TABLE OF CONTENTS PAUL H. WIRSCHING
Department of Aerospace and Mechanical Engineering
The University of Arizona, Tucson, AZ, USA 85721
E-mail: phw@u.arizona.edu
Fatigue is generally considered the most important failure mode in mechanical and structure systems. Modern reliability methods are available for managing the relatively large uncertainties in fatigue design factors. This chapter provides a review of fatigue reliability methods.
The physical process of fatigue is described in Fig. 1. Under the action of a longterm oscillatory stress, a fatigue crack initiates typically (but not always) on the surface at a point of stress concentration. In the second phase, the crack grows in a direction orthogonal to the stress. In the final phase, the crack reaches a point where the remaining material cannot support the quasi-static peak load.
Fatigue strength can be defined by an S-N curve as shown in Fig. 1. Fatigue data is characterized by relatively large scatter as measured by the coefficient of variation, C N, which can range from 25% to 150%.
It has been reported that fatigue accounts for 80% to 90% of all observed service failures in mechanical and structural systems. Fatigue failures are often catastrophic; many have come without warning and have caused significant property damage as well as loss of life. And many fractures have been observed in applications where failures previously had not been encountered.
There are several reasons for the dominance of this failure mode and the difficulties in trying to...
