Скачать или смотреть Impact testing and the FRF

Let’s talk about impact (or tap) testing, where we use an instrumented hammer to excite a structure and measure the vibration response with a transducer, such as an accelerometer. The purpose of this is to identify the frequency response function, or FRF, for the selected structure.

The video shows the hammer force input (red) in the top panel and the vibration response (blue) in the middle panel. We see that the hammer tap causes the structure to vibrate at its natural frequency and that the vibration decays over time. This decay is due to damping and the more damping that exists, the quicker the vibration attenuates. The moving dots let us see that the vibration continues after the hammer tap ends.

The bottom panel (black) displays the magnitude of the frequency response function (FRF). We see a peak at the natural frequency of 50.3 Hz. The peak height defines the dynamic stiffness. Taller means less stiffness, damping, or both and larger vibration.