255 微小き裂問題への特定位置応力法の適用

Abstract

Fatigue strength evaluation for small crack structures using fracture mechanics has a disadvantage as the value of threshold stress intensity factor range must be modified. Many modification models are presented by many researchers, in these modification equations the dominant parameters is crack length. But in actual engineering fields the determination of these small crack length are difficult as the surrounding structures near these small cracks are complicated. In previous papers we introduce critical distance stress theory for fatigue limit estimation of general stress concentrate structures such as circular or elliptical hole, stress singularity structures such as sharp notch, contact edge and adhesive edge structures. All estimated results coincided well with experimental results, and the availability of this method for more wide field structures can be confirmed. In this paper we apply this critical distance stress theory for fatigue strength evaluation of small crack structures. This method need only fatigue limit of smooth specimen σ_<w0>, and threshold stress intensity factor range ΔK_<th> of materials and stress distributions of structures near crack tips. The estimated fatigue limits of small cracked specimens coincided well with experimental results. Finally these estimated and experimental results are compared with other researchers estimated results using equivalent crack length, and the superiority of this critical distance stress theory can be confirmed.