Triangulation method as a valid tool to locate the damage in unidirectional cfrp laminates

Acoustic Emission (AE) has long been recognized as a viable technique for realtime monitoring of metallic and composite structures, giving useful information not only on the presence of defects, but also on their criticity. Compared to other Non Destructive Testing methods (NDT) AE offers the advantage to locate defects in real time. The acoustic wave emitted by a source, related to a damage start or propagation, travels inside the material and it is received in different time by acoustic sensors arrayed on the surface. Knowing the different arrival times it is possible to locate the emission source position by the triangulation technique. For homogeneous material, this technique is easy to develop. However, the anisotropy nature of a composite material does not allow to have the same sound velocity in all the directions, so the development of mathematical models and algorithms for the implementation of the triangulation technique is difficult to set up. Since the above mentioned problem, this work proposes an alternative method to locate the point of an event on CFRP plates by analyzing the time of arrival of the ultrasonic signals received by three passive sensors attached to the plate surface in a known triangular configuration. The method is based on a simple concept: the comparison between the three measured arrival times and the predicted ones by analytical formulations. It was applied and validated through experimental tests carried out on a square unidirectional carbon fibre laminate. From the results, a good agreement between the predicted and the real position of the sound source was found.