THE EFFECT OF ROLLING DIRECTION REVERSAL ON FATIGUE-CRACK MORPHOLOGY AND PROPAGATION

The effect of repeated rolling direction reversal on crack morphology, propagation and RCF life of rail steel is investigated in this paper. It has been established that reversal is of beneficial effect on RCF life. This effect is a function of the reversal regime. An optimum rev ersal is achieved when the number of rolling cycles per reversal is be tween 25% and 37% of the uni-directional RCF life cycles of the materi al. Under such a reversal regime, the RCF life is almost doubled. Roll ing direction reversal appears to affect RCF cracking propagation as w ell as morphology. A new mechanism, the 'variable crack face friction mechanism', is proposed to explain this effect.