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Chapter 16: Problem 22

(a) List four reasons why glass fibers are most commonly used for reinforcement. (b) Why is the surface perfection of glass fibers so important? (c) What measures are taken to protect the surface of glass fibers?

Short Answer

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#Answer# (a) Glass fibers are most commonly used for reinforcement due to their high strength, lightweight nature, corrosion resistance, and good electrical insulating properties. (b) Surface perfection of glass fibers is crucial for better adhesion between the fiber and the matrix material, which in turn affects the tensile strength, stiffness, and durability of the reinforced composite. Imperfections can lead to weak points and potential failure under stress or load. (c) Measures taken to protect the surface of glass fibers include coating them with sizing agents, careful handling and storage, proper cleaning procedures, and the appropriate selection of matrix materials. These measures ensure surface perfection, improved adhesion, and better mechanical properties in the final composite material.

Step by step solution

01

(a) Reasons for using glass fibers for reinforcement

Glass fibers are most commonly used for reinforcement due to the following reasons: 1. High strength: Glass fibers have high tensile strength, which makes them a suitable candidate for reinforcement purposes. 2. Lightweight: Glass fibers are lightweight, which allows for the production of lighter and more cost-efficient reinforced materials. 3. Corrosion resistance: Glass fibers do not corrode in harsh environments, making them suitable for use in various applications where corrosion resistance is necessary. 4. Good electrical insulating properties: Glass fibers have excellent electrical insulating properties, allowing them to be used in applications where electrical conductivity is undesirable.
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(b) Importance of surface perfection of glass fibers

The surface perfection of glass fibers is crucial because it directly affects the adhesion between the fiber and the matrix. A smooth, defect-free surface allows for a better bond between the fiber and the matrix material, which in turn affects the overall tensile strength, stiffness, and durability of the reinforced composite. Surface imperfections such as microcracks or defects can lead to weak points that can initiate failure in the composite material under stress or load.
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(c) Measures to protect the surface of glass fibers

Several measures are taken to protect the surface of glass fibers to maintain their surface perfection and improve adhesion with the matrix material. These measures include the following: 1. Coating fibers with sizing agents: Sizing agents are applied to the glass fibers to provide protection and enhance bonding with the matrix material. These agents can also act as lubricants, reducing friction between fibers and preventing damage during processing. 2. Careful handling and storage: Glass fibers should be handled carefully to avoid damage to the surface. Proper storage conditions, such as humidity and temperature control, should be maintained to prevent the development of defects. 3. Proper cleaning procedures: Contaminants present on the fiber surface can weaken the adhesion with the matrix. It is vital to use appropriate cleaning techniques to remove any contaminants and ensure surface perfection. 4. Appropriate selection of matrix materials: Choosing matrix materials that have good adhesion properties with glass fibers can prevent surface damage and ensure better bonding, leading to improved mechanical properties in the final composite material.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Composite Materials
Composite materials are engineered from two or more constituents with distinct physical and chemical properties. When combined, they create a material with characteristics different from the individual components. For instance, embedding glass fibers into a plastic matrix yields a composite that is robust yet lighter than metals, and this synergy is utilized in many industrial applications, from aerospace to automotive sectors.

Understanding these composites requires a grasp of how reinforcement materials like glass fibers work in conjunction with matrices to enhance properties such as strength, stiffness, and durability. The design of such composites is a sophisticated engineering task, where the objective is to achieve optimal performance for the intended use.
Tensile Strength of Glass Fibers
The tensile strength of glass fibers refers to their ability to withstand pulling forces. This trait is paramount for materials that face tension in their applications, as the glass fibers can significantly boost the tensile strength of the composite. Glass fibers are composed of fine strands of glass that are both strong and flexible, capable of enduring substantial loads without breaking.

This characteristic explains why glass fibers are the reinforcement of choice when high strength-to-weight ratio is a necessity. They enable the production of lighter structures that still maintain a high level of durability and structural integrity. Thus, understanding the tensile strength of these fibers is key to predicting the behavior of the composite material under load.
Corrosion Resistance
Corrosion resistance of glass fibers is one of their significant advantages. Unlike metals, glass fibers do not rust or degrade when exposed to harsh chemicals, humid conditions, or saltwater environments. This property is especially beneficial for applications where the composite material will be in contact with corrosive substances or exposed in outdoor settings.

The inherent resistance to corrosion contributes to the longevity and maintenance-free aspect of glass fiber-reinforced composites, making them a cost-effective solution over time.
Electrical Insulating Properties
Electrical insulating properties of glass fibers enhance the versatility of composite materials. Glass fibers do not conduct electricity, which means that they can be used to fortify materials requiring non-conductivity for safety or functional purposes.

Applications such as electrical insulators, circuit boards, and other electronic components benefit from the inclusion of glass fiber reinforcements. Additionally, these composites can provide electromagnetic interference (EMI) shielding, making them suitable for use in sensitive electronic equipment.
Surface Perfection Importance
The importance of surface perfection in glass fibers cannot be overstated. This aspect directly influences how well the fibers bond with the matrix. A pristine surface without defects ensures that the adhesion is strong, which is critical for transferring stress effectively within the composite material.

Any imperfections, such as scratches or voids, can act as points of weakness. These weak points are prone to crack propagation and may lead to premature failure of the composite when stressed. Therefore, achieving and maintaining a high level of surface perfection is crucial for the performance of glass fiber-reinforced materials.
Sizing Agents for Fibers
Sizing agents are applied to glass fibers to optimize their performance within a composite material. These agents are crucial for protecting fibers during handling and processing, and they play a significant role in enhancing the bond between the fibers and the matrix.

The selection of the appropriate sizing agent can also impart additional properties, such as improved resistance to moisture, enhanced mechanical strength, or better compatibility with certain matrix materials. The proper application of sizing ensures that the glass fibers maintain their structural integrity and contribute effectively to the composite's overall properties.
Matrix-Fiber Adhesion
The term matrix-fiber adhesion refers to the bond strength between the glass fibers and the surrounding matrix material. This adhesion is a defining factor in the composite material's performance. A strong bond means that the load can be effectively distributed between the reinforcement and the matrix, maximizing the composite's capability.

Improving adhesion may involve surface treatments of the fibers, selecting a matrix with compatible chemical properties, or tweaking the manufacturing process to promote better bonding. This adhesion is what allows composites to achieve such remarkable properties, combining the best qualities of the fibers with those of the matrix.

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Most popular questions from this chapter

Cite the distinction between carbon and graphite.

(a) What is a hybrid composite? (b) List two important advantages of hybrid composites over normal fiber composites.

A continuous and aligned fibrous reinforced composite having a cross-sectional area of \(970 \mathrm{mm}^{2}\left(1.5 \mathrm{in.}^{2}\right)\) is subjected to an external tensile load. If the stresses sustained by the fiber and matrix phases are \(215 \mathrm{MPa}\) \((31,300 \mathrm{psi})\) and \(5.38 \mathrm{MPa}(780 \mathrm{psi}),\) respec- tively, the force sustained by the fiber phase is \(76,800 \mathrm{N}\left(17,265 \mathrm{lb}_{\mathrm{f}}\right),\) and the total longitudinal composite strain is \(1.56 \times 10^{-3},\) then determine (a) the force sustained by the matrix phase (b) the modulus of elasticity of the composite material in the longitudinal direction, and (c) the moduli of elasticity for fiber and matrix phases.

(a) What is the distinction between matrix and dispersed phases in a composite material? (b) Contrast the mechanical characteristics of matrix and dispersed phases for fiber reinforced composites.

The mechanical properties of cobalt may be improved by incorporating fine particles of tungsten carbide (WC). Given that the moduli of elasticity of these materials are, respectively, \(200 \mathrm{GPa}\left(30 \times 10^{6} \mathrm{psi}\right)\) and \(700 \mathrm{GPa}\). \(\left(102 \times 10^{6} \mathrm{psi}\right),\) plot modulus of elasticity versus the volume percent of WC in Co from 0 to 100 vol\%, using both upper- and lowerbound expressions.
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