Fatigue and Tribological Properties of Plastics and Elastomers

Laurence W. McKeen

• Publisher: William Andrew
• Year: 2009
• eBook ISBN: 9781437778359
• Edition: 2
• Topic: Tecnología e ingeniería
• Subtopic: Ciencias de los materiales

Part of a series of core databooks within the William Andrew Plastics Design Library, Fatigue and Tribological Properties of Plastics and Elastomers provides a comprehensive collection of graphical multipoint data and tabular data covering fatigue and tribology.The concept of fatigue is very straightforward: if an object is subjected to a stress or deformation, and it is repeated, the object becomes weaker. This weakening of plastic material is called fatigue. Tribology is the science and technology of surfaces in contact with each other and therefore covers friction, lubrication and wear. The reduction of wear and fatigue and the improvement of lubrication are key bottom-line issues for engineers and scientists involved in the plastics industry and product design with plastics.Fatigue and Tribological Properties of Plastics and Elastomers, Second Edition is an update of all that has changed in the world of plastics since the 1st edition appeared nearly 15 years ago, and has been reorganized from a polymer chemistry point of view.- A hard-working reference tool: part of the daily workflow of engineers and scientists involved in the plastics industry and product design with plastics- The reduction of wear and fatigue and the improvement of lubrication are key bottom-line issues- The data in this book provide engineers with the tools they need to design for low failure rates

Chapter 1. Introduction to Fatigue and Tribology of Plastics and Elastomers

1.1. Introduction to Fatigue

There are two recently published books on the properties of engineering plastics in this series. The Effect of Temperature and Other Factors on Plastics¹ discusses the general mechanical properties of plastics. The mechanical properties as a function of temperature, humidity, and other factors are presented in graphs or tables. That work includes hundreds of graphs of stress versus strain, modulus versus temperature, impact strength versus temperature, etc. Time was not a factor in that book. The Effect of Creep and Other Time Related Factors on Plastics² discusses the long-term behavior of plastics when exposed to constant stresses or strains for long periods of time. This book adds another two layers of plastics performance criteria, fatigue, and tribology.

This book provides graphical multipoint data and tabular data on fatigue and tribological properties of plastics and elastomers. This first chapter deals with the types of stress and an introduction to fatigue. Tribology is discussed in Chapter 2. The chemistry of plastics follows in Chapter 3. The remaining chapters contain the data.

The idea of fatigue is very simple. If an object is subjected to a stress or deformation, and it is repeated, the object becomes weaker. This weakening of plastic material is called fatigue and occurs when the material is subject to alternating stresses over a long period of time.

1.2. Types of Stress

As noted in Section 1.1, fatigue occurs as a result of rapidly changing stress or strain. Stress and strain can be applied in a number of ways. Normal stress (σ) is the ratio of the applied force (F) over the cross-sectional area (A) as shown in Equation 1.1 and Figure 1.1.

Figure 1.1 Illustration of tensile stress and compressive stress.

(1.1)

1.2.1. Tensile and Compressive Stress

When the applied force is directed away from the part, as shown in Figure 1.1, it is a tensile force inducing a tensile stress. This is also called a normal stress as it is applied perpendicularly. When the force is applied toward the part, it is a compressive force inducing a compressive stress.

1.2.2. Shear Stress

A shear stress (τ) is defined as a stress which is applied parallel or tangential to a face of a material as shown in Figure 1.2. The shear force is applied parallel to the cross-sectional area “A”.

Figure 1.2 Illustration of shear stress.

Shear stress is also expressed as force per unit area as in Equation 1.2.

(1.2)

1.2.3. Torsional Stress

Torsional stress (τ) occurs when a part such as a rod for a shaft is twisted as in Figure 1.3. This is also a shear stress, but the stress is variable and depends how far the point of interest is from the center of the shaft. The equation describing torsional stress is shown in Equation 1.3.

Figure 1.3 Illustration of torsional stress.

(1.3)

In this equation, T is the torque and c is the distance from the center of the shaft or rod. K is a torsional constant that is dependent on the geometry of the shaft, rod, or beam. The torque (T) is further defined by Equation 1.4, in which θ is the angle of twist, G is the m...

Table of contents

• Cover image
• Table of Contents
• Copyright
• Preface
• Chapter 1. Introduction to Fatigue and Tribology of Plastics and Elastomers
• Chapter 2. Introduction to the Tribology of Plastics and Elastomers
• Chapter 3. Introduction to Plastics and Polymers
• Chapter 4. Styrenic Plastics
• Chapter 5. Polyether Plastics
• Chapter 6. Polyesters
• Chapter 7. Polyimides
• Chapter 8. Polyamides (Nylons)
• Chapter 9. Polyolefins and Acrylics
• Chapter 10. Thermoplastic Elastomers
• Chapter 11. Fluoropolymers
• Chapter 12. High-Temperature Polymers
• Index