Static force calibration of charpy impactors

A static force calibration method is developed which uses the test piece as a calibration load cell. A lever system generates a permanent but variable force for pressing the hammer against the test piece. As an example a calibration procedure is described. It was revealed with the tup under test that the calibration factor changes with force, i.e., is not a constant during a test. Additionally, it is found with this tup and verified by contact stress considerations that the tup changes its shape with time, which leads to a variety of stress distributions within the tup, thereby affecting the strain gauge signal. From these results is concluded that generally the tup calibration exhibits a sensitivity to the size of the contact area and, therefore, needs to be improved. This behaviour will not be restricted to the tup under test but is to be expected with the average of presently used tup instrumentations.