Dynamic Optical Investigations of Hypervelocity Impact Damage

Citation

Lamberson, Leslie Elise (2010) Dynamic Optical Investigations of Hypervelocity Impact Damage. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/AQJH-3D60. https://resolver.caltech.edu/CaltechTHESIS:05282010-183132978

Abstract

One of the prominent threats in the endeavor to develop next-generation space assets is the risk of space debris impact in earth’s orbit and micrometeoroid impact damage in near-earth orbit and deep space. To date, there is no study available which concentrates on the analysis of dynamic crack growth from hypervelocity impacts on such structures, resulting in their eventual catastrophic degradation. Experiments conducted using a unique two-stage light-gas gun facility have examined the in situ dynamic fracture of brittle polymers subjected to this high-energy-density event. Optical techniques of caustics and photoelasticity, combined with high-speed photography up to 100 million frames per second, analyze crack growth behavior of Mylar and Homalite 100 thin plates after impact by a 1.8 mm diameter nylon 6-6 right cylindrical slug at velocities ranging from 3 to 7 km/s (7000–15500 mph). Crack speeds in both polymers averaged between 0.2 and 0.47 cR, the Rayleigh wave speed (450–1000 mph). Shadow spots and surrounding caustics reveal time histories of the dynamic stress intensity factor, as well as the energy release rate ahead of the mode-I, or opening, crack tips. Results indicate that even under extreme impact conditions of out of-plane loading, highly localized heating, and energetic impact phenomena involving plasma formation and ejecta, the dynamic fracture process occurs during a deformation regime dominated by in-plane loading. These findings imply that the reliability of impacted, thin-walled, plate and shell space structures, idealized by the experimental configuration investigated, can be predicted by the well defined principles of classical dynamic fracture mechanics.

Thesis Files