Simultaneous Monitoring of Component Thickness and Internal Temperature Gradient Using Ultrasound

In the field of structural health monitoring (SHM), the use of ultrasonic transducers has been increasingly prevalent for thickness gauging and corrosion monitoring. Since temperature affects ultrasonic velocity, temperature fluctuations and non-uniform temperature distributions in components are a major source of uncertainty for ultrasonic measurements. Recently, ultrasound-based temperature sensing methods have gained increasing attention because of their ability to measure subsurface temperature distributions in solid media. While conventional ultrasonic techniques can either measure the thickness of a component at constant temperature or the (subsurface) temperature of the component at constant thickness, measurement accuracy and precision can be greatly compromised if both factors vary simultaneously. In this work, we explore a dual wave approach to overcome this limitation of the conventional methods. Results of simulation and experimental studies show that co-located shear and longitudinal pulse echo measurements can be used to determine both the thickness and through-thickness temperature gradient of a steel plate while the structure is undergoing thickness loss at rapidly changing temperature.