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* MEMORANDUM REPORT ARBRL-MR-(0951

F THE HUGON lOT OF 4340 STEEL RC 54-55

Robert E. FranzJoseph L. Robitalle

September 1979 D D

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MEMORANDL4 REPORT' 517RL. -W29I A

j The IW.goniot of 43A0 Steel RC 5-55 Foa

j Robert E ranx @W Joseph L./Robitaille '

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Shoi physiics~44 Steel

am &W aCVX ofw4 am OW a wem or : St 21.me1ugonlot of 4340 steel of Rockwell %C3E hardness 54-55 has been measured.

The a or b.c.c. phase iagos~tot can be rep"Seted by the equAtion U a 4.67The4 u whereoU is the ae vciy MWas uboie the parce velosityo o)t/i.The4 u wher U is the cave vcity pae above the paG rtil ocity pint i/sclose to that of roiled hamosms amr.

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TABLE OF CONTENTS

Nae

TAbLE OF CONTENrS ..... ............. .

1. INTRODUCTION .

II. EXPERIMENTAL . . . . . . . . . . . . . . . . . . . . . . . 5

III. RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . 7

REFERENCES ..... ...... ........................ 13

DISTRIBUTION LIST . ......... .................... IS

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1"A

1. INTRODUCTION

For some time the Ballistic Research Laboratory has been measuringand studying the mechanical and physical properties of materials ofinterest to the Army. This includes a spectrum of tests from slowlyapplied loads in convential testing machines to shock loading with light-gas gun impacts or high explosives. This report gives results of shockwave tests on 4340 steel of Rockwell "C" hardness 54-55. It, also,includes ultrasonic and quasi-static data which provide zero points onthe high pressure Hugoniot curves. Table I gives a chemical analysis ofthis material.

Like iron and rolled homogeneous armor (RHA), 4340 steel displays aphase transition under shock loading at approximately 13 GPa. Thiscauses the material to display a one, two, or three wave structure depend-

ing on the initial shock strength. Hlauver , 2 has discussed this phenominonin two recent reports on the Iugoniot of RHA. The experimental methodused for this study is the same as Hiauver's and consists of measuring andanalyzing the free surface motion of a sample of material shocked in theusual one-dimensional strain experiment. This motion can become compli-cated when the three wave structure is encountered. The analysis used isthe same as in the aforementioned reports. It is based on a mid-point ofthe wave analysis used by Barker 3, in which the wave velocities are meas-ured from the half amplitude points in the wave.

11. EXPER|MWNTAL

The experimental specimens were cut out of a IOM (4-inch) roundbar of material and heat-treated to RC 54-55 hardness. They were, then,machined to final dimensions. The heat-treatment consisted of soaking at860C for 30 minutes, oil quenching, drawing down at 315%: for I hout.and air cooling. The measured density of the material was 7800 kg/ms.

The experiments were performtsI with the BRI. light-Sas gun. The freesurface motion was measured with a laser velocity interferometer called aVISAR which was developed by Barker 4. Figure I shows the results of fivetests performed at different impact velocities. Four are symetricalimpacts of nominal 6.13mm thick plates of 4340 steel 7tm in diameter and

'G. IIziuver, "The A'a-ihao Hu;onfit of RolZ led HVenerto Amr.iOi",ballitie' Rceavarch !1,*orto#O Momran..k. .+port No. 2b1, Azguet 1979.

~'6. Nauvar and A. "'itZni. "Tho H l~Pa u iicomiot of Role4 fimwgaencoua Avor", or.ande Reort ARRL-X.R-02909, Mau h 179.

L.. . azrker, "Alp;-laae Mliwyot of Iro", &1. A a. Vol. 46,., , Juno ;.976 ' 2544-

I.'. ~~4. M. IRarker -and R?. E. Hoal enIbach, "L~zer Inte4rferrnteter for MeiasuringH~ih Vlooities of An A~~&U Sw'faoe', J. AiL p2.

;97', pp 4 66-1.So 'l NoqTe

1.6-

1.4 O EST NUMBERS

E 1.2o

1.0

LUU "0.8-

uj0.6-LU

.4

0.4

00 0.2 0.4 0.6 0.6 1.0 1.2

T IM E (p&,)

FIGURL 1: VISAR Results for S Tests with 4340 Steel

one (Test #6) is the result of the impact of a 3.0 thick tungsten plateon a 9.43 thick 4340 steel specimen.

The elastic wave velocity was measured using an ultrasonic deviceconstructed by Hauver1 and called by him "The Thumper". This velocity,which was used in subsequent data analysis, was 5.86 ki/s.

The low pressure a-phase goes through the bulk sound velocity at the:ero point. This velocity has been calculated from bulk modulus measure-ments made in quasi-static compression tests in which the volumetricchange with load was measured. This was accomplished by measuring boththe axial and circumferential strains using resistance strain gages

applied directly to circular cylindrical specimens. The volumetric strainwas then calculated from equation (1)

= I~ tl )(I+,: -1 , (1)a

where,

c\- axial strain

c -circumferential strain.

Since in a uiiiaxial strain experiment the pressure is one-third ofthe axial stress, the slope of the curve shown ir Figure 2 is the bulkmodulus. The calculated bulk sound velocity is then 4.67 km/s. Poisson'sratio was also directly calculated using the axial and circumferentialstrain measurements.

Il. ~RESULS

Table 11 shows in tabular for% the Itugoniot points deduced from thedata and one point measured in an experiment by Ilauver in which both RPIAind 4340 were shocked to high pressure with an explosively thrown steelplate. For the 14 or b.c.c. phase the shock velocity-particle velocityline is represented by the least squares equation U - 4.67 * 1.44 uwhere U is the shock velocity and u the particle velocity. The a to ror h.c.p. phase transition occurred at an average shock pressure of 13.2GPa. The average dynamic elastic limit was 2.4) GPa. The measuredPoisson's ratio was 0.288. This gives, according to Jones and Grahams ahydrostatic transition pressure of 12.2 tWa.

50. N.. Jonoo and R. A. GrahaR, "Shoar Strvgth E ffots o" Ta.e 2Wneitio"

Pyloaur-ae" P-tm-,iud S, ,Jhook-Coqreeeio'i ofrpr-p t~a" 3tpiposi w't nOiw Acourwat. Chat.-itriatim of the High Th'epuurv Fwirm~uent. U.S.Dopt. of Comwroo, Natiopul L au of Sz, ithvrebwV, D.,O~tcber 14-28, 2968.

7

The elastic limit measurements varied widely as did measurements by

Butcher and Canon 6 on this material. It is surprising and encouragingthat their average value was the same, 2.41 GPa.

Figures 3 and 4 show the U-u plots for 4340 RC 54-55 steel comparedto both RHtA and iron. It can be seen that the a-phase of each materialhas practically the same slope but the intercept depends on the bulk soundvelocity. The c-phase of RHA and 4340 are the same within the experimental

error.

ACKNOWLEDGENENTS

The authors would like to thank George [lauver for his help with theexperiments and especially for his explanations of the data analysis. Wewould like to vhank R. Benck and V. Diberardo for the quasi-static

measurements.

TABLE I

CUtMICAL ANALYSIS OF 4340 STEEL

11 L, 9MENT RESULTS %

Carbon 0.40; 0.39Manganese 0.69Phosphorus 0.005Sulfur 0.014Silicon 0.26Nickel 1.65Copper 0.15 - 0.25ChrLmium 0.7 0.9Vanad I m 0.01No I ybdcnum 0.2 - . 3Aluaminum 0.02

*Dept of Army Materials Laboratory. Frankfovd Arsenal. 16 September1976.

16B. R. Butcewr ami cl. R. Car-on, "Inftuenv (if Vorfivvfatim o" the

,qrumic Streeo-Strai' Lcnes of 4340 Steel", AIAA , Vol. 2, No. 12,

8

1 ~~ -41 N4

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0.8-

0.7-

0.6-

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K~ 170 GI~a

tAW

L 0.3-

0.2 BULK SOUND VELOCITY

4.67 km/s

0.1

00

FIGURE 2: Pressure vs. Volume Compression for 4340 Steel.The pressure is taken as -u/3 where o is the loaddivided by tho original area of the specimens.

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REFERENCES

1. G. llauver, "The Alpha-Phase Hugoniot of Rolled Homogeneous Armor".Ballistic Research Laboratory Memorandum Report No. 2651, August1976. (AD NB012871L)

2. ~. ilauver and A. Melani, "The Epsilon-Phase Hugoniot of RolledHomogeneous Armor", Memorandum Report ARBRL-MR-02909, March 1979.(AD OA096107)

3. L. M. Barker, "Alpha-Phase Ifugoniot of Iron", .1. Appl. Phys., Vol. 46,No. 6, June 1975, pp 2544-7.

4. 1.. M. Barker and R. E. Hollenbach, "Laser Interferometer for MeasuringIHigh Velocities of Any Reflecting Surface", J. Appl. Ph., Vol. 43,No. 11, November 1972, pp 4669-75.

S. 0. E. Jones and R. A. Graham, "Shear Strength Effects on Phase

Transition "Pressures" Determined from Shock-Compression Experiments",Symposium on the Accurate Characterization of the Ifigh Pressure

Environment, U.S. Dept. of Commerce, National Bureau of Standards,

Gaithersburg, MD., October 14-18, 1968.

b. B. M. Butcher and J. R. Canon. "Influence of Work-liardening on the

Dynamic Stress-Strain Curves of 4340 Steel", AIAA .., Vol. 2, No. 12,

December 1964, pp 2174-9.

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