Modal testing
Modal testing is the form of vibration testing of an object whereby the natural (modal) frequencies, modal masses, modal damping ratios and mode shapes of the object under test are determined.
A modal test consists of an acquisition phase and an analysis phase. The complete process is often referred to as a
There are several ways to do modal testing but impact hammer testing and shaker (vibration tester) testing are commonplace. In both cases
Impact Hammer Modal Testing
An ideal impact to a structure is a perfect impulse, which has an infinitely small duration, causing a constant amplitude in the frequency domain; this would result in all
Shaker Modal Testing
A shaker is a device that excites the object or structure according to its amplified input signal. Several input signals are available for modal testing, but the sine sweep and random frequency vibration profiles are by far the most commonly used signals.
Small objects or structures can be attached directly to the shaker table. With some types of shakers, an armature is often attached to the body to be tested by way of piano wire (pulling force) or stinger (pushing force). When the signal is transmitted through the piano wire or the stinger, the object responds the same way as impact testing, by attenuating some and amplifying certain frequencies. These frequencies are measured as modal frequencies. Usually a load cell is placed between the shaker and the structure to obtain the excitation force.
For large civil engineering structures much larger shakers are used, which can have a mass of 100
See also
- Modal Analysis
- Vibration
- Cushioning
- Shock absorber
- Shock (mechanics)
- Shock response spectrum
- Shaker (testing device)