Strength to weight ratio is one of the critical factors for designing of racing cars, ships and aircraft.
Engineers cum scientist tries to design a material which is lighter in weight and high in strength. One of the best examples of good strength to weight ratio materials is aircraft materials. In aircraft design, engineers to lower the weight of materials as compared to high strength.
Here comes a specific term in materials, i.e. composite materials.
Composite materials are high in strength to weight ratio. Composites are a combination of two or more constituent materials with significantly different physical and chemical properties. When two or more materials combine it give other material which is completely different individual materials.
One Common Example is
Sand+Stones+Cement+Iron= Concrete Pillar
Composites are widely used in aircraft’s and sports cars. Let’s dive into the aircraft composite materials.
In this post, you will come to know about
- Why aviation industry use composite materials?
- First commercial aircraft which used composite materials
- The types of aircraft composite materials
- Testing of composite materials
- Properties of composite materials
- Effect of environment on composite materials
- Boeing 767 composite materials parts labeling
- Advantages and Disadvantages
- Future aircraft composite materials
Composite materials are most preferred in aircraft design. Reasons are
- High strength to weight ratio
- High tensile strength and resistance to compression
- Saves Fuel consumption
- Improve the efficiency and performance of aircraft.
First Commercial Aircraft
Boeing 787 Dreamliner is the first commercial aircraft whose major structural components are made up of composites rather than aluminium alloys. Boeing 787 Dreamliner is going to use carbon laminates and carbon sandwich composites.
Types of Aircraft Composite Materials
Aircraft mostly use carbon fiber, glass fiber and Kevlar fiber.
Properties of Carbon Fiber
- Diameter is similar to 8mm.
- Strength is greater than 5GPa due to highly aligned planes of graphite.
- Stiffness is similar to 160-700 GPa, but 230-400 GPa is usual.
- Good in fatigue and non susceptible to degradation by chemicals.
- The Fibers bond well with surface treatment.
Properties of Glass fiber
- Diameter is similar to 10mm.
- Strength is greater than 3GPa due to defects in small diameter fiber.
- Stiffness is similar to 70 GPA for cheaper E glass.
- Susceptible to environmental attack and fatigue.
- The fibers need silent treatment to bond well to matrix.
Properties of Kevlar Fiber
- Stiffness is similar to 125 GPA in tension.
- Strength is greater than 3GPa because of highly aligned linear polymer chains.
- Much weaker and less stiff in compression as linear polymer chains comes apart.
- Susceptible to degradation by UV light and moisture.
- The fibers do not bond well at all, leading to a weak fiber/matrix interface.
Testing of Composite Materials
Composites are tested by mechanical stress test on various parts. Firstly the test goes on small scale model then progressively moved to larger parts of the structure and finally to the full structure.
Hydraulic machines are used to bend and twist composite material structures to check the worst expected conditions in real fights.
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Properties of Aircraft Composite Materials
- Composites have fairly very low electrical conductivity. That’s why a copper mesh is always integrated in aerospace laminates to protect aircraft from lightning strike damage.
- Composites have relatively low thermal conductivity and thermal expansion coefficients in and out of the aircraft.
- Composites have high strength to weight ratio, which is crucial for aircraft design.
- Composites are very damaging most tolerant.
- Composites are not very resistant to mechanical wear effects. That’s why External surfaces are treated with specific paints.
Effects of Environment on Composites
Composite materials have a lighter weight and similar strength as bulky materials. It is very easy to transport lighter composite materials.
Composites are more corrosion resistant, which means the pet will live longer. Traditionally produced composites are made from petroleum based fibers and resins, and are non biodegradable by nature.
This is a serious problem and scientists are doing research to make composites biodegradable.
There is another method which is used for sustainable development of aircraft composite materials i.e. Reuse. Aircraft manufacturing industries use decommissioned airplane composites for new one.
Composites Parts Used in Boeing 767
Advantages of Composite Materials
- Composites reduced the overall structural member weight by 20-50%.
- Composites are very corrosion and fatigue resistance.
- Composites have tolerable mechanical properties.
- Composites have lower assembly costs because it requires very few fasteners, bolts etc..
Disadvantages of Composite Materials
- Composites have high recurring costs.
- Composites are higher non recurring costs.
- Composites have higher material costs.
- Composites have very expensive repairs and maintenance.
- Composites needed isolation to prevent adjacent aluminium part galvanic corrosion.
Future Composite Materials
Ceramic Matrix Composites
This type of lightweight, high temperature composite materials is in the research process at NASA for use in aircraft parts.
Spider Silk Fibers
This future composite exhibits high ductility, allowing stretching of a fire up to 140% of its normal length. This is also under research process.
Hybrid Composite Steel Sheets
This future composite material can be stainless steel constructed with inspiration from composites and Nano tech fibers and plywood. This is again under research process.
Aircraft composite materials have high strength to weight ratio and lower electrical conductivity, thermal conductivity, thermal expansion coefficients and assembly cost.
There are some limitations of composites. Scientists are doing deep research on more advance composites which should be biodegradable, low recurring costs and easily available.
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