Page 34 - Materials Science and Engineering An Introduction

6 • Chapter 1 / Introduction

Figure 1.3 The Liberty ship S.S. Schenectady, which, in 1943, failed
before leaving the shipyard.
(Reprinted with permission of Earl R. Parker, Brittle Behavior of Engineering
Structures, National Academy of Sciences, National Research Council, John
Wiley & Sons, New York, 1957.)
Remedial measures taken to correct these prob- • Improving welding practices and establishing weld-
lems included the following: ing codes.
• Lowering the ductile-to-brittle temperature of In spite of these failures, the Liberty ship program
the steel to an acceptable level by improving steel was considered a success for several reasons, the pri-
quality (e.g., reducing sulfur and phosphorus im- mary reason being that ships that survived failure were
purity contents). able to supply Allied Forces in the theater of operations
• Rounding off hatch corners by welding a curved and in all likelihood shortened the war. In addition,
reinforcement strip on each corner. 7 structural steels were developed with vastly improved
resistances to catastrophic brittle fractures. Detailed
• Installing crack-arresting devices such as riveted analyses of these failures advanced the understand-
straps and strong weld seams to stop propagating ing of crack formation and growth, which ultimately
cracks.
evolved into the discipline of fracture mechanics.

7 The reader may note that corners of windows and doors for all of today’s marine and aircraft structures are
rounded.

1.4 CLASSIFICATION OF MATERIALS
Solid materials have been conveniently grouped into three basic categories: metals, ce-
ramics, and polymers, a scheme based primarily on chemical makeup and atomic struc-
ture. Most materials fall into one distinct grouping or another. In addition, there are the
Tutorial Video: composites that are engineered combinations of two or more different materials. A brief
What are the
Different Classes explanation of these material classifications and representative characteristics is offered
of Materials? next. Another category is advanced materials—those used in high-technology applica-
tions, such as semiconductors, biomaterials, smart materials, and nanoengineered mate-
rials; these are discussed in Section 1.5.