gigacycle fatigue behaviors in Fusion Zone and Heat Affected Zone of Q345 LA steel welded joints

摘要

The fatigue behavior in Fusion Zone (FZ) and Heat Affected Zone (HAZ) of widely used low alloy steel,Q345,in very high cycle fatigue regime was experimentally studied with ultrasonic fatigue testing system.It was found that the fatigue failure of HAZ specimen still occurred beyond 107 cycles,while a horizontal platform was obtained for FZ specimen in VHCF regime related to internal welding defects in fusing zone.A high-sensitivity infrared imaging system was used to measure the temperature changes during fatigue testing and the relationship of temperature variation and fatigue damage was discussed.The temperature of BM specimen would rise rapidly with the beginning of crack propagation.Fatigue crack propagation lives of HAZ and FZ were estimated by monitoring the natural frequency of specimen,which was varying with the crack size during the fatigue testing.Results showed that more than 99％ of the total fatigue life was occupied by the crack initiation process for base metal (BM) and HAZ.However,this number was scattered for FZ specimen at relatively low stress amplitude owing to the crack propagation from welding defects directly,without crack initiate life.