APA Sample on HOLLOW BUBBLES

Running head: HOLLOW BUBBLES (CENOSPHERES) 1
Application of Hollow Bubbles in Military Vehicles
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HOLLOW BUBBLES (CENOSPHERES) 2
Table of Contents
Table of Contents .......................................................................................................................... 2
List of Figures ................................................................................................................................ 3
Introduction ................................................................................................................................... 4
Use of Hollow Bubbles ............................................................................................................... 4
Potential Application of Titanium and Aluminum Metallic Foams ........................................... 6
Combination of Cenospheres and Aluminium ............................................................................ 7
Combination of Cenosphere and Titanium ................................................................................. 9
Application of Hollow Bubbles in Military Vehicles ............................................................... 11
Conclusion ................................................................................................................................... 12
References .................................................................................................................................... 13
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List of Figures
Figure 1: Aluminum stress curves .................................................................................................. 7
Figure 2: Cenospheres embedded on aluminum solid matrix ......................................................... 9
Figure 3: Youngs Modulus and the relative density of Titanium ................................................. 10
Figure 4: Engg Stress curves for Titanium ................................................................................... 10
Figure 5: Sandwiching of Aluminum metal foam ........................................................................ 12
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Application of Hollow Bubbles in Military Vehicles
Introduction
Military armored vehicles are used in battles and often encounter rough terrain, blasts, and
travel for long distances. These factors present a challenge if the vehicles used cannot withstand
such conditions. An example of a military armored vehicle used currently is M39A2 series which
way approximately 23 tons, having a lifespan of about 13 years and millage of 60,000 miles. It has
a maximum speed of 80km/h. The weight of this vehicle and its speed are crucial in war fronts and
therefore if the weight can be reduced and the speed increased while maintaining the lifespan, it
can be the best approach in improving their efficiency. Implementation of powder metallurgy and
hollow bubbles for a military vehicle can therefore solve the problem (Castro and Nutt, 2012).
This study is aimed at assessing a robust system for improving the military vehicle, enhancing
protection and increasing strength with reduced weight.
Use of Hollow Bubbles
Hollow bubbles in metals (metal foam) consists of a metal particularly aluminum that has
been filled with gas pores (Luong et al., 2015). The largest portion of the metal material has been
filled with air bubbles that are produced when the metal is melted while a stream of inner gas is
bubbled through it. After cooling, thousands of pores in the metal occur forming a metal foam
having high porosity with lower density than the metal without the hollow bubbles. The advantages
of the metallic foams are the retention of physical properties of the parent metal. The finished
product made from such metallic foams will always have about 75% reduction in weight and thus
being ultralight as compared to materials made without foaming. It has also been noted that thermal
expansion coefficient is retained but thermal conductivity is generally reduced in the metallic
foams. The strength of the final product is dependent on the square-cube law, which gives the
HOLLOW BUBBLES (CENOSPHERES) 5
relationship between the surface area and volumes of the material. This law depends on the shape
and size dynamics of the material. The change in these two parameters alters the relationship
between the surfaces areas and the volumes of different materials given the same conditions.
In current the world of technology, metallurgy has played a major role in designing
desirable machines with increased efficiency and resistance to tear and wear. In practice, hollow
bubbles technology has been used in the manufacturing of airplanes, ships, and submarines,
cryogen tanks, heat exchangers among others. Hollow bubbling can utilize an open-cell, closed-
cell or use of composite technology. Open-cell metallic foams are made from powder metallurgy
(foundry) where the powder is used to occupy the spaces produced during foaming process leaving
a foam structure called polyurethane skeleton (Peroni et al., 2014). The open-celled metal foams
have been used heat exchangers, cooling systems for electronics, lightweight optics, flow diffusion
systems and energy absorption systems. However, the open-celled metallic foams are expensive
to design and hence limited in aerospace and military manufacturing industries. The open-celled
foams have a very large surface area with a given unit weight, and often contain catalyst used in
their refining.
The closed-celled metallic foams are produced bubbling a foaming agent particularly an
inert gas through a molten metal. This process ends up creating bubbles in the metal, making it
more buoyant due to the reduced density. Such metal foam is able to float on a high-density liquid
and hence can be used in designing ships and submarines. Closed cell metallic foams are widely
used in designing impact resistant materials. These metal foams can be utilized in designing
military armored vehicles because of the impact resistant property. However, as compared to the
currently used impact resistant materials such as polymer foams (used in motorcycle helmets),
closed metal foams remain deformed after an impact and hence cannot be reformed.
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Another technology in hollow bubble metallurgy is the composite metal foaming which
involves the use of hollow beads of one metal embedded in another metal. An example of this is
the use of steel beads that are embedded in the aluminum solid matrix. When this is done,
aluminum becomes more strong (5-6 times stronger than the normal metal) with greater energy
absorption properties. It has been noted that 1-inch plate of this composite metal is able to resist a
standard M2 armor-piercing bullet and able to turn it into dust. It also offers ‘great resistance to
heat and hence can withstand fiery battlefields.
Potential Application of Titanium and Aluminum Metallic Foams
The major aim of using metallic foams in any manufacturing application, especially in the
automotive industry is to reduce the weight, increase the absorption abilities in case of crashes,
reduce sound spillage and resistance of impacts, especially in military armored vehicles. In the
current study, it is important to explore ways on how metallic foams can be used in designing
efficient military armored vehicles using titanium and aluminum metallic foams. The two metals
are compatible because of their contrasting properties. Titanium proves to be strong enough to
withstand adverse impacts while aluminum is light enough to reduce significantly the final weight
of the vehicle. As compared to the polymer foams, the combination of the two metals produces
metallic foams that are tougher, heat-resistant, non-toxic, magnetic field resistant, recyclable, and
soundproof. When used in vehicles the metallic foam of these two metals can confer the ability to
decreased weakness points especially those generated during car crashes and when the vehicle
vibrates. The cost efficiency of the two metals also makes them be the best option when designing
relatively affordable military vehicles. The target usage of these metallic foams such as diplomatic
motorcades, explorers, and military will find such vehicles being affordable, lightweight, fuel
efficient and fast in speed.
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In terms of energy absorption, the following graph shows the crash stress for aluminium
with different sponge status (Santosa et al., 2017).
Figure 1: Aluminum stress curves
The ductility nature of aluminum makes it a better material to form a base to which the
foamed titanium metal can be glued. Aluminum can, therefore, be used to obtain a composite
sandwich. From Figure 1, the metallic foams show a plateau of stress with as up to 80% crushing
impact.
Combination of Cenospheres and Aluminium
Since the revolution of aluminum metal matrix composites (metallic foams), many applications
have found their way into the automobile industry. Various studies have been done in the recent
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past to explore the possibility to make aluminum matrix using cenospheres to reinforce its
structure. Cenosphere are hollow structures with spherical shapes used as space holders during the
foaming process of metals. As the aluminum foams are filled with cenospheres they form
composites called syntactic foams. In attempts to make aluminum composites, melt infiltration
technique has been used in filling the foams with cenospheres. However, the use of this method is
coupled with a number of flaws since only small size of syntactic foams can be prepared. In other
studies it have explored on the compressive properties and deformation characteristics of
aluminium composite foams and reported that the deformation curves of syntactic metal foams
made using aluminum infiltration technique is similar to normal solid aluminum metal foams. It
has been also been observed that the plateau stress are higher in syntactic foams as compared to
the conventional foams.
Figure 2 below shows how the cenospheres are packed into the aluminum matrix (Goel et al.,
2012; Mondal et al., 2009)
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Figure 2: Cenospheres embedded in aluminum solid matrix
Use of this technique to produce high-quality aluminum foams combines several
parameters. Mechanical properties of the metal should be assessed in terms of hardness using
Vickers and Rockwell hardness tests and compression load using the universal testing machine.
The microstructure of both the titanium and aluminum should also be assessed by checking the
sample topography and composition with an aid of scanning electron microscope. Other physical
tests such as density and thermal conductivity also play an important role in metallurgy.
Combination of Cenospheres and Titanium
The application of this study is the use of aluminum foams between titanium foams (Ti-
foam) and kevlar. It is, therefore, important to note that the strength of Ti-foams is much greater
than the aluminum foams. Ti-foams have been observed to have high-energy absorption
capabilities. The strength of the Ti-foams is equivalent to that of the human bone (40-60 Mpa).
The sintering and densification properties (kinetic) of these foams are dependent on the addition
of foreign particles, such as Ti-powder. When cenospheres (Ti-foams) are added to the Ti-foams,
it has been observed that porosity of the Titanium reaches 80%. However, in order to increase the
strength of the Ti-foams, Ti- alloys have been produced (such as Ti-Mn and Ti-Al-V), coupled
with the addition of ceramic or cenospheres (micro balloons) through powder or liquid metallurgy
route. Addition of cenospheres in Ti-foams helps increase the strength of the metal and increase
the resistance to high compaction during crashes. Figure 3 shows the Youngs Modulus as a
function of porosity of the titanium (Mondal et al., 2012).
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Figure 3: Youngs Modulus and the relative density of Titanium
Figure 4 shows the Engg stress curves of Ti-cenosphere syntactic foam at different pressure
sintered at 1100
0
C (Mondal et al., 2012)
Figure 4: Engg Stress curves for Titanium