# The Effect of Creep and Other Time Related Factors on Plastics and Elastomers

## Laurence W. McKeen

# The Effect of Creep and Other Time Related Factors on Plastics and Elastomers

## Laurence W. McKeen

## About This Book

The second edition of the classic data book, T he Effect of Creep and Other Time Related Factors on Plastics and Elastomers (originally published in 1991), has been extensively revised with the addition of an abundance of new data, the removal of all out-dated information, and the complete rebuilding of the product and company listings.This new edition also has been reorganized from a polymer chemistry point of view. Plastics of similar polymer types are grouped into chapters, each with an introduction that briefly explains the chemistry of the polymers used in the plastics. An extensive introductory chapter has also been added, which summarizes the chemistry of making polymers, the formulation of plastics, creep-testing, test methods, measurements, and charts, as well as theory and plastic selection.Each chapter is generally organized by product and concludes with comparisons of brand or generic products. The appendices include a list of trade names, plastics sold under those names, and manufacturer. A list of conversion factors for stress measures is also included. ABOUT THE AUTHOR

Laurence W. McKeen earned a B.S. in Chemistry from Rensselaer Polytechnic Institute in 1973 and a Ph.D. in 1978 from the University of Wisconsin. He began his career with DuPont in 1978 as a mass spectroscopist, but moved into product development in the Teflon® Finishes group in 1980. Dr. McKeen has accumulated over 28 years of experience in product development and applications, working with customers in a wide range of industries, which has led to the creation of dozens of commercial products.

- More than 8 core chapters, which serve as a databank for evaluating the creep of plastics
- Over 600 uniform graphs for more than 45 generic families of plastics are explained
- Types of graphs include: (1) Isochronous Stress–Strain Curves at Various Times and Temperatures (2) Creep Strain or Creep Deformation versus Time at Various Stress Levels and Temperatures (3) Various Modulus Measures (Tensile, Compressive, Flexural) versus Time at Various Temperatures (4) Hoop Stress versus Time at Various Temperatures (5) Stress Cracking and Other Plastics Failure versus Time (6) Creep Rupture versus Time

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## Information

# Chapter 1

# Introduction to Plastics and Elastomers

## 1.1 Introduction

*The Effect of Temperature and Other Factors on Plastics and Elastomers*,

^{1}the general mechanical properties of plastics were discussed. These 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. However, when one starts designing products made of plastics, these graphs do not supply all the necessary information. This is because these graphs show the results of relatively short-term tests. Their value in design is in the initial selection of materials in terms of stiffness, strength, etc. Designs based on short-term data obtained from a short-term test would not predict accurately the long-term behavior of plastics. This is partly because plastics are viscoelastic materials. Viscoelastic by definition means possessing properties that are both solid-like and liquid-like. More precisely with reference to plastics, viscoelastic means that measurements such as modulus, impact strength, and coefficient of friction are sensitive not only to straining rate, temperature, humidity, etc., but also to elapsed time and loading history. The manufacturing method used for the plastic product can also create changes in the structure of the material, which have a pronounced effect on properties.

*The Effect of Temperature and Other Factors on Plastics and Elastomers*book, but it has been refocused on creep properties.

## 1.2 Types of Stress

*F*) over the cross-sectional area (

*A*), as shown in Equation 1.1:

### 1.2.1 Tensile and Compressive Stress

### 1.2.2 Shear Stress

### 1.2.3 Torsional Stress

*T*is the torque and

*c*is the distance from the center of the shaft or rod.

*K*is a torsional constant that depends 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 modulus of rigidity (material dependent), and

*L*is the length.

*K*) is dependent upon geometry, and the formulas for several geometries are shown in Fig. 1.4. Additional formulas for the torsional constant have been published.

^{2}

### 1.2.4 Flexural or Bending Stress

*M*is the bending moment (which is calculated by multiplying a force by the distance between the point of interest and the force),

*c*is the distance from the neutral axis (NA in Fig. 1.5), and

*I*is the moment of inertia. The cantilevered beam configuration, which is also shown in Fig. 1.5, has a similar formula. The formulas for

*M, c*, and

*I*can be complex, depending on the exact configuration and beam shape, but many have been published.

^{3}

### 1.2.5 Hoop Stress

_{h}) is the mechanical stress defined for rotationally symmetric objects such as pipe or tubing. The real world view of

*hoop stress*is the tension applied to the iron bands, or hoops, of a wooden barrel. It is the result of forces acting circumferentially. Figure 1.6 shows stresses caused by the pressure (

*P*) inside a cylindrical vessel. The hoop stress is indicated on the right in Fig. 1.6, which shows a segment of the pipe.

*P*is the internal pressure,

*t*is the wall thickness, and

*r*is the radius of the cylinder. The SI unit for

*P*is pascal (Pa), while

*t*and

*r*are in meters (m).

*axial*or

*longitudinal stress*(σ

_{1}) on the same pipe wall. The longitudinal stress, under the same conditions as in Fig. 1.6, is given by Equation 1.7:

*radial stress*(σ

_{r}). The stress in the radial direction at a point in the tube or cylinder wall is shown in Equation 1.8:

*P*is the internal pressure in the tube or cylinder,

*a*is the internal radius of the tube or cylinder,

*b*is the external radius of the tube or cylinder, and

*r*is the radius to the point in tube where the radial stress is calculated.

*equivalent stress*, which is determined using the Von Mises equivalent stress formula shown in Equation 1.9:

_{1}is the longitudinal stress, σ

_{h}is the hoop stress, and τ

_{c}is the tangential shear stress (from material flowing through the pipe).

## Table of contents

*The Effect of Creep and Other Time Related Factors on Plastics and Elastomers*(2nd ed.). Elsevier Science. Retrieved from https://www.perlego.com/book/1837009/the-effect-of-creep-and-other-time-related-factors-on-plastics-and-elastomers-pdf (Original work published 2009)

*The Effect of Creep and Other Time Related Factors on Plastics and Elastomers*. 2nd ed. Elsevier Science. https://www.perlego.com/book/1837009/the-effect-of-creep-and-other-time-related-factors-on-plastics-and-elastomers-pdf.

*The Effect of Creep and Other Time Related Factors on Plastics and Elastomers*. 2nd edn. Elsevier Science. Available at: https://www.perlego.com/book/1837009/the-effect-of-creep-and-other-time-related-factors-on-plastics-and-elastomers-pdf (Accessed: 15 October 2022).

*The Effect of Creep and Other Time Related Factors on Plastics and Elastomers*. 2nd ed. Elsevier Science, 2009. Web. 15 Oct. 2022.