Heat Dissipation Behavior of a Low-Strength-Steel Welded Joint in Ultrasonic Fatigue

The coupled effects of heat and frequency in very-high-cycle fatigue are known under ultrasonic testing, while the heat dissipation behavior of welded joints is less investigated. In this work, the specimen surface temperature of a low-strength-steel welded joint and its base metal were monitored by infrared thermal imaging technique under ultrasonic fatigue loading. Results showed that the surface temperature distribution of both welded and base metal exhibited a parabola shape, and the temperature evolved with three stages. The location of the highest temperature within the weld metal correlated well with fatigue failure location. The inhomogeneity and asymmetry of temperature distribution implied a dominant role for heat transfer mode and insignificant influence of microstructure heterogeneity or specimen type. The nature of heat dissipation in low-strength steel in ultrasonic fatigue was thermal–mechanical coupling effect, which should be paid close attention in the standardization of ultrasonic fatigue testing.