The Effectiveness of Glass Laminate Aluminum Reinforced Epoxy

Transcription

1 New York Institute of Technology The Effectiveness of Glass Laminate Aluminum Reinforced Epoxy FCWR 304: Prof. K. LaGrandeur Chelseyann Bipat 12/15/2011

2 2 Table of Contents Executive Summary... 3 Introduction... 3 Method... 5 Results Strength... 6 Impact Strength... 7 Tensile Strength... 8 Elastic Stress... 8 Fire Resistance... 9 Corrosion Strength... 9 Shear Strength Cost Density Conclusions Bibliography... 12

3 3 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.

4 4 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 F 3, and the wing area of the aircraft is increased by F 2 (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.)

5 5 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:

6 6 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.

7 Fig. 2: Quantifiable strength comparison between GLARE and Aluminum Alloy 2024-T3 Aluminum Alloy(2024-T3) GLARE Density (x1000) Tensile Modulus (x100) Shear Strength Melting Point (degrees Celsius x100) 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

8 8 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)

9 9 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

10 10 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.

11 % Cost of 1kg Aluminum Figure 3: Cost of GLARE compared to 2024-T T3 GLARE 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

12 12 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.

13 13 Beumler, T. (2004, March 23). A contribution to aircraft issues on strength properties in nondamaged and fatigue damaged glare structures. Retrieved from 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 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), (2004, April 04). Shuttle-mir history/references/glossaries/science glossary (a-f). Retrieved from 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

14 14 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.