5 - The Mechanical Behavior of Engineering Materials

Summary

Introduction

In the course of a career, an engineer can expect to be called upon to deal with the behavior of a great many different types of materials from which an object with a structural purpose is to be, or has been, fashioned. Metals, plastics, woods, and man-made composites of all kinds are plentiful in structural engineering practice. The paragraphs below provide a brief overview of these materials, starting with the metals.

The material that is used most extensively in modern engineering practice is steel. In comparison with other metals and composites, steels are cheap, and have the advantages of being stiff, strong, and hard. Thus steels are often the material of choice for vehicular applications such as automobile frames and aircraft landing gear. The superior high-temperature properties of certain alloy steels often results in their choice as a material for the structure of fuel-burning engines such as rockets. The principal drawback of steel for vehicular use is its relatively high weight density of approximately 0.28–0.29 lb/in³. There is presently a great variety of types of steel and steel alloys (Refs. [10–14]). There is also a great variety of designations of steels. Lists of specification equivalents can be found, for example, in Ref. [13]. The American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE) have agreed upon an AISI–SAE four-digit numbering system for steels that is widely, but not exclusively, used. It is outlined on p. 143 of Ref. [10].