**Introduction**

X Preface

**Chapter 1**

**Provisional chapter**

**Introductory Chapter: Background on Composite**

**Introductory Chapter: Background on Composite** 

DOI: 10.5772/intechopen.80960

"Composite materials" also referred to as "composition materials" or briefly "composites," as the most frequently used term, display materials consisting of two or more components; these two components display considerably diverse physical and/or chemical characteristics. Merging the two or more basic materials creates a new material with features different from the single constituents. Because the individual components remain distinct and separate within the final material structure, composites have to be strictly differentiated from material

The new composite material often displays many beneficial characteristics; in many cases, composites are stronger, of lower density, or less costly in comparison to established materials. Commonly, composites consist of two or more different components forming regions sufficiently large to be considered as continua; the basic components are usually strongly fused at the interface. A variety of both natural and synthetic materials confirm to this picture, such as mortar and concrete, reinforced rubber, alloys, polymers containing fillers, aligned and chopped fiber composites, porous and cracked media, polycrystalline (metal) aggregates,

Composite materials are composed of individual basic materials, which are referred to as socalled constituent materials. Two main categories of constituent materials are distinguished: the matrix (aka "binder") and the reinforcement. At least one representative from each category is needed to create a composite. The matrix phase embeds, surrounds, and supports the reinforcements by preserving their relative locations. The reinforcements contribute their specific physical and mechanical assets, thus enhancing the properties of the matrix. The achieved synergism between the two phases generates material properties not observed for

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Mohamed M. Dawoud and Hosam M. Saleh

Mohamed M. Dawoud and Hosam M. SalehAdditional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.80960

mixtures and solutions of solids.

**Materials**

**1. Overview**

and others [1].

**Materials**

#### **Introductory Chapter: Background on Composite Materials Introductory Chapter: Background on Composite Materials**

DOI: 10.5772/intechopen.80960

Mohamed M. Dawoud and Hosam M. Saleh

Additional information is available at the end of the chapter Mohamed M. Dawoud and Hosam M. SalehAdditional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.80960

**1. Overview**

"Composite materials" also referred to as "composition materials" or briefly "composites," as the most frequently used term, display materials consisting of two or more components; these two components display considerably diverse physical and/or chemical characteristics. Merging the two or more basic materials creates a new material with features different from the single constituents. Because the individual components remain distinct and separate within the final material structure, composites have to be strictly differentiated from material mixtures and solutions of solids.

The new composite material often displays many beneficial characteristics; in many cases, composites are stronger, of lower density, or less costly in comparison to established materials. Commonly, composites consist of two or more different components forming regions sufficiently large to be considered as continua; the basic components are usually strongly fused at the interface. A variety of both natural and synthetic materials confirm to this picture, such as mortar and concrete, reinforced rubber, alloys, polymers containing fillers, aligned and chopped fiber composites, porous and cracked media, polycrystalline (metal) aggregates, and others [1].

Composite materials are composed of individual basic materials, which are referred to as socalled constituent materials. Two main categories of constituent materials are distinguished: the matrix (aka "binder") and the reinforcement. At least one representative from each category is needed to create a composite. The matrix phase embeds, surrounds, and supports the reinforcements by preserving their relative locations. The reinforcements contribute their specific physical and mechanical assets, thus enhancing the properties of the matrix. The achieved synergism between the two phases generates material properties not observed for

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the individual constituent materials, while the unlimited number of binders and reinforcements enables the designer to develop optimum combinations, thus creating tailor-made composites [2].

Metal fibers are generally of low costs but have a relatively high specific mass. They are applied for reinforcement of metal matrices. Because of their high density, they are not highly demanded. The main function in preparation of the metal-metal composite is enabled by the high fiber-matrix compatibility. Carbon steel fibers are used for reinforcement of metal matrices to resist temperatures up to 300°C. To reinforce metal matrices to withstand even higher temperatures, fibers made of heat resistant metals, such as tungsten or molybdenum,

• Tungsten: used to strengthen heat resistant materials; drawback: they are extremely

• Boric: very light, yet rigid and solid; the production is not trivial. As typical representative, boric fibers should be mentioned, in which a boron layer is attached on the surface

against oxidation and boron diffusion into the matrix by attaching a thin SiC layer.

These polymers display ideal matrix materials, because they are conveniently processed, are of low density, and display desirable mechanical features. Consequently, high-temperature-

Thermosets and thermoplastics are two major types of polymers. Thermosets are characterized by a well-bonded 3D-molecular structure built up after curing. These materials decompose instead of melting at elevated temperature. Simply altering the resin's basic composition is sufficient to change the conditions appropriate for curing and to determine other properties. In addition, they can be retained in a partially cured condition over extended periods. Moreover, thermosets are of high flexibility. Thus, they are highly suitable as matrix bases for FRC used for advanced applications. Thermosets are widely used to generate chopped fiber composites, especially when using a premixed or molding compound with fibers of specific quality and aspect ratio as starting material, as it is the case for epoxy, polymer, and phenolic polyamide resins. Thermoplastics have one- or two-dimensional molecular structure; they melt at elevated temperature and typically exhibit exaggerated melting points. As an additional advantage, their softening at elevated temperature is reversible; hence, their original properties can be restored by cooling; this facilitates applications of established compression techniques used to produce molded compounds. Currently, resins reinforced with thermoplastics constitute a steadily emerging class of composites. A lot of R&D efforts in this area nowadays are dedicated toward improving the basic properties of the resins and toward extracting the highest possible functional advantages from them for defined applications. This includes endeavors to substitute precarious metals in die-casting processes. In crystalline thermoplastics, the reinforcement considerably changes the morphology, stimulating the

vapor; its surface is first protected

Introductory Chapter: Background on Composite Materials

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5

are applied. Some of the most commonly used fibers are listed below:

• Steel: often containing strengthening aluminum alloys.

of a thin tungsten wire by chemical deposition of BCl<sup>3</sup>

○ Inorganic nonmetallic matrix composite materials.

resistant polymeric resins are widely used in aeronautics [6].

○ Polymer matrix composites (PMCs).

reinforcement to allow nucleation.

heavy.

Well-known examples of composite materials are as follows:


Classification of composite materials occurs at two different levels:


A range of other classifications of composite materials exist as follows:

	- Metal matrix composites (MMCs)

Metal fibers are generally of low costs but have a relatively high specific mass. They are applied for reinforcement of metal matrices. Because of their high density, they are not highly demanded. The main function in preparation of the metal-metal composite is enabled by the high fiber-matrix compatibility. Carbon steel fibers are used for reinforcement of metal matrices to resist temperatures up to 300°C. To reinforce metal matrices to withstand even higher temperatures, fibers made of heat resistant metals, such as tungsten or molybdenum, are applied. Some of the most commonly used fibers are listed below:


the individual constituent materials, while the unlimited number of binders and reinforcements enables the designer to develop optimum combinations, thus creating tailor-made

• The first criterion of classification is based on the matrix (binder) constituent. The main composite families encompass organic matrix composites (OMCs), metal matrix composites (MMCs), and ceramic matrix composites (CMCs). The term OMC generally refers to two classes of composites, namely, polymer matrix composites (PMCs) and carbon matrix

• The second classification criterion refers to the reinforcement phases; here, fiber-reinforced composites (FRCs), laminar composites, or particulate composites are distinguished. FRC can be further separated into those containing discontinuous or continuous fibers, respec-

• FRC consists of fibers surrounded by matrix materials. Such composites are considered as discontinuous fiber composites or short fiber composites, if the composite properties are dependent on the fiber length. However, when the fiber length is like that, that any further increase in length does not result in further increase in the composite's elastic modulus, the composite is regarded as "continuous fiber reinforced." Fibers are generally small in diameter, and, when pressed axially, they easily twist, although they normally have proficient tensile properties. Consequently, these fibers need to be reinforced to prevent bending and

• Laminar composites consist of material layers stacked together by the matrix; sandwich

• Particulate composites constitute particles distributed or embedded in a binding matrix; the particles can be flakes or in powdered. For this category, concrete and wood particle

Well-known examples of composite materials are as follows:

• Pearlite (ferrite combined with cementite) [3, 4]

• Wood (cellulose fibers embedded in hemicellulose and the binder lignin)

• Bones (soft protein collagen combined with the hard mineral apatite)

Classification of composite materials occurs at two different levels:

composites, which are usually called carbon-carbon composites.

composites [2].

• Lignocellulosic (straw) in sludge

4 Characterizations of Some Composite Materials

tively, as reinforcements.

buckling of the individual fibers.

boards are well-known examples [5].

○ Metal matrix composites (MMCs)

structures are examples for this composite category.

**1.** Classification according to the type of matrix materials:

A range of other classifications of composite materials exist as follows:

These polymers display ideal matrix materials, because they are conveniently processed, are of low density, and display desirable mechanical features. Consequently, high-temperatureresistant polymeric resins are widely used in aeronautics [6].

Thermosets and thermoplastics are two major types of polymers. Thermosets are characterized by a well-bonded 3D-molecular structure built up after curing. These materials decompose instead of melting at elevated temperature. Simply altering the resin's basic composition is sufficient to change the conditions appropriate for curing and to determine other properties. In addition, they can be retained in a partially cured condition over extended periods. Moreover, thermosets are of high flexibility. Thus, they are highly suitable as matrix bases for FRC used for advanced applications. Thermosets are widely used to generate chopped fiber composites, especially when using a premixed or molding compound with fibers of specific quality and aspect ratio as starting material, as it is the case for epoxy, polymer, and phenolic polyamide resins. Thermoplastics have one- or two-dimensional molecular structure; they melt at elevated temperature and typically exhibit exaggerated melting points. As an additional advantage, their softening at elevated temperature is reversible; hence, their original properties can be restored by cooling; this facilitates applications of established compression techniques used to produce molded compounds. Currently, resins reinforced with thermoplastics constitute a steadily emerging class of composites. A lot of R&D efforts in this area nowadays are dedicated toward improving the basic properties of the resins and toward extracting the highest possible functional advantages from them for defined applications. This includes endeavors to substitute precarious metals in die-casting processes. In crystalline thermoplastics, the reinforcement considerably changes the morphology, stimulating the reinforcement to allow nucleation.

Whether crystalline or amorphous, these resins are able to change their creep properties over an extensive temperature range. However, this temperature range includes the point where usage of resins is impaired, and reinforcement in such systems can rise the failure load and their creep resistance.

• Preparation modes:

• Glass fiber composites.

• Hybrid fiber composites [9].

• Organic fiber composites.

**2. Characteristics of composites**

• Boron fiber or SiC fiber composites.

**1.** High specific strength and high specific modulus

**2.** Expedient fatigue resistance and high damage resistance

• Polymer pyrolysis: the currently most frequently used method; resorts to synthetic

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7

• Evaporation from the arc discharge between carbon electrodes; one resorts to the posi-

Boron is among the materials that are very challenging to make ductile, and it is highly reactive. Therefore, for use in a metal matrix, a thin layer of SiC is attached onto the fibers.

Based on the classification of composites, we are already familiar with the fact that there exists a myriad of different types of these materials. It is a common saying that different types of composites differ in their performance. Yet, composites also have some characteristics in common. Grace to their inherent beneficial characteristics, polymer matrix composites have developed to the fastest emergent and most extensively used composites. Compared with well-established materials like metals, polymer matrix composites display particular characteristics as follows:

The most important benefits of polymer matrix composites are their high specific strength and high specific modulus. Specific strength is defined as the ratio of strength to density, while the specific modulus is the ratio of modulus to density; in both cases, length is the corresponding dimension/unit. Under the premise of equal mass, these parameters are tools to quantify the material's bearing capacity and stiffness properties, which are very significant for aerospace structural materials. **Table 1** provides an overview of values for specific strength and specific modulus of several common structural materials; it is shown that carbon fiber resin matrix composites generally show higher specific modulus and specific strength. The high specific strength and high specific modulus of composites can be explained by the high performance and low density of reinforcing fibers. As a result of relatively low modulus and high density of glass fibers, the specific modulus of the

glass fiber resin matrix composites is slightly lower than measured for metallic materials.

The fatigue failure of metallic materials is frequently of no apparent warning to the strikingness of damage. The fiber/matrix interface in composites can avoid crack propagation. The fatigue failure always starts from those links of fibers prone to break. Crack growth or destruction propagates gradually for a long time; hence, there is a substantial forerun before

polymers like polyacrylonitrile (PAN) or to natural polymers. • Hydrocarbon pyrolysis: even production of nanofibers is possible.

tive pressure of argon. Whiskers can be produced.

Ceramic matrix composites (CMCs) and carbon-based composite materials like C/C composite materials are the best described representatives of inorganic nonmetallic matrix composites. Polymer matrix composite materials are divided into thermosetting resin-based composite materials and thermoplastic resin-based composite materials; moreover, they encompass one component polymer matrix composites and polymer blends matrix composites [7, 8].

	- Continuous fiber-reinforced composites
	- Fibrous fabric (textile), woven-reinforced composites
	- Sheet-reinforced composites
	- Very short fiber ("whiskers")-reinforced composites
	- Particle-reinforced composites
	- Nanoparticle-reinforced composites
	- Carbon and graphite fiber composites: typical characteristics of these carbon and graphite fibers:
		- Ten times more rigid and only half the density (1.8–2 g cm−<sup>3</sup> , comprises 90–95% pure carbon) in comparison to glass fibers.
		- Elongation at break is lower than observed for glass fibers.
		- Lower tensile strength at room temperature than for glass or aramid fibers; tensile strength does not decrease with temperature up to 1000°C.
		- Excellent thermal performance if oxidation-protected, stable and chemically inert up to 1000°C and when oxidation-protected: stability even up to 2000°C.
		- Minimal thermal expansion, sometimes even thermal contraction.
		- Drastically higher fatigue resistance than glass.
		- Electrical conductive.
		- A hundred times more expensive than glass.
		- High anisotropy.
		- Frequently poor adhesion to the matrix; therefore, surface modification is needed. The fibers can contain amounts of graphite, which differentiates them into carbon fiber composites, which contain predominantly amorphous carbon, and graphite fiber composites, which are characterized by a predominance of crystalline graphite.

• Preparation modes:

Whether crystalline or amorphous, these resins are able to change their creep properties over an extensive temperature range. However, this temperature range includes the point where usage of resins is impaired, and reinforcement in such systems can rise the failure load and

Ceramic matrix composites (CMCs) and carbon-based composite materials like C/C composite materials are the best described representatives of inorganic nonmetallic matrix composites. Polymer matrix composite materials are divided into thermosetting resin-based composite materials and thermoplastic resin-based composite materials; moreover, they encompass one

○ Carbon and graphite fiber composites: typical characteristics of these carbon and graph-

• Lower tensile strength at room temperature than for glass or aramid fibers; tensile

• Excellent thermal performance if oxidation-protected, stable and chemically inert up

• Frequently poor adhesion to the matrix; therefore, surface modification is needed. The fibers can contain amounts of graphite, which differentiates them into carbon fiber composites, which contain predominantly amorphous carbon, and graphite fiber composites, which are characterized by a predominance of crystalline graphite.

, comprises 90–95% pure

component polymer matrix composites and polymer blends matrix composites [7, 8].

**2.** Classification according to the nature of the dispersed phase:

○ Fibrous fabric (textile), woven-reinforced composites

○ Very short fiber ("whiskers")-reinforced composites

**3.** Classification according to the type of reinforcing fibers:

• Drastically higher fatigue resistance than glass.

• A hundred times more expensive than glass.

• Electrical conductive.

• High anisotropy.

carbon) in comparison to glass fibers.

• Ten times more rigid and only half the density (1.8–2 g cm−<sup>3</sup>

• Elongation at break is lower than observed for glass fibers.

strength does not decrease with temperature up to 1000°C.

to 1000°C and when oxidation-protected: stability even up to 2000°C.

• Minimal thermal expansion, sometimes even thermal contraction.

○ Continuous fiber-reinforced composites

○ Sheet-reinforced composites

○ Particle-reinforced composites

ite fibers:

○ Nanoparticle-reinforced composites

their creep resistance.

6 Characterizations of Some Composite Materials


Boron is among the materials that are very challenging to make ductile, and it is highly reactive. Therefore, for use in a metal matrix, a thin layer of SiC is attached onto the fibers.

• Hybrid fiber composites [9].
