Materials that are produced naturally or artificially in order to make usable objects are called materials. There are many types of materials available today.
According to the type of materials; It can be classified as ceramic, metallic, polymer, composite, elastomer and glass materials. Although composite actually means a mixture, it does not consist of soluble and dissolving components. There is no exchange of atoms between the components. Materials consisting of at least two components with different properties that cannot be dissolved in each other in order to improve some properties that are not available or limited in traditional materials are called composite materials. Composite components do not affect each other chemically and are produced by human design. If the atomic size of the composite components is below 300 nano, such composites are called nano composites. If the materials dissolve in each other, such materials become alloys, not composites. In composite materials, the components that make up the structure are not desired to dissolve in each other, especially in metallic systems, some dissolution contributes to the formation of strong bonds between the components.
In composite materials, there is a reinforcement phase in various forms and proportions, and a matrix material that makes up the majority in volume around this material. Of these two material groups, the reinforcement material plays a role in the strength and load-bearing properties of the composite material, and the matrix material prevents the crack propagation that may occur in the transition to plastic deformation and delays the rupture of the composite material.
Another purpose of the material used as the matrix is to hold the fiber materials together under load and to distribute the load homogeneously between the fibers. Thus, crack propagation that will occur when plastic deformation occurs in fiber materials is prevented. The advantage of composite materials is that they combine the best properties of their components. With the production of composite materials, it is aimed to develop one or more of the following properties.
High temperature performance
Thermal and acoustic conductivity
Ease of manufacture
History of Composite
The earliest composite materials were made from straw and mud, which were combined to form bricks for building construction. Ancient brick making has been documented by Egyptian tomb paintings.
Wattle and daub is one of the oldest composite materials, over 6000 years old. Concrete is also a composite material and is used more than any other synthetic material in the world.
Both real wood from trees and plants such as palm and bamboo produce natural composites that were used by humanity in prehistoric times and are still widely used in construction and scaffolding.
Plywood by the Ancient Mesopotamians 3400 BC; Bonding wood at different angles gives better properties than natural wood.
Cartonage layers of linen or papyrus dipped in plaster date to the First Intermediate Period of Egypt. A. They were used for 2181–2055 BC and death masks.
Cob mud bricks or mud walls (using mud and straw or gravel as a binder) have been used for thousands of years.
Concrete was described by Vitruvius in Ten Books on Architecture around 25 BC, writing down the outstanding types of aggregates suitable for the preparation of lime mortars. For structural mortars he recommended pozzolana, volcanic sands from Pozzuoli’s beds of brownish yellow-gray sands near Naples and reddish-brown sands in Rome. Vitruvius states the ratio of 1 part lime/3 parts pozzolan for cements used in buildings and 1:2 lime/pulvis Puteolanus ratio for underwater works, essentially the same ratio mixed for concrete used in the sea today. Natural cement-stones, after being burned, produced cements that were used in concrete from post-Roman times until the 20th century, with some properties superior to manufactured Portland cement.
Papier-mâché, a combination of paper and glue, has been used for hundreds of years.
The first man-made fiber reinforced plastic was a combination of fiberglass and bakelite made in 1935 by Al Simison and Arthur D Little at the Owens Corning Company.
One of the most common and well-known composites is fiberglass, in which small glass fibers are embedded in a polymeric material (normally an epoxy or polyester). Glass fiber is relatively strong and rigid (but also brittle), whereas the polymer is ductile (but also weak and flexible). The resulting fiberglass is relatively tough, strong, flexible and ductile.
Classification of Composites (According to Reinforcement Element)
Composite materials can be divided into five classes according to the shape of the reinforcing element used. These are particle-reinforced, fiber-reinforced, sheet, layered and filled composite materials.
This type of composites are materials formed by macroscopic or microscopic particles with a matrix. The average embedded particle size is greater than 1 mm and the reinforcement volume ratio is generally not more than 50%.
Fiber reinforced composites:
In such materials, the matrix transmits the load from the composite to the fiber, most of the load is carried by the fiber and its properties are anisotropic. Fiber forms are used directionally as braided, ribbon roving or sheets.
They are composites consisting of plate-shaped reinforcement elements in the matrix phase. The al-graphite system can be sheets, flakes, glass, mica and metal. The most known metal sheets are AlB2 and Be sheets.
Such composites are obtained by combining plates with different components in the form of sandwiches (on top of each other). These composites consist of unidirectional or bidirectional fiber-reinforced layers randomly oriented into the matrix.
They are composites produced by filling the reinforcement material form with a continuous skeleton structure with a matrix material. It is obtained by impregnating the matrix material to the preform (foam) structure with pressure, without pressure or by casting.
Classification of Composites (According to the Matrix Material Used)
Composite materials are divided into five main classes according to the type of matrix material used. These are polymer matrix, metal matrix, ceramic matrix, carbon/carbon and nano composite materials.
Metal matrix composites (MMC):
These materials are composites in which the matrix metal is the main structure and a ceramic reinforcement phase is generally used as the reinforcement element. There are almost no restrictions on the choice of these materials. Considering the experimental studies, it is striking that many different types are used. In the last 45-50 years, a lot of research has been done on MMKs and it has taken a positive place in the literature. Metal matrix composites are the greatest alternative to conventional materials. By combining the high elastic modulus of ceramics with the plastic deformation properties of metals, materials that are resistant to abrasion, have high fracture toughness and compressive stress are obtained. These composites are widely used in the automotive, aerospace and defense industries.
Ceramic matrix composites (SMK):
Ceramic materials are very hard and brittle. They also have high temperature resistance and relatively low density properties. Ceramic materials are materials with low thermal shock resistance and toughness. These; Al2O3, SiC, Si3N4, B4C, cBN, TiC, TiB, TiN and AIN. These compounds are in different structures and ceramic matrix composites are obtained by using one or more of them together according to the purpose. Sandwich armors, the production of various military-purpose parts and space vehicles are the main areas of use of these products. Carbon, ceramic and glass fibers added to the ceramic matrix are developed especially for special conditions such as high temperature applications. When ceramic materials are reinforced with ceramic fibers, the strength increases and the toughness increases. Recent studies on alumina and zirconia-based ceramic composites have led to the use of these materials not only in applications such as rocket heads and spacecrafts, but also as biomaterials in the human body.
Polymer matrix composites (PMK):
Polymer matrices, which are widely used as continuous fiber reinforced, are divided into two groups as thermoset and thermoplastics. The most important of these composites are polyester and epoxy resin matrix reinforced with continuous fibers. The main reinforcement materials used are glass fiber, kevlar fiber, boron fiber and carbon fibers. The most commonly used methods in the production of PMKs are hand spinning, wire wrapping, pouch molding process, pultrusion method, liquid flow technique, reinforced reaction, injection molding, extrusion and thermo formation methods. The main areas of use of PMKs are marine applications due to their corrosion resistance, automotive and other transportation industries due to their lightness, sports equipment, automotive interior decoration where non-flammability is required.
Carbon-carbon composites (CCC):
Carbon – carbon composites are obtained from the mixture of pure carbon particles (defined as the primary carbon component) with a carbon-based binder (this material forms the secondary carbon component during the carbonization process). After all, the material is all carbon, and carbons exist in two different forms. One of them is filler (primary) and the other is carbon, which is a binder (secondary). The heat capacity per unit weight of carbon used as a matrix material is quite high. It is used in rocket nozzles, protective shields in space vehicles, clutch and brake lining-disc systems. Although these materials provide relatively low volume for applications in the military and space fields that require high technology, they are very expensive materials with high added value.
Nano composites (NK):
Nanocomposites are mineral nano-filled composite materials containing less than 10% nano-sized minerals. Due to the high aspect ratio and surface area of the nano-sized particles used, the mechanical, non-flammability, thermal and barrier properties of composites can be improved very well. In the production of these composites, molten metal mixing, powder metallurgy and mechanical alloying are mostly used.
Production Methods of Composites
Since traditional materials such as metal, ceramic and polymer do not meet the needs in today’s technology, there is a tendency towards composite materials. The superior mechanical properties of composite materials compared to conventional materials have led to more intensive studies on their production techniques in recent years. However, the production cost of these composites is still high and some problems are encountered in the production stages.
In choosing the production method of composite materials; matrix, reinforcement element, desired mechanical and physical properties and part shape are taken into consideration. The production methods of composite materials can be grouped under two main headings as liquid state production techniques and solid state production techniques.
Usage Areas of Composites
The use of composite materials has been increasing in recent years. It is possible to see composite material applications in almost every field and in every sector. Various products made of fiberglass, glass, felt and glass woven and polyester resin are widely used in daily life. Glass fiber ratio is between 30-40%. Tea tray, table-chair, warehouse, bathtub, boat, boat and automotive industry are the application examples of these composites. In addition, formica, printed circuit board, electrician fibers, sports equipment and jumping poles, welding gear, tennis rackets and racing canoes are products made of different composite materials. The use of composite materials in the automotive, aerospace and aviation industries is primarily due to their lightness and durability. The aim is to consume less fuel, reach higher speed and provide efficiency. In this use, not only financial gain is considered, but also strategic performances. In particular, qualities such as vibration, fatigue and heat resistance are the leading advantages of composite materials in the aerospace industry. In recent years, the use of composite materials has become widespread, especially in space and aircraft vehicles. For example, more than 30% polymer matrix composites were used in Boeing757 and 767 aircraft. The wings and fuselage of Douglas AV8B Harier fighters are made of carbon fiber reinforced composites. Voyager aircraft used petroleum resistant composite material. Corvette, Ferrari, Avanti, Toyota and Ford automobile companies use composite materials in their vehicle production. America has used composite materials in satellite and satellite equipment, while NASA studies and develops composite materials in its research.
Composite materials are increasingly used in space and aerospace vehicles due to their valuable qualities. Today, the use of composite materials in a fighter bomber has reached half of the total aircraft weight. In this way, boron carbide, silicon carbide, alumina carbon, glass and kevlar fibers are used in the production of various composite materials with different resins. Although the use of composite materials in the production of weapons is not very common, there have been some studies for small diameter mortars such as 60 and 81 mm, which can withstand up to 3000 bar. Due to their lightness, these weapons increase the combat performance of the infantry. The role of composite materials in rocket production is quite large. For example, the engine launcher is made of fiberglass and epoxy in the M72, the fuselage is partly made of kevlar and epoxy in the apilast and other anti-tank rockets, and the nozzles are made of carbon composite in the M77 MLRS.
Composite materials are also partially used in ammunition production. In the M19 A/T mine, the body is made of ABS resin and glass fiber particles, and the small and large belleville springs of this mine are made of glass tissue and phenolic resin. The 155mm ICM ammo bodies have a fiberglass epoxy wrap. Kevlar and various resins are used for helmets. In bulletproof vests, armor plates for ballistic tests, glass and phenolic resins are produced from braided kevlar today.
High Tensile Composites
It is another type of high-performance composites designed to operate in a high-deformation environment and often used in deployable systems where structural flexing is advantageous. Although high tensile composites show many similarities to shape memory polymers, their performance is often dependent on fiber arrangement, as opposed to the resin content of the matrix.
Composites can also use metal fibers that reinforce other metals, such as in metal matrix composites (MMC) or ceramic matrix composites (SMK); these are bone (hydroxyapatite reinforced with collagen fibers), cermet (ceramic and metal) and concrete. Ceramic matrix composites are built primarily for fracture toughness, not strength. Another class of composite materials includes the woven fabric composite made of longitudinally and transversely bonded yarns. Woven fabric composites are flexible because they are in the form of fabric.
In addition, thermoplastic composite materials can be formulated with special metal powders resulting in materials with a density range of 2 g/cm3 to 11 g/cm3 (same density as lead). The most common name for this type of material is “high gravity compound” (HGC), but “lead substitution” is also used. These materials replace traditional materials such as aluminum, stainless steel, brass, bronze, copper, lead and even tungsten for weighting, balancing (for example, changing the center of gravity of a tennis racket), vibration damping and radiation shielding applications. High-density composites are an economically viable option when certain materials are considered hazardous and prohibited (such as lead) or when secondary processing costs (such as machining, finishing or coating) are a factor.
There have been several studies showing that interleaving flexible thermoplastic laminates with tough and brittle epoxy-based carbon fiber-reinforced polymer laminates can help make highly cured composites with improved impact resistance. Another interesting aspect of such interspersed composites is that they can be applied to any shape memory polymers or shape memory alloys, e.g. The balsa layers interspersed with hot glue are interwoven with aluminum layers, acrylic polymers or carbon fiber reinforced polymer laminates interspersed with PVC and polystyrene.
A sandwich-structured composite is a special class of composite material produced by bonding two thin but hard shells to a light but thick core. The core material is normally a low strength material, but its higher thickness gives the sandwich composite high flexural rigidity and generally low density.
Wood is a naturally occurring composite. Engineered wood includes a wide variety of different products such as wood fiber board, plywood, oriented strand board, wood plastic composite (recycled wood fiber in a polyethylene matrix), Pykrete (sawdust in an ice matrix), Plastic impregnated or laminated paper or textiles. Other engineered laminate composites such as Mallite use a central core of end grain balsa wood bonded to light alloy or FRP surface coatings. They produce low weight, high hardness materials.
Particulate composites have particulate as filler dispersed in the matrix, which can be non-metal, such as glass, epoxy. An automobile tire is an example of a particulate composite.
Fiber Reinforced Composites
High-performance products that need to be lightweight have generally gained popularity despite their high cost. For instance; aviation components (tails, wings, hulls, propellers), boat and paddle hulls, bicycle hulls and race car hulls. Other uses include fishing rods, storage tanks, swimming pool panels and baseball bats. The Boeing 787 and Airbus A350 structures, including the wings and fuselage, are largely composed of composites. Composite materials are also becoming more common in orthopedic surgery and are the most common hockey stick material.
Carbon composite is an important material in today’s launch vehicles and heat shields for the spacecraft re-entry stage. It is widely used in solar panel surfaces, antenna reflectors and spacecraft’s forks. It is also used in payload adapters, interstage structures and heat shields of launch vehicles. In addition, carbon / carbon material is used in the disc brake systems of airplanes and racing cars, and composite materials with carbon fiber and silicon carbide matrix have been used in luxury vehicles and sports cars.
In 2006, a fiber-reinforced composite pool panel was introduced for both residential and commercial in-ground swimming pools as a non-corrosive alternative to galvanized steel.
In 2007, an all-composite military Humvee was introduced by TPI Composites Inc and Armor Holdings Inc, the first all-composite military vehicle. By using composites the vehicle is lighter and allows higher payloads. In 2008, carbon fiber and DuPont Kevlar (five times stronger than steel) were combined with thermosetting resins developed to create military shipping cases by ECS Composites, creating high-strength 30 percent lighter cases.
Pipes and fittings for various purposes such as drinking water, firefighting, irrigation, seawater, desalinated water, chemical and industrial waste, and sewage are now manufactured from glass-reinforced plastics.
Composite materials used in tensile structures for facade application provide the advantage of being translucent. Woven base fabric combined with suitable coating provides better light transmission. This provides a very comfortable level of illumination compared to the full brightness of the outside.
The blades of wind turbines that grow to 50 m in length have been produced as composites for several years.
High-pressure gas cylinders, typically around 7-9 liters volume x 300 bar pressure for firefighters, are nowadays made of carbon composite. Type-4 cylinders contain metal only as a thread-bearing head for screwing into the valve.
Advantages - Disadvantages of Composites
Advantages of composites
It has superior physical and mechanical properties.
They show high resistance against bending and pulling.
Density / Strength ratios are high.
Fatigue resistance is high.
Many composite materials have corrosion resistance.
Optionally, insulation and conductivity can be added.
They are not affected by harmful chemicals, environmental and weather conditions.
If suitable matrix material is selected, they can operate at high temperatures.
They are flexible in making the desired design.
Manufacturing using composite material takes its final form. No further action is required afterwards.
It is not possible to assemble more than one piece of conventional material without using rivets or welding. In composite material, many complex parts can be made.
Since the number of parts will be less, there is ease of assembly.
It can gain high resistance against impacts.
A certain amount of ductile structures dampen vibration and sound.
It may have low phase and toxicity properties according to the selected matrix.
They do not need high temperature and pressure in their production. The cost for production machines is reduced.
Disadvantages of Composites
Some of the composites work in a certain direction. It can show different mechanical properties in different directions.
Material costs are higher.
It is not easy for them to be processed and their surface to be of high quality.
Its thermal resistance varies according to the matrix used. Generally, polymer-based matrices are used and therefore the thermal properties of composites are limited to plastics.
Its resistance to chemicals and environmental conditions varies according to the matrix used. For this reason, some of the composites have low resistance to environmental effects.
Because some composites absorb moisture from the air, their dimensional stability is affected.
Some of the brittle (brittle) composites do not show resistance to impact. They are easily damaged and difficult to repair.
Since their elongation at break is low, they limit their usage areas.
In the production of composites such as polymer-based matrix, toxic and carcinogenic gases are released.
Recycling is less.
How is Composite Material Produced?
- Plasma Spraying
Liquid Metal Impregnation
Compression or Liquid Forging Casting
Liquid Metal Mixing
Resin Injection Molding Technique (RTM)
Pressure and Non-Pressure Infiltration
Diffusion Bonding and Vacuum Pressing
Hot Pressing and Hot Isostatic Pressing
Production can be made using the Prepreg Molding Technique.
Composite Usage Areas
Due to the high strength and lightness of the composite material, its usage area is wide.
Materials with different internal structures are used in the construction industry and their internal structures must have the desired properties. Lifespan is also very important for this industry. Therefore, the material structure should be produced in accordance with the conditions in which the material will be applied. Facade protections, holiday homes, kiosks, bus stops, cold storages, construction molds are composite material applications. The design is flexible and easy, providing great advantages in transportation and assembly.
For example, void-free and dense material for strength and water impermeability, solid material for soundproofing and heat insulation should be produced with the required amount and size of voids to provide sound absorbing and reduce heat conduction.
As composite technology develops in the world, the use of technology in the defense industry has also increased. Composite materials have an important place in this sector because they can be made more durable and lighter than the components that make up them with various combinations. Taking advantage of this situation, composite armors were started to be developed by applying them to armors, which are indispensable for the defense industry.
Space Technology and Aviation Sector
When we look at the usage areas of composite, we see that there are very wide application areas in the aviation industry. Based on the superior mechanical properties of composite materials compared to their lightness, it is used in the interior design of aircraft and helicopters, and in the production of structural materials.
Compressor Blades, Body, Internal Equipment: B/Al, SiC/Al, Gr/Al
Turbine Blades: Wolfram and Tantalum reinforced materials.
Helicopter Parts: B/Al, SiC/Al, Gr/Al, Gr/Mg, Al2O3/Mg, Al2O3/Al
The purpose of using composites in the automotive industry is to lighten the skeleton of the vehicle and increase its impact resistance. Based on fluid dynamics, the acceleration time and fuel efficiency of the vehicle can also vary depending on the use of composite material.
windshield wiper; 30% Glass+PBT
filter box; Mercedes, 35% Glass+ Polyamide 66
pedals; 40% Glass+ Polyamide 6
Rear View Mirror; 30% Glass+ABS
Headlight Body; BMW, 30% Glass + PBT
Air Inlet Manifold; BMW, Ford, Mercedes, 30% Glass+ Polyamide 6
Automobile Dashboard; GMT
Car Spoilers; FRP
Automobile Side Body Frame; Ford, CTP
Auto Body; Corvette, SMC CTP
Tractor body, cabin, seating unit; SMC
public transport seating; SMC
Bus ventilation ducts, roof rack parts, instrument panel; FRP
Open field service (Golf car) vehicles body, roof; FRP
container base; GMT (Pressable reinforced thermoplastic)
Cable car; FRP
Another area where composite is widely used is the healthcare field. Composite material is used as an internal and external connection system for broken bone repair in orthopedics. In dentistry, composite resins are used as tooth filling, and epoxy resin reinforced with collagen fiber is used as tooth support material. In addition, orthodontic wires; They are made of nylon, polypropylene, polymethylmethacrylate reinforced with glass fiber. Polymethylmethacrylate composites reinforced with collagen, glass or kevlar are used as bridges due to their low cost and easy preparation.
Other Uses of Composite
Musical Instruments Industry
Food and Agriculture Sector
Sports Equipment Manufacturing (high jump poles, tennis rackets, surfing, racing boats, skiing etc.)