FATIGUE-CRACK GROWTH IN CONSIDERATION OF MEAN STRESS AND DAMAGE ACCUMULATION

A fatigue crack growth rate in consideration of fatigue damage accumulation and the mean stress on fatigue material elements ahead of a crack tip are derived using both Miner's rule and the Manson-Coffin relationship. The theoretical equation of fatigue crack growth rate is shown in terms of J-integral range, size of a fatigue material element, fatigue damage parameter and stress ratio on the fatigue material element in front of the crack tip, etc. The stress ratio of the crack tip fatigue material element varies with the applied stress ratio and fraction of plastic component of J-integral range. As the fraction of plastic component of J-integral range increases, the fatigue crack growth rate increases. The theory formally predicts the experimental phenomenon that under elastic-plastic fatigue loading the shorter crack grows faster than the longer crack for the same J-integral range. The theoretical fatigue crack growth rates am compared with previous experimental results.