STUDY ON LOW CYCLE FATIGUE CRACK PROPAGATION BEHAVIOR UNDER TWO-STEPS VARIABLE AMPLITUDE

摘要

Low cycle fatigue in steel caused by earthquakes can result in large cyclic strain failures. In the studies conducted to date, low cycle fatigue crack propagation has primarily been investigated under constant amplitude loading. However, actual seismic motions are characterized by amplitude changeability from high to low or from low to high levels, and the effect of these alterations on crack growth in steel has not yet been clarified. Accordingly, this study examines crack propagation patterns under two-steps variable amplitude loading, which has two different uniform amplitude steps. The first part of this paper examines crack growth rates under constant amplitude conditions to obtain basic characteristic. Then, several patterns of two-steps variable amplitude loading are investigated. Research results show that, when compared to constant amplitude conditions, crack growth rates in steel increase when the amplitude decreases from high to low levels. Finally, a formula containing finite element analysis parameters was constructed and verified, thus providing a new method for obtaining good estimations of the crack growth rate.