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Impact Damage Thresholds in Brittle Materials Impacted by Water Drops.
Final rept. 1 Mar 75-31 Dec 78,
ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
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The damage threshold for brittle materials impacted by water drops has been studied by using a combination of analytic and numerical approaches to obtain solutions for the impact stress fields and dynamic stress intensity factors. It has been shown that expressions for the damage threshold, which consists of the activation of pre-existent surface microcracks, can be derived from these solutions. The expressions identify three types of behavior, depending upon the adjacence of the pre-existent cracks to the impact center, vis-a-vis their size, and describe the respective roles of the three important target parameters, the fracture toughness, the elastic wave velocity and the pre-existent flow size. An absolute damage threshold has also been defined. The conditions at this threshold are demonstrated to be reasonably consistent with available threshold measurements. Author
APPROVED FOR PUBLIC RELEASE