Size effects in gigacycle fatigue of high-strength steel under ultrasonic fatigue testing

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