Effects of Striker Shape and Attached Position of Strain Gage on Measured Load in Instrumented Charpy Impact Test

Abstract

Instrumented Charpy impact test is widely used for the evaluation of toughness of many kinds of materials such as steel, aluminum alloys, polymers and ceramics with small scale specimens. In the test, therefore, it is important to record an accurate impact load. Generally, one can obtain measured load in the instrumented Charpy impact test by multiplying the output signal from strain gage attached to the instrumented striker by load-calibration factor assuming a liner relationship between the strain gage signal and applied load. Although JIS or ISO describes about the instrumented striker, amplifier, data processing parameter and etc., detailed method on load measurement is hardly described in any standard.
In the present study, two types of striker were used. The strain gages were attached to 4 positions in each striker. Instrumented Charpy impact test was carried out using these strikers in order to investigate the effect of gage position on actual impact load. By the finite element analysis, the effect of the strain gage position on the measured load was also investigated. As the result, it became clear that the accurate impact load was not measured around the end of slit which was introduced to release the constraining effect of deformation of the gage position from surrounding hammer; the effect of the vibration of the hammer appeared strongly around this position. However, it was possible to prevent the effect of such vibration by attaching the gage away from such position.