OS1708 微小き裂部位の疲労強度評価

Abstract

Fatigue strength evaluation for small crack using fracture mechanics has a disadvantage that the value of stress intensity factor is low than long crack. We apply the critical distance theory to that. Critical distance theory is fatigue strength evaluation that the stress is fatigue limit when stress distribution of crack specimen matches a point of a stress distribution of smooth specimen and threshold stress intensity factor. Pulsating fatigue test conditions are 20Hz of frequency and 0 of stress ratio. Based on the critical distance theory, we applied analysis of stress distribution using FEM to evaluate the fatigue strength evaluation. As the crack lengths approach small crack, stress distribution of crack tips tend to reduce. As the result of critical distance theory using stress distributions, fatigue strength evaluations for long cracks using fracture mechanics were consistent to critical distance theory. On the other hand, fatigue strength evaluation for small cracks using critical distance theory and fatigue test results were convergent to a point of fatigue limit of smooth specimen. As the result, fatigue strength evaluation based on the critical distance theory is effective in all crack lengths. However, because the results depend on the fatigue limit of smooth specimen and the threshold stress intensity factor, we need to find the accurate value based on the experiment.