The Modal Punch: A New Impacting Development

The Modal Punch is a variable length shai? with an impact tip and load cell attached to one end. It is held against the surface of the test structure and struck with a hammer. The force input spectrum of the Modal FTmch is controlled by the combination of the stiffness of the tip on the punch and the hammer that used to strike the punch. Considerations of the force window used with the Modal Punch will be discussed. The application of the Modal Punch to test an automotive axle in its housing will bc described, Sometimes during the course of an impact modal test, the need arises to impact at locations that are inaccessible to a conventional impact hammer. The Modal Punch has been developed to give the test engineer an option to overcome the limitations of this situation. ln the past, uninstmmcntcd punches have beat used out of necessity to impact on these locatmns. Xx punch was struck with an instrumented hammer, and the output of the impact hammer load cell was meawed and assumed to be the force imparted to the structure, However, the force imparted to the structure through the punch is not the same as the striking force. IJnderstanding the differences between these two force chwacteristics is paramount to the need for and proper “se of the Modal Punch.