Non-contact Measurement of Creep in Ultra-High-Temperature Materials

Our team has developed a novel approach to measuring creep at extremely high temperatures using electrostatic levitation (ESL). This method has been demonstrated on niobium up to 2300°C, while ESL has melted tungsten (3400°C). High-precision spheres, 2-3 mm diameter are levitated in the NASA MSFC ESL, a national user facility, and rotated at up to 250,000+ RPM at the measurement temperature. The rapid rotation loads the sample through centripetal acceleration, causing it to deform. The deformation of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The deformations analyzed to determine the constitutive constants in the creep relation. Furthermore, the non-contact method exploits stress gradients within the sample to determine the stress exponent in a single test, versus the many tests required with conventional methods. This method was validated in collaboration with the University of Tennessee for niobium at 1985 °C, with agreement within the uncertainty of the conventional measurements. A similar method will be employed on Ultra-High-Temperature Ceramics of interest to the AFOSR, such as ZrB2 or HfB2 SiC composites.