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Determination of the compliance of NIST Charpy Impact Machines



Enrico Lucon


The compliance of a Charpy impact machine, CM, can be measured by means of a low-blow elastic test on an unnotched Charpy-type specimen, provided an instrumented striker is used. The resulting force/time and force/displacement test records can be analyzed according to three different methods, each one resulting in an independent value of machine compliance. The three values are expected to be in agreement with each other within 10 %. In this investigation, we measured the compliance of all NIST Charpy machines equipped with instrumented strikers, ranging from large-scale pendulums for testing full-size specimens to small scale pendulums for testing miniaturized specimens. On each machine, three elastic low blow tests were performed to increase the statistics of CM values. In most cases, good repeatability and consistency was observed between different tests and different analytical approaches. Machine compliance was found not to depend on machine capacity or hammer weight, but only on the design of the machine itself and the type of hammer (C-type, U-type, etc.). Machine compliance, measured from an elastic low-blow test, can also be used for dynamically calibrating an instrumented striker, as an alternative to the conventional static calibration prescribed by test standards. For the NIST machines, dynamic conversion factors between applied force and striker output are systematically lower that static conversion factors, although the difference is generally small (less than 5 %).
NIST Interagency/Internal Report (NISTIR) - 8043
Report Number


Dynamic striker calibration, instrumented Charpy striker, low-blow impact test, machine compliance, static striker calibration, unnotched Charpy specimen


Lucon, E. (2015), Determination of the compliance of NIST Charpy Impact Machines, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed April 21, 2024)
Created February 10, 2015, Updated November 10, 2018