New York Institute of Technology

The Effectiveness of Glass Laminate Aluminum Reinforced Epoxy FCWR 304: Prof. K. LaGrandeur

Chelseyann Bipat 12/15/2011

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Table of Contents

Executive Summary ........................................................................................................................ 3

Introduction ..................................................................................................................................... 3

Method ............................................................................................................................................ 5

Results ............................................................................................................................................. 6

1. Strength ................................................................................................................................... 6

Impact Strength........................................................................................................................ 7

Tensile Strength ....................................................................................................................... 8

Elastic Stress ............................................................................................................................ 8

Fire Resistance ......................................................................................................................... 9

Corrosion Strength ................................................................................................................... 9

Shear Strength........................................................................................................................ 10

2. Cost........................................................................................................................................ 10

3. Density .................................................................................................................................. 11

Conclusions ................................................................................................................................... 11

Bibliography ................................................................................................................................. 12

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Executive Summary

When creating the world’s largest airplane, many factors have to be taken in

consideration. One of the most important of these is the material that it is built from. Ideally, this

material should demonstrate qualities that prove it nearly indestructible under the harshest

conditions. Although such material does not yet exist, GLARE, short for Glass Laminate

Aluminum Reinforced Epoxy, was chosen. This report examines its effectiveness for use,

compared to previous materials used in aircraft construction. The results found through

conducting this research shows that GLARE is effective in its role in aircraft construction

because of its tensile strength, impact strength, fire resistance, corrosion resistance, and elastic

stress, cost, and density. However, it is not effective in its shear strength.

Introduction

This report presents the results of an investigation done on the effectiveness of Glass

Laminate Aluminum Reinforced Epoxy, also known as GLARE. This research was done by

consulting various journal articles and books, and by extrapolating and interpreting data in

published lab reports.

Previously, aircraft were comprised of other composite material. The first aircraft were

made of wood. Then, metal composite materials slowly began to become normal in the use of

motorized, commercial aircraft. As the years progressed, carbon and glass composites began to

creep into the aircraft industry, and are used in the today’s aircraft. These composites were

mainly created at the Delft Institute of Technology in Holland, where most of the testing and

entry of these materials into the aircraft industry took place.

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Previous composites were used in the building of other aircraft, such as the Boeing 747.

Designed in 1970, the 747 was (until recently) the world’s largest aircraft. The advent of such a

large plane caused other aircraft manufacturers such as Airbus to seek to lay claim to the prestige

associated with creating the world’s largest aircraft. To do this, however, Airbus needed a

material that was structurally different from other materials, especially in strength and density.

Strength and density of the material are important in the development of large aircraft

like the 747, and future aircraft. This is because, when increasing the size of an aircraft, the

weight of the aircraft increases proportionally. If an aircraft size is increased by a factor F, then

the weight and volume of the aircraft is then increased by F3, and the wing area of the aircraft is

increased by F2

(Vlot, 2001). Because of the significantly large increase in weight, a lighter, less

dense material had to be developed in order to support the aircraft. GLARE then began to be

developed up until the early 2000’s, when it was eventually selected for use in the fuselage (main

body of an aircraft) of the world’s largest airliner, the Airbus A380. GLARE is a composite

material comprised of alternating layers of glass/epoxy and aluminum, bonded together. The

general composition of GLARE is shown below.

Figure 1: Composition of GLARE (Ardakani, Khatibi, Parsaiyan, n.d.)

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GLARE always consists of one more aluminum layer than glass/epoxy layer. For

example, if there are three layers of aluminum, there will be two layers of glass/epoxy, as shown

in Figure 1 above. When GLARE is made, the layers of aluminum are first anodized (coating it

with a substance using electrolytes) and primed to increase corrosion strength. The layers of

aluminum and glass/epoxy are then laid down alternately, with the aluminum layers on the

outside for an increase in durability. Next, the materials are subject to intense pressure for a day,

and then placed in a temperature of 100 degrees Celsius for up to four hours, in a process known

as postcuring.

However, GLARE does not always have to be laid down with the layers parallel to each

other; GLARE can be modified to suit different part of the fuselage of the aircraft. For example,

the glass/epoxy and aluminum can be bonded at different angles in order to either strengthen or

weaken the material. Because of this composition and its ability for its composition to be

modified, it is supposed that GLARE can be made stronger than a monolithic material (a material

consisting of solely one material), such as aluminum.

This report will investigate the strength properties of GLARE, as well as its economic

advantages and/or disadvantages. These properties will then be used to compare GLARE to

previous materials used in aircraft construction, such as aluminum alloy 2024-T3. From this

comparison, the effectiveness of the material will then be determined.

Method

The following methods were used to examine the effectiveness of GLARE:

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1. To determine background and history of the material, multiple texts by Ad Vlot, one of

the major creators of GLARE, were consulted.

2. Various journal articles from databases were retrieved and were used in order to examine

certain aspects of the strength of the materials and therefore the main quality of its

effectiveness.

3. GLARE was then compared to an aluminum alloy 2024-T3, a material frequently used in

aircraft construction.

Results

Over time, many experiments on the effectiveness of GLARE were conducted. This

report outlines the effectiveness of the material based on the following qualities of the material:

strength, cost, and density. These qualities are then compared to one of its counterparts, a

monolithic material known as 2024-T3, which is an aluminum alloy commonly used in aircraft

construction.

1. Strength

The strength of this material was evaluated on six major properties: impact strength,

tensile strength, elastic stress, fire resistance, corrosion strength, and shear strength. An overview

of all the quantifiable strength qualities of GLARE, compared to 2024-T3 is shown in Figure 2

below.

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Impact Strength

The first of these properties is impact strength. Impact strength is important because of

the materials that could possibly hit an airplane. Engine debris, birds, hail, or any material being

hurled at an aircraft while it is moving at an extremely high velocity could cause significant

damage to the outer structures of an airplane. For example, a bird simply hitting an aircraft while

it is in the air could deliver as much as 500 J of energy. Because of this, impact tests on the

materials that aircraft are constructed from are conducted (Wu, Yang, 2005).

When tests were conducted on different compositions of extremely thin sheets of GLARE

(as mentioned before, the layers can be arranged at different angles), it was found that they all

showed similar amounts in energy absorption (Sadighi and Dariushi, 2008), which means that

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4

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8

10

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Density (x1000) Tensile Modulus

(x100)

Shear Strength Melting Point (degrees

Celsius x100)

Fig. 2: Quantifiable strength comparison between GLARE and

Aluminum Alloy 2024-T3

Aluminum Alloy(2024-T3) GLARE

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regardless of the arrangement of glass/epoxy and aluminum, GLARE still displays the same

amount of resistance. Furthermore, in other impact tests, when a projectile delivering only one

joule of impact energy was aimed at the material, it took up to seventeen times of impact in order

for the surface of the GLARE sheet to be penetrated (Ardakani, Khatibi, Parsiayan, n.d.).

In another study, it was found that GLARE showed only a small internal damage to the

layers when an impact test was conducted. The aluminum alloy 2024-T3 however, showed large

dents on the outside of the structure when impact tests were conducted.

Tensile Strength

GLARE was also evaluated on its tensile strength. The tensile strength is the amount of

stress that the material can ultimately withstand, combined with the amount of energy that the

material can absorb. This property is ultimately dependent on the amount of aluminum sheets

found in GLARE, as well as the orientation of these sheets (the layers of GLARE can be oriented

in different angles in order to produce different types of composites). In the cases of GLARE

with sheets all aligned at zero degrees, or ninety degrees, the tensile strength of GLARE was

found to be greatest (Sadighi and Dariushi, 2008).

Also, in other lab studies, it was determined that GLARE has a tensile strength that is

comparable to that of a sheet comprised solely of aluminum (Vogelsang and Vlot, 2000).

However, when compared to aluminum alloy 2024-T3, it was found that GLARE exhibits about

50% more tensile strength than the 2024-T3 (Wu, Yang, 2005).

Elastic Stress

The third strength property is elastic stress, which is determined by the three-point

bending test. The three point bending test is a measure of how the material reacts when it is

subjected to a high compression force (in this case, up to approximately three thousand pounds)

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caused by bending. It was found that the material itself did not collapse immediately, but in fact,

individual fibers began to buckle, creating a force on the interface between the layers which

debonded, (a phenomenon known as delamination buckling), and then the layers began to crack.

This cracking is not visible when looking at a top view of the sheet, as it mainly occurs towards

the center of the material, but is noticeable when viewed from the side. This indicates that the

effects of compression strengths are only visible internally (de Jong, 2001).

Compared to 2024-T3, the effects are not similar, because the fibers in GLARE keep it

from buckling as quickly as 2024-T3 does (Wu, Yang, 2005). Therefore, GLARE can withstand

a larger compressional force than 2024-T3.

Fire Resistance

Fire resistance is also an important property to have in a material used in commercial

aircraft. In a test conducted by The Boeing Company, GLARE prevented fire at temperatures up

to 1200 degrees Celsius (approximately 2200 degrees Fahrenheit) from penetrating the material

for over fifteen minutes (Vlot, 2001). This quality is extremely important in an aircraft due to the

risk of fire during lightning storms. As shown in Figure 2, the melting point of 2024-T3 is only

455 degrees Celsius, showing that GLARE can withstand far more heat than its predecessors.

Corrosion Strength

When GLARE is first manufactured, the aluminum sheets are first anodized, which

means that “by electrolytic action…coating or plating a metal (usually aluminum) with a

protective material.” (NASA, 2004). Then, the aluminum is primed, and the sheets are placed on

the outermost layers of the material. This process decreases effects from the environment, which

means that its corrosion strength is increased. This plays an important role in the utilization of

GLARE. In studies conducted where GLARE and aluminum sheets were subjected to 175 hours

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of accelerated exfoliation corrosion, the corrosion of the aluminum sheets was slightly higher

than the corrosion found in GLARE. The materials were once again put through a fatigue test,

where the aluminum “failed after 48 to 62 kcycles, while testing of the Glare specimens was

stopped after 100 kcycles, without failure having taken place.” (Vlot, Gunnik, 2001).

Shear Strength

Shear properties are extremely important in an aircraft because of the way that material is

to be manipulated during the aircraft manufacturing process. The material is obviously subjected

to lots of bending. In order to test a composite material, an Iosipescu test, which is a test for

maximum shear load is done.

Shown in Figure 2, the results from the Iosipescu test show that the shear strength at

room temperature of GLARE is only about 50% than the shear strength of 2024-T3. However,

studies were only available for the shear strength of the materials at room temperature, and there

has not been many studies done at elevated or decreased temperatures in order to finitely

determine the shear mechanical behavior of GLARE (Wu, Yang, 2005).

2. Cost

The cost of GLARE plays an important role in its usage. This is because, in order to be

able to sell aircraft to large airline companies, the prices must be affordable, especially in the

current economy in the airline industry. Therefore, the cost of the aircraft must be low, and then

a suitable profit must be gained. Figure 3 below shows how the cost of GLARE compares to

cost of 2024-T3.

Furthermore, as GLARE exhibits remarkable corrosion strength, less maintenance is

required on the aircraft, and therefore it is cheaper to have over a long period of time.

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Based on the chart, it is evident that GLARE is 2% cheaper than 2024-T3, as GLARE

costs 8% as much as 1 kilogram of Aluminum, while 2024-T3 costs 10% as much as 1 kilogram

of Aluminum.

3. Density

As mentioned before, in order to design a larger aircraft, a lighter material must be

considered. Density is an important quality of the material that directly affects its weight.

Compared to 2024-T3, GLARE has a density that is at least 8% less (Wu,Yang, 2005).

Considering that the density of 2024-T3 is 0.10 pounds per cubic inch, and the density of air at

sea level is approximately 0.44 pounds per cubic inch, the development of GLARE was

successful in regards to density and weight.

Conclusions

Based on the results presented, it was found that GLARE is mostly effective. Compared

to 2024-T3, it is stronger for the most part, cheaper, and lighter. These three main qualities set

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% C

ost

of

1kg

Alu

min

um

Figure 3: Cost of GLARE compared to 2024-T3

2024-T3

GLARE

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GLARE apart from other materials are extremely important in the aircraft manufacturing

process.

The strength of GLARE included aspects of its impact strength, tensile strength, elastic

stress, fire resistance, corrosion strength, and shear strength. Compared to 2024-T3, GLARE

showed tensile strength that was 50% greater, greater impact strength, greater elastic strength,

greater corrosion strength, and a higher melting point. However, the shear strength of GLARE

was only 50% of that of the 2024-T3. This is an extreme downside because of the fact that

bending and torsional loads are placed on the material during the manufacturing process. It can

be viewed in such a way however, that GLARE’s other properties compensate for this one lack

in strength, since other materials do not exhibit such strength in other areas.

The cost of GLARE was found to be significantly lower than that of 2024-T3.

Furthermore, the cost of GLARE is also cheaper in a long term sense, in that less capital would

be required to maintain the material itself, as its corrosion strength protects it from

environmental factors.

Finally, the density of GLARE was also found to be lower than that of 2024-T3. This

makes the aircraft lighter, and allows the size of the aircraft to be increased. The density of this

material could also possible make room for future increases in size in the aircraft industry.

Bibliography

Ardakani, M., Khatibi, A., Parsaiyan, H. (n.d.) An experimental study on the impact

resistance of glass-fiber-reinforced aluminum (GLARE) laminates.

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Beumler, T. (2004, March 23). A contribution to aircraft issues on strength properties in non-

damaged and fatigue damaged glare structures. Retrieved from

http://repository.tudelft.nl/view/ir/uuid:cee40186-6a76-4843-b740-0c0df081b87e/

This is a dissertation done at the Delft University of Technology, which is famous for

their studies on aircraft material, that compares GLARE to other materials previously

used in aircraft and is therefore useful for my research.

Botelho, E., Pardini, L., Rezende, M., & Silva, R. (2006). A review on the development and

properties of continuous fiber/epoxy/aluminum hybrid composites for aircraft structures.

Materials Research, 9(3).

This journal article is useful because it helps to show the effectiveness of using GLARE in

aircraft.

Delft University of Technology (2007, September 26). New Material For Aircraft Wings

Could Save Billions. ScienceDaily. Retrieved from

http://www.sciencedaily.com/releases/2007/09/070926094727.htm

This article shows the cost advantages of GLARE, and will therefore be useful to my

project.

Hahn, H.T., Seo, H.&, Yang,J. (2008) Impact damage tolerance and fatigue durability of

GLARE laminates. Journal of Engineering Materials and Technology, 130.

This journal article is an experimental lab report that tests the actual qualities of GLARE

in order to prove that it is ideal for an aircraft and therefore useful for my research.

Sadighi, M., Dariushi, S.. (2008). An experimental study of the fibre orientation and laminate

sequencing effects on mechanical properties of glare. Aerospace Engineering, 222(7), 1015

1024.

(2004, April 04). Shuttle-mir history/references/glossaries/science glossary (a-f). Retrieved

from http://spaceflight.nasa.gov/history/shuttle-mir/references/glossaries/science/sc-gloss

a_f.htm

Vlot, A., Gunnik, J.. (2001). Fibre Metal Laminates: an introduction. Netherlands: Kluwer

Academic Publishers.

Vlot, A. (2001). Glare: history of the development of a new aircraft material. Netherlands:

Kluwer Academic Publishers.

This book is useful for my research because it gives a description of the history of

GLARE and how it evolved to work in the aircraft industry. It provides information on

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how GLARE is created, and how its makeup helps its uses.

Vogelsang, L. B., R. ,. Marissen, and J. ,. Schijve. (1981). A New Fatigue Resistant

Material: Aramide Reinforced Aluminium Laminate (ARALL). Delft: University of

Technology.

Wu, G., Yang, J. (2005, January). The mechanical behavior of GLARE laminates for aircraft

structures. Journal of Metals,72-79.