PARAMETERS OF SHOCK-COMPRESSED GAS IN TECHNOLOGICAL GAP

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PARAMETERS OF SHOCK-COMPRESSED GAS IN
TECHNOLOGICAL GAP AND ITS INFLUENCE ON THE WELDED
SURFACES
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S. Yu. Bondarenko, O. L. Pervukhina, L. B.
Pervukhin and D. V. Rikhter
PARAMETERS OF SHOCK-COMPRESSED GAS IN
TECHNOLOGICAL GAP ON THE NATURE OF PROCESSES
TAKING PLACE IN TECHNOLOGICAL GAP DURING
EXPLOSIVE WELDING
2010
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1. General view of the pattern of calculation of
   shock-compressed gas area

Flow over a body with a flat forward part (Photo
from Air Flow Branch, U. S. Army Ballistic
Research Laboratory)
ment - The entrained mass of air mout - The
outflow mass of air
Flow over the welded plates by shock-compressed
gas
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2. Two jointly solved problems
The equations connecting with gas parameters
astride the disintegration of discontinuities
The theoretical mass flow of gas for a time unit
and its theoretical outflow velocity
ex
Whence taking the expression
any desired relation of parameters can be
expressed.
f the area of output cross-section ?
adiabatic exponent for the flowing out gas ?1
gas density between plates ?1 specific volume
of gas ?1 ? ?0 the absolute pressures between
the plates into the shock-compressed gas area and
surrounding atmosphere.
?1 ? ?0 the absolute pressures in the
shock-compressed gas area and surrounding
atmosphere V1 ? V0 gas volumes before and
after compression ?1 ? ?0 gas densities
behind and before break ? adiabatic
exponent ? Mach number.
mout - The expiring mass of air
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3. Equations of dependence determining the size
of shock-compressed gas area
Dependence l f(t)
Dependence l f( L)
Dependence of extent of shock-compressed gas zone
(l), from the distance passed by a contact point
(L).
Dependence of extent of shock-compressed gas area
(l) from the contact point velocity (V?) and the
width of welded sheets (b).
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4. The characteristic layers and components of
velocity
Contact line
shock-compressed gas area
The components of velocity forming the total
velocity of shock-compressed gas element V?
the velocity of contact point ? outflow
velocity of gas.
The characteristic layers of hydrodynamic wall
area 1 a solid body 2 an external "atomic"
metal layer 3 Knudsen sublayer 4 a viscous
boundary layer 5 flow core. .
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5. The thermal action of shock-compressed gas
area on the surface

• heat flow from gas to the plates surface

St Stanton number ?? Thermal capacity of gas
? Density of gas ???? temperature of
shock-compressed gas ?0 initial temperature.
- Stanton number at the turbulent flow of plates
by gas stream
- The warming up law of metal plates
? ? ? Heat conductivity and heat diffusivity of
plates material
- Depth of fusion of metal
The velocity of a contact point V?, m/s The maximal heating temperature of the metal surface, ??, ? Depth of fusion of metal, ?, µm. Heat time ?, s
2500 600 0 10?10-5
3000 900 0 8,3?10-5
3500 1200 0 7,2?10-5
4000 1500 0,3 6,3?10-5
4500 2000 1,5 5,5?10-5
5000 2500 6 5?10-5
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6. Calculation of ionization degree of
shock-compressed gas area

• Saha equation
• for unitary ionization

? - degree of gas ionization, i.e. a number of
free electrons, falling on an initial atom I -
ionization potential ? temperature ?
density V specific volume N atoms quantity
in 1g of gas at known temperature ? and density ?
or specific volume V.
Ionization of shock-compressed gas area
?10-10 Ionization of air in a boundary layer
?10-1 In view of associative
ionization N ? 2,8 ?? NO e
ionization of air in a boundary layer
?1
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7. Calculation of the surface ionization degree
- ionization coefficient
- ionization degree
n0 Stream of atoms on 1 square centimeter in 1
second n ? n Streams of positive ions and the
neutral atoms evaporating from the same surface
for 1second
For a stationary case (n0 n n)

• Saha-Langmuir equation

- the relation of statistical weights of
ionic and atomic state of the adsorbed atom fk
work function Fk collection of areas with
work function fk e ion charge I - ionization
potential - reflection coefficient for ions
and atoms accordingly
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8. Calculation of ionization degree for
shock-compressed gas area
velocity of contact point V?, m/s ionization degree of near-surface layer, ionization degree according to the mechanism N?2,8 ?? (NO) e,
2500 11 100
3000 15 100
3500 22 100
4000 36 100
4500 55 100
5000 70 100
(Me'-O)(Me'- Me")O Me ? Me" Atoms of metals
on interfaced surfaces, O - Oxygen
The near-surface layer of solid bodies is
essentially nonequilibrium system with high
mobility of particles. Its irradiation by ionic
or plasma streams is a cause of surface
modification. At surface modification a
destruction of organic pollutions on the surface
and oxides, and also lattice of metal in a
near-surface layer is occurred. I.e. there is an
activation of welded surface. In real conditions
the efficiency of emission depends on surface
condition.
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9. Research of processes ahead of the contact
point

hSurface Thickness of metal removed from a
surface of a welded sheet, ?m Splate The area
of sheet, mm2 S trap The area of trap, mm2.
Samples Samples The size of "trap" mm calculated layer thickness on trap surface according to, ?m calculated layer thickness on trap surface according to, ?m calculated layer thickness on trap surface according to, ?m Experimental data ?m
The sizes of plates, mm Material (Atmosphere) The size of "trap" mm Konon, Explosion welding Deribas, Physics of hardening and explosion welding Baum, Physics of explosion Experimental data ?m
500?1200 Steel-steel (air) 250? 500 48 528 192 no
500?1200 Steel-titanium (air) 250? 500 48 528 192 20-80
1400?5900 Steel-steel (air) 250? 1400 236 2600 944 no
2700?2800 Steel-titanium (argon) 250? 2700 112 1232 448 no
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10. The mechanism of cleaning and activation of
welded surfaces
Hypothesis
The supersonic flow (56 Mach numbers) of
shock-compressed gas gives rise to thermal
ionization of gas ahead of the contact point
accompanied by formation of thin layers of
low-temperature plasma. Dissociation oxides and
pollution occurs at influence of plasma. The
positive ions of the metals which have formed as
a result dissociation come back to the cleaned
surface. Atoms of oxygen, nitrogen, carbon form
the elementary gaseous connections ??2 and ?2?
which are taken out from technological gap by the
shock-compressed gas . Dissociation oxides leads
to the sharp increase of activation of welded
surfaces before contact point.
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11. The mechanism of cleaning and surfaces
activation
Activation of a surface
Stream of activating particles
Structure of a surface
Line of ledges
Line of hollows
The original
Intermediate condition
After activation
Condition of a surface
Metod Density of energy, w/m2 Time of influence of plasma, second Time of influence of plasma, second Thickness of deleted layer, ?m
Metod Density of energy, w/m2 in a zone of durability stabilization on other site Thickness of deleted layer, ?m
Plasma-arc clearing 103 5-10 5-10 200-300
Shock Plasma 1010 7,610-6- 1,2 10-5 2,4 10-5- 1,12 10-4 3-5
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Scheme of joint formation
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Initial condition
shock-compressed gas area
The beginning of process, formation of the
shock-compressed gas area
heats gas
Clearing and activation of welded surfaces
t 7,610-6- 1,12 10-4 s.
Plasma
Formation of physical contact
Volumetric interaction with formation of
connection behind a contact point.
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Sequence of joint formation
At pressure welding Our suggestion
1. Formation of physical contact 2. Surface activation 3. Volumetric interaction Cleaning and surface activation of welded plates occurs due to the interaction of shock-compressed gas and plasma stream formed at high-rate flow and plastic deformation in deformation hillock in the localised zone the limited isobar of high pressures Formation of physical contact and joint in contact point 3. Volume interaction with joint formation and plastic deformation behind a contact point
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Conclusions 1. Joint solution of the two
problems (1) piston pushing with determination of
gas parameters behind the shock wave and (2)
determination of gas outflow rate from the gap
has allowed to define the sizes of
shock-compressed gas area ahead of the contact
point. Gas parametres in this area are defined
pressure, temperature and density. It is shown
that the size of shock-compressed gas area is
limited. The effect of stabilization of the sizes
of shock-compressed gas area provides constant
parameters of process on almost unlimited
surfaces. 2. Thermal ionisation of gas and
formation of thin layers low-temperature plasma
occur at supersonic flow (56 Mach numbers) of
shock-compressed gas of welded surfaces on their
border of section in a technological gap ahead of
a contact point. The irradiation ionic or plasma
streams leads to modification of surfaces. .