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With the advent of ASTM Test Method for Measurement of Fatigue Crack Growth Rates (E 647-91) and the associated annexes for nonvisual methods of monitoring crack length, there exists a need to address many aspects of the role that automation plays in generating fatigue crack growth rate data. The current ASTM standard provides primary guidance for visual methods of monitoring crack length and manual control of the test. The associated annexes provide guidance for two common nonvisual methods of monitoring crack length. Although they are good guides for both manual and automated control, they lack detail on many important considerations related to stress intensity (K) control, crack length precision, and load precision. This paper will emphasize the effect of sampling rate and resolution on crack length precision, dynamic load precision, and control. The issues will include analog-to-digital conversion resolution, digital filtering, peak reading, and multichannel phase considerations.
fatigue crack growth, test automation, analog-to-digital conversion, data acquisition rates, peak readings, fracture (materials), fatigue (materials), testing methods, data analysis
Director, Fracture Technology Associates, Bethlehem, PA