Nondestructive Methods to Characterize Rock Mechanical Properties at Low-Temperature: Applications for Asteroid Capture Technologies
Date of Graduation
Statler College of Engineering and Mineral Resources
Christopher A Noble
Recent government initiatives and commercial activities have targeted asteroids for in situ material characterization, manipulation, and possible resource extraction. Most of these activities and missions have proposed significant robotic components, given the risks and costs associated with manned missions. To successfully execute these robotic activities, detailed mechanical characteristics of the target space bodies must be known prior to contact, in order to appropriately plan and direct the autonomous robotic protocols. Unfortunately, current estimates of asteroid mechanical properties are based on limited direct information, and significant uncertainty remains specifically concerning internal structures, strengths, and elastic properties of asteroids. One proposed method to elucidate this information is through in situ, nondestructive testing of asteroid material immediately after contact, but prior to any manipulation or resource extraction activities. While numerous nondestructive rock characterization techniques have been widely deployed for terrestrial applications, these methods must be adapted to account for unique properties of asteroid material and environmental conditions of space. For example, asteroid surface temperatures may range from -100°C to 30°C due to diurnal cycling, and these low temperatures are especially noteworthy due to their deleterious influence on non-destructive testing.;As a result, this thesis investigates the effect of low temperature on the mechanical characteristics and nondestructive technique responses of rock material. Initially, a novel method to produce low temperature rock samples was developed. Dry ice and methanol cooling baths of specific formulations were used to decrease rock to temperatures ranging from -60°C to 0°C. At these temperatures, shale, chalk, and limestone rock samples were exposed to several nondestructive and conventional mechanical tests, including Schmidt hammer, ultrasonic pulse velocity, point load, and uniaxial compression. Experimental results show that rock mechanical properties (i.e. uniaxial compressive strength and Young's modulus) and nondestructive test responses (i.e. P-wave velocity and Schmidt rebound) are both influenced by low temperature, and the nature of the response depends on the rock type. Chalk and limestone show increased Young's moduli and decreased Schmidt rebounds and P-wave velocities with decreased temperature, while shale shows decreased Young's modulus and increased P-wave velocity. A significant increase in uniaxial compressive strength is observed for limestone samples with decreased temperature, though the inconsistent strength of chalk and shale samples at room temperature impaired the significance of correlations between decreased temperature and strength change for these samples. Altogether, these results indicate that ultrasonic pulse velocity and impact hammer methods may be suitable for in situ characterization of asteroid material; however, these methods will require temperature correction factors.
Savage, Kara A., "Nondestructive Methods to Characterize Rock Mechanical Properties at Low-Temperature: Applications for Asteroid Capture Technologies" (2016). Graduate Theses, Dissertations, and Problem Reports. 6573.