Modeling gun bore heat transfer and degradation

10 Pages·0.075 MB·English

by  Sopok Samuel.

AIAA 2010-5063
10th AIAA/ASME Joint Thermophysics and Heat Transfer Conference
28 June - 1 July 2010, Chicago, Illinois
AIAA-2010-5063

(10th AIAA Joint Thermophysics & Heat Transfer Conf, June 2010, Chicago)

MODELING GUN BORE HEAT TRANSFER & DEGRADATION

Samuel Sopok

U.S. Army RDECOM-ARDEC-Benet Labs, Watervliet, New York

ABSTRACT A practical thermal-chemical vented
combustor erosion model is described. It was a
Vented combustor experiments are often natural extension of our thermal-chemical-
successful at providing relative erosion results but mechanical erosion model for medium and large
these results are typically inconclusive when caliber cannons [1-5]. Benet Laboratories has had
compared to other vented combustor experiments. the U.S. Army mission for characterizing eroded
As a result of this deficiency, a new method for cannons for many years. These characterizations
successfully modeling erosion of vented have allowed us to develop erosion theories that
combustor cannon bores materials has been we have repeatedly verified for a broad spectrum
developed. This modeling method, in conjunction of these gun systems [1-7]. Both of these erosion
with limited scale firings, provides a cost effective model types require a systems approach where
means of comprehensively studying erosion of variations in bore material type (coating, substrate
coated cannon bore materials. The method is and axial position), charge type (propellant,
derived from our very successful similar method loading density and ablatives), and/or projectile
for modeling coated cannon bore erosion of type (round type and rounds fired) are considered.
medium and large caliber gun systems. These Most commonly, these erosion calculations are
system models are based on years of eroded made for either a constant bore material type with
cannon characterizations and erosion theory varied charge types or a varied bore material
development. We have fired and modeled gun types with a constant charge type.
steel, chromium, tantalum, molybdenum, rhenium,
and niobium cannon bore protection materials. Our calculations of erosion between
Each of these material types has a different set of various vented combustor system samples
erosive degradation thresholds that are governed depends on erosive gas-wall combustion
by the presence of a less reducing (more metal chemistry, degree of achievement of bore material
oxidizing), more reducing (more metal degradation thresholds (measured wall
carburizing), or intermediate reducing solid temperature onsets), and time spent above these
propellant combustion environment. Erosion bore material degradation thresholds. Without
modeling predictions are computed for these six modeling, vented combustor experiments are
materials at the various reducing combustion often successful at simulating relative erosion
environment degrees. Our modeling results show results but are typically inconclusive at simulating
that all of these materials, with the exception of absolute erosion results. Our vented combustor
chromium, have significant differences in their erosion modeling can do absolute erosion
erosive thresholds/performance for our typical predictions because it accounts for variations in
solid propellant combustion environment geometry, cannon bore material type, charge type,
spectrum. The degree of these differences and projectile types.
explains why these materials erode differently at
the more metal carburizing and oxidizing solid COMPUTATIONAL AND EXPERIMENTAL
propellants combustion environment extremes. METHODS

INTRODUCTION Our vented combustor and cannon
erosion models consist of a number of interactively
linked codes and are used to predict wall
temperature profiles and erosion profiles [1-5].
“Approved for public release, distribution unlimited”.
This is declared a work of the U.S. Government and not This overall erosion code includes the CCET
subjected to copyright protection in the United States. thermochemistry cannon code [1-5,8],
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This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.
XNOVAKTC interior ballistics code [1-5,9], MABL Figure 2 shows its reproducible baseline IMR4895
boundary layer cannon code [1-5,10], and the solid propellant firings.
MACE thermal-erosion cannon code [1-5,11].
These erosion predictions are guided and Figure 3 shows typical nondestructive
calibrated by substantial firing data and fired magnifying borescope substrate exposure and
specimen analyses. Our vented combustor erosion data from monitoring a vented combustor
modeling approach requires a burst disk and a sample throughout its life at the mid-sample
pseudo-projectile with at least minor bore position. Substrate exposure is based on crack-pit
resistance. frequency, coating shrinkage-contraction, and
crack-pit widths. This technique is used due to the
A borrowed 200 cc vented combustor [12] lack of a thermal-mechanical crack-pit model.
was fired at our Building 112 range in 1994 and
then at an ARDEC range in the following years. The use of these magnifying borescope
Each Safety Office required a detailed description substrate exposure measurements allows
of each firing test that was supported by modeling modeling of the conductive and convective
calculations. This combustor used electric match exposed gun steel interface temperatures at the
ignition, 0.17 g/cc IMR4895 baseline solid base of coating cracks-pits. Figure 4 shows typical
propellant, numerous other erosive solid maximum values of exposed substrate interface
propellants, and burst disks that achieved-failed at temperatures as a function of coating crack-pit
30 kpsi. Cased igniters-charges were more width throughout its life at the vented combustor
reproducible than their cellophane bagged mid-sample position. Based on these exposed gun
counterparts. For the baseline IMR4895 solid steel interface temperatures, we thermally,
propellant firings, the BLAKE composition is metallurgically, and thermochemically use the
NC1315 at 88.8%, DNT at 7.2%, DPA at 0.6%, KS model to degrade the exposed gun steel substrate
at 0.9%, H2O at 1.0% and ETOH at 1.5% [13] interface through these coating cracks-pits
which produces a 2830 K peak flame temperature. producing coating platelet spallation and
Pressure transducer data were captured, amplified subsequent exposed gun steel gas wash to
and input through an IEEE-488 interface bus condemnation.
controller to a data reduction computer. These
models are calibrated by pressure gages, A gas-wall kinetic rate characterization
thermocouples, and gas-wall thermal, technique is used to study coating and substrate
metallurgical, and chemical characterizations. steel degradation thresholds and reaction rates as
a function of temperature, pressure and time. This
RESULTS AND DISCUSSION technique determines degradation thresholds of
bore coating and substrate materials for their
We developed vented combustor erosion transformation, carburization, oxidation-scale,
testers for screening, assessing, and optimizing other reactions, oxide melting, and metal melting
gun bore protection materials. Their environment thresholds. Figure 5 shows typical normalized gas-
approximates specific gun system core flow and wall coating and substrate steel oxidation rate data
combustion products. Most of these combustors as a function of wall temperature at the vented
have associated erosion models. Progressively combustor mid-sample position. My main erosion
increasing the energies and densities of charges related thrust for implementing vented combustors
requires increased erosion resistant cannon bore in 1994 was to measure gas-wall kinetic rate
protection materials. Vented combustor cannon functions of bore protection materials.
bore protection material samples include medium
and large caliber plates, rings, and ring sections. Figure 6 shows typical ring sample erosion
Cannon bore protection material types include gun throughout its life at the vented combustor mid-
steel, pure chromium, HC chromium, LC sample position. Sample types include gun steel
chromium, pure tantalum, pure molybdenum, pure and 0.002” HC chromium plated steel. This vented
rhenium, and pure niobium (columbium). combustor was more than an order of magnitude
more erosive than a typical gun system. Ideally,
From 1994 to the present, Benet Labs and vented combustor firing intensity should be similar
ARDEC have conducted vented combustor firings to gun system firing intensity in order to simulate
to assess cannon bore protection materials [14]. its correct cannon erosion mechanisms for a given
Figure 1 depicts a 200 cc vented combustor and propellant.

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Figure 7 shows a flow chart of the vented passivation (chromium and tantalum) but they
combustor/cannon coating erosion models. The form a network of radial cracks due to
various codes, their inputs, and their outputs have shrinkage/thermal shock allowing the exposed gun
respective boxes with solid borders, fine dashed steel substrate to erode. This leads to coating
borders, and coarse dashed borders. spallation, pitting, and increased surface
roughness that further increases heat transfer,
There are three main reasons why vented turbulence, boundary layer separation, spallation,
combustor experiments have only been successful and pitting.
at simulating relative erosion results. The first
reason is that varying loading density of a given Pure molybdenum is the classic example
charge type will affect the lack of achievement or of different vented combustor tests producing a
degree of achievement of the various degradation broad range of erosion resistant results. The lack
thresholds for each bore material type. Variations of achievement or degree of achievement of the
in loading density of a given charge type will affect measurable sublimation of pure molybdenum at
its maximum pressure and velocity with little effect about 1080 K determines its erosion related
on flame temperature. outcome.

The second reason is that varying gas- Based on their associated erosion models,
wall combustion chemistries (single or multiple gun system and vented combustor system erosion
propellant types) will affect the lack of comparisons can be made for the same bore
achievement or degree of achievement of the material types and charge types. Quantitative
various degradation thresholds for each bore calculations of erosion between the vented
material type. Single propellant gas/wall combustor samples and the various positions on
combustion chemistry variations will affect gas- the cannon bore depend on erosive gas-wall
wall degrading/reacting species, gas-wall combustion chemistry, bore material degradation
degradation/reaction enthalpies but have little thresholds (measured wall temperature onsets),
effect on flame temperature. Multiple propellant and time spent above these bore material
gas/wall combustion chemistry variations will degradation thresholds. By varying the vented
affect gas-wall degrading/reacting species, gas- combustor propellant loading density, vented
wall degradation/reaction enthalpies and flame combustor sample erosion can be made to
temperature. correspond to different eroded positions on the
cannon bore.
The third reason is that each bore material
type has a different set of erosive bore material All of the above cannon system and
degradation thresholds. For each material, the vented combustor system erosion modeling efforts
degree of combustor charge type conditions start with interior ballistic and thermochemical
affects the lack of achievement or degree of modeling. These codes allow for the simultaneous
achievement of its lowest erosive threshold. With calculation of pressure, temperature and velocity
relatively mild gun system conditions using typical core flow conditions at the desired bore or sample
solid propellants, some bore material types position as a function of time. The core flow and
achieve their lowest erosive bore material thermochemical output data allows for the
degradation thresholds such as the measurable subsequent boundary layer calculation. Then the
sublimation of pure rhenium at about 670 K or the core flow, thermochemical, and boundary layer
measurable flaking oxidation of pure niobium output data allows for the thermal and erosion
(columbium) at about 680 K. With relatively calculation.
moderate gun system conditions using typical
solid propellants, other bore material types Figure 8 gives a summary of bore material
achieve their lowest erosive bore material degradation thresholds (measured and calculated
degradation thresholds such as the measurable wall temperature onsets) based on a spectrum of
flaking oxidation of gun steel (mostly iron) at about typical solid propellants. These six bore materials
1050 K and the measurable sublimation of pure types include gun steel, pure chromium, pure
molybdenum at about 1080 K. Even with relatively tantalum, pure molybdenum, pure rhenium, and
severe gun system conditions using typical solid pure niobium (columbium). Their thresholds
propellants, other bore material types do not include measurable transformations, reactions,
achieve their lowest erosive bore material reaction product melting points, and metal melting
degradation thresholds due to oxidation points. In the following paragraphs, each of these
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bore material types will be discussed in greater susceptible to oxygen, hydrogen and nitrogen
detail based on typical solid propellants. embrittlement above 400 K.

Gun steel (mostly iron) bore and substrate Pure molybdenum coating degradation of
degradation of surfaces, cracks, pits and surfaces, cracks, pits and interfaces is computed
interfaces is computed by the area under a by the area under a temperature-time curve above
temperature-time curve above a given degradation a given degradation threshold such as the
threshold such as the measurable 1000 K measurable 1080 K accelerated oxidation onset
transformation onset of steel which may induce (trace onset at 1030 K) and sublimation of
heat checking, measurable 1050 K diffusion onset molybdenum by oxygen forming MoO3 (oxide
of carbon into the steel, measurable 1050 K evaporates as formed), measurable 1080 K
accelerated flaking scale type oxidation onset melting point onset of MoO3 solid that is the same
(trace onset at 670 K) of iron by oxygen forming as the measurable molybdenum oxidation onset
iron oxide (FeO), measurable 1270 K accelerated due to sublimation, measurable 2470 K melting
flaking scale type oxidation onset of iron by sulfur point onset of MoC2, and measurable 2890 K
forming iron sulfide (FeS), measurable 1420 K melting point onset of molybdenum.
white layer eutectic melting point onset of iron
carbide, measurable 1470 K melting point onset of Pure rhenium coating degradation of
iron sulfide, measurable 1640 K melting point surfaces, cracks, pits and interfaces is computed
onset of iron oxide, measurable 1700 K melting by the area under a temperature-time curve above
point onset of gun steel, and measurable 2110 K a given degradation threshold such as the
melting point onset of iron carbide. measurable 670 K accelerated oxidation onset
(trace onset at 420 K) and sublimation of rhenium
Although chromium plate for cannon bores by oxygen forming Re2O7 (oxide evaporates as
is not pure, the following values are quite close to formed), measurable 670 K melting point onset of
pure chromium despite variation in cannon Re2O7 solid that is the same as the measurable
chromium plate types. Chromium coating rhenium oxidation onset due to sublimation,
degradation of surfaces, cracks, pits and measurable 2700 K melting point onset of Re4C3,
interfaces is computed by the area under a and measurable 3450 K melting point onset of
temperature-time curve above a given degradation rhenium.
threshold such as the measurable 2000 K
accelerated oxidation onset (trace onset at 1960 Pure niobium (also columbium or Cb)
K) and passivation of chromium by oxygen forming coating degradation of surfaces, cracks, pits and
Cr2O3, measurable 2110 K transformation onset interfaces is computed by the area under a
of chromium, measurable 2130 K melting point temperature-time curve above a given degradation
onset of chromium, measurable 2540 K melting threshold such as the measurable 680 K
point onset of Cr2O3, and measurable 4070 K accelerated flaking scale type oxidation onset
melting point onset of Cr3C2. Chromium forms an (trace onset at 300 K) of niobium by oxygen
interfacial intermetallic with iron above 1050 K and forming Nb2O5, measurable 1760 K melting point
is subject to intergranular corrosion above 1090 K. onset of Nb2O5, measurable 2740 K melting point
Its is also susceptible to hydrogen, nitrogen, and onset of niobium, and measurable 4070 K melting
oxygen embrittlement above 400 K. point onset of NbC. The measurable 680 K
accelerated flaking scale type oxidation onset of
Pure tantalum coating degradation of niobium by oxygen, forming Nb2O5, is due to
surfaces, cracks, pits and interfaces is computed nucleation and growth of the porous oxide that
by the area under a temperature-time curve above keeps a continuously refreshed surface of niobium
a given degradation threshold such as the exposed to corrosion. Niobium forms an interfacial
measurable 720 K accelerated oxidation onset intermetallic with iron above 1050 K and is
(trace onset at 570 K) and passivation of tantalum susceptible to oxygen, hydrogen and nitrogen
by oxygen forming Ta2O5, 2150 K measurable embrittlement above 400 K.
melting point onset of Ta2O5 (possibly as low as
1830 K if this oxide is slightly less than 18.1% The vented combustor or gun system
oxygen), measurable 3270 K melting point onset reaction energy is all the energy for future
of tantalum, and measurable 4150 K melting point reactions and melting. This reaction energy is
onset of TaC2. Tantalum forms an interfacial enthalpy driven and highly dependent on all
intermetallic with iron above 1050 K and is chemical species present, reactions present, and
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their chemical kinetics. A given propellant forms intermetallics with iron. Hydrogen is
chemistry type with a constant loading density available in lesser amounts for this fully oxidizing
may be mainly oxidizing to some wall materials case and its absorption is diminished.
while mainly carburizing to other wall materials
depending on the gas-wall temperatures and Pure molybdenum has the next least
chemical species present. metal oxidative erosion resistance due to its
accelerated oxidation/sublimation product MoO3
Erosion predictions of these six bore formed at about 1080 K. A trace of its dominant
protection materials are computed for numerous carbide product Mo2C is still measurable.
typical less metal reducing (more oxidizing) solid Oxidation resistant molybdenum alloys have better
propellants combustion environments and more erosion resistance than pure molybdenum.
metal reducing (more carburizing) solid propellants
combustion environments. The more oxidizing Gun steel (mostly iron) has the next least
propellant types typically have a higher flame metal oxidative erosion resistance due to its
temperature with more erosive combustion accelerated flaking scale oxidation products FeO
species and a minor level of carburization. The and FeS formed at about 1050 K and 1270 K,
more carburizing propellant types typically have a respectively. These oxidation products
lower flame temperature with less erosive respectively melt at about 1640 K and 1470 K.
combustion species and a minor level of oxidation. This 1050 K formation of FeO is less damaging
It should be noted that the more oxidizing and than the oxidations coupled with sublimations
more carburizing solid propellant types are at the mentioned above. This oxide scale is porous and
ends of a spectrum of oxidation and carburization flakes exposing a continuously refreshed surface
combinations which contains a range of flame of metal to corrosion. A trace of its dominant
temperatures and gas-wall combustion chemistry. carbide product Fe3C is still measurable. Gun
Figure 8 shows that some bore material types steel transforms at about 1000 K.
such as gun steel may be nearly equal in their
oxidation and carburization levels. Although chromium plate for cannon bores
is not pure, the following values are quite close to
Calculated initial erosive threshold pure chromium despite variation in cannon
predictions for typical more metal oxidizing (less chromium plate types. This chromium has the next
reducing) solid propellant types are summarized in least metal oxidative erosion resistance due to its
Figure 9. These calculations tend to represent the metal melting point at about 2130 K. It also forms
solid propellant metal oxidation boundary or a non-damaging accelerated oxidation product
extreme for this study. Cr2O3 at about 2000 K which melts at about 2540
K. This oxide scale is passivated and does not
For the more metal oxidizing solid expose a continuously refreshed surface of metal
propellant types, pure rhenium has the least to corrosion. A trace of its dominant carbide
erosion resistance. This is due to its accelerated product Cr3C2 is still measurable. At high
oxidation/sublimation product Re2O7 formed at temperatures, pure chromium is susceptible to
about 670 K. A trace of its dominate carbide hydrogen, nitrogen and oxygen embrittlement and
product Re4C3 is still measurable. Rhenium alloys forms intermetallics with iron.
with iridium are much more oxidation and erosion
resistant than pure rhenium. Pure tantalum has the most metal
oxidative erosion resistance due to its oxidation
Pure niobium (columbium) has the next product Ta2O5 melting point at about 2150 K
least metal oxidative erosion resistance due to its (possibly as low as 1830 K if this oxide is slightly
accelerated flaking scale oxidation product Nb2O5 less than 18.1% oxygen). The 2130 K Cr2O3
formed at about 680 K. This oxide melts at about melting point is slightly exceeded by the 2150 K
1760 K. This oxide scale is porous and flakes Ta2O5 melting point but would significantly
exposing a continuously refreshed surface of exceed the1830 K Ta2O5 melting point if this
metal to corrosion. A trace of its dominant carbide oxide had slightly less than 18.1% oxygen. It forms
product NbC is still measurable. Oxidation this non-damaging accelerated oxidation product
resistant niobium alloys have better erosion Ta2O5 at about 720 K. This oxide scale is
resistance than pure niobium. At high passivated which does not expose a continuously
temperatures, pure niobium is susceptible to refreshed surface of metal to corrosion. A trace of
hydrogen, nitrogen and oxygen embrittlement and its dominant carbide product TaC2 is still
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measurable. At high temperatures, pure tantalum embrittlement and forms intermetallics with iron.
is susceptible to hydrogen, nitrogen and oxygen Hydrogen is available in large amounts for this
embrittlement and forms intermetallics with iron. fully carburizing case and its absorption and
Tantalum has the potential at high temperatures to embrittling effect are significant. Free and/or
absorb up to 700 times its own volume of loosely bound oxygen is available only in trace
hydrogen which can severely embrittles the metal. amounts for this fully carburizing case and its
Hydrogen is available in lesser amounts for this absorption is limited.
fully oxidizing case and its absorption is
diminished. Pure tantalum has the most metal
carburization erosion resistance due to its metal
Similar calculated initial erosive threshold melting point at about 3270 K. A trace of its
predictions for typical more metal carburizing dominant oxide product Ta2O5 is still measurable.
(more reducing) solid propellant types are also At high temperatures, pure tantalum is susceptible
summarized in Figure 9. These calculations tend to hydrogen, nitrogen and oxygen embrittlement
to represent the solid propellant metal and forms intermetallics with iron. Tantalum has
carburization boundary or extreme for this study. the potential at high temperatures to absorb up to
700 times its own volume of hydrogen which can
For the more metal carburizing solid severely embrittles the metal. Hydrogen is
propellant types, pure gun steel (mostly iron) has available in large amounts for this fully carburizing
the least erosion resistance. This is due to its case and its absorption and embrittling effects are
carbide product Fe3C white layer eutectic melting significant. Free and/or loosely bound oxygen is
point at about 1420 K. It begins forming this available only in trace amounts for this fully
carbide product Fe3C at about 1050 K. A trace of carburizing case and its absorption is limited.
its dominant oxidation products FeO and FeS are
still measurable. Gun steel transforms at about Propellant composition, propellant loading
1000 K. density, and combustor (or gun) geometry
determine the time and position dependent
Although chromium plate for cannon bores combustion gas pressures, temperatures,
is not pure, the following values are quite close to velocities, and high energy chemical combustion
pure chromium despite variation in cannon gas species/radicals produced. These resultant
chromium plate types. This chromium has the next combustion gas features determine the time and
least metal carburization erosion resistance due to position dependent wall heating and gas-metal
its metal melting point at about 2130 K. A trace of wall chemical reactions.
its dominant oxide product Cr2O3 is still
measurable. At high temperatures, pure chromium The various erosive thresholds for
is susceptible to hydrogen, nitrogen and oxygen combustion gas degradations and reactions of
embrittlement and forms intermetallics with iron. these metal walls depends on the wall
temperatures as well as the types and amounts of
Pure molybdenum has the next least high energy metal carburizing and oxidizing
metal carburization erosion resistance due to its combustion gas chemical species present.
carbide product Mo2C melting point at about 2470
K. A trace of its dominant oxide product MoO3 is Very high energy propellant components
still measurable. have higher energy bonds within their molecules.
If all else is equal, increasing the percentage of
Pure rhenium has the next least metal these very high energy propellant components
carburization erosion resistance due to its carbide tends to increase erosion of traditional gun bore
product Re4C3 melting point at about 2700 K. A wall materials.
trace of its dominant oxide product Re2O7 is still
measurable. A number of conclusions can be drawn for
each metal in Figure 9 based on their initial
Pure niobium (columbium) has the next erosive threshold ranges for their more metal
least metal carburization erosion resistance due to oxidizing and carburizing solid propellant types.
its metal melting point at about 2740 K. A trace of Chromium has no variation between its initial
its dominant oxide product Nb2O5 is still erosive threshold metal oxidation and
measurable. At high temperatures, pure niobium is carburization extremes. Gun steel has a small
susceptible to hydrogen, nitrogen and oxygen variation between its initial erosive threshold metal
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oxidation and carburization extremes. Tantalum, 2. S. Sopok, P. O’Hara, G. Pflegl, S. Dunn,
molybdenum, rhenium, and niobium (columbium) D. Coats, “Thermochemical Erosion
have large variations between their initial erosive Modeling of M242 Gun Systems”,
threshold metal oxidation and carburization Proceedings of the 8th Army Symposium
extremes. If everything else is equal, modeling on Gun Dynamics, Newport RI, May 1996.
predictions indicate that differences between a 3. S. Sopok, P. O'Hara, P. Vottis, G. Pflegl,
metal’s initial erosive thresholds due to its metal C. Rickard, and R. Loomis, “Erosion
oxidation and carburization solid propellant Modeling of the 120mm M256/M829A2
extremes produce similar variations in erosion Gun System”, Proceedings of 32nd ADPA
resistance. Variations in degree/type of solid Gun & Ammunition Technical Meeting,
propellant reducing environment explains why a San Diego, April 1997.
material’s erosion resistance may vary from one 4. S. Sopok “Cannon Coating Erosion Model
vented combustor experiment to another. Ideally, With Updated M829E3 Example”,
vented combustor firing intensity should be similar Proceedings of the 36th AIAA Joint
to gun system firing intensity in order to simulate Propulsion Conference, Huntsville AL,
its correct cannon erosion mechanisms for a given June 2000.
propellant. 5. S. Sopok, M. Fleszar, “Ablative Erosion
Model for the M256/M829E3 Gun
Also for a given metal, oxidation and System”, Proceedings of the 37th JANNAF
carburization embrittlement variation results in Combustion Meeting, Monterey CA,
large differences in erosion resistance. This is due November 2000.
to variations in radial crack density and contraction 6. P. Thornton, J. Senick, J. Underwood, S.
that induces crack widening and exposes the gun Sopok, J. Cox, "LP Gun No.2 Materials/
steel substrate to the corrosive combustion gases. Failure Analysis", U.S. Army ARDEC
Special Publication SP92-1, Watervliet
In 1999, we developed a robust time NY, 1992.
dependent gun tube boundary layer (GTBL) code 7. G. Capsimallis, J. Cox, P. O'Hara, M.
[15] to complement and eventually replace our Witherell, S. Sopok, J. Underwood, G.
current steady state gun tube mass addition Pflegl, P. Cote, "M242/ M919 Multi-
boundary layer (MABL) code [10]. In that same Disciplinary Analyses", U.S. Army ARDEC
year, when conventional interior ballistic models Special Publication SP92-2, Watervliet
failed us, we successfully began using the GTBL NY, 1992.
code for Future Combat System rarefaction wave 8. D. Coats, S. Dunn, S. Sopok, “A New
gun (RAVEN) and associated vented combustor Chemical Equilibrium Code with
systems. In these RAVEN systems, high velocity Compressibility Effects (CCET)”,
combustion gases exit both a breech venting Proceedings of the 33rd JANNAF
nozzle for recoil reduction as well as the Combustion Meeting, Monterey CA,
conventional muzzle venting after projectile exit October 1996.
[16]. Our RAVEN modeling efforts make it possible 9. P. Gough, "The XNOVAKTC Code," Paul
to reject design configurations without full scale Gough Associates, Portsmouth NH, U.S.
firing tests which produces significant savings. Army BRL-CR-627, February 1990.
10. J. Levine, "Transpiration and Film Cooling
REFERENCES Boundary Layer Computer Program
(MABL) - Numerical Solution of the
1. S. Dunn, S. Sopok, D. Coats, P. O'Hara, Turbulent Boundary Layer Equations with
G. Nickerson, G. Pflegl, “Unified Computer Equilibrium Chemistry”, NASA Marshall
Model For Predicting Thermochemical N72-19312, Huntsville AL, June 1971.
Erosion In Gun Barrels”, Proceedings of 11. S. Dunn, "Materials Ablation Conduction
the 31st AIAA Joint Propulsion Erosion Program (MACE)," Software and
Conference, San Diego, July 1995; Also, Engineering Associates User’s Guide,
S. Sopok, S. Dunn, D. Coats, P. O'Hara, Carson City NV, June 1989.
G. Pflegl, “Unified Computer Model For 12. Dr. Art Bracuti, private communications on
Predicting Thermochemical Erosion In borrowed combustor, U.S. Army ARDEC,
Gun Barrels”, AIAA Journal of Propulsion Dover NJ, 1994.
and Power Vol. 15, Num. 4, July 1999.
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American Institute of Aeronautics and Astronautics
13. Larry Werner, private communications on 15. S. Dunn, D. Coats, S. Sopok, “Gun Tube
propellants, IMR Power Company, Virginia Boundary Layer Code (GTBL)”, Software
Beach VA and Plattsburgh NY, 1994. and Engineering Associates User’s Guide,
14. S. Sopok, G. Pflegl, P. O’Hara, M. Carson City NV, 1999.
Cipolla, J. Keating, P. Webber, “Vented 16. E. Kathe, R. Dillon, S. Sopok, M. Witherell,
Combustor Firings To Assess Cannon S. Dunn and D. Coats, "Rarefaction Wave
Bore Protection Materials”, Benet Gun Propulsion," Proceedings of the 37th
Laboratories Memorandum Report, JANNAF Combustion Meeting, Monterey
Watervliet NY, 1994. CA, November 2000.

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American Institute of Aeronautics and Astronautics
Fig. 1 – 200 cc Vented Combustor Fig. 2 -Reprod. Vented Combustor
Firings
35

30

25
)
si 20
p
k
( 15
P
10
5

0
0.030 0.060 0.090 0.120
t (ms)

Fig. 3 -Vented Combustor Fig 4 -Vented Combustor Exposed
Magnifying Borescope Data Substrate Interface Temperature

e 30 K) 1200
sur 25 p. (
o m
xp 20 e 1150
E T
ate 15 erf.
bstr 10 x Int 1100
u a
S 5 M
% 1050
0
0 0.05 0.1 0.15 0.2
0 20 40 60 80 100
Coating Crack/Pit Width (mm)
% Erosion Life
Fig. 5 -Gas-Wall Oxidation Rate Fig. 6 -Vented Combustor Ring
Sample Erosion
1 30
e
t
a 25
R 0.8
x. 20
W R 0.6 substrate ngs 15 Steel
G- 0.4 coating Firi 0.002"
m. 10 Cr/Steel
or 0.2 5
N
0 0
600 1000 1400 1800 0 0.01 0.02 0.03
Twall (K) Erosion Depth (in)
9
American Institute of Aeronautics and Astronautics
Fig. 7 – Flow Chart Of Cannon/Vented Combustor Coating Erosion Models

initial chem./matls. input gas/g-w products input
CCET Thermochemical Code
system defining input NOVA Interior Ballistics Code Pg & Vm input
matls. properties input MABL Boundary Layer Code thermocouple input
g-w kinetic rate input MACE Main Erosion Code rounds-types fired input
microscopic matl void input t-c-m thermal & erosion profile Rx, diffusion, phase degrad.
(cracks,pits,interf,surf) output as f(x, t, rds-types fired) input (cracks,pits,interf,surf)
Fig. 8 -Summary Of Measured & Calculated Bore Material
Degradation Thresholds For Solid Propellant Spectrum
4500
Tt (M)
4000
3500 Tr (M-O)
) 3000
K Tr (M-C)
all ( 22050000 Tr (M-S)
w
T 1500 Tm (M-O)
1000
Tm (M-C)
500
Tm (M-S)
0
Tm (M)
GS Cr Ta Mo Re Nb
Typical Bore Material Types
Fig. 9 -Calculated Initial Erosive Thresholds
3500
typical metal
3000
oxidizing
2500 solid
)
K propellant
all ( 2000
w 1500
T typical metal
1000
carburizing
500 solid
propellant
0
GS Cr Ta Mo Re Nb
Typical Bore Material Types
10
American Institute of Aeronautics and Astronautics