Abstract
Fatigue strength evaluation for small crack structures using fracture mechanics has a disadvantage as the value of threshold stress intensity factor range has to be modified. Many modification methods are proposed by the researchers. The most dominant parameter is the crack length which is applied to the modification equations. However, in actual engineering fields, the determination of such small crack length is difficult, because the surrounding condition near the small crack is complicated. In our previous papers, we introduced the critical distance stress theory for fatigue limit estimation of general stress concentrating structures such as circular and elliptical holes, stress singularity structures with sharp notch, contact edge and adhesive edge structures. The prediction by the theory successfully agreed with the corresponding experimental results, and the availability of the method was confirmed for wider field structures. In the present paper, we apply this critical distance stress theory to the fatigue strength evaluation for small crack structures. This method requires only the fatigue limit of the smooth specimen, threshold stress intensity factor range of the material and the stress distribution near the crack tip. The estimated fatigue limit for small cracked specimens coincided well with the experimental results. The estimated limits are compared with those proposed by other researchers using the equivalent crack length in order to check the availability of this critical distance stress theory.
