Effect of Mass Loading

I recently used this simple example to demonstrate the effect of mass-loading in a vibration test. This was done as a part of our PolyLab program. The goal was to show that anytime you attach something to the structure under interest, it will affect its dynamic behavior. Of course, whether this effect matters in the broad scheme of things depends on the end-user and the application.

I like to show this example, especially in a university setting to students on their first encounter with vibrations. It clearly shows the shift in natural frequency when mass is added to a system. In this case, the sample under test was a tuning fork - designed for 256 Hz. A magnet was then attached to it weighing approximately the same as two tear-drop accelerometers. A laser Doppler vibrometer (VibroGo), or LDV, was used as a vibration sensor. The frequency shift is evident in the graph below.