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A brief review is given of basic definitions and concepts applicable to linear elastic analysis of dynamic fracturing. It is noted that determinations of the crack-extension force, ς, based upon conservation of energy may require adjustment for energy losses elsewhere than at the crack tip. From direct observation of running crack stress fields, crack speed increases rapidly with K toward a limiting speed which is maintained until K becomes large enough to cause crack division. The minimum K value of this relationship is termed KIm. Estimates of KIm by use of the test methods termed KId (dynamic initiation) and KIa (crack arrest) are of practical interest. The uncertainties associated with such estimates as well as testing difficulties are restricted mainly to the region above nil-ductility transition temperature where toughness increases rapidly with test temperature. Use of deep face grooves to overcome testing problems in the high toughness range introduces serious questions as to applicability of test results to natural cracks in heavy section structures.
crack propagation, dynamic fracturing, fracture (materials), fracture strength, fracture properties
Visiting professor of mechanical engineering, University of Maryland, College Park, Md.