Q1) State the Classification of Composite Material.

A1) Microspheres

They're thought to be among the most useful filters. The most extreme property for switching products without losing profitability or physical qualities is gravity, fixed particle amplitude, power, and managed density. Stable microspheres have a low density, which affects the completed product's commercial value and weight. Their specific strength is covered in the finished mould in which they form a component, according to studies. Hollow microspheres are silicate-based structures with a controlled specific gravity.

They're bigger than the stationary glass spheres used in polymers, and they come in a variety of particle sizes.

Filled Composites

The filler might be a primary component or a secondary component in a composite. Filler particles can be random in shape or contain precise geometric shapes like polyhedrons, tiny fibres, or spheres. Filled composer fillings can be used as a stand-alone component or as part of a composite.

Filler particles can be random in shape or contain precise geometric shapes like polyhedrons, tiny fibres, or spheres.

Flakes Structure:

Flakes are frequently substituted for fibre because they may be kept in dense packs. Metal flakes in polymer matrixes that are in close contact with each other can conduct electrical energy or heat while opposing mica flakes and glass.

Flexes will be inexpensive to create and will typically cost less than fibre.

Particulate Reinforced Composites:

Particle reinforced composites are metal and ceramic composites with microstructures that exhibit particles of one phase distributed throughout another. The square, triangular, and spherical reinforcement shapes are all recognised, but the proportions of all their sides are generally similar.

It differs from dispersion hardened material due to its size and volume concentration.

Laminar Composite:

Laminar composites can be regarded as materials in which layers of material are bonded together. They can be found as a number of materials in a variety of combinations.

As many layers of two or more metal components alternately or in a predefined order are required for a certain purpose, these can be made.

Fibre Reinforced Component:

Fibres are necessary for reinforcement because they meet specific requirements and impart strength to the matrix element, improving its qualities.

Q2) Write a Short note on Natural Composites.

A2) A composite is a material made by fusing two or more materials together to produce better qualities. Almost majority of the materials we perceive in our environment are composites. Woods, bones, and stones, for example, are natural composites since they are either formed in nature or formed through natural processes. Wood is a fibrous material made up of thread-like hollow elongated organic cellulose that makes up around 60-70 percent of wood, with 30-40 percent of it being crystalline and insoluble in water and the remainder being amorphous and soluble in water. Cellulose fibres have a high strength-to-weight ratio. The cellulose that is packed closer together has a higher density and strength. The principal load-bearing components of trees and plants are the walls of these hollow elongated cells. When trees and plants are alive, the load acting on a specific piece (for example, a branch) effects the growth of cellulose in the cell walls present there, reinforcing that part of the branch that is subjected to larger stresses. This self-strengthening mechanism is a one-of-a-kind phenomenon that may also be seen in living bones. Collagen fibres, which are inorganic calcium carbonate threads distributed in a mineral matrix called apatite, are found in bones. The fibres normally develop and become orientated in the load direction. Skeletons are the basic structural frameworks that sustain many sorts of static and dynamic loads in humans and animals. A tooth is a form of bone that has a flexible core and a hard enamel top. The tooth's compressive strength varies depending on its thickness. The exterior enamel is the most durable, having a compressive strength of up to 700 MPa. The tooth appears to contain piezoelectric capabilities, meaning that pressure causes reinforcing cells to develop. The low density, strong, and stiff fibres found in woods and bones are placed in a low density matrix, resulting in a strong, stiff, and lightweight composite (Table 1.1). It's no surprise that wood was used as one of the primary structural materials in the early development of aeroplanes, and that about two hundred million years ago, huge flying amphibians, pterendons and pterosaurs, with wing spans of 8-15 m, could soar from the mountains like modern-day hang-gliders. In many ways, woods and bones might be regarded forerunners to modern man-made composites.

Early men effectively employed rocks, forests, and bones in their quest for survival against natural and external pressures. The primitive humans used these materials to manufacture weapons, tools, and a variety of utility items, as well as shelters. They mostly used these materials in their original state in the beginning. They gradually learned to make better use of them by cutting and moulding them into more useful shapes. They then used additional materials like as vegetable fibres, shells, clays, as well as animal horns, teeth, skins, and sinews.

Q3) Explain the Matrix Composites.

A3) Ceramics offer significant oxidation resistance and give strength at high temperatures well exceeding 15000C. They have a high elastic modulus, a high Peierls yield stress, low thermal expansion, poor thermal conductivity, a high melting point, superior chemical and weather resistance, and great electromagnetic transparency, among other properties. Ceramics, on the other hand, have a significant disadvantage in terms of plasticity. Ceramics' limited strain capability is a key source of concern, as it frequently leads to catastrophic failure. As a result, ceramics are not regarded as structurally sound materials. Ceramic matrix composites, on the other hand, may not have such limits, as appropriate reinforcements may help them attain desirable mechanical qualities, such as toughness. Glass, glass ceramics (lithium aluminosilicates), carbides (SiC), nitrides (SiN4, BN), oxides (Al2O3, Zr2O3, Cr2O3, Y2O3, CaO, ThO2), and borides are the most common ceramic matrices (ZrB2, TiB2). Particles, flakes, whiskers, and threads can be used as reinforcements, which are usually high-temperature inorganic materials such as ceramics. Carbon, silicon carbide, silica, and alumina are the most often utilised fibres. Ceramic matrix composites are experiencing a comeback in research and development due to their resistance to wear, creep, low and high cycle fatigue, corrosion, and impact, as well as their high specific strength at high temperatures. An alumina-SiC whisker cutting tool has a ten-fold higher cutting rate than traditional tools. Because of its high specific strength at high temperatures, ceramic composites can be used in aero-engine and automobile engine components to reduce weight and hence improve engine performance with higher thrust to weight ratios. Because of its light weight, automotive engines have higher efficiency, better performance at high operating temperatures, and a longer life due to exceptional heat and wear resistance. Table 2.9 lists a number of high-temperature uses for ceramic matrix composites.

Carbon-carbon composites are the most common type of ceramic matrix composite that can resist temperatures of up to 30000 degrees Celsius. They are made up of carbon fibres that are arranged in a carbon matrix. Pyrolysis of polymer impregnated carbon fibre fabrics and preforms under pressure or chemical vapour deposition of carbon or graphite are used to create them. The thermosets (furfurals, phenolics), thermoplastic pitches (coal tar and petroleum based), and carbon-rich vapours are the three types of polymers employed (hydrocarbons such as methane, propane, acetylene, benzene). In the production of carbon-carbon composites, phenolic resins are more typically used. On pyrolysis, the phenolic resin impregnated carbon fibre preforms transform to a significant fraction of amorphous carbon char. After the initial pyrolysis, the composite material is discovered to be porous. It is then impregnated with phenolic resin and pyrolised, usually under vacuum and pressure, with the process being repeated numerous times to reduce void content and achieve the material's ideal density. The main advantage of carbon-carbon composite is that different fabrics and shapes of preforms with multidirectional fibre alignments can be impregnated with resins and pyrolised to produce a wide range of one directional (1D), two directional (2D), three directional (3D), and multidirectional composite blocks of various shapes and sizes, which can then be machined to produce the desired dimensions. They are useful materials in high temperature applications because of their excellent wear resistance, increased coefficient of friction as temperature rises, high thermal conductivity, low thermal expansivity, and high temperature resistance. Carbon-carbon composites can sustain extremely high temperatures (30000C or more) for extended periods of time in the absence of oxygen. Because of their high biocompatibility, they're also used in prostheses.

Q4) Explain the term Reinforcements.

A4) Fibres make up the lion's share of the reinforcements utilised in structural composites. A fibre is defined as a material with a minimum 1/d ratio of 10:1, where 1 is the fibre's length and d is its smallest lateral dimension. The lateral dimension d (in the case of a circular fibre, the diameter) is considered to be smaller than 254 m. Fibre diameters used in structural composites typically range from 5 to 140 metres. A filament is a continuous fibre with an infinity l/d ratio. A whisker is a single crystal with a fibre-like appearance.

Lighter materials, particularly those based on low-atomic-number elements, are used to make common low-density fibres (e.g., H, Be, B, C, N, O, Al, Si, etc.). A fibre's cross-section can be circular, as in glass, boron, and Kevlar fibres, although certain fibres can have regular prismatic cross-sections (such as whiskers) or random cross-sections (e.g., PAN, rayon and special pitch based carbon fibres). Anisotropy in the fibre may be introduced by the uneven cross-section. Figure 2.1 depicts the typical microstructural morphology of common fibres.

Fibres can be amorphous (glass), polycrystalline (carbon, boron, alumina, etc.) or single crystals in terms of microstructure (silicon carbide, alumina, beryllium and other whiskers). A fibre's strength and stiffness qualities are much greater than those of the bulk material from which it is made. The majority of ordinary fibres are fragile by nature. Because the shape and magnitude of a fault that the bulk material may possess controls the tensile strength, it is significantly lower than the theoretical strength. Because a fibre's diameter is so small, any flaws it may include must be less than the diameter of the fibre. The criticality of the fault is reduced as a result of the lower flaw size, and thus the tensile strength is improved. An conventional glass (bulk) may have a tensile strength of 100-200 MPa, but an S-glass fibre may have a tensile strength of 5000 MPa. A flawless glass fibre, on the other hand, has a tensile strength of 10350 MPa based on intermolecular forces. Furthermore, crystallite arrangement along the fibre direction aids in significantly enhancing the strength qualities. A whisker is a single crystal that, unlike polycrystalline fibres, is not prone to crystal flaws and has extremely high strength and stiffness qualities. A graphite whisker has tensile strength and modulus of up to 25000 MPa and 1050 GPa, respectively. When compared to commercial fibres, these figures are fairly considerable. A commercially available PAN-based T300 fibre has typical longitudinal tensile parameters of 2415 MPa (strength) and 220 GPa (tension) (modulus). Tables 2.1 and 2.2 list typical thermomechanical and thermal characteristics of common fibres, respectively.

Structural composites can be made with both inorganic and organic fibres. Glass, boron, carbon, silicon carbide, silica, alumina, and other inorganic fibres (including ceramic fibres) are the most widely utilised. The number of structural grade organic fibres is relatively small. The most widely used organic fibre is aramid. Another recent addition is Spectra 900, a high-strength polyethylene fibre with a low density and great impact resistance. Carbon fibres are sometimes lumped in with organic fibres, however they're more commonly thought of as ceramic (inorganic) fibres. Inorganic fibres are robust, rigid, thermally stable, and moisture resistant in general. They are fatigue resistant, but have a low energy absorption capacity. Organic fibres, on the other hand, are less expensive, lighter, and more flexible than synthetic fibres. They have a higher strength and are more impact resistant.

Q5) Factors That Determine the Mechanical Properties of a Metal

A5) Many aspects must be addressed while selecting materials for engineering uses. Manufacturers are aware that each metal alloy has its own set of qualities that react differently to mechanical and chemical processes. Understanding these qualities and determining which alloy is best suited for the work at hand is critical in order to maximise the efficiency and cost savings of any job.

Grain size, heat treatment, air exposure, and temperature are all important elements in determining the mechanical characteristics of metal. These characteristics work together to influence how a metal reacts to the stresses it encounters in industrial operations. Manufacturers must thoroughly test alloys to determine how they will be affected and under what conditions they will fail.

Different procedures have different effects on metals. The concept of stress and strain is an important one. When comparing specimens of different sizes, the load per unit area, also known as normalisation to the area, must first be calculated. The force is divided by the area to calculate stress. The relevant area while conducting tension and compression testing is perpendicular to the force. For shear or torsion testing, on the other hand, the relevant region is perpendicular to the rotation axis.

Metal alloys can react in unfavourable ways as a result of stress and strain, so they must be thoroughly examined. The term "elastic deformation" refers to a condition in which the material can return to its original dimensions if the stress is eliminated. The ability to remain stable under stress, as well as the fact that the deformation is reversible and non-permanent, is indicated by the elasticity. Plastic deformation, on the other hand, indicates that the metal is unable to return to its original shape after the stress is removed. Instead, the tension has resulted in irreversible permanent deformity.

Metal's mechanical characteristics are influenced by a variety of factors. Changes in grain size, for example, affect yield strength, hardness, the ductile-brittle transition temperature, and susceptibility to environmental conditions, all of which can be improved.

Metals, such as aluminium, are made up of crystals, which are also called grains. Fine-grained aluminium is defined as having a tiny grain size, whereas coarse-grained aluminium has a big grain size. Fine grain aluminium alloys have higher tensile and fatigue strength than coarse grain aluminium alloys. Work hardening is easier with these alloys. Aluminum with coarser granules has a rougher surface and is harder to polish. The fact that coarse-grained aluminium is less robust and thus more likely to suffer irreversible distortion under stress is another effect of grain. Coarse-grained aluminium, on the other hand, provides advantages in terms of workability, hardenability, and forgeability. They also have distinct reactions at different temperatures. Fine-grained aluminium is stronger and tougher at room temperature, whereas coarse-grained aluminium has greater creep resistance at higher temperatures. The link can be determined using a simple formula: the strength of a metal is inversely related to the square root of the grain size. Temperature has an impact on a metal's mechanical properties, such as its tenacity and elastic limit. Heat treatment improves the mechanical qualities of aluminium and other metals, such as ductility, hardness, tensile strength, toughness, and shock resistance, and is used in many industrial operations. When it comes to aluminium alloys, heat treatment has various advantages. It has the ability to refine grain and increase machinability. Working with metal, whether hot or cold, causes internal tension, and heat treatment is one technique to relieve that tension. A changed grain structure and increased corrosion resistance, as well as more favourable chemical, magnetic, electrical, and thermal characteristics, are all added benefits.Atmospheric corrosion is a serious concern for metals, and it must be taken into account by producers. When metals are exposed to the atmosphere for long periods of time, they oxidise. This oxidation of the metal surface forms a coating, which is more common in the presence of moisture, sulphur dioxide, and hydrogen sulphide, and lowers the material's electrical resistivity.The atmospheric effect is influenced by a number of elements, including the metal's properties, the protective surface film's quality, the presence of particular chemicals that might lessen corrosive effects, and the presence of surface fissures or discontinuities.

Q6) Write a short note on Benefits of Composites.

A6) Almost any article which can be produced in traditional materials such as metals can be manufactured from composites. Whilst the use of composites will be a clear choice in many instances, material selection in others will depend on factors such as working lifetime requirements, number of items to be produced (run length), complexity of product shape, possible savings in assembly costs and on the experience and skills of the designer in tapping into the optimum potential of composites. In some instances, best results may be achieved through the use of composites in conjunction with traditional materials. Let’s have a brief look at the benefits of composites.

Light Weight

Composites are light in weight compared to most woods and metals. Their lightness is important in automobiles and aircraft, for example, where less weight means better fuel efficiency. Designers of airplanes are greatly concerned with weight, since reducing a craft’s weight reduces the amount of fuel it needs, and increases the speeds it can reach. Some modern airplanes are built with more composites than metal – including the Boeing 787 Dreamliner.

High Strength

Composites can be designed to be far stronger than aluminium or steel. Metals are equally strong in all directions. But composites can be engineered and designed to be strong in a specific direction.

Strength Related to Weight

Strength-to-weight ratio is a material’s strength in relation to how much it weighs. Some materials are very strong and heavy, such as steel. Other materials can be strong and light, such as bamboo poles. Composite materials can be designed to be both strong and light. This property is why composites are used to build airplanes—which need a very high strength material at the lowest possible weight. A composite can also be made to resist bending in one direction, for example. When something is built with metal, and greater strength is needed in one direction, the material usually must be made thicker, which adds weight. Composites can be strong without being heavy. Composites have the highest strength-to-weight ratios in structures today.

Corrosion Resistance

Composites can withstand the elements as well as severe chemicals that can eat away at other materials. Where chemicals are handled or stored, composites are a viable alternative. Outside, they can withstand extreme weather and temperature swings.

High-Impact Strength

Composites can withstand the elements as well as severe chemicals that can eat away at other materials. Where chemicals are handled or stored, composites are a viable alternative. Outside, they can withstand extreme weather and temperature swings.

Design Flexibility

Composites are easier to mould into complex shapes than most other materials. This allows designers to build practically any shape or form they choose. Fiberglass composites, for example, are used in the construction of most recreational boats today because they can be easily moulded into complicated shapes, improving boat design while cutting prices. Composites' surfaces can be moulded to resemble any surface finish or texture, from smooth to pebbly.

Part Consolidation

A single piece made of composite materials can replace an entire assembly of metal parts. Reducing the number of parts in a machine or a structure saves time and cuts down on the maintenance needed over the life of the item.

Dimensional Stability

When composites are hot or cold, wet or dry, they keep their shape and size. Wood, on the other hand, swells and shrinks in response to changes in humidity. In circumstances where tight, consistent fits are required, composites may be a preferable option. They're employed in aircraft wings, for example, to keep the shape and size of the wings consistent as the plane gains or loses altitude.

Nonconductive

Nonconductive means that composites do not conduct electricity. This feature qualifies them for applications like as electrical utility poles and electronic circuit boards. Some composites can be made conductive if electrical conductivity is required.

Nonmagnetic

Because composites do not include any metals, they are not magnetic. They can be used around electronic equipment that is sensitive. Large magnets used in MRI (magnetic resonance imaging) equipment function better because of the lack of magnetic interference. Both the equipment housing and the table are made of composites. In addition, composite rebar was used in the room's construction to reinforce the hospital's concrete walls and flooring.

Radar Transparent

Composites are great materials for use whenever radar equipment is used, whether on the ground or in the air, because radar signals pass directly through them. Composites are used extensively in stealth aircraft, notably as the US Air Force's B-2 stealth bomber, which is virtually radar-invisible.

Low Thermal Conductivity

Composites are good insulators—they do not easily conduct heat or cold. They are used in buildings for doors, panels, and windows where extra protection is needed from severe weather.

Durable

Composite structures have a long lifespan and require little maintenance. We don't know how long composites survive because many original composites haven't reached the end of their useful life. Many composites have been in use for over 50 years.

Q7) Enlist and explain any 4 Benefits of Composites.

A7) Strength Related to Weight.

Strength-to-weight ratio is a material’s strength in relation to how much it weighs. Some materials are very strong and heavy, such as steel. Other materials can be strong and light, such as bamboo poles. Composite materials can be designed to be both strong and light. This property is why composites are used to build airplanes—which need a very high strength material at the lowest possible weight. A composite can also be made to resist bending in one direction, for example. When something is built with metal, and greater strength is needed in one direction, the material usually must be made thicker, which adds weight. Composites can be strong without being heavy. Composites have the highest strength-to-weight ratios in structures today.

Corrosion Resistance

Composites can withstand the elements as well as severe chemicals that can eat away at other materials. Where chemicals are handled or stored, composites are a viable alternative. Outside, they can withstand extreme weather and temperature swings.

High-Impact Strength

Composites can withstand the elements as well as severe chemicals that can eat away at other materials. Where chemicals are handled or stored, composites are a viable alternative. Outside, they can withstand extreme weather and temperature swings.

Design Flexibility

Composites are easier to mould into complex shapes than most other materials. This allows designers to build practically any shape or form they choose. Fiberglass composites, for example, are used in the construction of most recreational boats today because they can be easily moulded into complicated shapes, improving boat design while cutting prices. Composites' surfaces can be moulded to resemble any surface finish or texture, from smooth to pebbly.

Q8) Describe the Reinforcement matrix interface. 

A8) The matrix is a completely continuous monolithic material into which the reinforcement is embedded. Unlike two materials sandwiched together, there is a channel through the matrix to any location in the material. The matrix is commonly a lighter metal, such as aluminium, magnesium, or titanium, in structural applications, and offers a compliant support for the reinforcement. Cobalt and cobalt-nickel alloy matrices are used in high-temperature applications.

The matrix constituent is a typical way to classify composite materials. Organic Matrix Composites (OMCs), Metal Matrix Composites (MMCs), and Ceramic Matrix Composites are the three basic composite classifications (CMCs). The term "organic matrix composite" is widely used to refer to two types of composites: polymer matrix composites (PMCs) and carbon matrix composites, often known as carbon-carbon composites.

Three common forms of composites result from these three sorts of matrices.

1. Ceramic fibres are used in a plastic matrix in polymer matrix composites (PMCs), of which GRP is the most well-known example.

2. Silicon carbide fibres are commonly inserted in an alloy of aluminium and magnesium in metal-matrix composites (MMCs), but other matrix materials such as titanium, copper, and iron are increasingly being employed. Bicycles, golf clubs, and missile guidance systems are all examples of MMC applications; an MMC constructed of siliconcarbide fibres in a titanium matrix is now being researched for use as the skin (fuselage material) of the US National Aerospace Plane.

3. Ceramic-matrix composites (CMCs) are the third major category, with silicon carbide fibres set in a borosilicate glass matrix as an example. They are particularly well suited for usage in lightweight, high-temperature components, such as parts for aeroplane jet engines, due to their ceramic matrix.

Several factors influence the selection of a matrix alloy for an MMC. It's crucial to know if the composite will be reinforced constantly or intermittently. When continuous fibres are used as reinforcements, the majority of the load is transferred to the reinforcing filaments, and composite strength is mostly determined by fibre strength. The matrix alloy's principal functions are to transport load efficiently to the fibres and to soften cracks in the case of fibre failure, hence the matrix alloy for continuously reinforced composites may be chosen for toughness rather than strength.

In continuously reinforced composites, lower strength, more ductile, and harder matrix alloys may be used. The matrix may control composite strength in discontinuously reinforced composites. The choice of matrix will then be determined by the necessary composite strength, which may necessitate the use of higher strength matrix alloys. Potential reinforcement/matrix reactions, either during processing or in service, which could result in degraded composite performance; thermal stresses due to thermal expansion mismatch between the reinforcements and the matrix; and the influence of matrix fatigue behaviour on the cyclic response of the composite are all factors to consider when choosing the matrix. Indeed, the behaviour of composites under cyclic loading situations is something that needs to be taken into account. The difference in melting temperatures between the matrix and the reinforcements is an additional issue in composites intended for use at high temperatures. Even at temperatures near the matrix melting point, a substantial melting temperature differential can cause matrix creep while the reinforcements remain elastic. When there is a tiny melting point difference in the composite, however, creep in both the matrix and reinforcement must be considered.

Q9) What are Natural Fibres?

A9) The term "natural fibre" refers to fibres that are acquired from (or produced by) animals and plants. These fibres are used in the production of composite materials in a variety of ways. Matting different layers of natural fibres into sheets can be used to make paper and felt (a type of textile material).

Most natural fibres are well-known for their ability to absorb sweat and other liquids. Natural fibres can be used to create a wide range of textures (either individually or through a combination of two or more natural fibres). Cotton fibres (natural fibres generated from the cotton plant) are used in the creation of cotton garments that are known for their low weight and delicate texture. Cotton fibre also has the advantage of being able to be weaved into clothes of various sizes and colours. Clothing made of natural fibres (such as cotton) is frequently chosen over clothing made of synthetic fibres, particularly by those who live in hot and humid climates.

Q10) State the examples of Natural Fibres.

A10) Plant fibres and animal fibres are the two primary groups of natural fibres. In this subsection, examples of plant and animal fibres have been offered.

Plant Fibres

• Seed fibres are the fibres derived from the seeds of many plants.

• Leaf fibres — natural fibres extracted from the leaves of specific plants. Pineapple and banana leaf fibres are two examples.

• Fruit fibres are the natural fibres obtained from a plant's fruit (coconut fibre, for example).

• Stalk fibres – these are natural fibres derived from the stalks of some plants. Wheat straws, bamboo fibres, fibres obtained from the stalks of rice and barley plants, and straw are examples.

• Bast fibres — natural fibres derived from the outer layer of the stem's cells. Jute fibres, flax fibres, vine fibres, industrial hemp fibres, kenaf fibres, rattan fibres, and ramie fibres are all examples of bast fibres. These fibres are commonly utilised in fabric and packaging due to their long-lasting properties.

Animal Fibres

Animal fibres are natural fibres that contain proteins such as fibroin, keratin, and collagen. The following are some common examples of animal fibres.

• Silk is a form of animal fibre derived from silkworms (different species produce different types of silk).

• Sinew — an animal fibre that joins the muscles and bones of certain animals.

• Wool is an animal fibre obtained by shearing the fur of specific sheep breeds.

• Mohair is an animal fibre made from the Angora goat's hair.

Q11) State the applications of Natural Fibres.

A11) Natural fibres, including certain glass fibres, are widely employed in the construction industry in a variety of building materials. Even when put in a matrix of synthetic polymers, such composites (also known as biocomposites) can be considered natural fibres. Cellulose fibre offers a wide range of applications in a variety of industries, including automotive and electronics. These natural fibres can be utilised for noise-absorbing panels and insulation.

Silk, wool, angora, and camel hair are the four most valuable animal fibres in terms of industrial value. Many plant fibres have important industrial applications as well. Cotton fibre, for example, is an important raw resource in the textile industry. Hemp fibre, jute fibre, and flax fibre are also important plant fibres in industry.

Natural fibres may also have medical applications since they can aid in the production of biomaterials. The natural fibre Chitin, for example, can be used to filter out certain hazardous contaminants from industrial wastewater.

Q12) What is Polyethylene?

A12) Polyethylene, often known as polythene or polyethene, is a type of plastic that is widely used around the world. Polyethylenes are known to be addition polymers and have a linear structure. Packaging is the most common use for these synthetic polymers. Plastic bags, bottles, plastic films, containers, and geomembranes are all made from polyethelyne. It's worth noting that about 100 million tonnes of polyethene are manufactured each year for commercial and industrial use.

Polyethylene can be expressed as (C2H4)n in its generic formula. The majority of polyethylene is thermoplastic (they can be remoulded by heating). Some modified polyethylene polymers, on the other hand, have thermosetting qualities. Cross-linked polyethylene is an example of this type of polyethylene (often abbreviated to PEX).

Ethylene is the most important component of polyethylene (an organic hydrocarbon with the chemical formula C2H4; IUPAC name: ethene). The normal parameters for polyethylene manufacture include less than 5 parts per million of oxygen, water, and other alkenes. Other pollutants can, however, be present during the polymerization reaction. Nitrogen, methane, and ethane are among of the most widely recognised pollutants in polythene manufacture.

Because ethene is a rather stable chemical, it requires special catalysts to polymerize it. It's worth noting that the process of converting ethylene to polyethylene is highly exothermic. Titanium(III) chloride is one of the most regularly used catalysts for the polymerization of ethylene (which is sometimes referred to as a Ziegler-Natta catalyst).

Q13) Enlist the uses of Uses of Polyethylene.

A13) • The most common use of polyethylene is in packaging materials. Plastic bags, plastic films, bottles, geomembranes, and containers are frequently made from this material.

• Crates, trays, milk or fruit juice containers, and other food packaging products are made of polyethylene.

• Toys, garbage cans, ice trays, and other household items are made of high-density polyethylene. This plastic's versatility makes it suitable for a wide range of applications.

• Ropes, fishing nets, agricultural nets, and industrial fabrics are all made of HDPE. This material is also commonly used in wiring and cables.

• Because of its great flexibility and low cost, low-density polyethylene (LDPE) is frequently utilised in the production of squeeze bottles, waste bags, laminations, and food packaging

• LDPE is also utilised in the manufacture of pipes and fittings. Because of its minimal water absorption and flexibility, it is perfect for such applications.

• Because it is a good insulator of electric current, polyethylene is often utilised for cable jacketing.

Q14) State the term Aramid.

A14) Any of a range of synthetic polymers (substances made up of long chainlike multiple-unit molecules) in which repeating units containing big phenyl rings are bonded together by amide groups (full aromatic polyamide). Amide groups (CO-NH) produce strong, solvent- and heat-resistant bonds. Phenyl rings (also known as aromatic rings) are six-sided carbon and hydrogen atom groups that keep polymer chains from rotating and twisting around their chemical connections. As a result, aramids are stiff, straight, high-melting, and mostly insoluble molecules, making them excellent for spinning into high-performance fibres. Nomex, a high-melting fibre used in flame-resistant protective equipment, and Kevlar, a high-strength fibre used in bulletproof vests, are the most well-known aramids.

Nylon, a related class of polyamides made by reacting acids having carboxyl groups (CO2H) with substances containing amino groups, was developed before aramids (NH2). Researchers at E.I. Du Pont de Nemours & Company (now DuPont Company) in the United States developed methods for extending this class to compounds with carbon rings in the 1950s and 1960s. These procedures entailed dissolving the acids and amines in suitable solvents and reacting them at low temperatures, as devised by Paul W. Morgan and Stephanie L. Kwolek. DuPont introduced Nomex, or poly-m-phenylene isophthalamide, in 1961, made from isophthalic acid chloride and m-phenylenediamine, and Kevlar, or poly-p-phenylene terephthalamide, in 1971, made from terephthalic acid chloride and p-phenylenediamine. The structure of the molecules distinguishes these two polymers, with Nomex having meta-oriented phenyl rings and Kevlar having para-oriented phenyl rings.

Q15) According to Synthetic Organic Fibres describe the term Rings.

A15) Nomex melts and decomposes at around 350 degrees Fahrenheit (660 degrees Fahrenheit); Kevlar melts at temperatures around 500 degrees Fahrenheit (930 degrees Fahrenheit). Kevlar's higher melting temperature, as well as its stiffness and tensile strength, are due in part to its molecules' regular para-orientation. The polymer takes on a liquid-crystal structure in solution, which allows the molecules to be spun and pulled into highly ordered fibres with ultrahigh stiffness and strength. (Kevlar is five times stronger than steel in terms of weight.) Twaron (from the Dutch business Akso NV) and Technora are two more trademarked Kevlar-type fibres (from the Japanese company Teijin, Ltd.). Teijin also produces a Nomex-like fibre under the Conex brand.

Although aramids are rarely produced in the same amount as commodity fibres like nylon and polyester, their high unit price makes them a lucrative market. End uses for aramids in the house are limited (Nomex-type fibres have been used to make ironing board covers), but industrial applications are growing (especially for aramids of the Kevlar class) as product designers learn how to take advantage of these strange materials' qualities. Kevlar and its competitors are used in radial tyre belts, cables, reinforced composites for aircraft panels and boat hulls, flame-resistant garments (especially in blends with Nomex), and sports equipment such as golf club shafts and lightweight bicycles, as well as as asbestos replacements in automobile clutches and brakes. Filters for hot-stack gases, clothes for presses applying permanent-press finishes to fabrics, dryer belts for papermakers, insulation paper and braid for electric motors, flame-resistant suits for fire fighters, military pilots, and race-car drivers, and automobile v-belts and hoses are all made from Nomex-type fibres.

Q16) Enlist and explain the Inorganic Fibers.

A16) Glass fibre, amorphous fibre like rock wool, carbon fibre, polycrystal fibre like alumina fibre, and monocrystal fibre like wollastonite and potassium titanate fibre are all examples of inorganic fibres. Because there is no grain boundary, amorphous fibre has a high strength despite having a low modulus elasticity. Because polycrystalline fibre is made up of tiny crystals, it has a higher heat resistance. Because of the whisker-like tiny fibres, monocrystalline fibre has an incredibly high strength.

Glass fiber

Chopped strands with a fibre diameter of 6–20 m and a fibre length of 3–25 mm with exceptional heat resistance and dimension stability are the glass fibres most commonly used for papermaking. Because of its properties, glass fibre sheets are utilised for flooring, insulation, and building materials.

Carbon fiber

Carbon fibres are divided into two categories: Types based on PAN (polyacrylonitrile) and pitch (petroleum oil and coal)

Mechanical strength, modulus of elasticity, heat resistance, and chemical resistance are all advantages of the fibres. They have similar electric resistance and heat conductivity to metals. As a result of their low thermal expansion coefficient, they are used to make electromagnetic shields, electrodes, and heat-resistant structures.

Alumina Fibre

These are ceramics made by spinning a slurry of alumina particles and additives into a yarn and then heating it under regulated conditions. At high temperatures, fibres maintain their strength. At high temperatures, it also has good electrical insulation. It has a high hardness and wear resistance.

• Silica fibres are sodium silcate fibres (water glass). They're employed in heat protection (asbestos replacement) as well as packings and compensators. They can be manufactured to be almost completely free of non-alkali metal complexes.

After that, sodium silicate fibres can be used to make silica fibres, which is preferable than making them from a melt containing SiO2 or by acid-leaching glass fibres. Wet webs, filter linings, and material reinforcement can all benefit from silica fibres.

They can also be utilised to make silicic acid fibres using a dry spinning process. These fibres possess qualities that make them suitable for use in friction-reducing materials. 1st

Boron Fibers

PMCs and, to a lesser extent, MMCs are reinforced with boron fibres. Boron fibres are made as monofilaments (single filaments) by CVDing boron onto a tungsten wire or a carbon filament, with the latter being the most common. In comparison to most other reinforcements, they have rather enormous diameters (100–140 m). Table 3 shows characteristic parameters of tungsten-cored boron fibres with a diameter of 140 m. Effective fibre qualities are influenced by the ratio of overall fibre diameter to tungsten core diameter. Fiber specific gravity, for example, is 2.57 for 100 m fibres and 2.49 for 140 m fibres. Because boron fibres are more expensive than many forms of carbon fibres, they are used in far fewer applications.

Q17) State the Particulate reinforcements.

A17) Because of their low cost, particle reinforcements have been frequently utilised to improve the characteristics of polymeric matrixes. Particles can be easily blended with polymers in powder form for the SLS process, liquid form for the SLA process, and even extruded into printable filaments for the FDM process (Wang et al., 2017). The development of PMCs addresses and resolves commercialization and real-world uses of polymers. Hwang et al. (2015) recently investigated the thermo-mechanical characteristics of metal reinforced PMCs using the FDM technique. Copper and iron particles with average sizes of less than 24 and 43 m, respectively, were used. The effects on the characteristics of the 3D printed composite were studied using metallic particle reinforcements in various concentrations ranging from 10% to 80%. The viscosity was lowered while the tensile strength was raised by raising the temperature during extrusion from 190°C to 220°C. Furthermore, increasing the reinforcement content boosted ductility, but when the filler level above a certain threshold, ductility began to drop (Chung, 2001).

The physical, chemical, and mechanical properties of the polymeric matrix can all be improved by the presence of particle reinforcements. Furthermore, the inclusion of reinforcement particles can help to resolve several issues that arise during the printing process. Because monolithic polymers have a significant thermal expansion, poor bonding between layers is a major challenge in the printing process. Metallic particles can aid to reduce the thermal expansion of the final composite and improve the bonding between the layers (Chung, 2001).

The use of various hydrogel compositions (e.g., alginate, chitosan, and gelatin) in 3D printing of cell-laden scaffolds reinforced with HAp particles has been studied (Kesti et al., 2015; Wenz et al., 2017). The results reveal that adding HAp particles to hydrogels significantly improves their mechanical properties and promotes osteogenic differentiation in vivo, making them suitable for mending bone tissue defects (Wenz et al., 2017; Bendtsen et al., 2017).

Nikzad et al. (2011) investigated the impact of copper and iron particles reinforcing the ABS matrix. The results revealed that the presence of iron particles reduced ABS tensile strength, resulting in a composite that was tougher and more brittle than the matrix. Masood and Song et al. Created a metallic powder reinforce PMC by inserting iron particles in the P301 nylon matrix with diameters ranging from less than 30 to 80 m. (Masood and Song, 2004). The composite that emerged was found to be suitable for direct quick tooling applications. It was also discovered that the mechanical qualities of the 3D printed product can be harmed by reinforcements with greater particle sizes. In other words, it was discovered that particulate reinforcements with lower particle sizes could improve the polymeric matrix's characteristics. The use of nanoparticles to improve PMC characteristics will be described in the next subsections.

Q18) Explain the term Reinforcement – matrix interface.

A18) The matrix is a completely continuous monolithic material into which the reinforcement is embedded. Unlike two materials sandwiched together, there is a channel through the matrix to any location in the material. The matrix is commonly a lighter metal, such as aluminium, magnesium, or titanium, in structural applications, and offers a compliant support for the reinforcement. Cobalt and cobalt-nickel alloy matrices are used in high-temperature applications.

The matrix constituent is a typical way to classify composite materials. Organic Matrix Composites (OMCs), Metal Matrix Composites (MMCs), and Ceramic Matrix Composites are the three basic composite classifications (CMCs). The term "organic matrix composite" is widely used to refer to two types of composites: polymer matrix composites (PMCs) and carbon matrix composites, often known as carbon-carbon composites.

Three common forms of composites result from these three sorts of matrices.

1. Ceramic fibres are used in a plastic matrix in polymer matrix composites (PMCs), of which GRP is the most well-known example.

2. Silicon carbide fibres are commonly inserted in an alloy of aluminium and magnesium in metal-matrix composites (MMCs), but other matrix materials such as titanium, copper, and iron are increasingly being employed. Bicycles, golf clubs, and missile guidance systems are all examples of MMC applications; an MMC constructed of siliconcarbide fibres in a titanium matrix is now being researched for use as the skin (fuselage material) of the US National Aerospace Plane.

3. Ceramic-matrix composites (CMCs) are the third major category, with silicon carbide fibres set in a borosilicate glass matrix as an example. They are particularly well suited for usage in lightweight, high-temperature components, such as parts for aeroplane jet engines, due to their ceramic matrix.

Several factors influence the selection of a matrix alloy for an MMC. It's crucial to know if the composite will be reinforced constantly or intermittently. When continuous fibres are used as reinforcements, the majority of the load is transferred to the reinforcing filaments, and composite strength is mostly determined by fibre strength. The matrix alloy's principal functions are to transport load efficiently to the fibres and to soften cracks in the case of fibre failure, hence the matrix alloy for continuously reinforced composites may be chosen for toughness rather than strength.

In continuously reinforced composites, lower strength, more ductile, and harder matrix alloys may be used. The matrix may control composite strength in discontinuously reinforced composites. The choice of matrix will then be determined by the necessary composite strength, which may necessitate the use of higher strength matrix alloys. Potential reinforcement/matrix reactions, either during processing or in service, which could result in degraded composite performance; thermal stresses due to thermal expansion mismatch between the reinforcements and the matrix; and the influence of matrix fatigue behaviour on the cyclic response of the composite are all factors to consider when choosing the matrix. Indeed, the behaviour of composites under cyclic loading situations is something that needs to be taken into account. The difference in melting temperatures between the matrix and the reinforcements is an additional issue in composites intended for use at high temperatures. Even at temperatures near the matrix melting point, a substantial melting temperature differential can cause matrix creep while the reinforcements remain elastic. When there is a tiny melting point difference in the composite, however, creep in both the matrix and reinforcement must be considered.

Q19) What is Interfacial bonding?

A19) In a wide range of industries, such as construction, automotive, and aerospace, the adhesion and corrosion resistance of polymer/oxide/metal interphases in functional composite materials is an enormously significant component of engineering. To protect the functional qualities of the composite, interphases in polymer/metal junctions must survive strong mechanical pressures and corrosive attack over long periods of time. Factors such as alloying element enrichment and the presence of intermetallic precipitates at the metal-polymer interface are well known to have a significant impact on the corrosive de-adhesion of organic layers. Despite decades of research, the adhesion between metals and polymers (organic coatings and adhesives) as well as the loss of adhesion in the presence of an aqueous environment are still under investigation.

The complex interaction of: - Molecular forces at the interface (chemical bonding, van der Waals bonding, hydrogen bonding, acid-base interactions, etc.) determines adhesion and de-adhesion processes.

- Within the interphase, the polymeric chains are arranged supramolecularly.

- The metal substrate's surface chemistry.

- The metal oxide layer's, interphase's, and bulk polymer phase's mechanical properties.

- Within the interphase, the defect density.

- The metal oxide's and surrounding polymer's electrical characteristics.

- The interphase's hydrolytic and oxidative resistance.

- The interphase's barrier qualities.

Q20) Explain the Methods for measuring bond strength.

A20) You're looking for a new glue and notice that the most recent alternative on the market claims to have unrivalled binding strength. You're definitely interested because adhesive strength and reliability can make or break the success of a restoration. But what does it mean when the firm claims the product has the strongest bond strength, and how did they assess it?

While the figures are appealing, it's critical to understand where they come from. There are a variety of bond-strength testing methods, each of which operates differently and yields different findings.

Dr. John Flucke, DPR's technology editor who practises in Lee's Summit, Mo., adds, "Bond strength is a phrase and process that may be quantified in many different ways." “It's critical to understand how bond strength estimates from a manufacturer were calculated if you're going to depend on them.”

To measure bond strength, there are two types of testing (static and dynamic), although within these categories, there are multiple approaches, each with its own set of strengths and weaknesses. It's helpful to know which approach was used when evaluating adhesive bond strength so you can compare goods from different manufacturers on the same scale.

Static tests:

The more common of the two methods of testing is static testing, which involves applying a load to a test specimen while it is stationary. There are two types of static tests: macro tests (when the bond area is greater than 3 mm2) and micro tests (where the bond area is less than 3 mm2) (where the bond area is less than 3 mm2, and is usually 1 mm2 or less). 1

Macro testing:

Macro testing is divided into three main methods: shear, tensile, and push-out. It is known for its simplicity.