Date of Award
2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Materials Science
Committee Chair
Judith Schneider
Committee Member
Cheng Chen
Committee Member
Gang Wang
Research Advisor
Judith Schneider
Subject(s)
Friction stir welding, Ultrasonics, Thermometers, Temperature measurements
Abstract
Friction Stir Welding (FSW) is a solid-state joining process widely used for aluminum alloys in aerospace and structural applications due to its ability to produce high-quality joints without melting. The thermal history of the weld tool and surrounding material plays a critical role in governing material flow, microstructural evolution, and resulting mechanical properties. However, accurate measurement of temperature at the tool–workpiece interface remains challenging due to the transient nature of the process, geometric constraints, and ability to obtain subsurface temperature. This thesis investigates the use of ultrasonic thermometry as a non-destructive, high-temporal-resolution method for measuring time dependent, site-specific temperatures from a rotating FSW tool as it transverses the length of a butt weld. Ultrasonic thermometry exploits the temperature dependence of elastic wave velocity in solids, enabling indirect temperature measurement through monitoring changes in ultrasonic time of flight. The physical basis of the technique is established by deriving a linear relationship between temperature change and fractional time-of-flight variation, characterized by a material-dependent velocity expansion coefficient. Experimental calibration procedures are developed to determine this coefficient for an H13 steel weld tool under controlled thermal conditions. To adapt this technology to any FSW equipment, a Smart Tool was designed and instrumented with an ultrasonic transducer (UT). The tool was installed on a standard FSW equipment and equipped with a slip ring to transmit the UT signal from the rotating tool to a data collection system allowing real-time data acquisition. Temperature measurements were obtained at both the shoulder and pin regions of the tool during welds performed on three 2xxx series aluminum alloys with two different thicknesses to evaluate differences as a function of the tool rotation.
Recommended Citation
Aiken, Daniel Tyler, "Real time temperature measurement of weld nugget during friction stir welding operation using ultrasonic thermometry" (2026). Theses. 838.
https://louis.uah.edu/uah-theses/838