Materials Science and Engineering: An Introduction

William D. Callister, Jr. David G. Rethwisch

ISBN #9780471736967

7th Edition

771 Questions

65,043 Students Helped

Homework Questions

Summary

Learning Objectives

Key Concepts

Example Problems

Explanations

Common Mistakes

Summary

This textbook section provides an in-depth overview of the structural and mechanical behavior of polymers, discussing key phenomena such as stress–strain responses, viscoelasticity, and fracture. It explains how molecular features and processing techniques influence critical properties—such as tensile modulus, strength, and ductility—by modifying structure through methods like drawing, heat treatment, and additive incorporation. Additionally, the section covers polymer synthesis via addition and condensation polymerization and describes multiple forming techniques. Overall, understanding these fundamentals is essential for designing polymer-based materials with targeted performance characteristics in a wide range of applications.

Learning Objectives

Key Concepts

CONCEPT

DEFINITION

Ceramics Fabrication Techniques

The methods and processes used for shaping, forming, and consolidating ceramic materials into final products with desired properties.

Example Problems

Example 1

From the stress-strain data for poly(methyl methacrylate $)$ shown in Figure $15.3,$ deter mine the modulus of elasticity and tensile strength at room temperature $\left[20^{\circ} \mathrm{C}\left(68^{\circ} \mathrm{F}\right)\right]$, and compare these values with those given in Table 15.1.

Example 2

In your own words, briefly describe the phenomenon of viscoelasticity.

Example 3

For some viscoelastic polymers that are subjected to stress relaxation tests, the stress decays with time according to $\sigma(t)=\sigma(0) \exp \left(-\frac{t}{\tau}\right)$ where $\sigma(t)$ and $\sigma(0)$ represent the timedependent and initial (i.e., time $=0$ ) stresses, respectively, and $t$ and $\tau$ denote elapsed time and the relaxation time; $\tau$ is a time independent constant characteristic of the material. A specimen of some viscoelastic polymer with the stress relaxation that obeys Equation 15.10 was suddenly pulled in tension to a measured strain of $0.5 ;$ the stress necessary to maintain this constant strain was measured as a function of time. Deter$\operatorname{mine} E_{r}(10)$ for this material if the initial stress level was 3.5 MPa $(500$ psi), which dropped to $0.5 \mathrm{MPa}(70 \mathrm{psi})$ after $30 \mathrm{s}$.

Example 4

In Figure 15.27 , the logarithm of $E_{r}(t)$ versus the logarithm of time is plotted for PMMA at a variety of temperatures. Make a plot of $\log E_{r}(10)$ versus temperature and then estimate its $T_{g}$.

Example 5

On the basis of the curves in Figure 15.5, sketch schematic strain-time plots for the following polystyrene materials at the specified temperatures: (a) Crystalline at $70^{\circ} \mathrm{C}$ (b) Amorphous at $180^{\circ} \mathrm{C}$ (c) Crosslinked at $180^{\circ} \mathrm{C}$ (d) Amorphous at $100^{\circ} \mathrm{C}$