Eight applications and technological advances of carbon fiber composites

Carbon fiber is a very important inorganic high performance fiber, and its first marketed application was the commercially available carbon fiber reinforced resin fishing rod in 1972. Since then, carbon fiber applications have rapidly developed to the high-end represented by aerospace materials.

The most important application of carbon fiber is as a reinforcement for resin materials, and the resulting carbon fiber reinforced resin (CFRP) has excellent overall performance in missiles, space platforms and launch vehicles, aircraft, advanced ships, rail vehicles, electric cars, trucks, wind power blades, fuel cells, power cables, pressure vessels, ultra-high speed centrifuges for uranium enrichment, special tubing, public infrastructure There are actual and potential applications in sixteen fields, including medical and industrial equipment, sports and leisure products, and fashion and lifestyle appliances.

CFRP is widely used in aerospace applications such as missile weapons, space platforms and launch vehicles. In missile weapons applications, CFRP is mainly used to manufacture primary and secondary load-bearing structural components such as bullet fairings, composite supports, instrument pods, decoy pods and launch barrels; in space platform applications, CFRP ensures low structural deformation, good load-bearing capacity, radiation resistance, aging resistance and good space environment tolerance, and is mainly used to manufacture load-bearing barrels, honeycomb panels, substrates, camera mirror barrels and In launch vehicle applications, CFRP is mainly used in the manufacture of arrow fairing, instrument bay, shell, interstage section, engine throat liner and nozzle. At present, the application of CFRP in spacecraft has become mature, and it is an indispensable key material to realize the light weight, miniaturization and high performance of spacecraft.

CFRP as a structural material for aircraft

In large aircraft, CFRP is widely used as the main load-bearing structural material. CFRP is also used as a structural material in the recently developed new airships.

The oil crisis in the mid-1970s was the direct reason for the use of carbon fiber in aircraft manufacturing. In order to alleviate the energy crisis, the U.S. government launched the "Aircraft Energy Efficiency Program". Modern aircraft fuselages are made of steel, aluminum, titanium and other metals and composites. To save fuel and improve operational efficiency, reducing fuselage mass has been one of the core challenges in aircraft design and manufacturing technology. The mature application of CFRP in aircraft fuselage manufacturing has provided an effective way to reduce the mass of aircraft fuselage. For example, the fuselage mass of a Boeing 767 made mainly of metal (with only 3% CFRP) is 60t, and when the CFRP dosage is increased to 50%, the fuselage mass of the new aircraft drops to 48t, which alone greatly enhances the energy and environmental benefits of the aircraft.

The Boeing 777X and the newest Boeing 787 both have a 50 percent fuselage composite. The Boeing 777X is a large twin-engine airliner being developed based on the Boeing 777, with the first aircraft to be delivered into service in 2020. The main wing of the Boeing 777X aircraft is made of CFRP and has a wingspan of approximately 72m (235 feet), making it one of the longest wingspans of any airliner currently available. The longer the wingspan, the greater the lift, resulting in very competitive fuel consumption and operating costs per seat for the Boeing 777X. In addition, the CFRP wings are not only strong and flexible, but also foldable at the end so that most airports can accommodate its wide wingspan for parking. The main load-bearing structures of the Boeing 787, including the main wing and fuselage, are manufactured using carbon fiber prepreg from Toray of Japan. in November 2005, Toray signed a 10-year agreement with Boeing to supply carbon fiber prepreg for the Boeing 787 Dreamliner. on November 9, 2015, Toray announced a comprehensive agreement with Boeing to supply carbon fiber prepreg for Boeing's production of both the 787 and 777X aircraft with carbon fiber prepreg. Boeing plans to increase monthly production of the 787 aircraft, which will increase from 10 in 2015 to 12 in 2016 and 14 in 2020; also, the ratio of large modules will increase, which will significantly boost the demand for CFRP. In order to ensure the supply of materials for Boeing 787 aircraft after the monthly production of 12 aircraft, Toray Composites (USA) has completed the expansion of production in January 2016; at the same time, Toray Japan decided to build an integrated production line containing raw silk, carbon fiber and prepreg at the Spartanburg County plant, with a design capacity of 2,000t per year, which is the first time Toray has built an integrated carbon fiber production line in the United States for the development of the Boeing 777X aircraft and to meet the demand for 14 Boeing 787 aircraft per month.

On August 17, 2016, a large blimp developed in the UK completed its maiden voyage. The blimp is a lighter-than-air spacecraft designed to perform reconnaissance, surveillance, communications, transportation of cargo and rescue supplies, and passenger transportation. The airship uses a polyarylene-based fabric from Kuraray Japan as the skin, which is filled with pressurized helium; the shape of the structure is made of CFRP to minimize the airship's own mass. The airship can float unattended for up to five days at a time.

CFRP is very obvious to improve the structure, energy consumption and maneuverability of the ship.

Sweden has a traditional advantage in shipbuilding technology, its sandwich composite technology is among the world's first-class, early use of CFRP technology to develop military ships. The ship is 73.0m long, 10.4m wide, with a draft of 2.4m and a displacement of 600t; the hull is made of CFRP sandwich structure, which has excellent properties such as high strength, high rigidity, low mass, impact resistance, low radar and magnetic field signals, and electromagnetic wave absorption.

In 2010, the German company Kockums built a new concept solar-powered expedition ship with almost all CFRP. The ship is 31.0m long and 15.0m wide, powered by solar energy, and on September 27, 2010, a Swedish explorer set sail on an expedition around the world.

CFRP has also been used in the manufacture of naval propeller blades, integrated masts and advanced surface ship superstructures.

Low noise and quiet operation is a core technology in the field of military ships and is a key indicator of the performance of ships (especially submarines). CFRP blades are not only lighter and thinner, but also can improve the performance of vacuoles, reduce vibration and underwater characteristics, and reduce fuel consumption.

CFRP is used to manufacture propeller blades for submarine and cargo ship propulsion systems (a is the propeller used in Israeli submarines; b is a CFRP propeller for large cargo ships)

In addition, stealth is also an important indicator to evaluate the level of sophistication of military ships. To improve stealth performance, it is necessary to reduce the radar reflection cross-section of the ship's hull and to reduce its optical characteristics. In the past, the ship's superstructure was covered with multiple antenna masts hung with various whips and strips, which greatly hindered the ship's stealth capability in detection equipment. 1995, the U.S. Army began to study the one-piece mast system, which designed various antennas into planar or spherical arrays and integrated them into a one-piece mast system made of composite materials that can reflect radio waves and protect against weather and salt spray. . And furthermore, the entire superstructure of the next generation of U.S. combat ships is made of composite materials.

The ship is the U.S. Navy's next-generation main battle ship, which integrates today's most sophisticated naval ship technology, hull shape, electric drive, command and control, intelligence and communications, stealth protection, detection and navigation, firepower configuration and other performance are beyond. Especially noteworthy is that the ship's superstructure and embedded antenna system are designed and manufactured by Raytheon Company of the United States, which adopts an integrated modular composite structure with light mass, high strength, rust and corrosion resistance, good wave-transparency, and excellent stealth performance with less than 10% probability of being detected.

Lightweighting is a key technology to reduce the energy consumption of train operation. Although the metal-made rail trains have high body strength, they have high mass and high energy consumption.

CFRP is the focus of the new generation of high-speed rail train body material selection, which not only can make the rail train body lightweight, but also can improve high-speed operation performance, reduce energy consumption, reduce environmental pollution, enhance safety. At present, the application trend of CFRP in the field of rail vehicles: from the box interior, car equipment and other non-load-bearing structure parts to the car body, frame and other load-bearing components to expand; from the skirt, deflector and other parts to the top cover, driver's cab, the whole car body and other large structure development; to metal and composite materials mixed structure is the main, CFRP dosage increased significantly.

The mass ratio of each part of the vehicle in the middle of a subway train, of which the body mass accounts for about 36%, the on-board equipment accounts for about 29%, the interior decoration accounts for about 16% . In 2000, the French state railroad company developed a double-layer TGV trailer using carbon fiber composite materials; based on this, the Korea Railway Science and Research Institute developed a 180km/h TTX-type swing train body, which uses a stainless steel reinforced skeleton, side walls and The sandwich structure is made of aluminum honeycomb core for the side walls and roof, and CFRP for the skin. The total mass of the car shell is reduced by 40% compared with the aluminum structure, and the car has good performance in terms of strength, fatigue strength, fire safety and dynamic characteristics, and was put into commercial operation in 2010.

In 2011, the Korea Railway Research Institute (KRRI) developed a CFRP subway bogie frame with a mass of 635kg, which is about 30% less than the mass of a steel frame. Japan Railway Institute of Technology (JRTI) and East Japan Passenger Railway Company jointly developed a CFRP high-speed train roof, which reduces the mass of each car box by 300-500 kg. In September 2014, Kawasaki Heavy Industries (Kawasaki), Japan, developed a CFRP frame side beam, which reduces the mass by about 40% compared to a metal beam.

Research by the Materials Systems Laboratory on materials for vehicle lightweighting and production cost reduction has shown that for every 10% reduction in vehicle mass, fuel consumption can be reduced by 6%. Of the available materials, CFRP has the best lightweighting effect; coupled with, the rapid development of automotive design and composite technology. All these make the application of CFRP in the field of automobile manufacturing much faster than people expect.

A conference was held in Munich in 2008 to revolutionize urban transport technology, establishing a "Project i" think tank with the sole mission of "forgetting everything we've done before and rethinking everything. In 2009, the think tank developed a new energy-saving concept, "Effective Power Vision," which laid the intellectual foundation for the company's subsequent research, calling for specialized design of body and drive systems to achieve new levels of energy efficiency. In 2011, the company established "Born Electric," which allowed people to use all-electric energy in their daily driving trips; in the same year, the first all-electric concept car realized a technology demonstration. 2012 saw the introduction of a concept car that combines high energy efficiency with better sports car performance. In 2012, a concept car with high energy efficiency and better sports car performance was launched, which used lightweight materials such as CFRP, aluminum and titanium to achieve a breakthrough weight reduction; in the same year, a new electric drive system was introduced to achieve zero emissions. In the same year, a new electric drive system was launched, achieving zero emissions. The new car was launched with an overall mass of only 1,245kg, a range of 200km on a single charge, and a unique flexibility with an acceleration time of 7.3s per 100km.

The "LifeDrive" modular body architecture design is composed of two parts: the occupant cabin module (Life) and the chassis drive module (Drive). The occupant cabin module, also known as the Life module, constitutes the passenger space for the driver and occupants. The Life module made of CFRP is light in weight, very safe, and has a spacious and homogeneous ride. The chassis drive module, also known as the eDrive drive system, has a structure made of aluminum alloy and integrates power components such as an electric motor (maximum power of 125kW and maximum torque of 250N-m), a battery and a fuel engine.

The company began producing its own carbon fiber needs after more than 10 years of research and development through a partnership with SGL Carbon Fiber Materials for Automotive. The manufacturing process for its new mid-vehicle life modules: carbon fibers are woven into fabric and then infiltrated with a special resin to make a prepreg; the prepreg is heat-set into rigid body parts; and the body parts are fully automated and bonded into complete body parts using a specially developed technology. The resulting CFRP body has extremely high compressive strength, can withstand faster acceleration, and the whole vehicle has excellent agility and road feel.

CFRP body manufacturing process

CFRP body structure for the new concept freight truck

Walmart, the world's retail giant, has a fleet of nearly 6,000 trucks in the U.S. that deliver products to thousands of stores across the country. The fleet has been aiming to "drive fewer miles and move more" to maintain sustained viability and efficiency, relying on driver driving skills, advanced tractor trailers and improved process and system planning to achieve a fleet of over 4.8 million kilometers and over 800 million containers between 2007 and 2015. Transport efficiency increased by 84.2% compared with 2005.

Among them, the performance of the tractor trailer to achieve the goal of "pull more, run less" is very important, so Wal-Mart invested heavily in the "advanced vehicle experience" of the new concept truck research program. The new concept truck has been developed to integrate cutting-edge technologies such as aerodynamics, microturbine hybrid drive system, electrification, advanced control system, and CFRP body. Major technical innovations: advanced aerodynamic design with elegant overall shape and 20% better aerodynamic performance than the current 386 truck; clean, efficient and fuel-saving microturbine hybrid electric drive system; driver's seat designed in the center of the cab with 180° view; electronic instrument panel provides customized range and performance data; sliding doors and folding steps improve safety and security performance The spacious cab features a retractable bedroom with folding bed. The entire body of the tractor trailer is made of CFRP, and the top and side walls are made of 16.2m (53ft) long monolithic panels, whose excellent mechanical properties ensure the structural strength of the body; advanced adhesive bonding is used to minimize the number of rivets; the convex nose shape design can effectively improve the aerodynamic performance while fully guaranteeing the cargo capacity; low-profile LED lights are more energy-efficient and durable.

At present, the program has completed 84% of the task volume, but there are still many innovative technologies to continue to develop. It is foreseeable that Wal-Mart's new concept truck has a very big role in advancing truck technology and expanding the application of carbon fiber.

Wind energy is the most cost-competitive renewable energy source, and wind power generation has made rapid development in the past 10 years.

In order to improve the wind energy conversion efficiency of wind turbines, increasing the unit capacity and reducing the mass per kilowatt is the key. early 1990s, the wind turbine unit capacity is only 500kW, but today, the single capacity of 10MW offshore wind turbines have been productized. Wind turbine blade is the key component of wind turbine to effectively capture wind energy, blade length increases with the increase of wind turbine unit capacity. According to the top-spin theory, in order to obtain greater power generation capacity, wind turbines need to install larger blades. Because of the blade length issue, the industry on the need to develop 10MW and above capacity wind turbines are controversial, but the mainstream view is the need for development. The relevant personnel believe that: the scientific law of the relationship between area and volume will eventually limit the continuous growth of impeller diameter, but has not yet reached the limit, the manufacture of 10MW wind turbine is technically feasible; and from the operational efficiency, to reduce the operating costs per MWh, the capacity of wind turbines must be increased.

The growth process of blade diameter

The increase in impeller diameter places lighter and higher demands on the quality and tensile strength of the blades.CFRP is a key material for manufacturing large blades, and it can make up for the lack of performance of glass fiber composites (GFRP). But for a long time, due to cost factors, CFRP in blade manufacturing is only used for beam cap, leaf root, leaf tip and skin and other key parts. In recent years, with the carbon fiber price steadily decreasing, coupled with the blade length further lengthening, the application parts of CFRP increased, the amount also has a large increase. 2014, successfully developed the longest domestic 6 MW wind turbine blade, the blade full length 77.7m, mass 28t, of which the main beam by 5t of domestic CFRP made. If GFRP design is adopted, the mass of this blade will be about 36t.

Carbon fiber paper as electrode gas diffusion material for fuel cell

A fuel cell is a device that directly converts chemical energy into electrical energy without combustion. Fuel cells work under isothermal conditions, and their use of electrochemical reactions to convert chemical energy stored in fuels and oxidizers directly into electricity is a highly regarded clean energy technology with very high conversion efficiency (except for 10% of the energy wasted in the form of waste heat, the remaining 90% is converted into usable heat and electricity) and environmentally friendly; in contrast, when using fossil fuels such as coal, natural gas and oil In contrast, when using fossil fuels such as coal, natural gas and oil to generate electricity, 60% of the energy is wasted in the form of waste heat, and 7% of the electricity is wasted in the transmission and distribution process, and only about 33% of the electricity can actually be used in the electricity-using equipment.

Comparison of fuel cell and fossil fuel power generation utilization

Among various types of fuel cells, the proton exchange membrane fuel cell (PEMFC) is an ideal power source for automobiles because of its high power density, high energy conversion rate, good low-temperature startability, and small size and portability. Proton exchange membrane fuel cell consists of 3 main parts: cathode, electrolyte and anode, which work on the following principles.

(1) The cathode ionizes the liquid hydrogen molecules. When the liquid hydrogen flows into the cathode, the catalyst layer on the cathode ionizes the liquid hydrogen molecules into protons (hydrogen ions) and electrons.

(2) Hydrogen ions pass through the electrolyte. The electrolyte located in the central region allows the passage of protons to reach the anode.

(3) Electrons pass through the external circuit. Since electrons cannot pass through the electrolyte, but only through the external circuit, a current is formed.

(4) The anode ionizes the liquid oxygen. When liquid oxygen passes through the anode, the catalyst layer on the anode ionizes the liquid oxygen molecules into oxygen ions and electrons and combines them with hydrogen ions to produce pure water and heat; the anode receives the electrons generated by ionization. Multiple proton exchange membrane fuel cells can be connected to form a fuel cell unit, which can increase the output of electric energy.

Fuel Cell Operating Mechanism

United Technologies Corporation is a global player in fuel cell product technology for military and civilian applications. Originally a business unit whose products were used in spacecraft, submarines, construction, buses and automobiles, United Technologies Power built and commercialized large stationary fuel cell power plants in the early 1990s. Since then, the company has been developing fuel cell technology for buses and automobiles for more than 10 years.

Since 2008, substantial progress has been made in the commercialization of fuel cells due to the breakthrough of technical bottlenecks such as cost and lifetime. The FCveloCity® fuel cell developed and produced by Ballard Power is a seventh-generation scalable modular fuel cell developed specifically for buses and light rail, which can be used to form a power supply of 30 to 200 kW. The 85kW-class FCveloCity® fuel cell, which was launched in June 2015, is mainly used for electric buses.

85kW class FCveloCity® type fuel cell

Application examples of modular fuel cells

Carbon fiber paper, a high-performance composite material, is an essential porous diffusion material for manufacturing the gas diffusion layer in the proton exchange membrane electrode of a fuel cell. The gas diffusion layer (GDL) constitutes the channel for gas diffusion from the flow tank to the catalyst layer and is the heart of the fuel cell. It is a very important support material in the membrane electrode set (MEA), and its main function is to serve as a bridge between the membrane electrode set and the graphite plate. The gas diffusion layer helps water, a by-product generated outside the catalyst layer, to flow away as soon as possible to avoid overflow caused by water accumulation; it also helps to maintain a certain amount of water on the surface of the membrane to ensure the electrical conductivity of the membrane; it helps to maintain heat transfer during fuel cell operation; in addition, it provides sufficient mechanical strength to maintain the membrane electrode set when water absorption expands Structural stability.

Carbon fiber paper, carbon fiber cloth and carbon fiber sheet for fuel cells

In both proton exchange membrane fuel cells and direct methanol fuel cells, the combined effect of using both carbon fiber paper and carbon fiber cloth as the gas diffusion layer is better. About 100m2 (i.e., 8kg) of carbon fiber paper is consumed for each fuel cell electric vehicle.

Alstom France has unveiled its newly developed world's first liquid hydrogen fuel cell electric train. The vehicle belongs to Alstom's regional trains. The newly released liquid hydrogen fuel cell electric train is all developed with mature technology, with hydrogen fuel cells on the roof and lithium batteries, converters and electric motors at the bottom of the passenger compartment, which will open up a larger market space for fuel cell applications and promote the further development of carbon fiber paper technology.

Source | Composite Materials, Advanced Materials

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