AD

AD-E403 027

Technical Report ARAET-TR-04017

EFFECT OF A BORE EVACUATOR ON PROJECTILE IN-BORE DYNAMICS

Donald CarlucciJulio Vega

Jennifer Cordes

November 2004

ARMAMENT RESEARCH, DEVELOPMENT ANDENGINEERING CENTER

Armaments Engineering & Technology Center

Picatinny, New Jersey

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1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To)November 2004 Final

4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER

EFFECT OF A BORE EVACUATOR ON PROJECTILE IN-BORE 5b. GRANT NUMBERDYNAMICS

5c. PROGRAM ELEMENT NUMBER

6. AUTHORS 5d. PROJECT-NUMBER

Donald Carlucci, Julio Vega, and Jennifer Cordes 5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATIONARDEC, AETC REPORT NUMBERFuze and Precision Armaments Technology (AMSRD-AAR-AEP-E)Picatinny, NJ 07806-5000

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)ARDEC, EMTechnical Research Center (AMSRD-AAR-EMK) 11. SPONSOR/MONITOR'S REPORTPicatinny, NJ 07806-5000 NUMBER(S)

Technical Report ARAET-TR-0401712. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

Projectile base pressure measurements were taken in a 155-mm M284 gun tube using an ArmamentResearch, Development and Engineering Center-designed instrumentation package incorporated into amodified XM982 artillery projectile. These measurements showed that the base pressure was affected as theprojectile passed the bore evacuator ports. The perturbation in base pressure generated a high frequencyresponse in the projectile. A simplified finite element model of the projectile was constructed and verified thatthe projectile dynamics were captured properly by the instrumentation. A dynamic response was alsowitnessed at abrupt changes in gun tub cross-section. This response has not been explained to date.

15. SUBJECT TERMS

155-mm Bore evacuator Pressure measurements --. Projectile Base pressure

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBE PERSONABSTRACT OF D. Carlucci, etc.

a. REPORT b. ABSTRACT I c. THIS PAGE PAGES 19b. TELEPHONE NUMBER (includearemU U U SAR 18 code) (973) 724-2486

Standard Form 298 (Rev. 8/98)Prescribed by ANSI Std. Z39.18

CONTENTS

Page

Introduction I

Experimental 2

Experimental Results and Discussion 2

Numerical Results and Discussion 6

Conclusions 12

References 13

Distribution List 15

FIGURES

I M284 gun tube geometry 2

2 Axial acceleration versus time - TRN 81 3

3 Projectile velocity, travel, and accelerations versus time - TRN 81 3

4 Pressure versus acceleration - TRN 81 4

5 Axial acceleration versus time - TRN 82 5

6 Projectile velocity, travel, and acceleration versus time - TRN 82 5

7 Pressure versus acceleration - TRN 82 6

8 Simple projectile model with M284 gun (all parts 360 deg in analysis) 9

9 Input accelerations with bore evacuator 8

10 Input accelerations without bore evacuator 8

11 Predicted axial accelerations with bore evacuator 9

12 Predicted axial accelerations without bore evacuator 10

13 Transverse axial accelerations with bore evacuator 10

14 Transverse axial accelerations without bore evacuator 11

15 Transverse contact force with and without the bore evacuator 11

INTRODUCTION

The guns on the tanks and howitzers that carry soldiers include a device called a boreevacuator. A bore evacuator expels propellant gases that could otherwise harm the crew. Thebore evacuator also changes the pressure pulse and the accelerations along the length of theprojectile.

As the use of electronic devices increases in gun-launched projectiles, the designer ismore and more interested in dynamic events that result in failure of these components. Thisinterest in component failure has led the engineering community to look closely at the dynamicaspects of gun launch through both modeling and instrumented firings. In the past, whencomponents were primarily mechanical, it was sufficient to examine the pressure-time history ofa worst case launch, perform quasi-static analysis using peak accelerations as the input, applya safety factor and design away. Since the failure of sensitive electronic components has beenfound to be highly dependent upon the frequency of the loading, this quasi-static approach isonly valid for a "first cut" at the design.

This interest in the dynamics of the gun launch has increased the use on on-boardinstrumentation in test firings. This on-board instrumentation has been configured in varioustests to measure accelerations, strains, and pressures as well as send signals on theperformance data.

Data obtained from on-board instrumentation used in 155-mm howitzer firings indicatethat critical electronic components tend to fail primarily during the muzzle exit transient. Duringthe exit of the projectile from the muzzle, the base pressure drops very rapidly (-0.1 ms). Thissets up axial and radial ringing in the projectile, which can occur at the natural frequencies ofthe electronic devices causing failure.

If one examines data from many firings, one can observe axial and lateral vibrations in theprojectile nearly 2 ms prior to the muzzle exit transient. This behavior was observed to be ofhigher magnitude when a bore evacuator was present. Two theories (both of which we believeare correct and additive) to explain this behavior were postulated. The first theory was thatinteraction of the axial stress waves caused by the projectile motion with the gun tube causedthe behavior. The second theory was that the bore evacuator caused a pressure spike on thebase of the projectile.

The interaction of gun tube stress waves with the projectile has been observed in tests inthe past (ref. 1). This mechanism comes about through the dilation and axial load placed on thetube by the projectile-charge combination. The stress imparted on the tube by the projectile isfairly large. Axial stress waves cause radial waves through poisson effects. At abruptdecreases in tube cross-section, the interaction of the radial waves intensifies, coupling into theprojectile response. This phenomenon appears to increase as the quadrant elevation (QE) ofthe weapon is decreased, possibly indicating some bending modes are affected.

1

Instrumented tests on the M203A5 howitzer (ref. 1) (using an M284 tube) have shown agreater intensity of radial excitement in the tube after the passage of the bore evacuator holes.This behavior (and other program concerns) required the development of an instrumented baseprojectile. This projectile contained both accelerometers and pressure transducers in the base.It was interesting to note that a pressure spike occurred as the projectile passed the boreevacuator holes and this corresponded to the increase in dynamic activity of the projectile. It isthe intent of this paper to describe the discovery of this phenomenon.

EXPERIMENTAL

A test was conducted at Yuma Proving Ground, Yuma, Arizona using an M284 155-mmcannon with five instrumented projectiles as described in reference 2. The projectiles containednine PCB 109A12 ballistic pressure gages and a tri-axial accelerometer package consisting ofEndevco 7270A-20k accelerometers. The projectiles were fired at ambient temperatures usingM4A2 bag charges, PXR6297A1 bag charges, and Modular Artillery Charge System (MACS) - 5charges. The rounds were all fired at a QE of 450 mils. Figure 1 depicts the geometry of thegun tube including the location of the bore evacuator holes.

198 in.IIII

126 in.II

TRAVEL DISTANCE MEASURED FROM THEINITIA POSITION OF THE OBTURATOR Bore Evu

II

II

41.60 in. 198 in.

Figure 1M284 gun tube geometry

EXPERIMENTAL RESULTS AND DISCUSSION

Tube round number (TRN) 81 was fired using an M4A2 charge. Figure 2 is a plot of theacceleration versus time from this firing. The axial acceleration is of the greatest interest in thisfigure. A look at the axial data clearly shows an acceleration spike shortly after 15 ms. Figure 3shows the velocity and displacement of the projectile superimposed on the acceleration-timecurve. The beginning of the dynamic behavior occurs around 125 in. from the seating locationof the projectile in the weapon's forcing cone. This is approximately where the bore evacuatorholes are located. Figure 4 is a plot of axial acceleration and base pressure data. It is clear inthis plot that the pressure discontinuity initiates the dynamic behavior in the projectile.

2

7000

7200e

01000

02 0

00005700

5400

0100

4000

rore Muzzle

00 Evau r Exit05000

' 2700

22400

1000oo1o00

15300

0 300

4500

-000

3000 126_____in____250____1___20_

0 0.002 01004 0.000 0.000 0.01 0.012 0.014 0.010 0.013 0.02 0.022

Time ( Seconds )

Figure 2Axial acceleration versus time - TRN 81

Velocity

rns Travel

0,q0000

45O 200

0 03

10000.Q t200

5100 0<400 200

40OO0 140

Fiur 30

o 5000 1o

25o,0T200EL100

1I000 *40

0 0002 0.004 0.000 0,000 0.01 0.012 0.014 0.510 0.010 0.02 0,022

Time ( Seconds)/

Figure 3

Projectile velocity, travel, and accelerations versus time - TRN 81

3

Acceleration(G's) Travel

noo0 (in.)25000 128024000 7000~

23000A40TRAVEL00 260

22000 DISTAN21000 6000

20000 220

1:000 198oin 50001 2oo

17000 g

11000450

15000 1610004000M 4 O O 1 4 0

,. 13000 1500

S 12000 000 120

11000

S1000000 100

9) 0000 2000 6

. 000

7000 10

1000 40

4000 $0S0 203000

2000

1000 "SO: -20

-t000 .10001 .40

-2000 -1500

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.016 0.02 0.022

Time ( Seconds)

Figure 4Pressure versus acceleration - TRN 81

TRN 82 was fired under the same conditions as TRN 81. Figure 5 is a plot of theacceleration versus time from this firing. This time the acceleration spike occurs shortly after 16ms. Figure 6 shows the velocity and displacement of this projectile with the acceleration-timecurve. The beginning of the dynamic behavior again occurs around 125 in. from the seatinglocation of the projectile. Figure 7 portrays axial acceleration and base pressure data. Unlikethe data for TRN 81, there is no definitive pressure spike that we have detected that initiates thedynamic behavior. Examination of this data indicates that the dynamics begin at the last abruptchange in gun tube cross-section. There are several postulated mechanisms for this reaction,though none were proven definitively.

4

0500

0000

5500

5000

4500BoeM zl

4000 Evacuator Exit• 3500

•3000

2500

2000

O 500

2000

o

500

-00

.1000

0 0,002 0.004 0.000 0,008 0.01 0.012 0.014 0.016 0,018 0.02 0.022 0.024

Time ( Seconds)

Figure 5Axial acceleration versus time - TRN 82

Velocitym/s Travel

(in.)6500 Boo 200

000oo VEL QCýITY 534 m/s •0 200

5500 2"00,• i • / / 50 20

__ ACCE RATION 240

40220

40"O

4 i000 4041000

3:00 100(ISO

< 00o.t °300140.... 120

2000 2 0 01300

500 so' 20200

.30 TRAVEL________ ______ _______0__20

0 0.002 0,004 0.000 0,000 0.01 0.012 0014 0.010 0.018 0.02 0022 0.024

Time ( Seconds )

Figure 6Projectile velocity, travel, and acceleration versus time - TRN 82

5

Acceleration(G's) Travel

28500 t(in.)

2550 TRAVEL 6

255 i C EL R TIi500 260

23500 DISTANCE- .--.-___24

23 00 24

22500 - 5000

21500 220

20500 198in .00 2001900018500 4 000 S17500 3 oL

51650000 I

S14500 12 ll 3000 140

13500 2500 120S12500 PRSU•'•25000 0100

E 10500

50000Soo PRSSLIZ60

7500 10006500 40

5500 5oo 204500

25001

.500 1000 -20

.50O

-1500_,_ 4

-2500 -1500 60

-3500

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 0.022 0.024

Time ( Seconds)

Figure 7Pressure versus acceleration - TRN 82

NUMERICAL RESULTS AND DISCUSSION

A simple projectile model was used to evaluate the accelerations and forces caused bythe bore evacuator in an M284 gun tube (ref. 2). Table 1 summarizes the length, weight, andstiffness of the projectile. The projectile had an outside diameter of 155 mm. The gun is about6100-mm long. Figure 8 shows the gun and projectile.

Table 1Simple projectile model

Base steel 200.2 0.32 10.3 166.4

Control section steel 200.2 0.32 7.0 159.6Nose alumnum0.3.2

6

1 • 00 .g• -22-V04-546-dmV10.od, MAQI/explicit 6.4-3 1%. S.P 23 0M00419 47T1 2004

Inc-r t 297443 Stop Ti 8.06021-03

Figure 8Simple projectile model with M284 gun (all parts 360 deg in analysis)

The gun and projectile were modeled using the general purpose finite element package,Abaqus Explicit. Eight node brick elements were used for the analysis. All parts were modeledas linear-elastic. Abaqus's alpha-type damping was used in the solid elements. Alpha wasbased on 5% critical damping at a frequency of 2000 Hz; alpha was 1256. It was also assumedthat 5% critical damping existed between the projectile and the gun. The axial and transverseaccelerations were calculated and compared to accelerations recorded by the on-boardrecorder for shot S81.

Acceleration was applied to the base of the projectile in the axial direction. The accel-eration was scaled from the pressure curve shown in figure 4. The scaling factor accounted forthe projectile weight plus 5% increase to account for the obturator diameter and blow-by. Thescaled acceleration is shown in figure 9. To determine the effect of the bore evacuator, theacceleration in figure 9 was altered by removing the bore evacuator perturbation (fig. 10). Inaddition to the acceleration load, a pressure load was used to model a non-axi-symmetricpressure on the outer diameter of the projectile. The side load was applied as pressure overone-quarter of the model and followed the pressure curve with a scaling factor of 0.05,assuming 5% unequal distribution of pressure.

7

G2 at Input BoreEvac Blowby5-5

XMIN O.OOOE+00

XMAX 2.600E-02 [xlO']YMIN O.OOOE+00 8.00

YMAX 6.646E+03

6.00 -------

S4.00..

S2.0 0 .. ... . .. . . . . .... - - - --

...... ...... - .-- i -.-. -........ !....... i.-.-....... . i . ..... - .-.-. ....... -. ..

0.00

-2.00 , I L i l I 10.00 8.00 16.00 24.00 [xlON

lime, Second

Figure 9Input accelerations with bore evacuator

G2 at Input NoBoreEvac Blowby5-5

XMIN O.OOOE+00

XMAX 2.600E-02 [X

YMIN O.OOOE+00 [aYMAX 6.646E+03 i Tfrr,1

6.00

S 4.00 ----- - ---

2.00 - - ------ ---- ---- ----

0.00

-2.00 I I I i I i0.00 8.00 16.00 24.00 [x10"1

"lime, Second

Figure 10

Input accelerations without bore evacuator

8

Results are shown in figures 11 through 14. Figure 11 shows the difference in thepredicted axial acceleration with and without the effect of the bore evacuator. When theprojectile passes the bore evacuator location, additional reversing accelerations in the axialdirection are noted for the bore evacuator load. Figures 13 and 14 shows the transverseaccelerations with and without the bore evacuator effect. For clarity, the recorded experimentalacceleration is shown as negative. As shown in Figure 14, the effect of the bore evacuator is atransverse acceleration pulse of about 7300 gs. The predicted pulse was 1500 gs in thetransverse direction, lower in magnitude. With higher blow-by pressures, the predictionsincreased up to about 9000-gs for a 25% blow-by pressure.

- G2 at OBR BoreEvac Blowby5-5- G2-S81-OBR-Acceleration-Recorded

XMIN O.OOOE+oo [x101]XMAX 2.600E-02 8.00

YMIN -7.646E+02YMAX 7.415E+03

6.00 ------- --- --------

0 4.000

S2.00

0 . 0 ...... ...... ...... ...........

-2.00

0.00 8.00 16.00 24.00 [xlo"JTime, Second

Figure 11Predicted axial accelerations with bore evacuator

9

G2 at OBR NoBoreEvac Blowby5-5G2 -S81-OBR-Acceleration-Recorded

XMIN O.0COE+00 [xOO0$

XMAX 2.600E-02

YMIN -7.707E+02YMAX 7.415E+03 ......

6.00 -- ----

~4.00

62.00 ..... .... .

... ....... J.... . . . .. , J

0• .00 ........ - ---• --- .....

0.00 k

-2.000.00 8.00 16.00 24.00 Ix1O0j

Time, Second

Figure 12Predicted axial accelerations without bore evacuator

G Transverse at OBR BoreEvac Blowby5-5- G-Transverse--Experimental-Neg

XMIN O.OOOE+00 XO 3

XMAX 2.600E-02

YMIN -7.352E+03

•.-0.50 ............. i ... ... . .. ....... .. .. -. .... ... .... . . .. .... . •. . .... ..

-2.00 I I

0.00 8.00 16.00 24.00 [xl04]

Time, Second

Figure 13Transverse axial accelerations with bore evacuator

10

- G Transverse NoBoreEvac Blowby5-5G- Transverse- Experimental-Neg

XMIN O.OOOE+00 [Xi-OS1XMAX 2.600E-02 2.00YMIN -7.352E+03YMAX 7.966E+02 1.50 ---

(A 10 ... .... .......... ...+ + + .+.. .... ..... .. ..

0.00 8.00 16.00 24.00 [xl,

Time: , Second,

..... i_ ...7 + ...+..,...: ,... ..++... + •T ...; .. ...+ .... . .. ......

-1.50 ---- - -- -- - -- -- - -- -- -- - -+---- +---- -- -

-2.oo F • t +, I0.00 8.00 16.00 24.00 [x10'J

Time, Second

Figure 14Transverse axial accelerations without bore evacuator

Figure 15 shows the contact force on the projectile base. The transverse accelerations atthe bore evacuator are probably the result of the projectile hitting the gun as indicated by thetransverse contact forces. It is not yet understood why the contact forces and transverseaccelerations increase at about 0.005 sec. In the analysis, the effect did not occur without thetransverse pressure, the assumed non-axi-symmetric load, on the projectile.

Contact Force BoreEvac Blowby5-5Contact NoBoreEvac Blowby5-5

XMIN O.OOOE+00 (XOOO3)XMAX 2.600E-02YMIN O.OOOE÷0011 ! ,YMAX 1.914E+0O4

15.00 .... ..- ---I 10.00

5.00 i

0.00 h .t..L L0.00 8.00 16.00 24.00 [x1 0o]

Time, Second

Figure 15

Transverse contact force with and without the bore evacuator

11

CONCLUSIONS

Measured base pressures appear to spike at the point in projectile travel where the boreevacuator is located in the M284 cannon. This pressure spike begins a ringing in the projectilethat can have adverse effects on electronic components. A finite element model was performedusing a simple projectile and the behavior was replicated. Observations have also been madethat dynamic activity in the instrumented projectiles increases at changes in gun tube cross-section. This effect is most notable where the tube diameter decreases in the vicinity of thebore evacuator. This effect is not fully understood at this time.

12

REFERENCES

1. Hollis, M.; Flyash, B.; Bahia, A.; Potucek, J.; Thomas, J.; Ellis, B.; and Carlucci, D.,"Empirical measurements of Cannon Launch Pressure on a Finned 155mm ArtilleryProjectile", 21' International Symposium on Ballistics, Volume 2, pp. 1152-1157, April2004. 1

2. Cordes, J. A.; Carlucci, D.; and Jafar, R., "Dynamics of a Simplifiedl55mm Projectile," 21'International Symposium on Ballistics, Volume 2, pp. 1164-1170, April 2004.

13

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