1970 Volume 19 Issue 206 Pages 994-1000
To perform a series of X-ray studies on low-cycle fatigue, the failure process of a pre-pulled 0.16%C steel under constant strain cycling was observed with X-ray diffraction technique. The results obtained in this study are as follows:
(1) The specimen pulled to 17% after preliminary annealing exhibited cyclic strain-softening in the first half of its fatigue process under the strain range of 2.0% without mean strain.
(2) The integral breadth of diffraction peak decreased with the progress of strain-softening. It was established by a profile analysis of diffraction peak that the increase in particle size decreased its integral breadth.
(3) During the process of strain-softening, the diffraction spots in the micro-beam Debye-Scherrer ring became fine and sharp. This microstructural change together with the result mentioned above in (2) revealed the fact that mechanism of strain-softening in low-cycle fatigue was the annihilation and rearrangement of dislocations produced by pre-tension.
(4) The failure process of the cyclic-softened specimens consisted of two stages, the first was the stage of development of surface roughness, and the last of the growth and multiplication of the cracks.
(5) Good correlation was found between the integral breadth and the extent of hardening in cyclic hardening and-softening processes.
(6) The hypothesis, that the surface roughness increased, while the cracks decreased, the integral breadth, would account for the mode of change in the integral breadth occasioned by the low cycle fatigue both of the cyclic hardened specimens and of the cyclic softened specimens. It was possible on that account to make clue of the integral breadth to detecting the fatigue damage like surface roughness and cracks.