Page 15 - Mechanical Behavior of Materials

14 Preface

Conversion in the opposite direction involves dividing by the equivalence value.
137.9MPa
= 20.0ksi
137.9MPa = MPa
6.895
ksi
It is also useful to note that strains are dimensionless quantities, so no units are necessary. Strains
are most commonly given as straightforward ratios of length change to length, but percentages are
sometimes used, ε % = 100ε.

MATHEMATICAL CONVENTIONS

Standard practice is followed in most cases. The function log is understood to indicate logarithms
to the base 10, and the function ln to indicate logarithms to the base e = 2.718 ... (that is, natural
logarithms). To indicate selection of the largest of several values, the function MAX() is employed.

NOMENCLATURE

In journal articles and in other books, and in various test standards and design codes, a wide variety
of different symbols are used for certain variables that are needed. This situation is handled by using
a consistent set of symbols throughout, while following the most common conventions wherever
possible. However, a few exceptions or modifications to common practice are necessary to avoid
confusion.
For example, K is used for the stress intensity of fracture mechanics, but not for stress
concentration factor, which is designated k.Also, H is used instead of K or k for the strength
coefficient describing certain stress–strain curves. The symbol S is used for nominal or average
stress, whereas σ is the stress at a point and also the stress in a uniformly stressed member. Dual
use of symbols is avoided except where the different usages occur in separate portions of the book.
A list of the more commonly used symbols is given inside the back cover. More detailed lists are
given near the end of each chapter in a section on New Terms and Symbols.

USE AS A TEXT

The various chapters are constituted so that considerable latitude is possible in choosing topics
for study. A semester-length course could include at least portions of all chapters through 11, and
also portions of Chapter 15. This covers the introductory and review topics in Chapters 1 to 6,
followed by yield and fracture criteria for uncracked material in Chapter 7. Fracture mechanics is
applied to static fracture in Chapter 8, and to fatigue crack growth in Chapter 11. Also, Chapters 9
and 10 cover the stress-based approach to fatigue, and Chapter 15 covers creep. If time permits,
some topics on plastic deformation could be added from Chapters 12 and 13, and also from
Chapter 14 on the strain-based approach to fatigue. If the students’ background in materials science
is such that Chapters 2 and 3 are not needed, then Section 3.8 on materials selection may still be
useful.