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

HOLLOW BUBBLES (CENOSPHERES) 3

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

HOLLOW BUBBLES (CENOSPHERES) 4

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.

HOLLOW BUBBLES (CENOSPHERES) 6

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.

HOLLOW BUBBLES (CENOSPHERES) 7

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

HOLLOW BUBBLES (CENOSPHERES) 8

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)

HOLLOW BUBBLES (CENOSPHERES) 9

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).

HOLLOW BUBBLES (CENOSPHERES) 10

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

C (Mondal et al., 2012)

Figure 4: Engg Stress curves for Titanium

HOLLOW BUBBLES (CENOSPHERES) 11

Application of Hollow Bubbles in Military Vehicles

Having explored the various properties of Aluminum and Titanium, lightweight military

vehicles can be designed by combining different properties of the two metals.

Figure 5 shows how the two metals can be used complementarily to design metallic frames of the

vehicles (Goel et al., 2012). The collective metallic frame of the material includes a sandwich

material such as Kevlar combined with Ti-foams. The aluminum syntactic foams can be used to

cover the sandwich. The combination produces a tough, combat resistant and very light vehicle

with high fuel efficiency because of the drag reduction that could otherwise increase the fuel

consumption. In order to make the use of Ti- and Al- foams practical, the ASTM standards should

be followed and the cost should not outweigh the benefits in the ultimate vehicle designed. All the

mechanics of the overall vehicles produced should always provide a room for improvement should

new knowledge of metallurgy be added. This flexibility property of the technology makes vehicles

designed be embraced for military, exploration among other functions.

HOLLOW BUBBLES (CENOSPHERES) 12

Figure 5: Sandwiching of Aluminum metal foam

Conclusion

The use of cenospheres as space holders and their combination with the metal foams give

a great sense of applications in automotive industry. As the current study explores to assess the

best way in which the metal foams can be used to provide an ultimate solution in the designing of

the military armored vehicles, it is important to explore other alternatives of technology. Due to

the scant knowledge on the physical, chemical, and mechanical properties of the metals, it is worth

putting into practices the use of the two metals into practice to determine their abilities to providing

quality military armored vehicles.

HOLLOW BUBBLES (CENOSPHERES) 13

References

Castro, G. , and Nutt, S. (2012). Synthesis of syntactic steel foam using mechanical pressure

infiltration. Materials Science and Engineering: A, 535, 274-280.

Goel, M. D. , Peroni, M. , Solomos, G. , Mondal, D. P. , Matsagar, V. A. , Gupta, A. K. , Larcher,

M. , and Marburg, S. (2012). Dynamic compression behavior of cenosphere aluminum

alloy syntactic foam. Materials & Design, 42, 418-423.

Luong, D. D. , Shunmugasamy, V. C. , Gupta, N. , Lehmhus, D. , Weise, J. , and Baumeister, J.

(2015). Quasi-static and high strain rates compressive response of iron and Invar matrix

syntactic foams. Materials & Design, 66, 516-531.

Mondal, D. , Das, S. , Ramakrishnan, N. , and Bhasker, K. U. (2009). Cenosphere filled aluminum

syntactic foam made through stir-casting technique. Composites Part A: Applied Science

and Manufacturing, 40, 279-288.

Mondal, D. , Majumder, J. D. , Jha, N. , Badkul, A. , Das, S. , Patel, A. , and Gupta, G. (2012).

Titanium-cenosphere syntactic foam made through powder metallurgy route. Materials &

Design, 34, 82-89.

Peroni, L. , Scapin, M. , Fichera, C. , Lehmhus, D. , Weise, J. , Baumeister, J. , and Avalle, M.

(2014). Investigation of the mechanical behaviour of AISI 316L stainless steel syntactic

foams at different strain-rates. Composites Part B: Engineering, 66, 430-442.

Santosa, S. P. , Arifurrahman, F. , Izzudin, M. H. , Widagdo, D. , and Gunawan, L. (2017).

Response Analysis of Blast Impact Loading of Metal-foam Sandwich Panels. Procedia

Engineering, 173, 495-502.

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