The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and λ and developed a method of formulating critical stress-singularity parameter Hth for each order of stress singularity λ by utilizing critical distance stress theories (point method and line method), which can be derived from two typical strength parameters, namely, fatigue limit σw0 and threshold stress-intensity factor range ΔKth. These estimated critical Hth (λ) value agreed well with the experimentally measured value. Using these simple critical distance stress approach we estimated the fatigue strength of general stress concentration structures such as, round hole, elliptical hole, V notch and contact edge structures. Then these critical distance stress approaches are applied to estimate the size effects of structures. And the eligibility of these estimated results are confirmed by comparing these estimated results with the experimental results. Finally these estimated results and experimental results are compared with the estimated results by other researchers such as, Neuber, Siebel, Ishibashi and Heywood. And we can confirm the superiority of this critical distance stress approach.

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