Influence of interval fatigue tests on fatigue characteristics of salt rock

The influence of no-stress intervals on the fatigue activities is studied by comparing the characteristics of the conventional fatigue tests with those of interval fatigue tests, which combine the cyclic stress and intervals with no stress. The samples from the interval fatigue tests and conventional fatigue tests present a large variety of differences caused by intervals: (1) Under the same conditions of stress, the fatigue lives of samples from the interval fatigue tests are lower more than 50 percent than those from the conventional fatigue tests; (2) The residual deformation of each stress period varies from the duration of interval and increases with it. The accumulated rate of plastic deformation behaves similarly to residual deformation; (3) In the mass, The unloading elastic modulus increases with the stress period number. This parameter of samples from the interval fatigue tests increases as the duration becomes longer. The mechanism of these phenomena is as follows: when the internal flaws develop and grow, the adjacent area yields in different spatial-temporal orders, resulting in uncoordinated response and the corresponding residual stress. Taking into account the Bauschinger effect, the plastic deformation will be larger in the following loading procedure.