On Low-Cycle Fatigue

Abstract: Popular Abstract in English The present work deals with fracture in structures which are exposed to relatively few cycles of static loading during their life-time (maximum some ten thousand). Structures exposed to nearly monotonic loading are rare, except for such loaded mainly by their own weight. In spite of this fact, fracture mechanic methods developed for monotone loading are commonly used on statically loaded structures, which may be exposed to several thousand major load cycles during their life-time. Examples are pressure vessels and oil tankers. The methods used for monotone loading are, in their simplest form, based on linear fracture mechanics. Generally, these methods can easily be used by engineers, and the basic expressions needed are found in handbooks, e.g. in Tada et al. (1973). However, often the load is so high that non-linear fracture mechanics has to be considered. The procedure then becomes much more complicated, and, what is more serious, the theoretical grounds become weaker (Broberg, 1977). The purpose of this work is to present a fracture mechanics method for cyclic loading which is easy to use and, at the same time, predicts the number of load cycles a structure can withstand until it fails. It concentrates on non-linear crack growth, which is usually not covered by methods to predict failure under high-cycle fatigue conditions. A requirement at the onset of the work was, that the method should be based on expressions and data available in handbooks, and that it should not involve extensive calculations.