Influence of loading frequency on the rules and mechanisms of fatigue crack growth in titanium alloys. Report 2

Abstract

1. The use of the\(\Delta K - \Delta K\sqrt v\) auxiliary coordinates makes it possible to present the results of investigations of fatigue crack growth rate in the form of a kinetic curve consisting of five regions, the near-threshold, the intermediate between the near-threshold and the next, the region of a quadratic relationship of fatigue crack growth rate to stress intensity factor, the intermediate between this region and the next, and the region of unstable fatigue crack growth. In each of these regions there is observed a certain percent relationship of the failure micromechanisms realized, departure beyond the limits of which is accompanied by a break on the kinetic curve and a change in the form of fracture surface on the macrolevel. 2. The cyclic loading frequency does not influence the failure mechanisms, which are not a function of deformation rate, but does cause a decrease in the parameters dependent upon the time of the material under the action of the maximum load, which are the sizes of the cells and the bands of the dislocation structure and, as a consequence, the spacing of the fatigue striations. With an increase in loading frequency the values of the stress intensity factor corresponding to the start of the region of agreement of the micro- and macrorates of fatigue crack growth do not change.