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# Introduction to Composite Materials

By Tri-Dung Ngo

Submitted: August 5th 2019Reviewed: January 21st 2020Published: February 25th 2020

DOI: 10.5772/intechopen.91285

## Abstract

Composite materials have played an important role throughout human history, from housing early civilizations to enabling future innovations. Composites offer many benefits; the key among them are corrosion resistance, design flexibility, durability, light weight, and strength. Composites have permeated our everyday lives such as products that are used in constructions, medical applications, oil and gas, transportation, sports, aerospace, and many more. Some applications, such as rocket ships, probably would not get off the ground without composite materials. This chapter addresses the advantages of fibre composite materials as well as fundamental effects, product development, and applications of fibre composites, including material chemistry, designing, manufacturing, properties, and utilisation of the materials in various applications.

### Keywords

• fibre
• matrix
• composite
• fibre composite
• thermoset
• thermoplastic
• natural fibre
• biopolymer

## 1. Introduction

Composites exist in nature. A piece of wood is a composite, with long cellulose fibres held together by a substance called lignin. Composite materials are formed by combining two or more materials that have quite different properties, and they do not dissolve or blend into each other. The different materials in the composite work together to give the composite unique properties. Humans have been using composite materials for thousands of years in different areas. The first uses of composites date back to the 1500 BC, when early Egyptians and Mesopotamian settlers used a mixture of mud and straw to create strong and durable buildings. The combination of mud and straw in a block of brick provides it a strong property against both squeezing and tearing or bending. The straw continued to provide reinforcement to ancient composite products, including pottery and boats [1]. In 1200 AD, the Mongols invented the first composite bow using a combination of “animal glue”, bone, and wood. The bows were pressed and wrapped with birch bark. These bows were powerful and accurate. Composite Mongolian bows helped to ensure Genghis Khan’s military dominance. Due to their advantages such as being light weight and strong, many of the greatest advancements in composites were the result of wartime needs. During World War II, many composite materials were developed and moved from the laboratory into actual production [1, 2].

The development and need for composite materials also result in the fibre-reinforced polymers (FRP) industry. By 1945, more than 7 million pounds of glass fibres were used for various products, primarily for military applications. Composite materials continued to take off after the war and grew rapidly through the 1950s. The composite innovators were ambitiously trying to introduce composites into other markets such as aerospace, construction, and transportation. Soon the benefits of FRP composites, especially its corrosion resistance, became known to the public sector. Boats were one obvious product that benefited. The first composite commercial boat hull was introduced in 1946. A full automobile body was made from composite and tested in 1947 [1, 2]. This led to the development of the 1953 Chevrolet Corvette. The advent of the automobile age gave rise to several new methods for moulding such as compression moulding of bulk moulding compound (BMC) and sheet moulding compound (SMC). The two techniques emerged as the dominant method of moulding for the automotive industry and other industries. In the early 1950s, manufacturing methods such as large-scale filament winding, pultrusion, and vacuum bag moulding were developed. In the 1960s, the marine market became the largest consumer of composite materials [1, 2]. In 1961, the first carbon fibre was patented and several years later became commercially available. In the 1970s the composites industry began to mature. Many better resins and improved reinforcing fibres were developed during this period for composite applications. In the 1970s, the automotive market surpassed marine as the number one market—a position it retains today. During the late 1970s and early 1980s, composites were first used in infrastructure applications in Asia and Europe. The first all-composites pedestrian bridge was installed in Aberfeldy, Scotland, in the 1990s. In this period, the first FRP-reinforced concrete bridge deck was built in McKinleyville, West Virginia, and the first all-composites vehicular bridge deck was built in Russell, Kansas. Composites continue to find applications today [1, 2, 3]. Nanomaterials are incorporated into improved fibres and resins used in new composites. Nanotechnology began to be used in commercial products in the early 2000s. Bulk carbon nanotubes can be used as composite reinforcement in polymers to improve the mechanical, thermal, and electrical properties of the bulk product [3].

Nowadays, the composite industry is still evolving, with much of the growth now focused around renewable energy. Wind turbine blades, especially, are constantly pushing the limits on size and require advanced composite materials, for example, the engineers can design to tailor the composite based on the performant requirements, making the composite sheet very strong in one direction by aligning the fibres that way, but weaker in another direction where strength is not so important. The engineers can also select properties such as resistance to heat, chemicals, and weathering by choosing an appropriate matrix material. In recent years, an increasing environmental consciousness and awareness of the need for sustainable development have raised interest in using natural fibres as reinforcements in composites to replace synthetic fibres [4, 5, 6, 7]. This chapter seeks to provide an overview of the science and technology in relation to the composite material, manufacturing process, and utilisation.

## 2. Polymer matrix

In general, a composite consists of three components: (i) the matrix as the continuous phase; (ii) the reinforcements as the discontinuous or dispersed phase, including fibre and particles; and (iii) the fine interphase region, also known as the interface [8, 9]. By carefully choosing the matrix, the reinforcement, and the manufacturing process that brings them together, the engineers can tailor the properties to meet specific requirements [10]. Over the recent decades, many new composites have been developed, some with very valuable properties.

Any material can serve as a matrix material for composite. However, matrix materials are generally ceramics, metals, and polymers. In reality, the majority of matrix materials that exist on the composites market are polymer. There are several different polymer matrices which can be utilised in composite materials. Among the polymer matrix composites, thermoset matrix composites are more predominant than thermoplastic composites. Though thermoset and thermoplastics sound similar, they have very different properties and applications. Understanding the performance differences can help to make better sourcing decisions and the product designs as composites [11].

Thermosets are materials that undergo a chemical reaction or curing and normally transform from a liquid to a solid. In its uncured form, the material has small, unlinked molecules known as monomers. The addition of a second material as a cross-linker, curing agent, catalyst, and/or the presence of heat or some other activating influences will initiate the chemical reaction or curing reaction. During this reaction, the molecules cross-link and form significantly longer molecular chains and cross-link network, causing the material to solidify. The change of the thermoset state is permanent and irreversible. Subsequently, exposure to high heat after solidifying will cause the material to degrade, not melt. This is because these materials typically degrade at a temperature below where it would be able to melt.

Thermoplastics are melt-process able plastics. The thermoplastic materials are processed with heat. When enough heat is added to bring the temperature of the plastic above its melting point, the plastic melts, liquefies, or softens enough to be processed. When the heat source is removed and the temperature of the plastic drops below its melting point, the plastic solidifies back into a glasslike solid. This process can be repeated, with the plastic melting and solidifying as the temperature climbs above and drops below the melting temperature, respectively. However, the material can be increasingly subject to deterioration in its molten state, so there is a practical limit to the number of times that this reprocessing can take place before the material properties begin to suffer. Many thermoplastic polymers are addition-type, capable of yielding very long molecular chain lengths or very high molecular weights [12].

Both thermoset and thermoplastic materials have its place in the market. In broad generalities, thermosets tend to have been around for a long time and have a well-established place in the market, frequently have lower raw material costs, and often provide easy wetting of reinforcing fibre and easy forming to final part geometries. In other words, thermosets are often easier to process than thermoplastic. Thermoplastics tend to be tougher or less brittle than thermoset. They can have better chemical resistance, do not need refrigeration as uncured thermosets (prepreg materials) frequently do, and can be more easily recycled and repaired. Table 1 presents a comparison between thermoset and thermoplastic. This table is not providing all but rather some information for the researchers and manufacturers when considering the utilisation of these materials.

ThermosetThermoplastic
ProcessingContain monomers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermosets ideal for high-heat applications such as electronics and appliancesPellets soften when heated and become more fluid as additional heat is applied. This characteristic allows thermoplastics to be remoulded and recycled without negatively affecting the material’s physical properties
Features and benefits
• There are multiple thermoset resins that offer various performance benefits

• Significantly improve the material’s mechanical properties, providing enhances chemical resistance, heat resistance, and structural integrity. Thermoset are often used for sealed products due to their resistance to deformation

• Cannot be recycled

• Cannot be remoulded or reshaped (not melt if heat)

• Easy to wet the reinforcing fibres and fillers

• More resistant to high temperatures than thermoplastics

• Highly flexible design

• Thick to thin wall capabilities

• Excellent aesthetic appearance

• High levels of dimensional stability

• More difficult to surface finish

• Cost-effective

• There is multiple thermoplastic that offer various performance benefits

• Commonly offer high strength, shrink-resistance, and easy bendability. Depending on the polymers, thermoplastics can serve low-stress applications such as plastic bags or high-stress mechanical parts

• Highly recyclable

• Can melt if heated, remoulding/reshaping capabilities

• More difficult to wet the reinforcing fibres and fillers

• High-impact resistance

• Chemical resistant

• Hard crystalline or rubbery surface options

• Aesthetically superior finishes

• Ecofriendly manufacturing

• Generally, more expensive than thermoset

### Table 1.

Thermoset vs. thermoplastic.

Thermosets are classified into polyester resins, epoxy resins, vinyl ester resins, phenolic, polyurethane, and other high-temperature resins such as cyanate esters, etc. The rapid industrialisation in developing economies the world over is one of the major boosting factors for the thermoset market. The demand for high-performance and lightweight materials from various end-use industries such as automotive, chemical tanks, and water tanks is expected to expand the global market for thermosets over the next 6 years. The growing demand for thermosets from emerging economies like Brazil, Russia, India, and China (BRIC) is expected to drive the market. BRIC nations are the four fastest-growing economies in the world with their GDP growth rates higher than the global GDP growth rate. However, frequent fluctuation in raw material prices acts as one of the major factors inhibiting the market growth. Asia-Pacific accounts for the biggest market for thermosets owing to the growth of the automobile market, primarily in China and India. Japan is a mature market and is expected to remain stagnant over the next years. China is the biggest automobile market in the world, and India also lists itself in the top five automobile markets in the world. Asia, along with being the largest market, is also the fastest-growing market for thermosets. The North American market for thermosets is primarily driven by the regulatory initiative to reduce automobile weight by 50% by 2020 in the USA in order to cut fuel consumption. Polyester resins and polyurethane account for the two most popular types of thermosets in the global market. The global market for thermosets is dominated by big multinational corporations which are present across the value chain. Some of the major companies operating in the thermosets market include Arkema, BASF, Asahi Kasei Chemical Corp, Bayer AG, Chevron Phillips Chemical Company LLC, Sinopec, Dow Chemical Company, Eastman Chemical Company, and Lyondell Basell Industries, among others [13]. To date, thermosets have been used predominantly in the industry. Thermosets are generally favoured for a variety of reasons, especially on commercial aircraft. Thermoset composites have been used for 30–40 years in aerospace. For example, the fuselage of the Boeing 787 is an epoxy-based polymer [14].

## 5. Composite applications

The most widely used form of fibre-reinforced polymer is a laminar structure, made by stacking and bonding thin layers of fibre and polymer until the desired thickness is obtained. By changing the fibre orientation among layers in the laminate structures, a specified level of anisotropy in composite properties can be achieved. Composites offer many benefits such as corrosion resistance, light weight, strength, lower material costs, improved productivity, design flexibility, and durability. Therefore, the wide range of industries uses composite materials and some of their common applications [3, 15].

### 5.1 Aerospace

The major original equipment manufacturers (OEMs) such as Airbus and Boeing have shown the potential of using composite materials for large-scale applications in aviation. NASA is continually looking to composite manufacturers for innovative approaches and space solutions for rockets and other spacecrafts. Composites with thermoset are being specified for bulkheads, fuselages, wings, and other applications in commercial, civilian, and military aerospace applications. There are several other applications of composites in the areas such as air-foil surfaces, antenna structures, compressor blades, engine bay doors, fan blades, flywheels, helicopter transmission structures, jet engines, radar, rocket engines, solar reflectors, satellite structures, turbine blades, turbine shafts, rotor shafts in helicopters, wing box structures, etc. [3, 15, 26, 37]

Composite materials offer flexibility in design and processing; therefore composite materials can be used as alternatives for metal alloys in appliances. Unlike most other industries, trends within the appliance segment move quite quickly. In addition, design and function are subject to both technology advancements and changing consumer taste. Composite materials are being used in appliance and business equipment such as equipment panels, frames, handles and trims in appliances, power tools, and many other applications. Composites are being utilised for the appliance industry in dishwashers, dryers, freezers, ovens, ranges, refrigerators, and washers. The components in the equipment that were utilised composites include consoles, control panels, handles, kick plates, knobs, motor housings, shelf brackets, side trims, vent trims, and many others [3, 73].

### 5.3 Architecture

With their aesthetic qualities, functionality, and versatility, the composite materials are becoming the material of choice for architectural applications. Composite materials allow architects to create designs that are impractical or impossible with traditional materials, improve thermal performance and energy efficiency of building materials, and meet building code requirements. Composite materials also offer design flexibility and can be moulded into complex shapes. They can be corrugated, curved, ribbed, or contoured in a variety of ways with varying thickness. Further, a traditional look such as copper, chrome or gold, marble, and stone can be achieved at a fraction of the cost using composite materials. Therefore, the architecture community is experiencing substantial growth in the understanding and use of composites in commercial and residential buildings [15].

### 5.4 Automotive and transportation

The automotive industry is no stranger to composites. This is one of the largest markets for composite materials. Weight reduction is the greatest advantage of composite material usage. A lower-weight vehicle or truck is more fuel-efficient because it requires less fuel to propel itself forward. In addition to enabling ground breaking vehicle designs, composites help make vehicles lighter and more fuel efficient. The composite materials are used in bearing materials, bodies, connecting rod, crankshafts, cylinder, engines, piston, etc. While fibre-reinforced polymers such as CFRP in cars get most of the attention, composites also play a big role in increasing fuel efficiency in trucks and transport systems. A number of US state Departments of Transportation are also using composite to reinforce the bridges those trucks travel on [3, 26, 37].

### 5.5 Construction and infrastructure

Construction is one of the largest markets for composites globally. The composites can be made to have a very high strength and ideal construction materials. Thermoset composites are replacing many traditional materials for home and offices’ architectural components including doors, fixtures, moulding, roofing, shower stalls, swimming pools, vanity sinks, wall panels, and window frames. Composites are used all over the world to help construct and repair a wide variety of infrastructure applications, from buildings and bridges to roads, railways, and pilings [3, 74].

### 5.6 Corrosive environments

Products made from composite materials provide long-term resistance to severe chemical conditions and temperature environments. Composites are often the material of choice for applications in chemical handling applications, corrosive environments, outdoor exposure, and other severe environments such as chemical processing plants, oil and gas refineries, pulp and paper converting, and water treatment facilities. Common applications include cabinets, ducts, fans, grating, hoods, pumps, and tanks [3, 37, 73]. Fibre-reinforced polymer composite pipes are used for everything from sewer upgrades and wastewater projects to desalination, oil, and gas applications. When corrosion becomes a problem with pipes made with traditional materials, fibre-reinforced polymer is a solution [3, 73].

### 5.7 Electrical

With the rapid growth of the electronics industry, and with strong dielectric properties including arc and track resistance, the composite materials are finding more and more in electronic applications. With strong dielectric properties including arc and track resistance, thermoset components include. Applications and components include arc chutes, arc shields, bus supports and lighting components, circuit breakers, control system components, metering devices, microwave antennas, motor controls, standoff insulators, standoffs and pole line hardware and printed wiring boards, substation equipment, switchgear, terminal blocks, and terminal boards [3, 75].

### 5.8 Energy

Material technology has grown from the early days of glass fibres as major reinforcements for composite material to carbon fibres which are lighter and stronger. The advancements in composites, particularly those from the US Department of Energy, are redefining the energy industry. Composites help enable the use of wind and solar power and improve the efficiency of traditional energy suppliers. Composite materials offer wind manufacturers strength and flexibility in processing with the added benefit of a lightweight components and products [3, 76]. The wind industry has set installation records over the last couple years. According to the Global Wind Energy Council, the trend for this industry may continue with global wind capacity predicted to double in the next few years. Composites play a vital role in the manufacture of structures such as wind turbine blades [3, 77].

### 5.9 Marine

Just like in the other engineering areas, the main struggle of naval architecture is to achieve a structure as light as possible. The marine industry uses composites to help make hulls lighter and more damage-resistant. With their corrosion resistance and light-weighting attributes, marine composite applications include boat hulls, bulkheads, deck, mast, propeller, and other components for military, commercial, and recreational boats and ships. Composites can be found in many more areas of a maritime vessel, including interior mouldings and furniture on super yachts [3, 78, 79].

### 5.10 Sports and recreation

The fibre-reinforced composite materials possess some excellent characteristics, including easy moulding, high elastic modulus, high strength, light in weight, good corrosion resistance, and so on. Therefore, fibre-reinforced composite materials have extensive applications in production the manufacturing of sports equipment. From bicycle frames, bobsleds fishing poles, football helmets, hockey sticks, horizontal bars, jumping board, kayaks, parallel bars, props, tennis rackets, to rowing, carbon fibres, and fibreglass composite materials help athletes reach their highest performance capabilities and provide durable and lightweight equipment [3, 80].

## 6. Summary

Composites have many advantages; a wide range of material combinations can be used in composites, which allows for design flexibility. The composites also can be easily moulded into complicated shapes. The materials can be custom tailored to fit unique specifications. Composites are light in weight compared to most woods and metals and lower density as compared to many metals. They are stronger than some other materials. The materials resist damage from weather and harsh chemicals. Composites have a long service life and require little maintenance. Due to the wide variety of available reinforcement, matrix, and their forms, manufacturing processes, and each resulting in their own characteristic composite products, the design possibilities for composite products are numerous. Therefore, a composite and its manufacturing process can be chosen to best fit the developing rural societies in which the products will be made and applied. Composite materials’ research continues. The areas of interest are nanomaterials—materials with extremely small molecular structures and bio-based polymers. To facilitate the advantages of the composites, several aspects must be considered: (a) concept development, (b) material selection and formulation, (c) material design, (d) product manufacturing, (e) market, and (f) regulations.

## Acknowledgments

The author acknowledges Mrs. Marian Parslow and Mrs. Laura Parslow for helping in editing of the chapter.

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Tri-Dung Ngo (February 25th 2020). Introduction to Composite Materials [Online First], IntechOpen, DOI: 10.5772/intechopen.91285. Available from: