Material is the matter from which a thing is or can be done. Material is anything made of matter, constituted of one or more substances. Like Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term material is used more generally it mention a substances or components with certain physical properties that are used as inputs to production or manufacturing. Choosing material for an aircraft is highly dependent on type of flight, i.e., whether it is a sonic, or a subsonic, or a hypersonic flight.
Some factors have been considered during the selection of a material for Aircraft structures. This material is submitted a various environments conditions like humidity, temperature and submitted under different types of mechanical solicitations like tension, compression, bending, cyclical forces, creep and torsion,
Nowadays, a lot of materials are available and it’s difficult to choose the better outcome because there are too many variables involved, and the cost is also an important factor to make a right decision. In Airframe structures, strength joined by lightness is most significance in material selection, when the material is stable in environment conditions. In the majority of situations, trials and errors could be very extensive and a good project and design is necessary. For the reasons mentioned above, the materials properties must be considered for structural application as:
Figure 1: Stress-strain curve
‘ Ultimate stress
‘ Yield stress
‘ Stiffness (modulus of elasticity)
‘ Temperature limits
‘ Corrosion resistance (hostile environment)
‘ Fatigue resistance (Stress-Number fatigue curve)
‘ Fracture toughness
‘ Fragility at low temperatures
‘ Crack growth resistance
‘ Ductility
‘ Maintainability (time for inspections, repair)
‘ Reliability (medium time between fail)
‘ Fabric ability [1]
Figure 2: Aircraft Materials
2. HISTORY
Materials in Aerospace Ever since the Wright brothers built their Flyer back in 1903, the materials used in airplane design have been constantly developing. The original Wright Flyer was comprised primarily of spruce and ash wood with muslin covering the wings, while today’s airliners are made mostly of aluminium with some structure made from steel.
In the mid 1960’s, scientists and engineers began working on a new breed of aerospace materials called composites. A composite is an engineered material made from two or more ingredients with significantly differing properties, either physical or chemical. While no longer used today, an early example of a composite material was a mix of mud and straw that was used to make bricks. Composites have two significant advantages over some of the more traditional materials: greater strength and lighter weight. [2] One of the most common forms of composite in use today is carbon fiber. It is made by heating lengths of rayon, pitch or other types of fiber to extremely high temperatures. The composition of aircraft has steadily changed from primarily aluminium in construction, to a mixture of materials, with composites now the main structural material.
The increasing use of lower density materials, such as composites and titanium alloys, has past to an overall reduction in aircraft weight, which in turn gives a reduced fuel burn, increased range and cargo capacity, whilst maintaining a cruising speed of Mach no 0.85 (561 mph, 903 km/h) at typical cruise altitudes. An engineered composite material must be formed to shape mud walls have been used for thousands of years. [3]
Figure 3: Material Use in Boeing and Airbus Aircraft by % weight and year of first flight
Figure 4: Material usage trends in fighter aircraft
3. MATERIALS
Main group of materials used in aircraft construction
‘ Wood
‘ Steel
‘ Aluminum alloys
‘ Titanium alloys
‘ Super alloys
‘ Ceramics
‘ Fiber reinforced composites.
Wood
The first aircraft were constructed from wood (spruce and birch) covered with canvas. Wood has a good Strength/weight ratio about 0.1 same as aluminum alloys. This is the reason of elected success, because Germans had all-metal structures. Decay, Wood wrapping, splits easily, Roughness when used in 4 stroke engine.
Figure 5: WOOD
At the very beginning of the materials, because of this not able to be changed technical condition, wood was the only variable material from which to build a Wing machine. When the Wright-brothers and their contemporaries made their first of all not certain leaps into the air, light weight structures were especially involving. The most successful a person who is among the first to explore an experimenters, including the Wrights, tested their aerodynamic research and light control systems using a no fuel-burning source .Because of the low airspeeds and limited lift-generating capacity of these aircraft, lightness was essential.[4] Wood was the only feasible substance from which to construct supporting surfaces light enough to and also strong enough to with stand light loads .Other factors that made wood the material of choice were the case with which it could be make into a particular form and repaired its low cost. Bear in mind that turn of the period it was still a decade or more before aluminum became willingly available at reasonable prices. [5]
Figure 6: wood-and-fabric biplane
Aluminum Alloys
Since 1920, aluminum alloys have been the mostly used material in airframe construction. Nowadays, there are a lot of aluminum alloys with very similar proprieties. The 2024 alloy has lower ultimate stress compared with 7075 alloy in the aged condition, but with better Physical proprieties. This is the reason why 7075 issued for upper surface and 2024 is used for lower surface inTupolev-154. For the lower surface, the physical proprieties are more important, due the tensile loads that element most of the time. In some applications, corrosion resistance of an aluminum alloy has been improved by a quality of pure aluminum. The aluminum alloys have worst corrosion resistance than commercial pure aluminum.Titanium is named after the titan’s .The great sons of the earth in Greek mythology. Titanium is the fourth abundant metal on earth crust (~0.86%) after aluminium, iron and magnesium .Titanium was used in Concorde and SR-71 airframes. Titanium has an excellent relation stress or weight, good resistance to corrosion and good order to avoid the proprieties. Titanium is a very extensive alloy, compared with steel, and its uses are limited for special proposes. In turbines, titanium is used mainly due the temperature resistance, low weight and corrosion resistance. After the combustion of the fuel, the temperature increases and Titanium alloys have been substituted by nickel alloys (super alloys).
Figure 9: Titanium alloys
Titanium and its alloys exhibit being the only on of its combination of mechanical and physical properties and corrosion resistance which have made them desirable for critical, demanding aerospace, industrial, chemical and energy industry service of the primary attributes of these alloys. With respect to mechanical properties, conventional near titanium alloys have a temperature capability up to 550C’600C. It seems, after 40 years of alloy development, that this defines an upper limit of this class of material. [8]
Example: A compressor circular objects, has niobium (5-10 at%) in ti-al based alloys supports the finer micro structure and increases the two phase volume proportions, no lightweight, damage tolerant material has the requisite maturity today to replace nickel-based alloys above 500C. Such a material could allow a significant performance boost through introduction of new light weight compressors no longer dependent on the use of large quantities of heavy nickel- based alloys. [9]
Most titanium alloys are metastable and tend to nature into coarse plates after heat-treated in the phase perception after long term process of growing at elevated temperature and forming of titanium alloys are mechanically deformed by enduring, sheet and ring rooling, machine, power metallurgy, super plastic forming more widely bonding Titanium also exhibits good creep properties at situated temperatures, the product is pure titanium is use able up to 595C. The melt temperature is greater than 1660C. While cost is about four times that of stainless steel, it is comparable to super alloys. Ti is highly corrosion resistant when processed using standard consideration techniques, such as casting and forging.