Influence of carbon content on surface stress evaluation of carbon steel by ultrasonic wave

Based on optimization of ultrasonic acoustoelastic formula, the influence of carbon content on ultrasonic acoustoelastic coefficient of carbon steel was discussed. Two ultrasonic transducers with the center frequency of 5 MHz were used to collect ultrasonic signal, the difference in flight time between the ultrasonic signals was calculated with cross correlation coefficient function, and the ultrasonic acoustoelastic coefficient of the carbon steel under tensile was obtained with linear fitting method. The tensile fracture morphology of the carbon steel was observed by SEM. The results show that comparing with 45 steel, the ultrasonic acoustoelastic coefficient of Q235 steel is higher, the difference in time of flight between the ultrasonic wave fluctuates more obviously. The difference between the turning point load of the experimental result and elastic limit load of Q235 steel is smaller. The difference in inhomogeneous plastic deformation of the specimen surface by initial stress is responsible for the above results, and coupling state between the ultrasonic transducer and the specimen also affects the results.