Comparative Assessment of Fatigue-Thresholds Estimated by Short and Long Cracks

Abstract

The safe life design philosophy of structural components is based on the knowledge of the fatigue threshold for long cracks (ΔKth). The emergence of the concept of short cracks, its numerous experimental verification and the continued studies on its growth behaviour over the past years have brought forward challenges to the basis of the safe life design philosophy. However, short cracks interestingly exhibit either single or multiple-thresholds. But prior investigations related to the determination and examinations of fatigue threshold for short cracks (ΔKthsc) in structural materials are limited in number. In an earlier communication [1], the largest value amongst the detected thresholds associated with short cracks has been referred as “near long crack fatigue threshold” (NLFTH) and the magnitude of NLFTH has been hypothesized as close to the fatigue threshold obtained from long crack experiments as illustrated using Fig.1. This investigation aims to explore the magnitudes of ΔKthsc and ΔKth for a few steels, to determine the NLFTH values for these materials and finally to make a comparative assessment of NLFTH with their corresponding ΔKth values.