At the present time, space and aerospace textiles are making a significant contribution to the increasing market for textiles, assert M V Ragavendra Pavan, Karthik Macharla and Dr J Hayavadana.

The history of textiles can be traced back to the age when human beings tried to cover their body for safety and protection - even well before the production of fabrics and other products started on machines. Today applications of textiles have crossed many barriers beyond the regular use which man never expected. One such area is space and aerospace. The design, manufacture and applications of textile composites in space and aerospace has become one of the most predominant aspects in present-day textiles.

The applications of these composites in space suits for launch and space walks require zero defect performance. They are made from PBI non-flammable high performance fibres, which require air purifying, cooling and pressurising systems, so that the suit should be thermal resistant and thermal insulated.

High specific modulus and high specific strength are the most desired characteristics of materials in aerospace structural applications. They should have good fatigue, stress resistant, better dimensional stability and conformability, which help in improving the fuel economy of the aircrafts. Carbon, Kevlar, Boron nitride fibres, etc, are used as composite reinforcements in making wings and other body parts for a variety of commercial and military aircrafts.

Today, the world advances in aerospace textiles by the use of composite materials based on ultra strong Aramid fibres, which have low density, high specific strength combined with attractive specific modulus. Fabricating of composite structures with these Aramid fibres will resist flame, high temperatures, organic solvents and lubricants. In addition, all these fibres are pliable and can easily be woven by conventional methods.

Space textiles

When astronauts travel through space, they face complex environment. Earth's gravitational attraction holds atmosphere comprising a mixture of gases like nitrogen, oxygen, carbon dioxide and thick form of water vapour. This atmosphere protects us from various factors. When the astronauts leave the surface of earth and travel into the space, they must be ready to meet the environment available there.

There are numerous health risks caused by the harmful radiations, when the astronauts are exposed to them. Some of the short-term effects and recoverable effects like nausea and long-term effects like cataract, cancer and damage to the central nervous system or even death are caused when exposed to these radiations over a period of time. Hence, there is a need for a system to determine, detect and prevent certain level of radiations, pressures and temperatures encountered by the astronauts to keep him alive in that environment. Such a system is a space suit. A space suit is a complex system of equipment, specially designed to protect and keep a person comfortable in the rough environment of outer space. This applies to the Extra Vehicular Activity (EVA) outside the spacecraft and is applied for walking on the moon.

Properties:

The space suit must possess the following properties:

1. Lighter in weight.
2. Flexible in handling.
3. Soft in touch.
4. Comparable in strength with metal.s
5. Modifiable in size and shape.
6. Thermal insulated and thermal resistant.

Space suits for space walks are made from PBI (Polybenzimidazole) non-flammable high performance fibres. The space walk suits have various requirements. They are employed with air purifying and cooling systems. Each suit is tailor made for a particular astronaut and is very expensive, as it involves the usage of various fabrics. Circular-woven fabrics together with layered structures of polyester, urethane and others are used. The outer layer of the suit, which is exposed to the radiations, is made of ortho-fabrics that consist of a blend of Gore-tex, Kevlar and Nomex materials.

As discussed earlier in the properties, the suit should be thermal insulated as well as thermal resistant, since the temperature range found in the space is a major hindrance. Hence the suit should be capable of maintaining the comfortable temperature.

UV radiations, radiations of electrically charged particles from sun and meteoroids are the other environmental factors encountered by the astronaut in the outer space. Meteoroids though are very small bits of rocks and metals, travel at very high velocities and can easily penetrate into the bodies of astronauts. Hence, the space suit of the astronaut should be capable of having high impact resistance and stability to withstand the major stresses caused by these particles, pressures and others.

An Extra Vehicular Mobility Unit (EMU) was designed by the NASA Engineers. It consists of 14 layers of structures to perform random functions such as thermal resistant, vapour absorbing and impact resistant layers. The inner layers of the suit do activities like cooling and ventilation. An EMU consists of wide operations in it like; Drink bag, communication systems, TV camera and lights, etc.

Beginning from the inner layers, first a layer made up of knitted form of Nylon tricot is lined, over which second layer of Spandex material fabric (a poly-urethane elastic thread) with plastic tubing is laced. The third layer is a Urethane-coated nylon fabric layer called the pressure bladder layer, over which a pressure-restraining layer made of Dacron, is laced. These two layers are employed to protect the astronauts from pressures balancing both internal and external pressures. Above these two layers, a thin liner of nylon coated with Neoprene is placed, followed by a series of 7 layers, thermal micrometeoroid garment of aluminised Mylar laminated with Dacron. These 7 layers are thermal insulated, protecting the astronaut from heat phenomenon and impact resistant protecting from meteoroids. The final or the outer layer of space suit, which is exposed to various radiations, is made of a blend of Gore-tex, Kevlar and Nomex materials.

Aerospace textiles

The astronauts travel to the space with the help of spacecraft, which is designed using high performance metals and textile composites. Based on 3D reinforcement, a narrow range of materials is used as textile composites.

Today almost all commercial jets, military aircrafts and space crafts encompass a wide range of textile composites in them. The aerospacing uses the broad range of polymer composite materials with textile reinforcements from woven, non-crimp fabrics to 3D textiles.

Properties:

The most required properties of textile composites in aerospace structural applications are:

1. High specific modulus.
2. High specific strength.
3. Resistant to chemicals and organic solvents.
4. Good fatigue.
5. Thermal insulated and thermal resistant.
6. Impact and stress resistant.
7. Better dimensional stability and conformability.
8. Low flammability.
9. Non-sensitive to harmful radiations.

Both uni-directional as well as multi-directional composites exhibit good properties in in-plane and out-plane directions. Weaves, knits, braids, and stitched are the variety of fabric structures included. It is well-known that most of the structural failures are caused due to fatigue. Hence a low cost moulding process called VARTM (Vacuum Assisted Resin Transfer Molding) is employed with ability to produce complex parts, which have good impact resistance.

As per the investigations, the bi-axial braided Carbon/Epoxy composites with different braid angles (25º, 30º and 45º) were employed for the structures of small business jet applications whereas carbon/epoxy, unstitched, stitched and Z-pinned plain woven composites are employed for aerospace structural applications under various tension compression fatigue loadings.

Textile composites in aerospace structures

Various researchers, designers, and manufactures are involved in the development of new products with textile composites. Some of the textile materials are used for reinforcement of pents and manufacture of aerospace structures are Carbon fibres, Kevlar fibres, Alumina-boria-silica fibres and Nylon 6, 6 materials.

The following is the graph, which gives the compressive properties of these different fibres.

Carbon fibre

It is the material consisting of extremely thin fibres about 0.0002 - 0.0004'' in diameter and contains mostly carbon atoms as it is produced from the pitch, which is produced as the byproduct during the cracking process of crude oil. It is also called as graphite fibre and its carbon percentage is almost equal to 100%. The specific gravity of this fibre is 1.5 - 1.6. Carbon fibre is known for its excellent tensile strength, heat resistance and chemical resistance. Keeping in the view of these properties, these fibres are used as reinforcing moulds, and heat insulating materials. Apart from this, these fibres are used as raw materials for the manufacture and design of special utility components of aviation machine, space rockets, etc.

These fibres are aligned parallel to the fibre axis, as the carbon atoms are bonded together, when observed under microscope. Superior to the other high performance fibres, this particular property of crystal alignment makes the fibre strong. The raw material is not in the fibre form, after chemical processing it is turned into the fibre form and bundle of these fibres are twisted together to form yarn, and on the desire of end-user it can be used by itself or can be woven into a fabric. If this is to be used in the form of a fabric, it becomes carbonised after.

Kevlar narrow fabrics

Aramid fibres are a class of heat resistant and very strong synthetic fibres, known for their good resistance to abrasion, organic solvents and good fabric integrity even at elevated temperatures. These fibres are better known under the trade names such as Kevlar. Kevlar fibres are known for the ability to provide quality and consistency, which are critical for aerospace applications.

These fibres have a very high molecular orientation, which implies the high strength and modulus of them. Kevlar fabrics are used in containment wraps, which perform the important role in preventing the broken engine blades from damaging the aircraft or entering the compartment of the passengers. These wraps, may be up to 1 kilometre in length. These fibres are known for excellent endurance, corrosion resistance and malleability. Alumina-boria-silica fibres The fabrics in the aerospace structures are woven from strong

Alumina-boria-silica fibres.

These fibres are continuous and are specially designed to pass FAA's 2000°F (1093°C) 15-minute flame penetration test. Nextel is a woven ceramic fabric and one of the most widely used shielding materials. It is a commercial name for alumina-boria-silica fibres, which shock the incoming projectiles and turn them into small, less threatening, debris fragments. It comes in many different styles and weights.

These fabrics are known to retain strength and flexibility with little shrinkage even at continuous temperatures up to 2012°F (1100°C). General aviation aircraft, large commercial jets are vulnerable to lightning strike. FAA-certified aircraft, for example, are typically struck once or twice a year. Unlike their metal counterparts, composite structures in these applications do not readily conduct away the extreme electrical currents and electromagnetic forces generated by lightning strikes. Composite materials are either not conductive at all (eg, fibreglass) or are significantly less conductive than metals (eg, carbon fibre), so current from a lightning strike seeks the metal paths available. For that reason, lightning strike protection (LSP) has been a significant concern since the first composites were used on aircraft more than 30 years ago.

Silicon carbide fibre

These fibres are similar to carbon fibres, as the principal constituent repeating unit is carbon in both of them. The tensile strength of the fibre is about 400 kg/mm². It is known for its outstanding heat resistance, as it withstands even at temperature as high as 1500°C. It is comparatively light with specific gravity of 2.7.

It has excellent properties like resistance against corrosive chemicals and elasticity. Hence, today its usage is done, in the fibre reinforcing metal compounding material (FRM) in manufacturing special pents of aviation machines.

Applications

The Figure 14 shows the composition of various fibres such as carbon, aramid and glass on the body segments of an aircraft.

Based on the properties like strength, resistance to heat, imparts and chemicals, these textile materials have a wide range of applications when concerned with aerospace structures,

1. By taking the advantage of the stiffness and strength of carbon fibre, which is lightweight and non-flammable, a light weight aircraft can be constructed by using some other high performance fibres.

2. All US commercial jets have their brakes made from carbon composites as they are the only ones, which can withstand the high temperatures generated, if the take off is aborted all of sudden.

3. Kevlar nonwoven felt liners are being used as fire barriers to cover the urethane foam seats on all the aircrafts so as to prevent the production of highly toxic cyanide gases, when such foams burn during the accidents.

4. Carbon and other high performance fibres are used in the rocket exhausts and nose cone covers for space shuttles, so as to protect them from heat, from air friction during launch and re-entry.

5. Generally, during the launch, the flame generated does not ignite the rocket body, as it is made from flame resistant, graphite-carbon-textile fibre exhaust shields.

6. The white hot fumes of high temperatures from the atmosphere friction do not consume or burn the shuttle as some of high performance fibres and ceramic structures provide the protection, to it which acts as shields.

7. Nylon 6, 6 of thickness 840D is used in the type cords of jet aeroplanes, as they require to withstand strong pressure and friction heat developed at the time of landing.

8. In order to meet demanding temperature and strength properties of space exploration, NASA has used alumina-boria-silica ceramic fibres. NASA and the Johnson Space Centre together have used these ceramic textiles to protect the space station "FREEDOM" from being punctured by space debris.

Advancements

With the new advancements, the utility of textile composites in various aircrafts predominantly increased. These textile composites are reinforced in the chassis, seats, wings, fans and other parts of the aircraft. Though the percentage of usage may vary, they vastly improve the strength, performance and fuel economy, which are the basic credit Irion for the aircraft. Below are some of the models of aircrafts, where the applications of textile composites are found.

1. The new Boeing 767 commercial jet contains 46% textile composites in its body segments and the McDonnell Douglas F-18 attack fighter uses 56% of textile composites in its body.

2. Grumman A-6 and F-14 military fighters contain significant quantities of textile composites. The air force's most advanced forward wing design X-29 airplane uses textile composites in its wings, since no other material can withstand the stresses and would easily twist off due to the winds. The Lear fan's body segments; structural ribs and the drive shafts are made of 100% carbon fibre composites.

3. Carbon Fibre Reinforced Plastic (CFRP) seems to replace the universal use of Aluminum, as it is being used in manufacturing the wings of A350, A380 and the structural components of A400M, the new military lift plane. Many helicopter manufacturers use these textile composites.

4. AIRBUS, in 1982, was first to use CFRP to make spoilers, elevators and rudders on A310-200, and to use in vertical fins of A310-300. Fibreglass consists of glass fibres embedded in a resin material. It is most commonly used composite material and was first used in Boeing 707 passenger jet in 1950s, though it comprised only about 2% of the structure.

5.The upper fuselage of A380 is designed from GLARE (GLAss Reinforced), which is the fibre metal laminate made from the alternating layers of glass fibres and aluminium.

About 6.70% of the outer skin areas of Euro fighter Typhoon are made from carbon fibre composites and the fuselage in Boeing 787 was made from the carbon fibre composites. The fuselage is 76 feet long with 30 feet diameter.

Conclusion

The development of space and aerospace textiles is a great boon to the present-day textile industry. The manufacturers of the polymer composite component, end-users, designers, structural material researchers and textile manufacturers are involving in the development of new products with the usage of these textile composites. Each new step forward is paving the way to further advancements. At the present time, these kinds of textiles are making a significant contribution to the increasing market for textiles. Hence, with the progressing steps and emerging trends in the textile industry, greater attention will be drawn from every nook and corner of the world, which ultimately improves the economic strategy of the world to a larger extent, proving that textiles are not only linked to the regular use of protection and safety but also to technological advances satisfying the needs of mankind globally.

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Mr M V Ragavendra Pavan,
University College of Technology, Osmania University,
Hyderabad, Andhra Pradesh.

Mr Karthik Macharla,
University College of Technology, Osmania University,
Hyderabad, Andhra Pradesh.

Dr J Hayavadana,
University College of Technology, Osmania University,
Hyderabad, Andhra Pradesh.