切欠き底に発生した微小疲労き裂の検出とき裂閉口の測定

抄録

Short fatigue cracks initiated at the notch root were successfully detected at a fairly high accuracy by the ultrasonic amplitude calibration method for the notched compact specimens of an A508-3 steel. Crack closure measurements by the ultrasonic and back-face strain compliance methods were also performed. Crack growth characteristics at the notch root are similar to those of delyed retardation caused by a single peak overload. Also, transitional behavior from short cracks to long cracks was interpreted in terms of effective stress intensity ΔK_eff. The relation between crack growth rate da/dN and ΔK_eff for short cracks shows a fairly good agreement with those for long cracks.