University of Illinois Engineering Experiment Station. College of Engineering. University of Illinois at Urbana-Champaign.
Abstract
The fatigue damage of a high strength 12% nickel maraging steel was observed to entail a change in axial stress range and a change in the substructure resulting from cyclic deformation at a constant strain range. Axial tests in low cycle fatigue and longer cycle fatigue were performed on samples of solution treated and on aged 12% nickel maraging steel at constant testing temperatures ranging from 32°F to 415°F. The substructure of untested samples and samples tested in static deformation was also observed by means of thin film electron microscopy. The change in stress range due to fatigue was resolved into two components of stress which were found to be different functions of the number of applied cycles of fatigue. A dislocation model based on the ordering of dislocation tangles was proposed and this model was supported by an activiation energy which was determined for the cyclic softening of 12% nickle maraging steel. Cyclic hardening was related to hardening by the generation of point defects from the observations made in this investigation as related to a previous investigation of LiF. Predictions of fatigue life based on the same amount of cyclic hardening at failure duplicated the experimental fatigue lives within 20% from 40 to 20,000 cycles.Bureau of Ships, Department of the Navy, Contract N0bs 94232, Project Serial No. SF 020-01-05; Task 729-
