Evaluation of the Performances of an Electromagnetic SHM System for Composite, Comparison between Numerical Simulation, Experimental Data and Ultrasonic Investigation

摘要

Recently, a new SHM system has been developed at ONERA. This system based on the interaction between an electromagnetic field and a composite structure, allows detecting all types of damages having an influence on the electrical characteristics of the structure such as carbon fiber breaking, organic matrix pyrolysis, liquid ingress... The basic principle of this SHM system, called HELP-Layer~(~R) (Hybrid ELectromagnetic Performing Layer), consists to induce eddy currents inside the structure and to perform a local measurement of the resulting electric field. All damages inducing a significant variation of the two main electrical parameters (i.e. electrical conductivity and dielectric permittivity), induce a significant variation of the resulting electric field. The sensitivity of this technique depends of the type of damage; as regard to "mechanical" damages (e.g. delaminations, fiber breaking, crack), the sensitivity is comparable to techniques using ultrasonic methods, as regard to other kind of damages (e.g. matrix pyrolysis, liquid ingress...) the electromagnetic method is more sensitive than ultrasonic methods. The analysis of the two resulting components of electric field (i.e. E_x and E_y, the conductivity direction being y) allows to determine the kind of damage (mechanical or other), by resolution of a part of the inverse problem, the direct problem being solved by the DPSM (Distributed Point Source Method) concept.