Temperature-compensated acoustoelastic measurements of the stress in bolts

Temperature is an important factor influencing the results of non-destructive acoustoelastic measurements of the internal stress in objects like bolts owing to its impact on the elastic modulus of the material. However, conventional methods that seek to obtain the temperature field of the measurement object independently suffer from high complexity and low accuracy. The present work addresses this issue by developing a method that eliminates the influence of temperature on the acoustoelastic measurements of stress in bolts based on the time interval between the head and coda waves of ultrasonic signals. The origin of coda waves in rod-shaped objects is investigated theoretically, and this understanding is applied for analyzing the relationship between the temperature and internal stress of the object and the time interval between the head and coda waves of ultrasonic signals. The analysis demonstrates that the observed time interval is related to temperature and stress in accordance with a linear relationship with the velocity of the longitudinal wave and the rod diameter. Finally, the obtained relationship is applied within an acoustoelastic measurement model to eliminate the influence of temperature from the measurement results.