al-4V
Alloys with Different Microstructures" in
Fundamental Issues and Applications of ShockWave and High-Strain-Rate Phenomena, Edited by
Staudhammer, K. P., Murr, L. E. and Meyers, M.
A, pp. 33-36 (2001).
5. Follansbee, P. S. and Gray, G. T., ffl, Metallurgical
Transactions A. 20A, pp. 863-874, May (1989).
6. Woei-Shyan Lee and Chi-Feng Lin, Material
Science and Engineering, A241, pp. 48-59, (1998).
7. da Silva, M. G. and Ramesh, K. T.,, Material
Science and Engineering, A232, pp. 11-22 (1997).
8. Nesterenko, V. F., Indrakanti, S. S., Goldsmith, W
and Gu, Y., International conference on
Fundamental Issues and Applications of ShockWave
and
High-Strain-Rate
Phenomena,
Albuquerque, New Mexico, U.S.A., June (2000).
9. Nesterenko, V. F., Indrakanti, S. S., Brar, S. and
Gu, Y., "Long Rod Penetration Test of Hot
Isostatically Pressed Ti-based Targets", in Shock
Compression of Condensed Matter, pp. 419-422,
(1999).
10. Nesterenko, V. F., Indrakanti, S. S., Brar, S. and
Gu, Y., Key Engng., Mater. 177-180, 243-248
(2000).
11. Nesterenko, V. F., Indrakanti, S. S., Goldsmith, W
and Gu, Y., in preparation.
PREP nonmilled fflPed material and PREP milled
HIPed materials with different microstructures
demonstrate the similar ballistic performance.
Probably the existence of texture in baseline
material and isotropic structure of HIPed material
are responsible for different crater shape in long
rod penetration test. No correlation was found
between shear bands pattern, dimple structure,
Hopkinson bar test results in the samples taken
from the targets with different plug velocities in
flat projectile tests. Lower ductility of HIPed
material can be responsible for different shear band
pattern in baseline and in HIPed material and the
difference in shape of the plugs in flat-ended
projectile penetration tests.
ACKNOWLEDGMENTS
The support provided by the ARO, MURI
DAAH 04-96-1-0376 (Program manager Dr. David
Stepp) is highly appreciated.
REFERENCES
1.
2.
Gooch, W.A., Burkins, M.S., and Frank, K.,
"Ballistic Performance of Titanium Against
Laboratory Penetrators." In Proc. of 1-st
Australasian Congress on Applied Mechanics,
Melbourne, Australia, 21-23 February (1996).
Meyer, L.W., Krueger, L., Gooch, W. and Burkins,
M., J.Physique IV, C3, pp. 415-422 (1997).
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