Thermobaric explosives (TBX), similar to fuel air explosives (FAE), rely on the rapid combustion of liquid or solid fuels with high heats of combustion to generate relatively long duration blast overpressures to defeat targets. When a conventional high explosive (HE) is detonated, a high pressure, short duration shock wave is created. The resulting impulse (integral of the pressure-time curve) of such a detonation is fairly low. In comparison, a TBX or FAE detonation generates a lower pressure, longer duration blast wave. The longer duration blast wave results from combustion of the thermobaric fuel additives which occur on a much longer time scale (milliseconds) than the detonation event (microseconds).

1. Detonation Calorimeter: Application and Operation for Thermobaric
Explosive Characterization and Evaluation
Andrew R. Davis*, Scott D. Hall and Gregory D. Knowlton
Nammo Talley, Inc.
P.O. Box 34299, Mesa, AZ 85277
e-mail address: adavis@nammotalley.com
ABSTRACT
The increased interest in thermobaric weapons has driven a need to develop and evaluate new
thermobaric explosives (TBXs) more efficiently. Nammo Talley traditionally uses theoretical
thermochemical codes to develop new TBX compositions. Following a down-selection of potential
candidates based on theoretical results; 1 to 2 pound charges of the most promising TBX compositions
are tested in an instrumented, reinforced concrete enclosure to characterize the real-world thermobaric
performance. This approach has worked well when there was a series of several formulations to test;
however, enclosure testing is cost prohibitive when performing single evaluations due to the personnel
required for setup, testing, and teardown. Furthermore, the thermochemical codes cannot always predict
the real-world TBX effects. Therefore, a need was identified to develop a better and more efficient
method to characterize and evaluate candidate thermobaric compositions before they are tested in the
enclosure.
In 2005, Nammo Talley collaborated with Parr Instruments to design and fabricate a detonation
calorimeter to aid in TBX development and evaluation. The final product was delivered and placed into
service at NammoTalley in 2006. The detonation calorimeter can quickly and economically characterize
gram-size TBX samples and gives a more precise total energy output value than the enclosure due to the
near adiabatic environment provided by the calorimeter. The energy released from a TBX detonation
under various atmospheric conditions can be readily quantified in the detonation calorimeter. The
energetic contributions of the both the detonation itself and subsequent combustion of the fuel rich
detonation products and thermobaric fuels can be differentiated. This is useful in determining the effects
of adding enhanced fuels to TBX compositions to optimize thermobaric performance. This paper will
discuss the operational characteristics of the detonation calorimeter and its use as an analytical tool to
characterize and evaluate candidate TBX compositions in order to predict real-world thermobaric
performance.
BACKGROUND
Thermobaric explosives (TBX), similar to fuel air explosives (FAE), rely on the rapid
combustion of liquid or solid fuels with high heats of combustion to generate relatively long duration
blast overpressures to defeat targets. When a conventional high explosive (HE) is detonated, a high
pressure, short duration shock wave is created. The resulting impulse (integral of the pressure-time
curve) of such a detonation is fairly low. In comparison, a TBX or FAE detonation generates a lower
pressure, longer duration blast wave. The longer duration blast wave results from combustion of the
thermobaric fuel additives which occur on a much longer time scale (milliseconds) than the detonation
event (microseconds). The heat from additive combustion drives the expanding fireball temperature
considerably higher resulting in increased blast pressures behind the initial shock wave. The increased
pressure and temperature mitigate attenuation of the shock wave allowing the blast to penetrate further
into caves and tunnels and travel around corners (1,2). The “afterburning” of the thermobaric additives
creates higher blast impulses which provide larger surface loads on structures than is attainable by an
equal mass of conventional explosives (3). Thus, structures such as buildings and bunkers are

2. particularly susceptible to defeat by TBX or FAE. Furthermore, the higher blast temperatures of TBX
and FAE can ignite flammable materials in the target area.
TBX and FAE, though similar in target defeat method, differ primarily on the system of fuel
dispersion and ignition. An FAE munition must rupture above or in the intended target to disperse a
cloud of fuel into the atmosphere. Once the fuel has sufficiently mixed with the air and the fuel/air ratio
is within explosive limits, the cloud is ignited in a second step to produce a deflagration or detonation.
This is the same FAE effect observed in numerous industrial accidents where finely divided dust clouds
(i.e. coal, grain, sugar, etc.) unexpectedly explode. Typically, FAE munition fuels are liquid
hydrocarbons and/or solid metal or organic powders. A major problem of FAE munitions is the precise
timing of both the dispersion of the fuel and the ignition/detonation of the fuel cloud. Thermobaric
explosives eliminate the FAE timing issues by dispersing and igniting the thermobaric fuels in a single
step. In a typical TBX, a solid metal fuel is mixed with a high explosive (HE) such as
cyclotetramethylenetetranitramine (HMX) or cylcotrimethylenetrinitramine (RDX), in an organic binder
to form a composition that can be detonated with a standard detonation train. Once detonated, the hot,
expanding gas cloud disperses the thermobaric fuel into the atmosphere. Heat from the detonation itself
and subsequent combustion of the fuel rich detonation products and organic binder provide a kinetically
favored environment to combust the dispersed thermobaric fuel with atmospheric oxygen. Due to the
reliability and ease of manufacture, TBX munitions have essentially replaced FAE munitions for
structure/cave defeat.
The development of TBXs typically involves the use of theoretical thermochemical codes to
predict performance. The results of such analyses can be examined for the presence of combustible
detonation products and the detonation velocity to infer blast performance (2). The calculated heat of
combustion can also be used as a metric for blast performance. A formulation having a large amount of
combustible detonation products, like hydrogen, would theoretically yield considerable post detonation
combustion heat. Once promising candidates have been selected, the TBXs are made and tested to
evaluate the thermobaric performance. Performance is evaluated through data obtained from momentum
gauges, pressure transducers and thermocouples. TBXs can be detonated either in the open air or inside
instrumented structures. However, because TBXs are designed to excel in confined spaces, their
performance in open air detonations may not be as high as expected (1).
Nammo Talley traditionally develops and evaluates TBXs using the Cheetah thermochemical
code (4) to formulate explosive compositions. Candidates are down selected based on the calculated heat
of combustion which is actually comprised of the heat of detonation and the heat associated with the
combustion of the fuel rich detonation products and thermobaric fuels. Because impulse is a function of
the heat of combustion, it is thought that the selection of promising candidates by the respective heats of
combustion would be reflected in the real-world thermobaric performance. One to two pound charges
of the selected TBX candidates are then tested in an instrumented reinforced concrete enclosure
specially designed to evaluate thermobaric performance. The enclosure is instrumented with pressure
transducers to measure both peak and quasi-static pressure for impulse calculations and thermocouples
to measure blast temperatures. In addition, the enclosure has a 19,800 lbs “floating” roof which is also
used to calculate impulse. A high speed camera captures the maximum height attained by the roof after
detonation which then can be mathematically related to an equivalent impulse. The impulse, calculated
from roof lift data, is relatively consistent with very low shot to shot variation. Photos showing the
Nammo Talley enclosure are given in Figure 1 on the following page.

3. Figure 1 Nammo Talley test enclosure before and immediately after TBX detonation
The aforementioned method of TBX development and testing has its limitations. First, the
relative performance of TBXs does not always match the Cheetah heat of combustion trends as
expected. There have been several test series where TBXs with high predicted heats of combustion have
been outperformed by TBXs with lower predicted heats of combustion. Standard Cheetah runs perform
calculations based solely on thermodynamics, while neglecting any kinetic limitations. For example,
Cheetah indicates that metal oxides will be preferentially formed over the oxides of carbon or hydrogen
during the anaerobic detonation event, even though the combustion of metal fuels occur over time scales
orders of magnitude greater than the detonation. Subsequent heat of detonation testing (under argon to
eliminate the thermobaric combustion reactions) indicated little, if any, metal oxides were formed.
Therefore, it has been concluded that non-ideal (i.e. TBX) explosive detonations are not adequately
modeled by the Cheetah standard run where reaction kinetics play a significant role in product
formation. Recent versions of Cheetah incorporate kinetic models along with thermodynamic
calculations, but the library of reactants is very limited, making more accurate predictions challenging.
Second, enclosure testing is quite labor intensive for set up and tear down, making testing rather
expensive when single or small groups of TBXs are to be evaluated. This amplifies the problem of using
Cheetah as a primary TBX predictive tool when less than desirable TBXs may not be screened out of the
enclosure test matrix. Thus, a need was recognized to more accurately and efficiently characterize and
screen TBXs before moving onto enclosure testing.
Nammo Talley began looking at small scale explosive testing methods to develop a new TBX
screening tool. It became apparent that calorimetry methods have been successfully implemented to
characterize the heat of detonation of common HE materials (5,6,7). However, little information
concerning the characterization of TBX heats of combustion through calorimetry existed in the
literature. Nevertheless, Nammo Talley sought to apply the same detonation calorimetry methods to
characterize TBXs. Taking successful design concepts from selected detonation calorimeters, Nammo
Talley collaborated with Parr Instruments to design and fabricate a detonation calorimeter for TBX
testing (8). The detonation calorimeter was delivered and became operational in 2006.
The calorimeter was initially checked out by performing heat of detonation and combustion
evaluations using composition C4, a common RDX based plastic bonded explosive. The experimental
values were compared to Cheetah predictions. Even though Cheetah is unable to accurately address non-
ideal explosive detonations, the code is suitable for ideal explosive detonations and heat of combustion
calculations for both ideal and non-ideal explosives. The C4 test results were approximately 5% to 18%
higher than Cheetah predictions. This was troubling, as Cheetah assumes the complete conversion of the
C4 to CO2, H2O and N2 when performing heat of combustion calculations. In other words, the Cheetah

4. value should reflect the maximum energy release possible, because CO2, H2O and N2 are the lowest
enthalpy products in a combustion reaction. A subsequent investigation found that the excess energy
was related to the condensation of water vapor (8). First, Cheetah assumes all water formed remains in
the vapor phase. However, significant quantities of condensed water vapor were found in the
calorimeter. The energy of condensation that Cheetah neglects was captured by the calorimeter leading
to higher than predicted heats of combustion. Second, the condensed water vapor hydrated, adsorbed
and/or absorbed onto the finely divided alumina powder remaining from the sample holder, releasing
additional energy not considered in the Cheetah prediction. This “crucible effect” was found to be
dependant upon the amount of water produced from the detonation and subsequent combustion of a
sample and is therefore quantifiable. When the condensation of water vapor and the “crucible effect”
were accounted for, experimental C4 values were 98.8% of the Cheetah prediction. Additional tests
were performed with various explosives, including TNT and TBX compositions, the results of which
were within 2% of Cheetah calculations when water condensation and the crucible effect were
accounted for (8). The results of the investigation demonstrated that the calorimeter is capable of
accurately determining the heats of combustion and detonation of explosive materials.
The ability to screen TBX compositions by predicting enclosure performance is a desired
function of the detonation calorimeter. Previous testing indicated that the calorimeter is very capable of
determining TBX heats of combustion. The finite volume, which promotes efficient heat and mass
transfer, along with the excess oxygen used for heat of combustion testing provides ideal combustion
conditions within the calorimeter. However, the real-world performance of TBX compositions is less
than ideal, as the performance is dependant upon both heat transfer and oxygen transport within the
expanding cloud of detonation products and thermobaric fuels. Typically, some thermobaric fuel
remains unreacted after a TBX detonation, resulting in lower than expected performance. Thus, in order
to mimic the non-ideal conditions experienced in real-world detonations, a test plan was developed to
operate the calorimeter at reduced oxygen levels to compare selected TBX heats of combustion to
enclosure performance (e.g. impulse) data. The goal of the investigation was to determine if there is a set
of calorimeter operating conditions that could provide performance trends similar to the enclosure.
EXPERIMENTAL
The objective of the study was to evaluate the ability of the Nammo Talley detonation
calorimeter to predict the impulse performance of TBX candidates. Because impulse is related to the
heat of combustion, it is thought that relative impulse trends from enclosure testing could be observed in
the calorimeter heat of combustion data. If similar trends existed, the calorimeter could be used as a tool
to predict enclosure performance. Selected TBXs were detonated in both the enclosure (to obtain
impulse and temperature data) and the calorimeter (to obtain heat of combustion data). Samples in the
calorimeter were evaluated under various oxygen deficient conditions in an attempt to create non-ideal
detonation/combustion behavior to mimic real-world detonations.
Four cast/cure explosive compositions were mixed in a one gallon Baker Perkins mixer with
varying levels of aluminum as a thermobaric fuel. The same polymeric binder was used for each
composition; however, the binder-to-solids ratio was adjusted to resolve mix viscosity issues associated
with increased aluminum loading. Enclosure and calorimeter samples of a given composition were cast
from the same mix. The selected composition formulations, along with the constituent mass percentages,
are given in Table 1 on the following page.

5. Table 1 Explosive formulations selected for the calorimeter/enclosure study
Explosive
Formulation Aluminum HMX
Polymeric
Binder
A - 87.0% 13.0%
B 10.0% 78.0% 12.0%
C 22.5% 61.5% 16.0%
D 35.0% 45.0% 20.0%
Explosive A, shown in Table 1, is a non-TBX composition used as a baseline to compare the
effects of aluminum and aluminum loading levels in the remaining 3 TBX candidates
Detonation Calorimeter
The NammoTalley detonation calorimeter system consists of the following:
• Spherical calorimeter bomb
o 1.25 in thick 316-SS
o 55 kg total mass
o 5.2 L internal volume
• 10 L water bucket with dual stirrers
• Precision thermometer
o Accurate to + 0.001 ºC
o Records temperature every 12 sec
• Dynamic pressure acquisition system.
• Initiating system
o RP-80 EBW detonator
o Teledyne-RISI EBW FS-10 Firing Set
Figure 2 Detonation calorimeter
The calorimeter is calibrated by combusting approximately 8 g of benzoic acid in 30 atm of
oxygen. The water equivalent energy (EE) value is calculated by dividing the expected heat value
(calories) by the experimental temperature rise (ºC). The EE value is then adjusted for the calibration
hardware that is removed for detonation runs. Test samples are prepared by loading alumina crucibles
with 10 to 25 g of a desired HE or TBX. The wall thickness of the alumina crucibles range from 1.6 to 4
mm. Five grams of C4 are placed on top of the HE or TBX sample as a booster charge to ensure
detonation of insensitive compositions. The EBW wires are fed through a hole in the crucible lid. The
EBW is then inserted into the sample or C4 booster and the lid is glued to the crucible using Sauereisen©
low expansion cement No. 29 (9), a nonreactive inorganic adhesive. Each crucible is assembled to
minimize gaps between the detonator, booster, and sample. Photos of a calorimeter test article are given
in Figure 3 on the following page.

6. Figure 3 Detonation calorimeter test article
After assembly, the EBW wires are connected to the insulated electrodes in the bomb lid,
allowing the crucible to hang freely in the bomb. Hardened, ¼ in thick steel plates are placed in the
bottom of the bomb and mounted to the underside of the lid to minimize fragment damage to the bomb.
After bolting the lid down, the bomb is purged 3 times with the appropriate test gas. Argon is used for
determining heats of detonation. Nitrox 50, a 50:50 by volume blend of oxygen and nitrogen, or pure
oxygen is used for determining heats of combustion. Once purging is complete, the bomb is charged to
the predetermined test pressure.
The bomb is lowered into the water bucket and 10 L of deionized water are added. The blast wire
leads are connected to the electrodes and the test is started. The calorimeter temperature is allowed to
stabilize for at least 20 min before the sample is fired. Once the sample is fired, the calorimeter stabilizes
until no further temperature change is observed. Total test time typically ranges from 50 min to 1 hr.
After detonation, the pressure data is reviewed to verify that a detonation occurred. The pressure system
has yet to be optimized for quantitative pressure measurement, but the occurrence of a detonation or
deflagration can easily be detected. Detonations are indicated by an immediate pressure spike followed
by a gradual pressure decay. Deflagrations are indicated by a low pressure rise over time. Once the
testing has been completed, the lid is removed and the calorimeter residue is analyzed for unreacted
material, large crucible pieces (indicative of a possible deflagration) or any unexpected color or odor.
Test Enclosure
The Nammo Talley test enclosure is a reinforced cast concrete room 12 ft long by 10 ft wide by
8 ft high with a 3 ft square window and 2 ft by 6 ft door. Explosive candidates up to 2 lbs are detonated
on a wood stand in the center of the room, positioned so the center of the test article is 4 ft from the
floor. Fixtures are embedded in the enclosure walls and floor to accept an array of pressure transducers
and thermocouples to collect performance data. Photos of the test enclosure were given previously in
Figure 1.
A key design feature is the 19,800 lbs timber and steel “floating” roof that rests on the enclosure
walls. After detonation of a test article, the roof rises to vent overpressure. Steel guides project down
from the roof along the outside of the enclosure walls to ensure the roof remains directly over the
enclosure during the vertical travel. In addition to venting overpressure, the maximum height attained by
the roof can be used to calculate impulse. The impulse, or relative average enclosure impulse (RAEI), is
calculated from roof rise using the equations on the following page.

7. v
A
m
dv
A
m
dt
dt
dv
A
m
dt
A
ma
dt
A
F
Pdtimpulse ⇒⇒⇒⇒⇒= ∫ ∫ ∫ ∫ ∫ (1)
ahvmahmv 2
2
1 2
=→= (2)
ah
A
m
impulse 2= (3)
P = pressure F = force
A = area (roof) a = acceleration (gravity)
t = time m = mass (roof)
h = height (roof rise) v = velocity (roof)
Equation 1 is the standard impulse/pressure-time relationship reduced to enclosure specific
variables; equation 2 is the conservation of energy equation. Substituting the conservation of energy
equation into the impulse equation gives a relationship of impulse to roof height (equation 3). To
determine the impulse of a TBX candidate, a high speed camera is used to record the detonation and
resulting enclosure roof rise. The final height attained by each roof corner is averaged to give an
effective roof height for impulse calculations.
The enclosure test articles are fabricated from thin walled aluminum screw top canisters to
mitigate fragment damage to the enclosure. A center burst tube is welded into the end of the canister to
accept a 65 g C4 booster charge. The TBX candidate is cast in the annular region between the canister
wall and the center burst tube. The TBX fill volume is approximately 550 ml which gives a typical TBX
charge mass between 900 g and 1,000 g, depending on the composition density. Before a TBX test series
is started, 800 g of C4 are detonated in the enclosure to check the data acquisition system and establish a
standard to compare test data to previous test series. A photo of the enclosure test article configuration is
given in Figure 4.
Figure 4 Enclosure test article

8. RESULTS AND DISCUSSION
To begin the study, three charges of each composition given in Table 1 were detonated in the
enclosure to establish the relative real-world performance trend to compare the calorimeter data to. The
data from the enclosure testing is given in Figure 5. The test articles exhibited different charge masses
due to composition density and fill height variations; thus, the data given in Figure 5 has been
normalized for mass. Furthermore, the “Avg. Relative Impulse” is calculated from the roof lift data; the
“Avg. Impulse” is calculated from the pressure transducer data.
Figure 5 Enclosure test data normalized by mass (average of three tests at each data point)
The data given in Figure 5 shows an impulse trend one would expect: TBX compositions provide
larger impulses than non-TBX compositions. A 10% improvement in impulse is achieved with the
addition of 10% aluminum in formulation B. However, as the aluminum percentage is further increased,
the impulse actually exhibits a slight decrease indicating there may be aluminum combustion
inefficiencies. For peak pressure, the data shows a maximum at 10% aluminum followed by a rapid
decay as aluminum loading increases. This behavior most likely is due to the severely reduced amount
of HMX in high aluminum formulations, as peak pressure is related to the detonation event provided by
the HMX. However, the 10% aluminum in formulation B actually provides a 15% improvement in peak
pressure over the baseline non-TBX composition A, even though there is less HMX in the formulation.
The data shows no distinct relationship between peak temperature and aluminum percentage.
However, the temperature integral appears to increase as the aluminum loading increases. The
temperature integral is affected by the afterburning of detonation products and aluminum combustion.
Aluminum has a very high heat of combustion (7450 calories/gram) compared to HMX (2100
calories/gram). Therefore, the aluminum combustion contributes a significant amount of heat to a TBX
detonation, even when combustion efficiency is poor. In an ideal scenario (100% combustion
efficiency), increasing the aluminum percentage of an explosive composition would increase both the
impulse and temperature integral. However, these two main TBX performance indicators show
conflicting behavior. Enclosure testing has shown that the highest impulse is attained with the 10%
aluminum composition B and the highest temperature integral is attained with the 35% aluminum
composition D. It appears there may be aluminum combustion efficiency issues associated with the
higher aluminum TBX compositions.
Following the enclosure testing, the calorimeter study was started by evaluating the heat of
combustion of each candidate in an oxygen rich environment. The calorimeter oxygen level for each test
was determined by adding 20% mole excess to the calculated stoichiometric oxygen requirement for 15
g of each candidate, the 5 g C4 booster and the EBW. The results of the heat of combustion testing are
given in Table 2 on the following page.
0.000
0.100
0.200
0.300
0.400
0.500
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
% Aluminum
Impulse(psi-ms/g)
0.000
0.020
0.040
0.060
0.080
0.100
PeakPressure(psi/g)
Impulse (psi-ms) Rel. Avg. Impulse (psi-ms) Peak Pressure (psi)
0.000
0.200
0.400
0.600
0.800
1.000
1.200
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
% Aluminum
Temp.Integral(C-Sec/g)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
PeakTemp.(C/g)
Temperature Integral Peak Temperature

9. Table 2 Heat of combustion data for the selected explosive formulations
Explosive
Formulation
%
Aluminum
∆∆∆∆Hcomb
(cal/g)
%
Theoretical
A - 3036 99.7%
B 10.0% 3597 102.3%
C 22.5% 4476 100.3%
D 35.0% 5312 98.0%
The data given in Table 2 shows good agreement with Cheetah standard run predictions. The
data exhibits a trend one would expect when aluminum is substituted for HMX; the candidates with
higher aluminum loadings produce higher heats of combustion. The same trend was noted with the
temperature integral data obtained from enclosure testing. The selected formulations were further
evaluated under decreasing oxygen levels and pure argon to determine if oxygen deficient atmospheres
could produce trends similar to the enclosure. Two samples were evaluated at each oxygen level.
Initially, the oxygen levels were set by calculating the stoichiometric requirement for each sample, the
C4 booster and the EBW and then reducing the total amount by a given percentage. This proved to be
tedious as each of the selected formulations required a different stoichiometric amount of oxygen and
thus required the bomb pressure to be varied from test to test. To simplify the test procedures the
remaining tests were performed by selecting specific oxygen levels to test each sample at. The gross
energy data for each oxygen level is given in Figure 6. The data has not been corrected for the
contribution of the EBW, C4, water vapor condensation or crucible effects because the energy
contribution of each source is difficult to quantify under reduced oxygen conditions. The energy of each
source is dependent upon the amount of oxygen available for combustion and thus becomes more
significant with increased oxygen levels. However, for a specific oxygen level, the correction factors are
approximately the same for all formulations. Thus, the corrected data would still exhibit the same trends,
just reduced slopes. The important aspect of Figure 6 is the relative trend between formulations not the
absolute energy values.
Formulation D:
y = 110281x + 29160
R2
= 0.9973
Formulation C:
y = 108741x + 27482
R2
= 0.9978
Formulation B:
y = 108228x + 25501
R2
= 0.9997
Formulation A:
y = 93761x + 25692
R2
= 0.9966
0.00
20000.00
40000.00
60000.00
80000.00
100000.00
120000.00
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Oxygen Level (moles)
GrossHeat(cal)
Figure 6 Detonation calorimeter oxygen level test data

10. The data in Figure 6 indicates that even at oxygen levels down to 0.18 moles, the relative
performance of each formulation is linearly related to the oxygen level and is dependant upon the
aluminum loading. Formulation D, having the highest aluminum loading, performed the best followed
by formulations with successively decreasing aluminum loading. Formulation A, the non-TBX
candidate, exhibited the lowest performance at all oxygen levels down to 0.18 moles. At 0.18 moles of
oxygen, the detonation residue from all tests were very sooty indicating the detonation products are
highly underoxidized. Under argon, the opposite performance trend was observed; the non-TBX
formulation A exhibited the highest performance followed by formulations of increasing aluminum
loading. The behavior under argon was quite surprising as Cheetah predicted the highest aluminum
formulation would have the best performance and the non-TBX formulation would have the lowest
performance, as was observed under oxygen containing atmospheres. The relative behavior between
zero and 0.18 moles of oxygen has yet to be determined, as testing has not been completed.
To determine why the TBX compositions failed to match predictions, the formulation D
detonation residue from the argon tests was inspected under a microscope. It was found that most, if not
all, of the aluminum in the composition was unreacted. In fact, the detonated aluminum particle
morphology and size appeared similar to the raw aluminum mixed into the explosive formulation. This
was also surprising, as it was believed that aluminum combustion begins with oxygen supplied by the
HMX in the initial detonation. Because the tests under argon eliminate any aluminum combustion
reactions with extraneous oxygen, any aluminum reactions would have to come from the interaction
with detonation products. When the Cheetah analysis was subsequently evaluated, aluminum oxides and
nitrides were found in the predicted detonation products. The Cheetah standard run assumes the
aluminum in the composition is preferentially oxidized over hydrogen or carbon species in the
detonation products. Inspection of the detonation residue showed this was not the case. When
performing a Cheetah run, the user has the option to input aluminum in one of two conditions: inert or
ordinary “reactive” aluminum. When inert aluminum is selected, Cheetah ignores any aluminum
reactions, as the name implies. Therefore, a second set of Cheetah runs were performed for the TBX
compositions using inert aluminum in the formulation to determine if the predicted behavior would
better reflect the calorimeter data. The additional analyses proved to be valuable, as the revised Cheetah
predictions matched the experimental trend of decreasing performance as aluminum content increases
when detonated under argon. Furthermore, the Cheetah derived heat of detonation values were
approximately 5% lower than the experimental values for each composition. Based on the argon test
results, it can be reasonably concluded that the aluminum predominately interacts with oxygen in the
calorimeter bomb atmosphere, not the detonation products as originally thought. However, the same
may not be true for TBX containing nano-aluminum.
Comparing the detonation calorimeter results to the enclosure tests, the impulse trend observed
for the selected compositions is not found in the calorimeter heat of combustion data. The calorimeter
data indicates that that heat of combustion is directly related to aluminum loading. Conversely, the
enclosure results indicate a maximum impulse at 10% aluminum loading followed by a slight reduction
in impulse as aluminum loading increases to 35%. Analysis of enclosure test high speed video may
provide an explanation of the relative performance trend mismatch. It was found that as the aluminum
loading increased, larger fireballs were observed coming out the enclosure window and door. As
designed, the enclosure window and door are centered on their respective walls. When the TBX charge
is detonated in the center of the enclosure, the line of sight is directly out the window and door,
facilitating the ejection of aluminum. Because the instrumentation and the roof lift measure the TBX
detonation and subsequent combustion occurring inside the enclosure, any material or energy liberated
outside the enclosure is effectively lost. Snapshots taken from high speed test videos when each fireball
reached a maximum size are given in Figure 7 on the following page.

11. Figure 7 High speed video of enclosure tests showing relative fireball intensity and size
The images given in Figure 7 clearly show the effects of adding aluminum to explosive
compositions, as each TBX fireball is more intense (hotter) and occurs longer after the initial detonation
than formulation A. Furthermore, the photos show a considerable amount of aluminum combustion
energy is lost outside the enclosure for formulations C and D when compared to formulation B. This
energy is not captured by the enclosure instrumentation or roof, leading to lower than expected
performance for the higher aluminum TBX compositions. It is believed that this is the cause of the
relatively flat impulse performance as aluminum loading is increased to 35%; excess aluminum is
simply combusting outside the monitored system. Thus, it is believed that the calorimeter may not match
enclosure impulse trends by simply reducing the level of oxygen in the calorimeter. However, before a
definitive conclusion is reached, additional calorimeter tests must be performed for oxygen levels
between 0 and 0.18 moles. Because, the calorimeter provides a closed system, the energy from the
combusting aluminum, regardless of the loading levels, is effectively captured. Even under oxygen
deficient atmospheres, the higher aluminum compositions outperform the compositions with lower
aluminum loadings. Therefore, a future experiment may repeat the enclosure testing with the window
and door sealed to determine if the impulse trends are more representative of the calorimeter trends.
CONCLUSIONS
The enclosure data indicated that a maximum impulse was obtained with 10% aluminum. As the
aluminum loading level increased, a slight decrease in impulse was observed. The relative performance
for all three TBX formulations is attributed to the ejection and combustion of material outside the
enclosure. Test video analysis indicated larger quantities of aluminum were reacting outside the
enclosure as aluminum content of the composition increased. This energy was not captured by the
enclosure instrumentation or roof, leading to lower than expected performance for the high aluminum
Formulation A, 0% Al Formulation B, 10.0% Al
Formulation C, 22.5% Al Formulation D, 35.0% Al

12. compositions. Lastly, all three TBX formulations provided higher impulses than the non-TBX
formulation, a result that was expected.
The calorimeter data indicated that heat of combustion directly correlated to aluminum loading
levels for all oxygen levels down to 0.18 moles. Formulation D with 35% aluminum gave the highest
performance followed by formulations with successively lower aluminum loading. When evaluated
under an inert atmosphere (argon) the data exhibited the exact opposite trend: as aluminum loading
increased, the performance decreased. The behavior under argon was unexpected as Cheetah predicted
the aluminum compositions would have higher performance than the non-TBX composition due to the
formation of aluminum oxides and nitrides. However, a large quantity of aluminum exhibiting the same
particle morphology and size as the aluminum added to the mix was found in the residue from the
detonation of composition D in argon. It appears that the aluminum is essentially inert in the first stages
of detonation and undergoes appreciable combustion only when oxygen is available in the atmosphere.
The objective of the study was to use the calorimeter to predict TBX performance in the
enclosure. The only similarity between the enclosure and calorimeter data sets was the TBX
compositions outperforming the non-TBX composition when detonated in oxygen containing
atmospheres. This result is expected as it’s the reason why TBXs are used for targets susceptible to
defeat from high impulses (i.e. buildings and caves). However, no comparable performance trends were
observed between the enclosure and calorimeter test data for any of the TBX compositions. The study
found that reducing the amount of oxygen in the calorimeter may not produce relative trends similar to
the enclosure impulse trends. However, additional testing between 0 and 0.18 moles of oxygen and the
enclosure testing with the door and window sealed must be completed before a definitive conclusion can
be made.
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