shaped charge

CLEARINGHOUSE FOR FEDK^AL SCIKNTTFlO^ND __ TECHXirAL INFORMATION

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c EFFECTS OF VELOCITY AND MATERIAL PROPERTIES ^ ON DESIGN LIMITS FOR LINEAR SHAPED CNAR6ES

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NAVWEPS REPORT 87S3 NOTS TP 3194

COPY 145

i I RobertG. S. Sewell Weopons Development Department

DDC NuV 8 . 1965

ODOiHA ABSTRACT. This report discusses the design limits For linear shaped charges that are caused by the behavior properties oF the liner material and by the nature oF the collapse geometry oF the linear shaped charge. In the study the jetting process For both mild steel and copper is examined.

Ptnalsslon to release to Clearinghouse for Federal SclentlflO and Teohnioal Information given by . S. Haval Ordnance Test Station, China Lake.

U.S. NAVAL ORDNANCE TEST STATION

China Like, California October 1965

U. S. NAVAL ORDNANCB TBST STATION AN ACTIVITY OF THE BUREAU OF NAVAL WEAPONS

J. I. HARDY. CART., USN WM. B. MCLEAN. PH.D. Cmmmmndmr Tmchnlcol Dirmctor

FOREWORD

The study described in this report was conducted at the U.S. Naval Ordnance Test Station ss part of the continuing warhead research program that is directed toward improving various types of conventional warheads and accomplishing ad- vanced studies snd analyses for anticipated development programs.

The work was accomplished in May 1965 under Bureau of Naval Weapons Tssk Assignment RMMO-42 994 216-IFOOS-08-06.

This report is released at the working level. Because of the continuing nature of the warhead research and development program, refinements and modifica- tions may later be made in this study.

Released by Under authority of M. M. ROGERS, Head, F. H. KNEMEYER, Head, AiT'tO'Surface Weapons Div, Weapons Development Dept. 27 August 1965

NOTS Technical Publication 3894 NAVWEPS Report 8793

Published by Publishing Division Technicsl Information Department

Collation Cover, 4 leaves, DD Form 1473, abstract cards First printing 290 numbered copies Security classification UNCLASSIFIED

(

it

NAVWEPS REPORT 8793

INTRODUCTION

The l.S. Naval Ordnance Test Station (\OTS) has a rnntinuinp interest in linear shaped charges for warhead applications. A preliminary analysis of the collapse process and a discus- sion of the applications of the end-initiated linear shaped charge are given in Ref. 1. As part of the continuing study, some of the design limits for linear shaped charges have been investigated theoretically. As stated in Ref. I, the limits to be experienced in the design of a linear shaped charge are caused by the behavior properties of the liner nuiterial and also bv the nature of the collapse geometry. In this paper, these limits are anal\/ed for steady-state and non-steady-state conditions.

STEADY-STATE JETTING ANALYSIS

Design limits are set by the velocity of the flow of ni

NAVWEPS REPORT 8793

With a wall velocity of \0 and a collapse angle of , the flow velocity into the collapse point is

/='., cot/9

NAVWEPS REPORT 8793

My using this asthr hasis for an approximation of the limits of the nonliMlnxiuiamu /one, we can again solve Kq, 7, with lOcr. substituted for.

IOCT, 2pl(r eom2 (Kl resulting in a series r /ones that can be portraxed a^ shown in l* ig. 2 (for mil! steclt and b ig. \ (for copper). These are a no-jet, too-fast zone, then a central region where the h\drod\namic theory applies, then a questionable zone of nonlndrodv namic beha\ior, and then a no-jet, too-slow limit zone.

The values used in these calculations are shown in Table I.

TABLE l. VALUES USED IN THE CALCI LATIONS

Iti-m Mild MMI (opptr

Velecit) "f sound ((!), f; MC 19,->()() 1 t.90()

Density, slues ft l.i.6 17.2-.

Dynamic yield sirvnulh, kilobflM 12 26

Ihere is considerable difference between mild steel and copper in behavior in the question able nonhydrodvnanic zone. \s soon as the nonludrodxnamic zone border is reached or the side of descending velocities (in other words, moving from the zone where the ludrodvnamic theory applies into the nonhydrodynamic zone), the jetting process for steel stops almost immediately, but for copper it continues nearly over In the limit of the no-jet, too-slow zone. Part of this is caused by the anomalous behavior of copper, in which it is \ery difficult to establish a set value of dynamic vield strength because the dynamic yield strength ll very dependent upon the rate of loading.

NON-STEADYSTATE JETTING ANALYSIS

It is possible to produce non-stead\-state jets even in the no-jet, too-slow region of the steady-state analysis. This is caused by the jump in pressure that results when the two vanes first contact, before the pressure has been spread throughout the impacting walls. When the shock conditions prevail, the pressure is represented not b\ I 2^1, ~ but in terms of the shock pressure

pCI. m 1 In- shock conditions \ield much higher pressures than do the stead\-state conditions until

I, approaches the value of the velocity of sound in the material. Hence, for < op|>er, it is found that the non-steady-state pressures sufficient for jetting can be produced at essentialU a zero- degree collapse angle with velocities as low as 210 ft sec; whereas for the stead\-state jet, the limit at I zero-degree angle for achieving the pressure limit is a velocit\ of 1.2H.") fl sec. For mild steel, the steadx-state pressur condition, exceeding the dynamic viHd strength, is achieved with a velocity of H9f) ft sec at zero-degree angle; whereas for the unsteadx, or shock condition, it is achieved at essentiallv 100 ft sec.

NAVWEPS REPORT 8793

100

S

i mm

8

WAll VtlOCITY, FT/StC X 10

FIG. Z. I.infrtr-ShapcH-rhargr Limits for Mild Sterl.

100

6 S 10 12 WAll VIIOCITY, FT/SIC X 10"3

18

FKa I. l.inrar-ShapiMl-fihargf l.imilN for (ioppcr.

NAVWEPS REPORT 8793

4

APPLICATION TO EXPLOSIVE WELDING PHENOMENA

It is possible that the difforoncr in values of the limit coadiliaM for ste.nK-st.ite and non- steady-state jetting may be one of the contributing causes for the MMtCWMCC of the periodic, or wavy, welds in material in explosive welding studies (Mef. 2 and I). In such studies, when the maieri! was first brought together, the dynamic yield strength would Itr rxceeded and jetting would begin. As soon as the jetting process had started, it would \'\v\(\ a pressure relief that would decrease the pressure below the limit required for jetting, and the jetting process would stop. Then, since the jetting process had stopped, the material would be as new materi.il striking again and would go back to the shock position, reapplyinp the pressure that Mould then cause jetting, which would relieve the pressure. This would occur periodically, giving rise to the wavy welds in material in the explosive welding studies (Kip. I).

FIG. 4. Mi rosir( lure of Wavy Weld in 1018 Steel.

CONCLUSIONS

This short study has shown that there exist (1) various regions in possible designs of linear shaped charges in which no |et results because the flow of material is either too fast or loo slow, (2) a questionable /one of nonhydrodynamic behavior, and (3) a zone of design parameters in which the hydrodynamic theory would apply quite nicely.

This information may be used by the designer of the linear shaped charge in determining the type of effect th.it he will produce. If he desires to produce an all-slug, no-jet charge, he ma\ do it with great confidence of success by designing the charge such that he will be in the no-jet, too- slow region. If he wishes to produce the optimum jet configuration, he will restrict his design to the region where hydrodvnamic theory applies and avoid the nonhvdrodynamic region.

However, as noted in Mef. 1, because of the gradient in velocity achieved along the vane of a conventional end-initiated linear shaped charge, even though the design parameters are chosen to start at the center of the vane in the hydrodynamic region, as the collapse angle increases and the wall velocit) decreases, there is a transition into the nonhydrodynamic /one and very possibly into the no-jet, too-slow region. At this point the distribution ol masses between jet and slug pre- dicted by the h\drodynamic theory no longer applies.

NAVWEPS REPORT 8793

REFERENCES

1. I .S. \avul Ordnance Test Station. The Collapse Process and Applications of the Knd- Initiated Linear Shaped Charge (1), by Robert d. S. Sewell and Paul K. Cordle. (ihin.i Lake, Calif., NOTS, August 1965. 28 pp. (NAVWEPS Report 86-49; NOTS TP .mi), CONFIDENTIAL.

2. Rinehart, John S., and John Pearson. Kxplosive Working of Metals. Londoi Pargamon Press, 1963.

.\. l.S. Naval Ordnance Test Station. Transactions of the Symposium on Warhead Research, 7-8 May 1963 (U). China Lake, Calif., NOTS, August 1963. Pp. 169-196. (NOTS TP 3301), CON- HDKNTIAL.

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2 ncPOMT ttCUMl TV C LAtllFICATlO" UNCLASSIFIED

26 OWOuP

i ntpomr TiTL* EFFECTS OF VELOCITY AND MATERIAL PROPERTIES ON DESIGN LIMITS FOR LINEAR SHAPED CHARGES

4 OKSCRIPTIVC NC-CS (Typt ol roporr mnd Inclutirm dm-f

AUJHOH(S) (Lmul r>mti: lim nmm Intllml)

Sewell, Robert G. S.

mtPonr OATF October 1965

CONTACT o OXANT NO Task Assignment RMMO-42/994/216/-1/F008-08-06

f> *moj*cr NO

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tms) NAVWEPS Report 8793 NOTS TP 3894

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13 ABSTRACT This report discusses the design limits for linear shaped charges that are caused by the behavior properties of the liner material and by the nature of the collapse geometry of the linear shaped charge. In the study the jetting process for both mild steel and copper is examined.

DD .ttTL 1473 0l0l-tO7-StOO UNCLASSIFIED Security Classification

NCLA5SIEIED Security CUtiification

14 KCV WOODS

LINK A

HOLK

LINK LINK C

Linear Shaped Charges Collapse Velocity Steady-State Jetting Non-Steady-State Jetting

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