2009 Volume 3 Issue 10 Pages 1101-1114
Fatigue crack growth tests of two ferrite-pearlite and two ferrite-bainite steels with different size and spacing of particle, where pearlite/bainite (hard) particles were uniformly distributed in the ferrite matrix, were carried out to investigate effect of second phase particle on fatigue crack growth behavior in Paris regime. The fatigue crack growth curves for the four materials did not coincide each other, even when the crack growth curves were arranged by the effective stress intensity factor range. From the in-situ observations, crack tip stress shielding phenomena, such as interlocking, branching, etc were found on the crack wake, which enhanced fatigue crack growth resistance. Small size and spacing of pearlite/bainite particle seemed to induce small but frequent crack deflections, which resulted in crack closure phenomena. On the other hand, large size of pearlite/bainite particle seemed to induce stress shielding phenomena and then contribute to high crack growth resistance, which was the main reason for lower fatigue crack growth rate of the large size and spacing of hard particle compared the small size of hard particle.
