Acoustic and Sweep Resonant Test
Theory
All objects vibrate
Each object has its own vibrational modes. Each mode represents a standing wave or resonance at a natural frequency. Vibrational modes of each object are unique as finger prints of the object. These modes describe the intrinsic dynamic properties of the object.
When we impact an object or apply swept sine, we can identify its dynamic behavior or frequency response function. In response to impact, all modes are excited and each mode vibrates at a specific frequency (Eigen frequency). Each mode is a degree-of-freedom of vibration, which vibrates as a damped sinusoid at its natural frequency. The overall vibration of an object is the superposition of all modal vibrations.
An object has infinite number of modes or natural frequencies, which appear as peaks in frequency response. The frequency of modes are a function of elastic properties and geometry (CAD drawing). These frequencies are independent of impact point and intensity, and sensor location.
We can model a mode (one degree-of-freedom) with the free vibration of a Mass-Spring-Damper. The natural frequency of vibration (without damping) is f=√(k/m). In structural vibration, k represents mechanical properties (Young modulus, Elastic properties), and m represents density and dimensions (geometry).
The modes can be calculated using FEM, which corroborate the experimental results.
