Acoustic Birefringence Changes in the Base Metal and Heat Affected Zone of ASTM 1020 Steel under Plastic Deformation and Fatigue

Abstract

This paper deals with metallographic studies and ultrasonic investigations of acoustic birefringence in the base metal and heat affected zone of welded specimens of ASTM 1020 steel under uniaxial tension and low-cycle fatigue. We examined microstructural changes on the surface using optical microscope. It was found that development of slip bands differs in the base metal and heat affected zone. The ultrasonic pulse echo method was used for the determination of acoustic birefringence and velocities of ultrasonic shear waves. The differences in the change in velocities in the base metal and in heat affected zone were revealed. Acoustic birefringence was found to change monotonously in the base metal under fatigue as well as in the base metal and heat affected zone under uniaxial tension. For heat affected zone, during fatigue, acoustic birefringence was found to change non-monotonously up to cycle ratio of 0.3 and decrease monotonously after cycle ratio of 0.3. Based on the relationship between relative number of loading cycles, or plasticity resource, and acoustic birefringence, ultrasonic techniques were proposed for assessing damage.