An improved strain gauge method for measuring the dynamic stress intensity factor, KID, of a running crack is described. By orienting the gauge relative to the crack propagation path the gauge response is optimized for the analysis. Higher order terms in the dynamic strain field representation are demonstrated to be important in the analysis. An application of the method is illustrated in the measurement of KID for a very hard alloy steel, 4340, with a crack propagating at 656 m/s.
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