Damage detection of cracks in carbon fibre reinforced composites by pulsed eddy-current testing

Abstract

Non-destructive evaluation techniques that are based on electromagnetic methods are commonly used for inspection of metallic and carbon fibre reinforced plastics parts. Some of these inspection methods are based on eddycurrents which are generated by the electromagnetic induction phenomenon occurring under variable magnetic induction field. In eddy-currents testing, the depth of penetration into the material is controlled by the conductivity of the tested material and also the work frequency. Transient eddy-currents, also called pulsed eddy-currents, is an emerging non destructive technique that employs a pulsed excitation to induce a transient electromagnetic response from defects lying deep within a conducting structure. Such defects are difficult to inspect by conventional techniques, such as harmonic eddy-currents or ultrasonics. A large number of recent scientific publications have dealt with the theoretical understanding of the pulsed eddy-currents phenomenon and have also undertaken the design feature of appropriate probes. Finite element solution of the governing equations has been used to simulate the output signals as function of the input electrical excitation signal. Considering a B-scan strategy, simulation of a pulsed eddy-currents based probe is performed in this work with the objective to assess detectability of small defects through monitoring impedance changes of a detection probe.