Dept. of Materials Science
Oregon Graduate Center
While it is theoretically true that useful information can be calculated from recorded instrumented impact test data, such calculations can be performed only if the correct calibration procedures and numerical methods are used. However, neither the literature nor existing standards contain useful guidance with respect to correct calibration procedures or adequate numerical methods. Two different homogenous populations of alloy 4340 steel Charpy bars were manufactured and tested by instrumented pendulum and drop tower versions of the Charpy impact tests. The salient dimensions and masses of the drop tower and pendulum machines were directly measured and the initial velocities were calculated from initial drop heights. Data were recorded using the COMPUTERSCOPE system manufactured by RC Electronics. The two instrumented tups were calibrated by applying known loads statically, by matching energy results to known ASTM E-23 (Charpy impact test) results and by matching calculated general yield loads to assumed values of general yield loads. Using the calibration data, absorbed energies, general yield loads, and total system compliance were calculated from the recorded tup output information for both populations and test machines using ASTIR, a computer program specifically designed and constructed for this work. The energy, load, and compliance data were compared statistically to one another and, in the case of absorbed energies, to standard ASTM E-23 values. It was found that the response of instrumented tups varies from almost totally strain rate insensitive to highly strain rate sensitive and that dynamic tup calibrations using energy standards can be dangerously misleading. It was shown that quite simple numerical methods are adequate for load and energy calculation and that approximately 80 data points are adequate for correct energy calculations. Methods for investigating the discrepancies uncovered in this study and for obtaining first principles dynamic tup calibrations are outlined.
Stevens, Ward C., "Factors affecting the validity and accuracy of instrumental impact tests with special reference to the pendulum and drop tower versions of the charpy test" (1987). Scholar Archive. 249.