Hybrid tactile probe for damage detection and material recognition

Two health monitoring systems for damage detection in composite structures have been developed. First, a probe with piezoelectric elements analyzes the local visco-elastic response of the structure produced at the moment of touching and stressing it. The same piezoceramic elements induce the mechanical solicitation and sense the response signal. The probes are compared in the analysis of damages induced in a coupon of quasi isotropic Carbon-epoxy material by various aggressions: 4 J- and 2 J-impacts inducing delaminations, a local burning by contact with a hot body and a simulated lightning impact by electric spark. Both probes show sensitivities to these various types of damage. For the piezoelectric probe, a "real-time" strategy, based on the processing of spectral power densities of the sensor signals, leads to an automatic measuring system classifying the damages. Software, based on fuzzy logic and implemented on a dedicated micro controller, elaborates the input data in order to realize the material damages classification. Secondly, an electromagnetic probe using electromagnetic properties of the material, has been developed at ONERA (Office National d'Etudes et de Recherches Aerospatiales, France). This concept, based on the detection of local electric conductivity variations and/or local dielectric permittivity variations, has allowed designing a demonstrator having a great sensitivity to detect main defects such as delaminations, fiber breaking, burning and liquid ingress. It allows to detect and localize main damages inside carbon epoxy structures by measurements of the electric field resulting. Combination the two techniques in a hybrid probe and use of the fuzzy logic procedure on the full signals to classify the structure response in a more subtle and extended way is the starting point of the design of a multisensor tactile probe which would be able to recognize damages for a given material (NDE) or several classes of materials (robotized examinations in hostile environments).