Composite Materials

Mechanics, Manufacturing and Modeling

Sumit Sharma

• Publisher: CRC Press
• Year: 2021
• Print ISBN: 9780367687557
• eBook ISBN: 9781000352184
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Mechanics

Composite materials find diverse applications in areas including aerospace, automotive, architecture, energy, marine and military. This comprehensive textbook discusses three important aspects including manufacturing, mechanics and dynamic mechanical analysis of composites.

The textbook comprehensively presents fundamental concepts of composites, manufacturing techniques and advanced topics including as advances in composite materials in various fields, viscoelastic behavior of composites, toughness of composites and Nano mechanics of composites in a single volume. Topics such as polymer matrix composites, metal matrix composites, ceramic matrix composites, micromechanical behavior of a lamina, micromechanics and nanomechanics are discussed in detail.

Aimed at senior undergraduate and graduate students for a course on composite materials in the fields of mechanical engineering, automobile engineering and electronics engineering, this book:

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• Discusses mechanics and manufacturing techniques of composite materials in a single volume.

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• Explains viscoelastic behavior of composites in a comprehensive manner.

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• Covers fatigue, creep and effect of thermal stresses on composites.

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• Discusses concepts including bending, buckling and vibration of laminated plates in detail.

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• Explains dynamic mechanical analysis (DMA) of composites.

1 Introduction

An article was published by Professor A. Kelly [1] in Composites Science and Technology titled “Composites in Context.” In that article, large-scale social changes which have influenced the development of new materials were reviewed, and new materials and processing methods were described and contrasted with some recent advances in composite materials science. Emerging technologies at the time included in situ metal matrix composites, carbon fiber-reinforced thermoplastic composites, SiC-reinforced aluminum as well as toughening of ceramics through the use of fiber reinforcement. Tremendous developments have been made in many aspects of composites research and technology during the two decades since the publication of Kelly’s paper. Recent advances in producing nanostructured materials with novel material properties have stimulated research to create multifunctional macroscopic engineering materials by designing structures at the nanometer scale. Motivated by the recent enthusiasm in nanotechnology, development of nanocomposites is one of the rapidly evolving areas of composites research.

According to American Ceramic Society, nanotechnology can be broadly defined as “The creation, processing, characterization, and utilization of materials, devices, and systems with dimensions of the order of 1–100 nm, exhibiting novel and significantly enhanced physical, chemical, and biological properties, functions, phenomena, and processes due to their nanoscale size.” By US National Nanotechnology Initiative (NNI) standards, nanotechnology involves the following according to Hunt [2]:

1. Research and technology development at the atomic, molecular, or macromolecular levels, approximately 1–100 nm in length (approximately 80,000 smaller than a human hair)
2. Creation and use of structures, devices, and systems that have novel properties and functions because of their small and/or intermediate size
3. Ability to control or manipulate on the atomic scale.

Current interests in nanotechnology encompass nano-biotechnology, nanosystems, nanoelectronics, and nanostructured materials, of which nanocomposites are a significant part. Through nanotechnology, it is envisioned that nanostructured materials will be developed using a bottom-up approach. “More materials and products will be made from the bottom-up, that is, by building them from atoms, molecules, and the nanoscale powders, fibers, and other small structural components made from them. This differs from all previous manufacturing, in which raw materials get pressed, cut, molded, and otherwise coerced into parts and products.” Scientists and engineers working with fiber-reinforced composites have practiced this bottom-up approach in processing and manufacturing for decades. When designing a composite, the material properties are tailored for the desired performance across various length scales. From selection and processing of matrix and fiber materials, and design and optimization of the fiber–matrix interface/interphase at the submicron scale to the manipulation of yarn bundles in 2-D and 3-D textiles to the layup of lamina in laminated composites and finally the net-shape forming of the macroscopic composite part, the integrated approach used in composites processing is a remarkable example in the successful use of the “bottom-up” approach.

Expansion of length scales from meters (finished woven composite parts), micrometers (fiber diameter), and sub-micrometers (fiber–matrix interphase) to nanometers (nanotube diameter) presents tremendous opportunities for innovative approaches in the processing, characterization, and analysis/modeling of the new generation of composite materials. As scientists and engineers seek to make practical materials and devices from nanostructures, understanding material behavior across length scales from the atomistic to macroscopic levels is required. Knowledge of how the nanoscale structure influences the bulk properties will enable the design of the nanostructure to create multifunctional composites.

A morphological characteristic that is of fundamental importance in understanding of structure–property relationship of nanocomposites is the surface area/volume ratio of the reinforcement materials. The change in particle diameter, layer thickness, or fibrous material diameter from micrometer to nanometer changes the ratio by three orders in magnitude. At this scale, there is often distinct size dependence of material properties. In addition, with the drastic increase in interfacial area, properties of the composite become dominated more by properties of the interface or interphase.

1.1 What Is a Composite?

Many materials are effectively composites. This is particularly true of natural biological materials, which are often made up of at least two constituents. In many cases, a strong and stiff component is present, often in elongated form, embedded in a softer constituent forming the matrix. For example, wood is made up of fibrous chains of cellulose molecules in a matrix of lignin, while bone and teeth are both essentially composed of hard inorganic crystals (hydroxyapatite or osteones) in a matrix of a tough organic constituent called collagen. Commonly, such composite materials show a marked anisotropy – that is to say, their properties vary significantly when measured in different directions. This usually arises because the harder constituent is in fibrous form with the fiber axes preferentially aligned in particular directions. In addition, one or more of the constituents may exhibit inherent anisotropy as a result of their crystal structure. In natural materials, such anisotropy of mechanical properties is often exploited within the structure. For example, wood is much stronger in the direction of the fiber tracheids, which are usually aligned parallel to the axis of the trunk or branch, than it is in the transverse directions. High strength is required in the axial direction since a branch becomes loaded like a cantilevered beam by its own weight and the trunk is stressed in a similar way by the action of the wind. Such beam bending causes high stresses along its length, but not through the thickness. Now, a formal definition of a composite may be given as follows:

A composite is a structural material that consists of two or more constituents that are combined at a macroscopic level and are not soluble in each other. One constituent is called the reinforcing phase, and the one in which it is embedded is called the matrix. The reinforcing phase material may be in the form of fibers, particles, or flakes. The matrix phase materials are generally continuous. Examples of composite systems include concrete reinforced with steel and epoxy reinforced with graphite fibers, etc.

Thus, a composite material is heterogeneous at a microscopic scale but statistically homogeneous at a macroscopic scale. The materials that form the composite are also called as constituents or constituent materials. The constituent materials of a composite have significantly different properties. Further, it should be noted that the properties of the composite formed may not be obtained from these constituents. However, a combination of two or more materials with significant properties will not suffice to be called as a composite material. In general, the following conditions must be satisfied to be called a composite material:

1. The combination of materials should result in significant property changes. One can see significant changes when one of the constituent materials is in platelet or fibrous from.
2. The content of the constituents is generally more than 10% (by volume).
3. In general, the property of one constituent is much greater (approx. 5 times) than the corresponding property of the other constituent.

The composite materials can be natural or artificially made materials. In the following sections, we will see the examples of these materials.

1.2 Why Composites?

There is unabated thirst for new materials with improved desired properties. All the desired properties are difficult to find in a single material. For example, a material that needs high fatigue life may not be cost-effective. The list of the desired properties, depending upon the requirement of the application, is given below:

1. Strength
2. Stiffness
3. Toughness
4. High corrosion resistance
5. High wear resistance
6. High chemical resistance
7. High environmental degradation resistance
8. Reduced weight
9. High fatigue life
10. Thermal insulation or conductivity
11. Electrical insulation or conductivity
12. Acoustic insulation
13. Radar transparency
14. Energy dissipation
15. Reduced cost
16. Attractiveness.

The list of desired properties is in-exhaustive. It should be noted that the most important characteristics of composite materials is t...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• Author
• Chapter 1 Introduction
• Chapter 2 Materials
• Chapter 3 Manufacturing Techniques
• Chapter 4 Mechanics of Composites
• Chapter 5 Linear Elastic Stress–Strain Characteristics of Fiber-Reinforced Composites
• Chapter 6 Micromechanics
• Chapter 7 Plane Stress Assumption
• Chapter 8 Global Coordinate System: Plane Stress Stress–Strain Relations
• Chapter 9 Classical Lamination Theory
• Chapter 10 The ABD Matrix
• Chapter 11 Failure Theories for Composite Materials
• Chapter 12 Mechanics of Short-Fiber-Reinforced Composites
• Chapter 13 Toughness of Composite Materials
• Chapter 14 Interlaminar Stresses
• Chapter 15 Laminated Plates
• Chapter 16 Viscoelastic and Dynamic Behavior of Composites
• Chapter 17 Mechanical Testing of Composites
• Index