Detailed Analysis of Impact-echo Signals of Specimens with Nonlinear Effects

This simple NDT method uses impact pulse as a simple wide-spectrum excitation for spectral analysis. Usually the frequencies of resonance components from impact-echo (I-E) signal are compared with standard forms and their deviations signalize non-ideality and defects. This NDT method is very cheap and effective especially for small bodies with expressive resonance properties, but it has a small sensitivity to relatively small defects and it cannot identify cracks. The new improved method consists in utilize of nonlinear acoustic properties of bodies with cracks (good known as SIMONRUS etc.) when the resonance frequencies depends on excitation. On the other hand, the complex analysis of full I-E signal is very complicated because there are among others tens of dominant harmonic components. Therefore we designed a program for detailed timefrequency analysis of I-E signals. We applied not only “single-mode model” with frequency shift, but also “multi-mode model” with nonlinear effects and also phase plane. By this way we obtain time dependencies of some harmonic components with marked low frequency periodicity.