Abstract
Evaluation method of the fatigue limit of material with small crack under tensile mean stress, using the stress ratio parameter and effective threshold stress intensity factor range (ΔK_<eff,th>), was proposed. By this method, the fatigue limit can be evaluated in high mean stress area and low mean stress area separately. In order to define the crack size, which is applied to the evaluation method, the variation of the small crack area affected by stress ratio was shown, using the relationship between threshold stress intensity factor range (ΔK_<th>) and the projected area of crack size in the direction of the load (√<area>). The higher stress ratio is, the smaller the upper crack size of small crack area is considered to be. Taking non-combustible Mg alloy as an example, tension-compression fatigue tests were carried out. Using the results of the tests, the validity of the proposed evaluation method was examined.
