Specimen size effects on gigacycle fatigue properties of high-strength steel under ultrasonic fatigue testing

Ultrasonic fatigue testing was conducted for high-strength steel, employing enlarged specimens with a straight section. The results showed good agreement with conventional servohydraulic fatigue test results, demonstrating the validity of ultrasonic fatigue testing using these enlarged specimens under conditions where fish-eye fractures occur. When the results were compared with those using conventional specimens, specimen size effects were clearly observed: enlarged specimens showed lower fatigue strength due to appearance of larger inclusions in the fish-eye fracture origin.