Fatigue Crack Propagation in Metals and Alloys

314 Pages·2007·5.76 MB·English

by  Ulrich Krupp

Ulrich Krupp
Fatigue Crack Propagation
in Metals and Alloys
Microstructural Aspects and
Modelling Concepts

Ulrich Krupp
Fatigue Crack Propagation
in Metals and Alloys
1807–2007 Knowledge for Generations
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Ulrich Krupp
Fatigue Crack Propagation
in Metals and Alloys
Microstructural Aspects and
Modelling Concepts
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VII
Foreword
Although it was understood very early that fatigue was a matter of creating and
propagating a crack to the point of ultimate failure of a specimen or structural
component, indeed long before “crystallization” theories of fatigue eventually died
from natural causes, no significant measurements of crack propagation kinetics
existed before the early 1960’s. Theories of crack growth existed before then, of
course, highly speculative and based on unrealistic models. Only after appropriate
fracture mechanics parameters were developed to allow the driving forces for
crack growth to be expressed for a wide variety of component geometries did pre-
dictive capability greatly improve for fatigue design purposes. The traditional
approach of designing against fatigue, known as the “total-life” approach, worked
adequately on the whole before the arrival of linear elastic fracture mechanics,
mainly because it was backed by extensive (and expensive) experimentation. It also
has undergone improvements, for examples in counting cycles during variable
load cycling and in strain (rather than stress)-based predictions, and continues in
wide use today, even in certain aerospace applications where usually fracture
mechanics considerations now dominate. The total-life approach can be valid in
situations where inspections for cracks are difficult or are economically prohibi-
tive. The success of fracture mechanics in applications to aircraft probably arises
from the necessity to use high stresses in aircraft and where relatively infrequent
very high stress cycles promote early crack initiation, even in the absence of signif-
icant manufacturing defects, on which some fracture mechanicians rely to justify
the approach.
Like most books on fatigue, the aim of Dr. Krupp’s book is to help to make bet-
ter fatigue life predictions. Although the title of his book implies an emphasis on
fracture mechanics, and does focus on fracture mechanics (and almost exclusive-
ly on metals), it contains an elaborate chapter on crack initiation, and it also deals
with the underlying physics of fatigue mechanisms. It is a well-balanced book in
other respects as well, in the referencing between early and recent publications,
between fundamental aspects such as dislocation considerations and modeling,
and particularly in the balance between mechanics and materials considerations.
It covers the range from elementary dislocation behavior to recent advances in
modeling. It is thus suited to a wide range of students from different backgrounds
and developmental stages; veterans of fatigue studies will find it interesting. In