ASM Metals HandBook Vol. 8 - Mechanical Testing and Evaluation
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39. D.J. Green, R.H.J. Hannink, and M.V. Swain, Transformation Toughening of Ceramics, CRC Press
Inc., 1989, p 5–93
40. G. Ravichandran and G. Subhash, A Micro Mechanical Model for High Strain Rate Behavior of
Ceramics, Int. J. Solids Struct., Vol 32 (No. 17/18), 1995, p 2627–2650
41. C.B. Ponton and R.D. Rawlings, Vickers Indentation Fracture Test, Part 1: Review of Literature and
Formulation of Standardised Indentation Toughness Equations, Mater. Sci. and Technol., Vol 5, 1989, p
865–960
42. C.B. Ponton and R.D. Rawlings, Vickers Indentation Fracture Test, Part 2: Application and Critical
Evaluation of Standardised Indentation Toughness Equations, Mater. Sci. and Technol., Vol 5, 1989, p
961–976
Shock Wave Testing of Ductile Materials
George T. (Rusty) Gray III, Los Alamos National Laboratory
Introduction
THE STUDY of the physical properties of ductile solids subjected to shock wave loading is undertaken to
understand how the thermodynamic conditions and strain rate affect material response. Much of the
development of the field of shock wave physics and metal plasticity has taken place since World War II and
stems from the engineering importance and scientific interest in this technical area related to conventional and
nuclear weapons. In contrast to quasi-static loading, the stress applied during shock loading is the result of the
inertial response of the sample to a rapidly applied external load. As with quasi-static loading, the behavior of a
material during shock loading is uniquely controlled by its stress-volume response or equation of state (EOS)
(Ref 1, 2). The Rankine-Hugoniot or “Hugoniot” of a material is the locus of end states obtained through a
shock process defining the pressure-volume relationship of a solid (Ref 3). Contrary to quasi-static loading, in
the case of shock loading, conservation of mass and momentum applied to the shock transition give extra
constraints allowing exact information on the stress, density, and material energy behind the shock. Numerous
review papers chronicle the EOS of materials during shock loading (Ref 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12). The
focus of this review is an introduction to the experimental techniques used to study the effects of shock wave
loading on ductile materials (primarily metals, although the techniques apply equally to polymeric solid), and
the scientific and engineering applications motivating these studies.
References cited in this section
1. W.J.M. Rankine, On the Thermodynamic Theory of Waves of Finite Longitudinal Disturbance, Philos.
Trans. R. Soc. (London), Vol 160, 1870, p 277–288
2. J.N. Johnson and R. Chéret, Shock Waves in Solids: An Evolutionary Perspective, Shock Waves, Vol 9,
1999, p 193–200
3. M.H. Rice, R.G. McQueen, and J.M. Walsh, Compression of Solids by Strong Shock Waves, Solid State
Phys., Vol 6, 1958, p 1–63
4. J.M. Walsh and R.H. Christian, Equation of State of Metals from Shock Wave Measurements, Phys.
Rev., Vol 97, 1955, p 1544–1556
5. J.M. Walsh, M.H. Rice, R.G. McQueen, and F.L. Yarger, Shock-Wave Compressions of Twenty-Seven
Metals: Equations of State of Metals, Phys. Rev., Vol 108, 1957, p 196–216
6. R.G. McQueen and S.P. Marsh, Equation of State for Nineteen Metallic Elements from Shock-Wave
Measurements to Two Megabars, J. Appl. Phys., Vol 31, 1960, p 1253–1269
7. R.G. McQueen, Laboratory Techniques for Very High Pressures and the Behavior of Metals under
Dynamic Loading, Metallurgy at High Pressures and High Temperatures, K.A. Gschneidner, Jr., M.T.
Hepworth, and N.A.D. Parlee, Ed., Gordon and Breach, 1964, p 44–132
8. R.G. McQueen, S.P. Marsh, J.W. Taylor, J.N. Fritz, and W.J. Carter, The Equation of State of Solids
from Shock Wave Studies, High Velocity Impact Phenomena, R. Kinslow, Ed., Academic Press, 1970, p
293–417, 515–568
9. C.P. Morris, Los Alamos Shock Wave Profile Data, University of California Press, 1981
10. L.V. Altshuler, K.K. Krupnikov, and M.I. Brazhnik, Dynamic Compressibility of Metals under
Pressures from 400,000 to 4,000,000 Atmospheres, Sov. Phys. JETP, Vol 7, 1958, p 614–619
11. C.E. Anderson, J.S. Wilbeck, J.C. Hokanson, J.R. Asay, D.E. Grady, R.A. Graham, and M.E. Kipp,
Sandia Shock Compression Database, Shock Waves in Condensed Matter—1985, Y.M. Gupta, Ed.,
Plenum, 1986, p 185–190
12. L.V. Altshuler, R.F. Trunin, V.D. Urlin, V.E. Fortov, and A.I. Funtikov, Development of Dynamic
High-Pressure Techniques in Russia, Phys. Usp., Vol 42, 1999, p 261–280
Shock Wave Testing of Ductile Materials
George T. (Rusty) Gray III, Los Alamos National Laboratory
Development of Shock Wave Studies
The earliest study of the relation between the propagation of elastic pulses and the formation of brittle fracture
was documented in the work of John Hopkinson in 1872 (Ref 13). Hopkinson studied the strength of steel wires
subjected to impulsive tensile loading. He explained the observed phenomena in terms of one-dimensional
elastic wave propagation. Studies concerned with the response of ductile metals subjected to shock wave
loading date to the seminal work of Bertram Hopkinson, John Hopkinson's son, in 1921. Hopkinson described
how shock wave loading influenced mechanical behavior and fracture response of iron and steel samples
subjected to an impulse load generated from exploding “gun cotton” placed in contact with a metal sample (Ref
14).
Hopkinson was the first to document how shock-induced fracture in a ductile metal could be initiated due to the
interaction of the reflected wave from the rear surface of a sample assembly with the tail of the release wave
from the impactor. Bertram Hopkinson documented in his paper “The Pressure of a Blow” (Ref 14) that when
gun cotton was exploded on a 12.7 mm (0.5 in.) thick steel plate it punched out a hole of its own diameter
through the plate. When the same explosive charge was detonated on a 19 mm (0.75 in.) thick plate, a scab of
steel was formed. Experimenting with a still thicker plate revealed the formation of an internal crack parallel to
the surface of the plate. This formation of internal damage and cracking, but not complete separation of the
target plate to form a scab, is now called incipient spall (Ref 15). Rinehart (Ref 16) in 1952 referred to this
process as scabbing following the terminology previously used by Hopkinson. This impulse-driven fracture
process, previously termed Hopkinson fracture (Ref 17, 18), or scabbing (Ref 16), is today more generically
called spallation (Ref 15). Spallation is known to be strongly influenced not only by bulk mechanical properties
but also by microstructure in materials as summarized in several reviews (Ref 15, 19, 20, 21, 22, and 23).
Work on the EOS, strength effects, and development of shock recovery techniques on ductile metals has its
origins with the research of Walsh, McQueen, Marsh, and Rice (Ref 3, 5, and 6). The beginning of studies of
metallurgical substructure and postmortem strengthening effects of shock wave loading on metals began with
the pioneering article of Cyril Stanley Smith (Ref 24) in 1958. In this article Smith describes how the uniaxial
strain, high-strain-rate loading, characteristic of shock wave loading, affects the generation and storage of
defect structures in metals and alloys. His article further describes the genesis of the method of shock recovery
first developed at Los Alamos National Laboratory during the Manhattan Project era. Through the use of shock
recovery experiments, samples can be subjected to high-pressure shock through impact and subsequently
recovered for the purpose of allowing postmortem metallurgical evaluation of the effects of the shock straining
on the microstructure of a material. This technique, which introduced the use of impedance-matched radial
momentum trapping rings, as well as a backing plate to prevent radial release and spallation, respectively,
within the sample, when coupled with water deceleration of the sample, lead to recovery of intact shocked
samples.
Studying the physical properties of materials during the very rapid loading rate and short time interval during
the actual passage of a shock wave through a material is difficult. Shock recovery experiments provide insights
into the processes occurring during shock wave loading through the analysis of carefully recovered samples.
Characterization and quantification of “soft” recovered samples provides a mechanism to quantify the defect
generation and storage mechanisms operative in materials subjected to impulse loading histories (Ref 25).
Smith (Ref 24) in his study using optical metallography first described how substructural studies of shock-
recovered samples can provide valuable insight into the hydrodynamic effects of shock loading on materials.
Since 1958, a number of in-depth reviews have summarized the systematic changes in structure and the
commensurate property changes produced by the passage of shock waves through metals and alloys (Ref 26,
27, 28, 29, 30, 31, 32, 33, 34, and 35). In each of these reviews, the microstructure/mechanical property
changes observed in shock-recovered samples have been correlated with the shock compression characteristics
imposed (e.g., peak pressure, duration, rarefaction rate, and temperature) and the specific shock-induced defects
produced. In addition, for a variety of metals and alloys, the defects produced during shock prestraining have
been compared and contrasted with those typically observed following quasi-static deformation.
Applications of Shock Wave Tests. Interest in studying the effects of shock wave loading on materials has two
components. The first gives knowledge of its pressure-volume (EOS) behavior during the actual time interval of
the shock process. These studies include “real-time” shock physics diagnostic experimental methods, which
quantify the response of a material during the passage of the shock wave through it as registered in the shock
wave profile and other measurements, such as temperature, resistivity, and x-ray diffraction (Ref 36). The
second experimental aspect of shock wave research includes analysis of samples subjected to an impact
excursion to examine the postmortem signature of the shock prestraining and/or Hopkinson fracture process as
described above. Postmortem studies are a type of Sherlock Holmes exercise in which scientific quantification
of the structure/property manifestations in a material, due to exposure to a shock wave, is utilized to provide
insight into the physical processes during shock wave loading. Experimental programs that couple both real-
time and postmortem aspects offer the most promising opportunities to the understanding of shock processes in
ductile materials and to the support of the development of physically based theoretical models describing shock
loading (Ref 37, 38, and 39).
Types of Shock Waves. In typical shock-loading experiments, there are up to three distinct waves (Ref 40, 41,
and 42):
• Elastic wave
• Plastic wave (termed the plastic I wave)
• Phase transformation wave (termed the plastic II wave)
The magnitude of the imposed shock on a material determines whether a “purely” elastic wave or an elastic
plus a plastic wave traverses a sample. In the case of materials that undergo a pressure-induced change of
phase, such as iron, tin, bismuth, titanium, zirconium, and halfnium, a third wave that we call the second plastic
wave traverses the sample (Ref 40, 42, 43, and 44). Figure 1 is the wave profile for a sample configured to
study the spallation of tin. This profile illustrates the fundamental aspects of elastic-plastic behavior in a ductile
metal, which are observed during shock loading of a ductile material. Relative scales are given in Fig. 1 to
illustrate the high velocities and short times typical for shock wave profiles. The range of possible experimental
techniques to quantify the structure/property effects of planar shock waves on ductile materials (specifically
metals and alloys) due to the manifestations of wave propagation through a material are presented in this article.
Fig. 1 Shock wave profile for tin illustrating various shock processes. Source: Ref 45
References cited in this section
3. M.H. Rice, R.G. McQueen, and J.M. Walsh, Compression of Solids by Strong Shock Waves, Solid State
Phys., Vol 6, 1958, p 1–63
5. J.M. Walsh, M.H. Rice, R.G. McQueen, and F.L. Yarger, Shock-Wave Compressions of Twenty-Seven
Metals: Equations of State of Metals, Phys. Rev., Vol 108, 1957, p 196–216
6. R.G. McQueen and S.P. Marsh, Equation of State for Nineteen Metallic Elements from Shock-Wave
Measurements to Two Megabars, J. Appl. Phys., Vol 31, 1960, p 1253–1269
13. B. Hopkinson, A Method of Measuring the Pressure Produced in the Detonation of High Explosives or
by the Impact of Bullets, Philos. Trans. R. Soc. (London) A, Vol 213, 1914, p 437–456
14. B. Hopkinson, The Pressure of a Blow, The Scientific Papers of Bertram Hopkinson, Cambridge
University Press, 1921, p 423–437
15. M.A. Meyers and C.T. Aimone, Dynamic Fracture (Spalling) of Metals, Prog. Mater. Sci., Vol 28,
1983, p 1–96
16. J.S. Rinehart, Scabbing of Metals under Explosive Attack: Multiple Scabbing, J. Appl. Phys., Vol 23,
1952, p 1229–1233
17. I.C. Skidmore, An Introduction to Shock Waves in Solids, Appl. Mater. Res., Vol 4, 1965, p 131–147
18. H. Kolsky, The Waves Generated by Brittle Fracture in Glass, Trans. Soc. Rheology, Vol 20, 1976, p
441–454
19. D.R. Curran, L. Seaman, and D.A. Shockey, Dynamic Failure of Solids, Phys. Rep., Vol 147, 1987, p
253–388
20. D.R. Curran, L. Seaman, and D.A. Shockey, Linking Dynamic Fracture to Microstructural Processes,
Shock Waves and High Strain-Rate Phenomena in Metals, M.A. Meyers and L.E. Murr, Ed., Plenum,
1981, p 129–167
21. D.R. Curran, L. Seaman, and D.A. Shockey, Dynamic Failure in Solids, Phys. Today, Vol 30 (No. 1),
1977, p 46–55
22. A.K. Zurek and M.A. Meyers, Microstructural Aspects of Dynamic Failure, High Pressure Shock
Compression of Solids II: Dynamic Fracture and Fragmentation, L. Davison, D.E. Grady, and M.
Shahinpoor, Ed., Springer-Verlag, 1996, p 25–70
23. P. Chevrier and J.R. Klepaczko, Spall Fracture: Mechanical and Microstructural Aspects, Eng. Fract.
Mech., Vol 63, 1999, p 273–294
24. C.S. Smith, Metallographic Studies of Metals after Explosive Shock, Trans. Metall. Soc. AIME, Vol
214, 1958, p 574–589
25. G.T. Gray III, Influence of Shock-Wave Deformation on the Structure/Property Behavior of Materials,
High-Pressure Shock Compression of Solids, J.R. Asay and M. Shahinpoor, Ed., Springer-Verlag, 1993,
p 187–216
26. D.G. Doran and R.K. Linde, Shock Effects in Solids, Solid State Phys., Vol 19, 1966, p 230–290
27. S. Mahajan, Metallurgical Effects of Planar Shock Waves in Metals and Alloys, Phys. Status Solidi (a),
Vol 2, 1970, p 187–201
28. W.C. Leslie, Microstructural Effects of High Strain Rate Deformation, Metallurgical Effects at High
Strain Rates, R.W. Rhode, B.M. Butcher, J.R. Holland, and C.H. Karners, Ed., Plenum Press, 1973, p
571
29. L.E. Murr, Residual Microstructure—Mechanical Property Relationships in Shock-Loaded Metals and
Alloys, Shock Waves and High Strain Rate Phenomena in Metals, M.A. Meyers and L.E. Murr, Ed.,
Plenum, 1981, p 607–673
30. L.E. Murr, Metallurgical Effects of Shock and High-Strain-Rate Loading, Materials at High Strain
Rates, T.Z. Blazynski, Ed., Elsevier Applied Science, 1987, p 1–46
31. D. Raybould and T.Z. Blazynski, Non-Metallic Materials under Shock Loading, Materials at High
Strain Rates, T.Z. Blazynski, Ed., Elsevier Applied Science, 1987, p 71–132
32. K.P. Staudhammer, Shock Wave Effects and Metallurgical Parameters, Impact Loading and Dynamic
Behaviour of Materials, C.Y. Chiem, H.-D. Kunze, and L.W. Meyer, Ed., DGM
Informationsgesellschaft mbH, 1988, p 93–112
33. G.T. Gray III, Shock Recovery Experiments: An Assessment, Shock Compression of Condensed
Matter—1989, S.C. Schmidt, J.N. Johnson, and L.W. Davidson, Ed., Elsevier, 1990, p 407–414
34. G.T. Gray III, Shock Experiments in Metals and Ceramics, Shock-Wave and High-Strain-Rate
Phenomena in Materials, M.A. Meyers, L.E. Murr, and K.P. Staudhammer, Ed., Marcel-Dekker, 1992,
p 899–912
35. G.T. Gray III, Shock Loading Response of Advanced Materials, High Pressure Science and Technology
1993, S.C. Schmidt, J.W. Shaner, G.A. Samara, and M. Ross, Ed., American Institute of Physics, 1994,
p 1161–1164
36. R.A. Graham, Impact Techniques for the Study of Physical Properties of Solids under Shock Wave
Loading, J. Basic Eng. (Trans. ASME), Vol 89, 1967, p 911–918
37. G.T. Gray III, R.S. Hixson, and C.E. Morris, Bauschinger Effect During Shock Loading, Shock
Compression of Condensed Matter—1991, S.C. Schmidt, R.D. Dick, J.W. Forbes, and D.G. Tasker, Ed.,
Elsevier, 1992, p 427–430
38. J.N. Johnson, R.S. Hixson, D.L. Tonks, and G.T. Gray III, Shock Compression and Quasielastic Release
in Tantalum, High Pressure Science and Technology 1993, S.C. Schmidt, J.W. Shaner, G.A. Samara,
and M. Ross, Ed., American Institute of Physics, 1994, p 1095–1098
39. J.N. Johnson, G.T. Gray III, and N.K. Bourne, Effect of Pulse Duration and Strain Rate on Incipient
Spall Fracture in Copper, J. Appl. Phys., Vol 86, 1999, p 4892–4901
40. E.G. Zukas, Shock-Wave Strengthening, Met. Eng. Q., Vol 6, 1966, p 1–20
41. C.M. Fowler, F.S. Minshall, and E.G. Zukas, A Metallurgical Method for Simplifying the
Determination of Hugoniot Curves for Iron Alloys in the Two-Wave Region, Response of Metals to
High Velocity Deformation, P.G. Shewmon and V.F. Zackay, Ed., Interscience, 1961, p 275–308
42. G.T. Gray III, Shock-Induced Defects in Bulk Materials, Materials Research Society Symp. Proc., Vol
499, 1998, p 87–98
43. E. Hornbogen, Shock-Induced Dislocations, Acta Metall., Vol 10, 1962, p 978–980
44. S. Mahajan, Metallurgical Effects of Planar Shock Waves in Metals and Alloys, Phys. Status Solidi (a),
Vol 2, 1970, p 187–201
45. L.M. Barker and R.E. Hollenbach, Interferometer Technique for Measuring the Dynamic Mechanical
Properties of Materials, Rev. Sci. Instrum., Vol 36, 196, p 1617–1620
Shock Wave Testing of Ductile Materials
George T. (Rusty) Gray III, Los Alamos National Laboratory
Techniques for Shock-Loading Materials
Samples are most frequently shock loaded under laboratory or controlled firing-point conditions using either
high-exposure (HE) explosives, gun-launched impactors (also referred to as flyer or driver plates), exploding
foils, or direct radiation impingement, including lasers and electron beams (Ref 3, 7, 8, 12, 25, 34, 36, 46, 47,
48, 49, and 50). Given sufficient lateral extent of the load and sufficiently thin sample thickness, a sample is
shocked in a one-dimensional plane strain manner; the sample experiences uniaxial strain loading and uniaxial
unloading. Each of these techniques offers advantages and disadvantages as summarized below.
Explosive-Driven Shock-Loading Methods. A controlled shock history can be imparted to a sample of interest
using several different explosive-driven system designs. A review of HE-driven shock assemblies used for
shock experimentation is detailed in several reviews including Dieter (Ref 46), Zukas (Ref 40), Duvall (Ref
51), Graham (Ref 36), Fowles (Ref 47), and McQueen (Ref 49). Explosive-driven shock-loading systems offer
the advantage of shock loading very large sample assemblies and components. Impact velocities up to
approximately 6 mm/μs ( in.μs) and a large range in shock pressures up to approximately 5 Mbar in ductile
metals can be readily obtained. HE-driven experiments can be relatively low cost. The disadvantages of using
HE-driven shock-loading methods are that they provide less control over flyer-plate velocity than other
methods and they cause tilt and bow of the driver plate.
Figure 2 shows several common HE-driven shock assembly designs. A driver plate is positioned either parallel
or inclined and displaced at the necessary standoff distance from the target. An explosive is detonated by a line
wave or plane wave generator that then either directly drives a driver plate or serves to uniformly ignite a main
HE charge that accelerates a driver plate into a sample assembly.
Fig. 2 Explosive-driven shock-loading assemblies. (a) Inclined-plate system. (b) Parallel-plate glass
system. (c) Plane wave generator lens
The inclined-plate assembly, sometimes termed a “mouse-trap plane wave initiator” (Ref 47), as seen in Fig.
2(a), has been used for low-velocity (<15 GPa, or 2.2 × 10
6
psi), peak shock pressure shock experiments. A line
wave generator is comprised of a perforated triangle of HE sheet that is initiated at one end of the generator
with a blasting cap and a small starter charge. Passage of the detonation front between the series of carefully
spaced holes in the line generator results in an essentially linear wave front arrival at the base of the generator.
The “mouse-trap” loading technique is used only when a rough approximation to planar impact is required due
to limitations imposed by edge effects and the requirement for high precision during assembly manufacture
(Ref 47).
Parallel Plate Glass Assembly. At higher pressures a parallel-plate-driven or plane wave lens-driven assembly
design is used (Ref 40, 46). Parallel plate-driven shock assemblies offer the opportunity to shock load large
assemblies to high peak pressures while still retaining plane wave loading. In a parallel-plate design (Fig. 2b),
point detonation of a line wave generator is used to produce line detonation of a starter charge of HE sheet,
such as plastic explosive with a pentaerythritol tetranitrite (PETN) base, placed on top of a thin sheet of steel or
of glass. In the first case, a thin steel sheet positioned at a preset angle above the main charge is made to impact
uniformly across the main charge to provide plane wave loading of the driver plate (Ref 52). In the second
instance, shown in Fig. 2(b), two overlapping sheets of plastic explosive fracture a glass sheet upon which they
are resting. The preset angle of the glass sheet above the main charge provides a planar shower of high-speed
glass fragments resulting in simultaneous detonation over the entire main charge surface.
Plane-Wave Generator Lens Assembly. As shown in Fig. 2(c), a driver plate in a parallel-plate configuration
can be driven using a plane wave generator lens placed directly above the main explosive charge (Ref 6, 7). In a
plane wave lens, a pyramidal construct of HE is fabricated using an outer layer of higher-detonation explosive
surrounding a lower-detonation inner explosive. Careful design of the lens geometry and explosives used will
produce planar shock arrival at the base of the lens. Plane wave lenses offer the highest degree of planar shock
wave drive. The disadvantage of using a plane wave generator lens is the substantially increased cost associated
with the fabrication, casting, and machining of HE lenses.
Diagnostic Techniques. For real-time shock-physics experiments the assembly designs shown in Fig. 2 can be
modified to allow placement of diagnostics immediately behind or adjacent to the shock assembly. The range of
diagnostic techniques applied to quantifying the physical property changes occurring during the passage of a
shock wave through a sample is diverse, including:
• Shorting pins to measure the impactor velocity and tilt
• Free surface velocity using capacitors (Ref 53), interferometric techniques (Ref 45, 54), or magnetic
technique (Ref 53) to record the particle-velocity time history at the rear of the specimen
• High-speed or streak photography to record shock wave breakout at the rear of the specimen (Ref 55,
56)
• Electrical conductivity or piezoelectric or piezoresistance response
• X-ray diffraction to quantify sample structural changes (currently a developmental technique)
Wave profile measurements, manganin pressure gages, or interferometry (specifically velocity interferometer
system for any reflector, or VISAR), can be used to quantify the broad range of phenomena illustrated in Fig. 1
for shock-loaded tin. For experimental configurations where the intent is to recover the shock-prestrained
sample, the HE-driven sample assembly is placed above a deceleration medium, such as a water tank or soft
wet sand (Ref 52). Deceleration and simultaneous cooling of the sample by firing the sample into water has
been shown to be effective in minimizing the microstructural and substructural changes that slow cooling can
allow (Ref 46, 52). The water effectively minimizes these changes by removing the residual heat induced in the
sample due to the dissipative shock compression process.
Gas/Powder Launcher-Driven Shock Loading. Based on the reproducibility of projectile launch velocity and
impact planarity, convenience of use in a laboratory setting, and ability to perform controlled oblique impact
(such as for combined pressure-shear studies, described in Ref 57), guns or launchers have become the method
of choice for many ductile material EOS, shock recovery, and spallation studies. For impacts at peak shock
stresses below approximately 700 GPa (100 × 10
6
psi) the precise control afforded by launchers is unequaled.
Gas- and propellant-driven launchers additionally offer unequaled control of impactor-target alignment and
impact planarity through the use of long-axis projectiles to minimize tilt (Ref 58, 59). Angular misorientations
between the projectile and target assembly of a few tenths of a milliradian are routinely achieved. Higher
velocities (up to 2 km/s, or 1.2 miles/s) can be achieved using propellant-driven launchers. Projectile velocities
up to 8 km/s (5.0 miles/s) are routinely achieved using a two-stage light-gas gun (Ref 60). Launchers and/or
guns of various designs usually possess smooth-bore launch tubes with barrel lengths from 3 to 30 m (10–100
ft). Acceleration of the projectile is accomplished using a compressed light gas (air, nitrogen, helium),
hydrogen, a propellant, or a combination of these. While hydrogen can result in substantially increased launcher
performance, the environmental and safety hazards commensurate with the use of hydrogen have reduced its
use except in the case of two-stage launchers. The disadvantages of fixed launchers are their high initial cost,
limited sample sizes (typically <100 mm, or 4 in., in diameter), and their significant facility sizes, making them
less portable than explosive-driven systems. Figure 3 illustrates many of the key design features of a launcher,
including its breech, launch tube, experimental chamber, and catch tank. As in the case of HE-driven shock
experiments, a broad range of diagnostics can be positioned directly adjacent to the sample during loading to
facilitate real-time measurements. Deceleration of samples for post mortem evaluation following shock
prestraining or Hopkinson fracture (spallation) testing can be achieved using a water-filled catch assembly or
soft rags positioned immediately behind the shock assembly in the catch tank (Ref 61, 62). Details of the
parameters used to design either real-time or recovery fixtures for postmortem studies using either HE- or
launcher-driven shock loading are discussed below.
Fig. 3 Schematic of 80 mm (3.1 in.) launcher at Los Alamos designed to facilitate soft recovery shock
wave testing
Shock-Loading Methods Using Exploding Foil and Laser-Driven Impactors. Shock loading of samples can also
be accomplished using impactors accelerated with an exploding foil (Ref 47) or a laser-driven flyer plate (Ref
63).
In the exploding-foil technique, shock loading is accomplished by discharging a high-energy capacitor bank
through a metallic foil, causing it to explode (Ref 64, 65). A flyer plate positioned adjacent to the exploding foil
is thereby accelerated. The impact velocity of the flyer plate is controlled by the energy of the discharge, the
mass per unit area of the foil, and the standoff distance between the flyer plate and the specimen. The electrical
energy transferred into the flyer can be augmented by placing a sheet of explosive between the foil and flyer
plate. An intermediate layer of explosive positioned in this manner is used to generate higher-amplitude,
longer-duration pulses. The principal advantage of this technique is its ability to generate very-short-duration
pulses facilitating attenuation shock studies and the ability to do many experiments in a short time.
Disadvantages of the exploding-foil technique include the fact that flyer-plate planarity is lower than achievable
with gas and propellant launchers, and tilt is generally not measured. Additionally, small flyer-plate dimensions
impose restrictions on the pulse durations and sample thicknesses that can be loaded in one dimension, and the
electrical fields commensurate with the capacitance-bank loading technique yield a high electrical field.
Laser-driven impactors are also used to shock load materials. In this technique a high-power laser is directed
through a quartz substrate to a metal-substrate interface (Ref 66). The metal layer, made from aluminum or
copper, is physically vapor deposited to a thickness of 0.5 to 50 μm thick on the quartz substrate. The laser
energy is deposited into the ablative layer, thus accelerating the metal layer (Ref 66). The high-temperature and
high-pressure ablative layer serves to accelerate the remaining tamped solid metal as a miniature flyer plate.
The flyer plate launched is the same diameter as the laser beam, which is typically 0.4 to 1 mm (0.016–0.04 in.)
in diameter. Miniature flyer plates using this technique can be accelerated to velocities ranging from 0.5 to
more than 6 mm/μs (0.02–0.24 in.). The advantage of this loading technique is its compact size scale, ability to
produce very-short-duration shock pulses, and potential as a means to interrogate interfaces in bicrystals (Ref
67). The disadvantages of this technique include the fact that the very thin flyer plate limits the shock pulse
duration to short times (e.g., <100 ns), and the short pulse duration and the rapid attenuation of the short pulse
lengths produced by the thin flyer plates will not support steady shocks in thicker samples (>0.5 mm, or 0.02
in., thick), thereby limiting the usefulness of this technique to studying bulk phenomena, such as spallation, in
polycrystals.
Radiation-Driven Shock-Loading Methods. Shock loading of materials can also be achieved through direct
application of a penetrating radiation impulse to a ductile material (Ref 47). This can be achieved using electron
beam impulse loading (Ref 68), direct laser impingement (Ref 69), or exposure to an underground near-nuclear
weapon (Ref 12).
Pulsed electron beam machines can produce electron energies of more than 5 MeV, fluences of several hundred
calories per square centimeter, and pulse durations of a few tens of nanoseconds (Ref 68). Electron beams can
be used to produce beams of essentially uniform power over areas of a few square centimeters. The stress pulse
in the sample is generated by the extremely rapid heating of the sample at depths in the material, which cannot
be relaxed by a rarefaction wave during the deposition time of the pulse.
Direct laser impingement on the surface of a sample can similarly be used to induce a shock wave in a material
(Ref 69, 70, 71, 72, and 73). In this type of shock-loading experiment a high-power laser is focused on a thin
sample. Testing is conducted in a vacuum to avoid air ionization. The irradiated metallic surface is vaporized
producing a plasma, which induces a compressive shock wave in the target. The duration of the pressure pulse
in the target is of the same order of magnitude as that of the laser pulse, typically 0.5 to approximately 30 ns.
The amplitude of the stress pulses induced by laser heating can induce strong shocks up to 200 GPa (29 × 10
6
psi) depending on the irradiation intensity. Uniaxial strain can be achieved in a central portion of thin samples
as long as the diameter of the irradiated spot is larger than the sample thickness. The advantages and
disadvantages of this technique are analogous to the miniature flyer discussed above. The principal
disadvantage to direct laser irradiation for shock wave studies is the attainment of a steady shock wave through
a polycrystalline material. The short pulse duration and the attenuation of these pulses restricts testing to
samples typically less than 1 mm (0.04 in.) thick.
Exposure to Nuclear Explosion. The final direct radiation-driven shock wave technique results from the
placement of samples in the near zone of an underground nuclear explosion. Such experiments proved capable
of supporting studies of the compressibility of metals such as iron, lead, copper, and uranium in the pressure
range up to 20 TPa (29 × 10
12
psi) (Ref 12, 74, 75, and 76). Experimental tests of this type have yielded
extremely high-pressure compressibility and EOS information on a range of ductile metals, as summarized in
the references, but has not produced absolute EOS information.
References cited in this section
3. M.H. Rice, R.G. McQueen, and J.M. Walsh, Compression of Solids by Strong Shock Waves, Solid State
Phys., Vol 6, 1958, p 1–63
6. R.G. McQueen and S.P. Marsh, Equation of State for Nineteen Metallic Elements from Shock-Wave
Measurements to Two Megabars, J. Appl. Phys., Vol 31, 1960, p 1253–1269
7. R.G. McQueen, Laboratory Techniques for Very High Pressures and the Behavior of Metals under
Dynamic Loading, Metallurgy at High Pressures and High Temperatures, K.A. Gschneidner, Jr., M.T.
Hepworth, and N.A.D. Parlee, Ed., Gordon and Breach, 1964, p 44–132
8. R.G. McQueen, S.P. Marsh, J.W. Taylor, J.N. Fritz, and W.J. Carter, The Equation of State of Solids
from Shock Wave Studies, High Velocity Impact Phenomena, R. Kinslow, Ed., Academic Press, 1970, p
293–417, 515–568
12. L.V. Altshuler, R.F. Trunin, V.D. Urlin, V.E. Fortov, and A.I. Funtikov, Development of Dynamic
High-Pressure Techniques in Russia, Phys. Usp., Vol 42, 1999, p 261–280
25. G.T. Gray III, Influence of Shock-Wave Deformation on the Structure/Property Behavior of Materials,
High-Pressure Shock Compression of Solids, J.R. Asay and M. Shahinpoor, Ed., Springer-Verlag, 1993,
p 187–216
34. G.T. Gray III, Shock Experiments in Metals and Ceramics, Shock-Wave and High-Strain-Rate
Phenomena in Materials, M.A. Meyers, L.E. Murr, and K.P. Staudhammer, Ed., Marcel-Dekker, 1992,
p 899–912