Materials for a Business Jet - Essay Example

Materials for a Business Jet The most commonly used materials for a business jet include the aluminum alloys 7475, 2124, and 5052 as well as the composite materials carbon fibre reinforced plastics (CFRPs) and Kevlar. This paper compares the cost of these five materials. Then various material properties of the five selected materials are compared. After comparison of the five materials, a single aluminum alloy and composite material is chosen for our aircraft design. The conclusion of this paper discusses the reasons for the material choices. In table 1, a comparison of the related costs of using the five different aircraft materials is shown. When using CFRP, there are also savings of assemble manpower. There will also be savings due to the reduced weight of using composite materials like CFRP and Kevlar. Table 1 - Cost Comparison of Aircraft Materials Alum 7475 Alum 2124 Alum 5052 CFRP Kevlar Initial material cost ($/kg.) 6 6 6 Very expensive 4.50 Manufacturing cost Expensive to manufacture sheets Expensive to manufacture sheets Expensive to manufacture sheets Low assembly cost High due to concentrated sulfuric acid Maintenance cost Higher due to corrosion Higher due to corrosion Lower due to better corrosion resistance Low due to no corrosion *Kevlar cost depends on the type of fibre used. Maintenance cost of a material is determined by several variables. These include the density, utimate tensile strength, tensile yield strength, durability (fatigue) and fracture toughness properties listed in table 2. Maintenance cost also depends on corrosion. The manufacturing cost of Kevlar is high due to the difficulty of using the concentrated sulfuric acid during the manufacturing process. In table 2, the properties of the five materials studied here are displayed. The aluminum alloys have properties which are specific to the number of the series they belong to. The alloy series is categorized by the metal that is the major alloying element. For instance, the 5xxx series aluminum alloys contains magnesium as the major alloying element. The 5xxx series alloys have moderate to high strength and good corrosion resistance. They are not heat treatable. Mechanical properties and strength are less desirable than in the 2xxx and 7xxx series. The 7xxx series aluminum alloys have zinc as the major alloying element. These alloys have the greatest strength of the heat-treated alloys. The 7xxx series alloys also have good heat-treating qualities. The 2xxx series aluminum alloys contain copper as the major alloying element. They have high strength and are hard and machineable. This series can also be heat-treated. CFRPs are strong and light but very expensive. The plastic used in CFRPs can be epoxy, polyester, vinylester, or nylon. Kevlar has a good strength-to-weight ratio: this ratio is 5 times greater for Kevlar than for steel (Wikipedia, 2006). Table 2 - Material Properties for Common Aluminum Alloys and Composites Alum 7475 Alum 2124 Alum 5052 CFRP Kevlar Fracture toughness (MPa m) ~36, < Alum 2124 ~36, > Alum 7475 ~36 32 Hardness (Bhn = Brinell hardness) 148 120 68 Ultimate tensile strength (ksi) 82 68.2 38 290 435 Tensile yield strength (ksi) 71 47.1 31 .0305 Fatigue strength (ksi) 20.3 18 Shear modulus (ksi) 3920 3920 3760 4.06 Shear strength (ksi) 47.9 41.3 21 4.5 .0479 Density(lb./in3) 0.102 0.1 0.097 0.052 Modulus of elasticity-tension (ksi) 10.2 10.6 10.2 31.9 Modulus of elasticity- torsion (ksi) 3.9 4 3.8 note on units: ksi = 103 psi In table 2, the particular conditions and tempers used to obtain the material property values are as follows: For aluminum 7475, the T61 temper was used. For aluminum 5052, the H34 condition properties were used. For aluminum 2124, used T351 condition/temper. Kevlar K49 used for density, shear strength and modulus, and yield strength. For density and ultimate tensile strength, used Dupont Kevlar 49 Aramid fiber. For CFRP, data is for Type P-VSB-32 (Union Carbide) carbon fibers. Aluminum alloy 7475 has lower impurity limits than 7075. Aluminum 7475 is used for aircraft structures because of its good fracture toughness. As noted in table 2, fracture toughness is greater in the 2xxx series aluminum alloys than in the 7xxx series aluminum alloys. Fracture toughness for all of the aluminum alloys is approximately 36 MPa m. There is a different thermal/heat treatment for each of the aluminum alloys. Aluminum 2124 responds to heat treatment by developing good toughness and strength. Machinability is optimum with the T 851 precipitation heat treated condition. The heat treatment is as follows: the alloy is "solution annealed at 920 F followed by water quench. Precipitation hardening is done at 375 F for 12 hours and air cooling - this produces the T 851 temper." (Metal Suppliers, 2006). Heat treatment of aluminum 7475 is proprietary to Alcoa. The 5052 aluminum alloy cannot be hardened by heat treatment: It hardens due to cold working. Aluminum alloy 2124 has been selected for the main use of our aircraft. The reasons for this are: although aluminum 2124 has a lower strength and lower hardness than 7475, the fracture toughness is higher in aluminum 2124. This will contribute to a lower maintenance cost for aluminum 2124, all other things held equal. Other mechanical properties of aluminum 2124 and aluminum 7475 are virtually the same. The shear strength and shear modulus of aluminum alloys 2124 and 7475 are very similar. Their densities are almost exactly the same, as well as their moduli of elasticities. The composite selected for our aircraft is Kevlar. The reason for using Kevlar is its high ultimate tensile strength, which is almost twice as high as CFRPs. Kevlar is the lightest material that was studied here; according to table 2, Kevlar has the lowest density. Kevlar also has a relatively low cost; according to the research done for table 1, Kevlar was found to be cheaper than the aluminum alloys. The locations of the materials in our aircraft design are as follows: the aluminum alloy 2124 will be used for the fuselage skin; and Kevlar will be used for the empennage and for the ailerons, elevators and rudder of our aircraft design. Composite materials such as Kevlar can be used in these aircraft areas in order to save weight. This is similar to the Boeing Business Jet 2 (BBJ 2), which uses Kevlar, graphite and CFRPs for the ailerons, elevators and rudder (Aerospace-technology, 2006). Kevlar is made by Dupont, and is an aramid (aromatic polyamide) synthetic fibre. Kevlar can be made as a sheet of fabric or spun into ropes. The fibres do not corrode, which decreases maintenance cost for the material. Kevlar has three grades: Kevlar, Kevlar 29 and Kevlar 49. Of these, Kevlar 49 has the greatest tensile strength, and is the grade used most often in aeroplanes. There are some weaknesses of Kevlar. This includes the fact that it decomposes in alkaline conditions. Kevlar also has a tendency to buckle under compression, like all fibres. References Aerospace Materials (2006) Handy Data. Retrieved 5 Sep 2006 from http://www.aerospacematerials.com/handyData/alumHints.htm Aerospace-technology.com (2006) Boeing Business Jet 2 (BBJ 2) Long-Range Business Jet, USA. SPG Media Limited. Retrieved 5 Sep 2006 from http://www.aerospace-technology.com/projects/bbj/ Hale, R.D. (2006) Aluminum Cost Per Unit Volume for Wrought Metals and Plastics Relative to Carbon Steel. Retrieved 5 Sep 2006 from http://www.engr.ku.edu/~rhale/ae510/aluminum.pdf MatWeb Material Property Data (2006). Search MatWeb for Property Information. Automation Creations, Inc. Retrieved 5 Sep 2006 from http://www.matweb.com/search/search.asp Metal Suppliers Online (2006) 2124 Aluminum Material Property Data Sheet. Retrieved 2 Sep 2006 from http://www.suppliersonline.com/propertypages/2124.asp Metal Suppliers Online (2006) Aluminum 5052. Retrieved 2 Sep 2006 from http://www.suppliersonline.com/Research/Property/result.asp?FamilyID=2 &MetalID=472&Chemical=1&Physical=1&Mechanical=1 Wikipedia (2006) Kevlar. Retrieved 5 Sep 2006 from http://en.wikipedia.org/wiki/Kevlar Read More