Electrochemical fatigue sensor study of fatigue in copper and Ti-6Al-4V under variable-amplitude loading
The problem of fatigue damage accumulation under variable-amplitude loading remains unresolved, despite decades of research. Although numerous models of damage accumulation have been proposed, none have been found that are wholly satisfying. The scientific challenges to the development of such a model include the varying fatigue behavior of metals and alloys that are of concern in fatigue, and the difficulty inherent in collecting data that bear on the problem. This experimental difficulty also relates to economics, for the techniques that permit collection of relevant data are costly. This work explores concepts underlying this problem---variation of the fatigue limit, load interaction, and equivalent states of damage---with the aid of the electrochemical fatigue sensor (EFS). The EFS is a device that exploits controlled electrochemical reactions to reveal information about damage accumulation continuously during the fatigue process. Materials that exhibit widely differing fatigue behavior are emphasized: oxygen-free, high-conductivity (OFHC) copper; and Ti-6Al-4V. With copper, parameters of the EFS response during fatigue correlate with the development of persistent slip bands (PSBs), and cracks. Changes in copper PSB activity are observed and concluded to be evidence of a damage-induced effect on the fatigue limit. Load-interaction effects, also connected to PSB activity, are observed under block loading of copper. In tests with Ti-6Al-4V, EFS-based data correlate with the formation and propagation of cracks; evidence of a load-interaction effect on propagation is observed. Parameters of the EFS response that relate to the concept of equivalent states of damage---a feature of various models of fatigue damage accumulation---are found in tests with both materials. The experimental results demonstrate the utility of the EFS in damage-accumulation studies; the conclusions drawn from the results should aid in the formulation of improved cumulative-damage models in the future. ^
Engineering, Materials Science
Andrew B Witney,
"Electrochemical fatigue sensor study of fatigue in copper and Ti-6Al-4V under variable-amplitude loading"
(January 1, 2006).
Dissertations available from ProQuest.