Dynamic Calibration of Instrumented Charpy Strikers

Published

April 22, 2024

Author(s)

Akobuije Chijioke, Nicholas Vlajic, Enrico Lucon

Abstract

Charpy V-notch testing of metallic materials involves application of kilonewton-range force pulses on millisecond time scales, generated by impacting the notched test specimen with a striker mounted to a swinging pendulum. In the instrumented version of the test, strain gauges are affixed to the striker, and the voltage output from a strain gauge bridge amplifier is recorded in real time during the impact event. Calibration of the striker allows the voltage output to be converted to an indicated force. The striker is typically calibrated statically, by dismounting it from the pendulum and loading it with a universal testing machine. The highly dynamic impact conditions of a test can lead to errors in the force measurement based on such static calibration, and furthermore the dynamic response of the instrumented striker may be dependent on the pendulum and the mounting of the striker to the pendulum. Therefore we seek to perform a dynamic calibration of the instrumented Charpy striker, and to perform this calibration on the striker as mounted in the Charpy pendulum. We have developed a dynamic calibration method for instrumented Charpy strikers based on a very short force pulse, approximating a delta function in time. By impacting the striker against brittle and small ceramic test specimens, we are able to generate force pulses as short as approximately 10 microseconds. Such short pulses have nearly uniform force spectral amplitude up to a high frequency, allowing determination of the striker's frequency response function and impulse response function shapes. Furthermore, the calibration is carried out in conditions closely simulating those that occur in the use of the calibrated striker on test specimens. We present the results of such dynamic calibrations for instrumented Charpy strikers on two different Charpy machines, with very different geometries.

Proceedings Title

Proceedings of the XXIV IMEKO World Congress

Conference Dates

August 26-29, 2024

Conference Location

Hamburg, DE

Conference Title

XXIV IMEKO World Congress

Pub Type

Conferences

Keywords

instrumented Charpy testing, dynamic force, dynamic force calibration

Citation

Chijioke, A. , Vlajic, N. and Lucon, E. (2024), Dynamic Calibration of Instrumented Charpy Strikers, Proceedings of the XXIV IMEKO World Congress , Hamburg, DE (Accessed November 20, 2024)