Design Optimization of Instrumented Strikers for Charpy Pendulum Impact Testing: Instrumented strikers with a radius of 8 mm (ASTM)

The Charpy impact test was originally devised to measure the amount of energy absorbed by a material during fracture. Instrumentation of the striker extended the scope of this inexpensive dynamic test significantly. By not only recording the absorbed energy but also the force applied to the specimen as a function of time, additional information about the material’s properties is obtainable. At present day however, no internationally accepted procedure to calibrate or verify the measured dynamic force exists. From an engineering viewpoint, an instrumented striker for which a static force calibration is sufficient to accurately measure the force applied to the specimen during a Charpy impact test would be ideal. To investigate if such an instrumented striker can be designed, the influence of the striker geometry, the location of the strain gauges and the static force calibration procedure on the force measured by an instrumented striker is assessed using finite element analysis. In continuation of previous work on strikers with a radius of 2 mm, instrumented strikers with an 8 mm radius are addressed in this article. It is demonstrated that when the strain gauge bridge on the striker is sensitive to the load distribution at the striking edge, the voltage response for the Charpy impact test deviates from the static force calibration curve and the conversion of the voltage readout to force values introduces an error in the force value and hence a discrepancy between computed and angle-based energy. A striker with a height of 12 mm and strain gauges positioned at 17 mm from the striking edge is nearly insensitive to the load distribution and a static force calibration is sufficient to accurately measure the force during an impact test.