NBSIR 87-3634

Research Information Center

National Bureau of Standards

Gaithersburg, Maryland 20899

NOV 2 1987

ifco i Dynamic Microindentation of RDX:

Effect of Rate on Plasticity and

Fracture

R. S. Polvani, A. W. Ruff, and J. C. Robbins

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Metallurgy Division

Gaithersburg, Maryland 20899

June 1987

Issued September 1987

Final Technical Report

Contract No. N001 4-85-F0065

Reproduction in whole or part is permitted for any purpose of the

United States Government.

Prepared for: Department of the Navy

Office of Naval Research

Mechanics Division

Arlington, Virginia 22217-5000

NBSIR 87-3634

DYNAMIC MICROINDENTATION OF RDX:

EFFECT OF RATE ON PLASTICITY AND

FRACTURE

R. S. Polvani, A. W. Ruff, and J. C. Robbins

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Metallurgy Division

Gaithersburg, Maryland 20899

June 1987

Issued September 1987

Final Technical Report

Contract No. N0014-85-F0065

Reproduction in whole or part is permitted for any purpose of the

United States Government.

Prepared for: Department of the Navy

Office of Naval Research

Mechanics Division

Arlington, Virginia 22217-5000

U.S. DEPARTMENT OF COMMERCE, Clarence J. Brown, Acting Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

DYNAMIC MICROINDENTATION OF RDX: EFFECT OF RATE

ON PLASTICITY AND FRACTURE

R.S. Polvani, A.W. Ruff, and J.C. Robbins

Metallurgy Division

National Bureau of Standards

Gaithersburg, MD 20899

Submitted to:

Office of Naval Research

Mechanics Division

Department of the Navy

Arlington, VA 22217-5000

FINAL REPORT

June 1987

DYNAMIC MICROINDENTATION OF RDX: EFFECT OF RATE

ON PLASTICITY AND FRACTURE

R.S. Polvani, A.W. Ruff, and J.C. Robbins

Metallurgy Division

National Bureau of Standards

Gaithersburg, MD 20899

ABSTRACT

Microindentation measurements have been made on RDX

crystals to determine the effect of load and time of

loading on their mechanical response. A spherical

indenter tip was used. The results are compared to

those obtained earlier using pyramidal Vickers

indenters. At the shortest loading periods a higher

than expected plastic response was found which may

indicate that local heating resulted from the

indentation process.

INTRODUCTION

The uses of energetic materials such as explosives and rocket

propellants require materials with controlled ignition behavior.

Material characteristics that can lead to pre-ignition are not

acceptable. In the case of propellants the material must burn

evenly after ignition. There is still disagreement over the

basic process of ignition as a result of mechanical impact.

A theory which we support and are investigating together with the

University of Maryland (Prof. R. Armstrong) and the Naval Surface

Weapons Center (Dr. W. Elban) predicts that impact deformation

causes dislocation generation and motion, and subsequent behavior

of the dislocations causes ignition [1,2]. Piling-up of

dislocations at internal obstacles and their subsequent sudden

release are key factors of the theory. Both the kinetic and

self-energy of the dislocation substructure are large and either

1
can change suddenly. Concentration of much of the dislocation

substructure at barriers or obstacles is postulated to cause

formation of local "hot spots" and subsequent ignition.

However, in most materials there are two competing energy

dissipation modes, plasticity and cleavage fracture. The role of

dislocations in these two modes is different, and the potential

for release of energy by dislocations would also be expected to

be different. Principal thrusts of this work were to determine

the plastic and fracture characteristics, and particularly any

rate effects, of a prototype energetic material, RDX. We will

report here recent measurements of the response to indentation

deformation of RDX (cyclo-trimethylene trinitramine ) with respect

to the magnitude and duration of loading. Earlier studies using

this method have been described [3-5].

EXPERIMENTAL

The NBS Dynamic Microindentation Instrument is uniquely suited to

this study. It can work with very small crystals, which are the

only available form of production RDX material, and provide

mechanical data from within still smaller regions that may

correspond to the size of hot spot sites. Further, detailed

observations of deformation behavior can be made over a wide

range of loading rates even up to impact rates.

The instrument is shown schematically in Figure 1. It uses an

2
electromagnetic driver to force an indenter into the specimen's

surface. The loading waveform can be varied in shape, magnitude,

and duration. Particular specimen areas can be positioned under

the indenter. Since instantaneous values of indenter position

and force are recorded during both loading and unloading

(Figure 2), it is possible using the resulting load-displacement

curve to describe the complete mechanical response of the

specimen material [6,7].

Three significant improvements were made recently to the dynamic

capabilities of the instrument to better simulate mechanical

impact conditions. They required major mechanical and electronic

revisions of the instrument. First, dynamic recording capability

was extended to shorter times and the lumped load cell/ sample

resonance was reduced. Samples are now set directly into the

load cell. Second, by eliminating the coupled mass of a separate

holder, resonance effects are minimized and dynamic range

improved. Testing is performed down to 0.001 second duration,

which is a 10 fold gain over the previous configuration. The

minimum duration limitation is now due to the inertial mass of

the indenter assembly. Third, a new depth measuring instrument

has been added which has two advantages. Depth sensitivity,

volts(out) / urn ( displacement ) , is improved by a factor of 60X;

the resolution is now < 0.03 urn. Further the dynamic

capabilities are much better; the 3 db band pass limit is

22 kHz rather than 7 kHz. The indenter shape was also changed for

3
this study. A ball, 794 \m diameter, was used rather than a

Vickers pyramidal indenter [3]. Advantages of a ball are that it

maximizes the tendency of samples to deform plastically, and

test results are more easily related to conventional engineering

properties. Lastly, by using a spherical shape, the indentation

is thought to better correspond to the loading conditions

occurring in an RDX aggregate.

Material for the current test series was production RDX (Holston

Grade D from Lot #925) which we obtained from the Naval Weapons

Center at White Oak. Containing a significant concentration of

HMX, production RDX is an impure material. The HMX takes the form

of a couplet, a single liquid droplet within a matrix void. No

attempt was made to quantify the HMX concentration. Optical

examination at 500x magnification revealed a distribution of

sizes ranging down to the smallest detectible size. The

concentration and void morphology are believed typical of RDX.

When mounting the six (6) different samples into the instrument

care was taken to maintain the same crystallographic alignment

for all samples. Further, a means of both preparing sample test

surfaces and a much improved means of mounting samples into the

instrument was developed by recognizing that RDX is hydrophobic.

As necessary, test surfaces were lapped flat using water

lubricated metallographic polishing wheels. Samples are cemented

to the load cell using a water based aliphatic glue. This avoids

4
the contamination which we found organic binders caused, and aids

achieving a good coupling of samples to the load cell.

Photographs of the mounted crystals are shown in Figure 3

Three loads and loading durations were used. "Slow" runs had a

100 second duration, "intermediate" runs were 1 second, and

"fast" runs had a duration of 1 millisecond. Applied loads of

.5, 1, 2 and 3 Newtons were used. Because the 794 ym ball

produced broad and shallow impressions not easily observed,

indentations at . 5 N had no obvious residual impression.

Indentation loading times ranged over five orders of magnitude;

for each indentation recordings were made of the instantaneous

load and depth of penetration.

RESULTS AND DISCUSSION

Representative load-displacement curves for RDX at 1 N load for

slow and fast loading durations are shown in Figure 4 and are

quite different. The area under the fast curve is greater and

the curve is more rounded. The area under a load displacement

curve gives the total deformation energy, which can be subdivided

into elastic, and plastic components as shown schematically in

Figure 5. Table 1 gives individual values measured on the RDX

crystals of the three energy components; Table 2 gives the

average for each load and time condition. Consistent with Figure

4, we found RDX generally absorbs more deformation energy with

increasing rate of loading. The increase is largely due to

5
enhanced plasticity; the plastic energy component increases while

the elastic energy component remains nearly constant. These

trends are shown graphically in Figures 6-8. The total energy

(area under the load-displacement curve) shown in Figure 6

increases slightly with shorter loading times. However, the

plastic energy (Figure 7) increases significantly with decreasing

loading time while the elastic energy actually decreases slightly

(Figure 8). Thus the deformation response to indentation -becomes

more plastic at shorter loading times. At the highest load of 3

N this trend is different because of the onset of fracture in all

the crystals.

A photograph showing a series of seven indentations in an RDX

crystal using the spherical indenter is shown in Figure 9.

Because of the large radius of curvature, the indentations are

not completely visible, rather, the presence of cracks at each

indentation is seen in the optical photograph.

In contrast when a pyramidal indenter is used [ 3 ]

,

both the

indentation and the associated cracking (if any) are readily seen

as indicated in Figure 10. It is also possible to detect

fracturing associated with indentation from the characteristics

of the load vs displacement curve. Figure 11 shows the

difference between a plastic response to indentation in RDX and a

fracture response; the difference in curves can be understood as

resulting from an extended displacement associated with crack

growth and perhaps spalling of material in the latter case.

6
Through microscopic inspection of the indentations and study of

the load vs displacement data, we have determined the extent of

fracture associated with indentations produced over the range of

loads and loading times used in this study. The results are

shown in Figure 12 which also includes results from the earlier

study [3]. Data were obtained over a range of four decades in

load and five decades in loading time. It is seen that three

regions exist: (1) where both indenter shapes cause fracture, (2)

where only the pyramidal shape causes fracture, and (3) where

neither shape does. This is clear evidence for the importance of

indenter (or projectile) shape in affecting the mechanical

response of RDX and possibly other energetic materials.

Previously we have measured the response of RDX crystals similar

to the ones used here to indentation with a Vickers pyramid.

Those results, shown in Figure 13, for a slow loading period of

100 s, established the existence of a load threshold for

fracture. The curve of load vs diagonal indentation length in

the plastic region has a slope of 1.92 which is close to the

theoretically expected value of 2.0. In the fracture region, the

slope has a much lower value of 0.60. Plain strain fracture

mechanics analysis would predict a slope of 1.5. Apparently the

fracture process in RDX under conditions of pyramidal indentation

is more complex. It also appears to differ from that found [2]

in MgO, even though MgO has been used in some cases as a model

material for RDX and other energetic solids.

7
The difference found in response of RDX to mechanical indentation

using two different shapes indicates the need for analytical

solutions for the subsurface stress and strain fields in this

problem. Keer et al. [8] have reported a three-dimensional

static solution to fracture under Vickers pyramidal indentation.

Because of the observed rate effects and the complex mixing of

plastic and fracture response, accurate calculations for a

material like RDX would be difficult. An approach similar to

that taken by Evans et al. [9] would seem desirable as a first

effort. Figure 14 gives a result from that work for the impact

of a 400 urn diameter spherical projectile onto a ZnS surface at

860 m/s. It is seen that a large plastic zone is formed of a size comparable to that of the surface crater (200 urn). The

impact time interval was of the order of 1 i±s. During the

unloading period (particle rebound) tensile stresses develop at

the edge of the plastic region - in this case as large as

0.5 GPa. Crack growth in these regions would be expected.

The results presented here using a spherical indenter are thought

to indicate that near-adiabatic loading of the RDX samples was

achieved for the short loading intervals. One would expect that

under isothermal indentation conditions, presumably present for

the longer loading intervals, any increase in the rate of loading

would reduce the extent of plastic deformation and increase the

proportion of elastic deformation. However, the opposite was

observed in RDX since the proportion of plastic deformation

8
increased with loading rate. In a rate sensitive deformation

process the conversion of mechanical energy to heat requires

consideration of two factors. One is the effect of loading rate

on dislocation mobility, and second is the effect of barriers

such as the microscopic regions present in these crystals that

contain residual HMX. We believe that the HMX regions can act as

obstacles for dislocation glide. Thus in one extreme, at slow

loading rates and under isothermal conditions, the dislocations

in RDX should be mobile, glide at velocities near the speed of

sound, and entrapment times at barriers should be short. Thermal

conduction during the relatively long loading period can prevent

a temperature rise at the barrier sites. In the other extreme,

at high rates, the situation may be far different. Dislocations

then spend most of the time trapped at or trying to escape from

barriers. In the short time available, conductivity in RDX is

too low to quickly dissipate any heating; thus the process is

nearly adiabatic in nature. This local heating may be an

important factor in "hot spot" formation in energetic materials

at high loading rates.

CONCLUSIONS

As a result of this work two important mechanical characteristics

of RDX can be recognized. The first involves the importance of

indenter geometry. At high loading rates, the plastic behavior of

RDX depends on the stress concentration effect of the indenter

geometry. Previously [3] we had not found the usual evidence of

9
plasticity (instead finding cleavage fracture), and concluded

this was a general property of RDX. This appears only to be true

for the Vickers indenter, a high stress concentration geometry.

Thus it appears now that RDX is not inherently brittle.

Irrespective of the rate with a ball indenter RDX was* found to

deform plastically for loadings up to 2 N. The second

characteristic was that unexpectedly RDX became more ductile

under conditions of rapid indentation. This may have resulted

from local heating of critical regions in the RDX crystals.

Further studies of these rate effects and shape effects would be

needed to better understand the material itself.

ACKNOWLEDGEMENTS

The assistance of several staff members at the Naval Surface

Weapons Center, White Oak, Maryland, in providing information and

test specimens on several occasions through the course of this

research is gratefully acknowledged. We are also indebted for

many helpful discussions to Dr. Wayne Elban and Dr. Ron

Armstrong. Partial support for this research was provided by the

Office of Naval Research Energetic Materials Program.

10
REFERENCES

1. R.W. Armstrong and W.L. Elban, in Energetic Material

Initiation Fundamentals Workshop , Los Alamos National

Laboratory, October 14, 1986.

2. R.W. Armstrong and W.L. Elban, in Microindentation Techniques

in Materials Science and Engineering , ed. P.J. Blau and B.

R. Lawn, ASTM STP 889 (Philadelphia, PA, 1986 ) .pp. 109-126

3. R.S. Polvani and A.W. Ruff, in Workshop on Energetic

Materials , Chestertown, MD, January 29, 1986. Also

unpublished report to the Office of Naval Research.

4. R.S. Polvani, A.W. Ruff, and E. P. Whitenton, J. Testing and

Evaluation (ASTM, 1987, in press).

5. R. S. Polvani , A.W. Ruff, and J.C. Robbins, in Workshop on

Dynamic Deformation, Fracture, and Transient Combustion , Chestertown, MD, May 12, 1987.

6. H.M. Pollock, D. Maugis, and M. Barguins , in

Microindentation Techniques in Materials Science and

Engineering , ed. P.J. Blau and B. R. Lawn, ASTM STP 889

(Philadelphia, PA, 1986). pp. 47-71.

7. M. F. Doerner and W.D. Nix, J. Materials Research 1, 601-609

(1986) .

8. L.M. Keer, T.N. Farris, and J.C. Lee, J. American Ceramic

Soc. 69, 392-396 (1986) .

9. A.G. Evans in Treatise on Materials Science and Technology , 16 , ed. C.M. Preece (Academic Press, N.Y., 1979). pp.1-67.

11
Figure 1. A schematic diagram of the NBS

Dynamic Microindentation Instrument.
(

• ATP/saw jfi 09 ) avcn NOIXYIN3GNI

Figure 2. Load vs. displacement curve obtained

from an NBS copper microindentation

standard material using a Vickers

indenter
Figure 3. Photographs of the six

indentation tested. A

included.

RDX crystals as mounted and

millimeter scale is also
Figure 4. A comparison of representative

load-displacement curves for RDX

for two loading durations:

(a) 100 seconds

(b) 0.001 second
Load

Displacement

Figure 5. Schematic representation of the

load-displacement curve.

(a) After loading, curve 0, recovery

can be elastic, curve 1, plastic,

curve 2, or some combination.

(b) The mechanical response can be

quantified by the relative energy

or area under the curves,

associated with plastic response,

Ap, and elastic response, Ae

.
Total

Energy

(gm

—

urn)

Total Energy versus Duration Time

Log Loading Duration Time (seconds)

Figure 6. Total energy in g»]im for RDX crystals at indicated

loads and loading times.
Plastic

Energy

(gm

—

E

Log Load Duration Time (seconds)

Figure 7

Plastic component of energy in g«um for RDX crystals

at indicated loads and loading times
Elastic

Energy

(gm-um)

Elastic Energy versus Duration Time

Log Loading Duration Time (seconds)

Figure 8. Elastic component of energy in g*|im for RDX crystals

at indicated loads and loading times.
Figure 9. Group of seven indentations on

RDX crystal using spherical

indentor at 3 N load. Fracture

has occurred within each indent

and can be seen in this optical

micrograph.

Figure 10. Indentation using a Vickers

pyramid (arrow) in an RDX

crystal
Figure 11. Load displacement curves for an RDX

crystal showing the characteristic

differences associated with plastic

response and fracture response to

indentation with the pyramidal

indenter
REGIONS

IN

LOAD

VS

LOADING

TIME

SPACE

WHERE

FRACTURE

(F)

OR

PLASTIC

(p)

RESPONSE

IS

FOUND

FOR

RDX

WITH

TWO

SHAPES

OF

INDENTER

USED

-

VICKERS

PYRAMID

AND

HEMISPHERE.

Figure 12. Effect of load and loading time on plastic or

fracture response of RDX crystals.

(n) even

LOADING

TIME

(sec)
Log

Applied

Load

(Newtons)

Log Vickers Diagonal Length (mm)

Figure 13. Relationship of load to diagonal length of pyramidal

indentation produced in a previous study [ 3 ] of RDX

crystals under slow loading conditions (100 s).
Distance

Below

Impacted

Surface

(

Cni )

PENETRATION PHASE

0.04 0.03 0.02 0.01 0

ressive Stress ,•#////

9 t t / • » *

... i Plastic Wave Front

x ::: : :: jril j 0 0.01 0.02 0.03 0.04

Distance From Impact Center

Unloading Phase

(c ) 0.5 GPa ' In-Plane Tensile Stresses

i » i

Figure 14. Analytical results of stresses produced by spherical

particle impact on ZnS according to Evans et al.

[9]. The penetration (loading) phase produces

considerable plastic deformation. The unloading

phase produces relatively large in-plane tensile

stresses. Similar stress patterns might be

expected during high rate loading with a spherical

indenter
Table 1. Individual measurements of indentation

response of RDX crystals showing

elastic and plastic proportions.

LOAD

N

TIME

5

ELASTIC

iit-gi

PLASTIC

ufe-gc

TOTAL ut-gsEL/PL

0.49 ioo 0.25 0.03 0.2& 5.00 0.48 100 0.20 0.04 0.24 4.67

0.48 100 0.26 0.02 0.28 12.73

AVS = 0.48 100 0.23 0.03 0.27 8.46

STD /- = 0.00 0.03 0.01 0.02 3.31

0.48 1 0.18 0.10 0.28 1.76 0.47 1 0.19 0.09 0.27 2.21 0.47 1 0.19 0.07 0.26 2.79

AVS = 0.47 1 0.19 0.09 0.27 2.25

STD +/- = 0.00 0.00 0.01 0.01 0.42

0.46 0.001 0.19 0.11 0.30 1.67 0.40 0.001 0.15 0.15 0.29 1.00

0.51 0.001 0.18 0.19 0.37 0.94

0.49 0.001 0.18 0.16 0.33 1.11

AVS = 0.46 0.001 0.17 0.15 0.32 1.18 STD +/- = 0.04 0.02 0.03 0.03 0.29

1.07 100 0.78 0.29 1.07 2.69

1.07 100 0.81 0.28 1.09 2.94

1.07 100 0.83 0.23 1.07 3.61

AV6 = 1.07 100 0.81 0.27 1.07 3.08

STD +/- = 0.00 0.02 0.03 0.01 0.39

0.96 1 0.31 0.09 0.41 3.33

0.97 1 0.33 0.10 0.43 3.22

0.97 1 0.38 0.15 0.52 2.56

AVS = 0.97 1 0.34 0.11 0.45 3.04

STD +/- = 0.00 0.03 0.02 0.05 0.34

1.20 0.001 0.86 0.79 1.65 1.10

1.14 0.001 0.76 0.63 1.39 1.20

1.12 0.001 0.75 0.75 1.49 1.00

1.02 0.001 0.76 0.75 1.51 1.02

1.17 0.001 0.71 0.76 1.47 0.93

AVS = 1.13 0.001 0.77 0.74 1.50 1.05 STD /- = 0.06 0.05 0.05 0.09 0.09
LOAD

N ME ELASTIC PLASTIC TOTAL EL/PL

s 1.95 100

1.95 100

1.95 100

AVG = 1.95 100 STD +/- = 0.00

2.24 0.001

2.01 0.001

2.11 0.001

AVG = 2.12 0.001

STD /- = 0.09

2.95 100 2.95 100

AVG = 2.95 100 STD +/- = 0.00

2.52 0.001

2.44 0.001 2.46 0.001

2.47 0.001

AVG = 2.47 0.001

STD /- = 0.03

us-gt ui-gi UB-QS

1.56 0.46 2.02 3.41 1.63 0.42 2.05 3.88

1.77 0.51 2.28 3.47

1.65 0.46 2.12 3.59 0.09 0.04 0.11 0.21

1.65 1.45 3.10 1.14 1.39 1.06 2.45 1.31 1.58 1.55 3.13 1.02

1.54 1.35 2.89 1.16 0.11 0.21 0.31 0.12

1.44 3.56 5.00 0.41

1.74 3.67 5.41 0.47

1.59 3.61 5.20 0.44 0.15 0.06 0.20 0.03

2.22 3.75 5.97 0.59

2.30 4.00 6.30 0.57 2.69 3.76 6.45 0.71 2.59 3.72 6.31 0.70

2.45 3.81 6.26 0.64 0.19 0.11 0.17 0.06
Table 2. Test parameters and measured energy values for indentation

of RDX crystals with hemispherical indenter.

ENERGY

Load Time Elastic Plastic Total EL/PL

(N) (S) (um-g) (um-g) (um-g)

AVG 0.48 100

STD DEV

AVG 0.47 1

STD DEV

AVG 0.46 0.001

STD DEV.

AVG 1.07 100

STD DEV

AVG 0.97 1

STD DEV

AVG 1.13 0.001

STD DEV

AVG 1.95 100

STD DEV

AVG 2.12 0.001

STD DEV

AVG 2.95 100

STD DEV

AVG

STD DEV

0.001

0.23 0.03 0.27 8.46

0.03 0.01 0.02 3.31

0.19 0.09 0.27 2.25

0.00 0.01 0.01 0.42

0.17 0.15 0.32 1.18

0.02 0.03 0.03 0.29

0.81 0.27 1.07 3.08

0.02 0.03 0.01 0.39

0.34 0.11 0.45 3.04

0.03 0.02 0.05 0.34

0.77 0.74 1.50 1.05

0.05 0.05 0.09 0.09

1.65 0.46 2.12 3.59

0.09 0.04 0.11 0.21

1.54 1.35 2.89 1.16

0.11 0.21 0.31 0.12

1.59 3.61 5.20 0.44

0.15 0.06 0.20 0.03

2.45 3.81 6.26 0.64

0.19 0.11 0.17 0.06

2.47
NBS-T14A (rev. 2-60

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

, REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 87-3634 SEPTEMBER 1987

4. TITLE AND SUBTITLE

Dynamic Microindentation of RDX: Effect of Rate on Plasticity and Fracture

5. AUTHOR(S)

R.S. Polvani, A.W. Ruff, and J.C. Robbins

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No. N0014-86-F0065

t. Type of Report & Period Covered

FINAL

3. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

Office of Naval Research

Mechanics Division

Department of the Navy

Arlington, VA 22217-5000

10. SUPPLEMENTARY NOTES

| 1 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bibliography or literature survey, mention it here)

/

'

Microindentation measurements have been made on RDX crystals to determine the effect

of load and time of loading on their mechanical response. A spherical indenter tip

was used'. The results are compared to those obtained earlier using pyramidal Vickers

indenters. At the shortest loading periods a higher than expected plastic response

was found which may indicate that local heating resulted from the indentation process

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Dynamic properties, energetic material, f racture , mechanical

,

gitc-E-jp indantati «-n- pla s-fc- ic-i t y- ,—RDX

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