Impact-echo method. Part I: Theoretical principles

The impact-echo method is a technique far flaw detection in concrete, which is based on monitoring the surface motion resulting from a short-duration mechanical impact. The method overcomes many of the barriers associated with ultrasonic methods. One of the key features of the method is the transformation of the recorded time domain waveform of the surface motion into the frequency domain. The impact gives rise to modes of vibration and the frequency of these modes is related to the geometry of the rest object and the presence of flaws. The principles involved in frequency analysis are discussed. The importance of the impact duration in relation to flaw detection and other factors affecting the smallest flaw that can be detected are also reviewed.