Effect of the Strength of the Material of a Plate Accelerated by Low-Rate High Explosives.pdf

Combustion, Explosion, and Shock Waves, Vol. 38, No. 1, pp. 119{122, 2002

Eect of the Strength of the Material

of a Plate Accelerated by Low-Rate High Explosives

Yu. P. Besshaposhnikov, 1

V. E. Kozhevnikov, 1

UDC 621.791.76:621.7.044.2

V. I. Chernukhin, 1

and V. V. Pai 2

Translated from Fizika Goreniya i Vzryva, Vol. 38, No. 1, pp. 135{138, January{February, 2002.

Original article submitted December 15, 2000.

Plate acceleration by a gliding detonation wave is studied experimentally for detona-

tion rates of 950{2000 m/sec. It is found that regular elastic waves occur at the

surface of the projectile plate made of a rather strong material, which disappear upon

attainment of the upper limit of the detonation rate.

The behavior of materials under an explosive load

as applied to welding, hardening, and compacting by

means of a plane impactor (plate) accelerated by a glid-

ing detonation wave is usually calculated without al-

lowance for strength properties of the material. In most

cases, this approach is well justied from the viewpoint

of simplifying the calculation model and has been shown

experimentally to be valid for detonation rates of a high-

explosive (HE) charge D & 2000 m/sec [1]. However,

in the case of explosive welding of materials prone to

produce intermetallides or materials with substantially

dierent melting points, or materials that produce low-

melting eutectics, the optimal values of D can be much

lower than 2000 m/sec [2{4]. At the same time, for rea-

sonably low D, the pressure of explosion products on

the surface of an accelerated plate can be comparable

with the dynamic ultimate strength of the plate mate-

rial. This brings up a natural question: How does the

material strength aect the geometry of plate accelera-

tion and, hence, kinematic parameters? Therefore, it is

of considerable practical interest to determine the mini-

mum (boundary) values of D for which the applicability

of the calculation models that ignore the strength of a

material under an explosive load is justied.

In this paper, we give results of an experimen-

tal study of the prole of a plate accelerated freely

by a gliding detonation wave for a detonation rate D

950{2000 m/sec. Plates from St. 3, 08Kh18N10T, and

Fig. 1. Diagram of experimental study of the geome-

try of plate acceleration: 1) accelerated plate; 2) HE;

3) contact transducers for detonation-rate measure-

ment; 4) Nichrome-wire transducer; 5) loop for de-

termining the beginning of the process; 6) insulator.

10Kh17N13M2T steels, VT1-0 titanium, KhN65MV

Hastelloy, M1 copper, AD0 aluminum, and S1 lead were

tested with the use of the well-known potentiometer-

transducer method [5] according to the diagram shown

in Fig. 1. Under the plate covered by an HE layer, a

Nichrome wire (potentiometer transducer) 0.1 mm in

diameter was xed at a certain angle to the plate. At

the \point" O, the wire was in electric contact with the

plate. In some cases, the \point" O was insulated by a

thin uoroplastic spacer 0.03 mm thick, which made it

possible to determine more distinctly the beginning of

the process in the form of a step. This step was ensured

by a small Nichrome-wire loop connected to the trans-

ducer at the \point" O at one end and to the grounded

plate at the other end. The detonation rate was mea-

sured by contact transducers located at the plate surface

under the HE layer. Ch3-34 (Ch3-35) frequency meters

0010-5082/02/3801-0119 $27.00 c 2002 Plenum Publishing Corporation

1 Uralkhimmash, Ekaterinburg 620010;

liom@ekb.su.

2 Lavrent'ev Institute of Hydrodynamics, Siberian Division,

Russian Academy of Sciences, Novosibirsk 630090.

119

120

Besshaposhnikov, Kozhevnikov, Chernukhin, and Pai

TABLE 1

Results of an Experimental Study of the Plate Prole

Yield

Pressure

Wave parameters

Test

Material of the plate

point of the

Thickness

Detonation

at the plate

at the detonation

No.

and its dimensions [mm]

plate

of the charge,

rate,

front, surface, mm

material, mm

m/sec

MPa

length

height

MPa

08Kh18N10T steel,

302

950

301

10.40

0.15

450 300 1

AD0 aluminum,

1000

333

Waves were not

450 350 5

detected

KhN65MV Hastelloy,

579

1090

396

13.50

0.34

500 300 4

VT1-0 titanium,

407

1095

400

9.00

0.20

400 250 2

450 300 3

287

1000

333

15.55

0.39

450 300 3

287

1040

360

7.00

0.23

450 300 3

287

1120

347

9.00

0.33

450 300 3

287

1125

350

12.60

0.45

St. 3 steel 450 300 2

287

1150

366

7.25

0.35

450 300 3

287

1300

563

Waves were not

detected

450 300 3

287

1430

682

|00|

450 300 3

287

1600

800

10.0

0.15

480 300 3

287

1900

876

Waves were not

detected

10Kh17N13M2T steel,

351

1440

691

|00|

500 300 5

M1 copper,

122

1300

563

|00|

450 300 3

S1 lead, 450 300

1255

521

|00|

Notes. One asterisk indicates the values measured by the standard method; two asterisks indicate that calculations were performed

by the formula p = D 2 =(k + 1), where p is the pressure at the detonation front, is the density of the HE charge, D is the

detonation rate, k is the integral (eective) polytropic index determined by the method of [1, 5]; three asterisks indicate that waves

were articially formed at the plate surface.

were used as chronometers. When accelerated, the plate

struck the Nichrome transducer, and the length of the

part of the latter that had not yet touched the plate de-

creased with time. Obviously, the electrical resistance

measured with the use of the circuit shown in Fig. 2

decreased in proportion to this length. An impulse of

current (0:25{0:5 A) of duration 200 sec formed by

a current generator was passed through the resistance

of the potentiometer transducer. The voltage drop at

the transducer ends was recorded by an S9-8 digital os-

cillograph. The current passing through the transducer

remained constant within the period of recording; there-

fore, the voltage drop across the transducer was propor-

tional to the resistance, which simplied the processing

of the oscillograms obtained. Particular attention was

given to the choice of the angle of the transducer ,

since the stability of the transducer, ensured by taking

the angle very close to the limiting angle of rotation

, is more dicult to achieve when the plate is acceler-

ated by a low-rate HE (D < 1500 m/sec). Only in this

case does the velocity of the \plate{transducer" contact

point exceed the velocity of sound in the material of the

transducer. It is clear that, if the angle is smaller than

the limiting angle , the essential and most important

part of the desired signal is not recorded.

It was found in tests that, for D 950{1150 m/sec,

regular waves of length 7{15 mm and height

0:15{0:45 mm were formed at the surface of plates made

Strength of the Material of a Plate Accelerated by Low-Rate High Explosives

121

Fig. 2. Circuit for measuring the resistance of the

potentiometer transducer.

Fig. 4. Oscillograms of the acceleration prole of a

steel plate with articial grooves at the surface (a)

and a smooth surface (b).

Fig. 3. Oscillograms of the acceleration prole:

(a) St. 3 steel plate of thickness = 3 mm, HE

charge of thickness H = 60 mm, and D = 1300 m/sec

(there are no waves at the plate surface); (b) St. 3

steel plate of thickness = 3 mm, H = 60 mm,

and D = 1000 m/sec (there are waves at the plate

surface); (c) AD0 aluminum plate of thickness =

5 mm, H = 40 mm, and D = 1000 m/sec (there are

no waves).

of rather strong materials (St. 3, 08Kh18N10T, VT1-0,

and KhN65MV) (see Table 1). Obviously, this eect

is associated with elastic properties of the plate mate-

rial [6, 7] since the waves vanished after the acceleration

was completed (no traces of the waves were detected

on the plate). However, when an aluminum plate was

accelerated at the same velocities D (test No. 2), no

waves were observed (the oscillogram of the process was

smooth). Probably, even for these low values of D, the

pressure at the detonation-wave front does not allow no-

ticeable manifestation of elastic properties in aluminum.

Acceleration of St. 3 steel plates was studied in

more detail. For these plates, the upper limit of the

detonation rate (D lim 1300 m/sec) at which the waves

vanish was determined. Figure 3 shows the oscillograms

of three typical experiments, which clearly illustrate this

eect.

To verify the conclusion about the occurrence of

elastic waves for low-rate acceleration and to study the

potentialities of the potentiometer method for recording

similar waves, we performed additional tests on plates

with wavy surfaces striking the potentiometer trans-

ducer. The waves (grooves) were oriented transversely

to the detonation-rate direction. The length of the wave

was 10 mm, and its height was 0:15{0:20 mm. The ac-

celeration regime is described in Table 1 (test No. 12).

122

Besshaposhnikov, Kozhevnikov, Chernukhin, and Pai

Since these tests were aimed at obtaining a wave-like os-

cillogram as a consequence of a wavy surface of the plate

rather than numerical values, the signal was recorded

by an S1-74 analog oscillograph. In this case, the wavy

character of the oscillograms is easier to detect, and the

measurement accuracy is of no principal importance.

Figure 4 compares the oscillograms of accelerated plates

with wavy and smooth surfaces. It is clear from the

oscillograms that the potentiometer method possesses

a fairly high resolution and allows one to detect wavy

irregularities as small as the Nichrome-wire diameter.

Thus, the wavy character of the oscillograms can be ex-

plained only by the occurrence of waves at the surface of

accelerated plates and not by the specic features of the

measuring equipment. Consequently, the \elastic-wave

eect" can be considered to be an established fact.

In summary, to avoid the above-described eect in

explosive welding of metals with substantially dierent

strength properties (for example, aluminum and steel

or lead and steel) for detonation rates much lower than

2000 m/sec, one should use a plate from a less strong

material as an accelerated element.

2. V. E. Kozhevnikov, \Determination of practical re-

gions of explosive welding of copper{titanium, copper{

aluminum, and titanium{aluminum bimetals," in: Pro-

cessing of Materials by Impulsive Loads (collected scien-

tic papers) [in Russian], Novosibirsk (1990), pp. 236{

244.

3. H. E. Otto and S. H. Carpenter, \Explosive cladding of

large steel plates with lead," Welding J., 51, No. 7, 7{13

(1972).

4. V. I. Lysak, S. V. Kuz'min, V. S. Sedykh, and V. R. Mas-

lennikova, \Relation between the type of metallurgical

interaction of metals and location of optimal boundaries

of their explosive welding," in: Explosive Welding and

Properties of Welded Joints (collected scientic papers)

[in Russian], Volgograd (1991), pp. 13{21.

5. G. E. Kuz'min, V. I. Mali, and V. V. Pai, \Accelera-

tion of at plates by layers of condensed explosives," Fiz.

Goreniya Vzryva, 9, No. 4, 558{562 (1973).

6. L. A. Merzhievskii and A. D. Resnyanskii, \Modeling

of shock-wave deformation and failure of materials," in:

High-Energy Action on Materials, Proc. 9th Int. Conf.,

Novosibirsk (1986), pp. 224{228.

7. M. I. Orlov, Yu. N. Pashukov, and V. Ya. Solov'ev,

\Mathematical model of acceleration of an ideal-elastic

plate under the action of a detonation wave propagating

over its surface," in: Processing of Materials by Impulsive

Loads (collected scientic papers) [in Russian], Novosi-

birsk (1990), pp. 195{202.

REFERENCES

1. Yu. P. Besshaposhnikov, V. E. Kozhevnikov, V. I. Cher-

nukhin, and V. V. Pai, \Plate propulsion by mixed-

explosive layers," Fiz. Goreniya Vsryva, 24, No. 4, 129{

132 (1988).

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