Thermo-acoustoelastic determination of third-order elastic constants using coda wave interferometry

Accurate determination of third -order elastic constants (TOECs) is important for quantifying the nonlinear elastic responses of solid materials. However, conventional experiments are laborious and may produce data with large error margins, so the TOECs of many isotropic materials have not been obtained. To solve this problem, a reliable and accurate measurement method based on the thermo-acoustoelastic effect was developed to determine the TOECs of isotropic materials. Additionally, the relationships between the thermo-acoustoelastic constant (TAEC) of bulk waves and TOECs under different constraints were derived. Subsequently, the thermal effect was employed as the driving force for bulk wave velocity change, and a simple thermal cycling experimental procedure was constructed to investigate the thermo-acoustoelastic responses of 6061-T6 aluminum. The experimental results indicated that bulk wave velocity changes caused by thermal strain were 19.4 times greater than in conventional acoustoelastic experiments. This heightened sensitivity could significantly reduce experimental measurement errors. Furthermore, the linear regression slope of thermal hysteresis curves was used to calculate TAEC, demonstrating excellent repeatability and reproducibility. Notably, the TAEC estimation error was within 3.54%, which is nearly unattainable with conventional methods. Finally, the effectiveness of the proposed method was verified by comparing TOECs obtained from thermal cycling experiments and acoustoelastic experiments. This study provides new insights into thermo-acoustoelastic behavior and will promote the development of nonlinear ultrasonic testing techniques.