The 8 th International Conference of the Slovenian Society for Non-Destructive Testing »Application of Contemporary Non-Destructive Testing in Engineering« September 1-3, 2005, Portorož, Slovenia, pp. 223-228 EDDY CURRENT EXAMINATION OF CARBON FIBRES IN CARBON-EPOXY COMPOSITES AND KEVLAR R. Grimberg 1 , A. Savin 1 , R. Steigmann 1 , A. Bruma 2 1 National Institute of Research and Development for Technical Physics, Iasi, Romania 2 Al.I Cuza University, Iasi, Romania ABSTRACT This paper proposes a special eddy current transducer, send receive type and a holographic method for signal processing, able to emphasize the delaminations and massive breaking zones in carbon fibres. To evaluate individual fibres breaking, a eddy current microscopy method is proposed. Keywords: Carbon fibres, Carbon epoxy composites, Kevlar, Eddy current examination, Eddy current holography, Eddy current microscopy 1. Introduction Given their specific characteristic, the carbon-epoxy composites are used in different application, from airspace industry to sporting goods. As compared to the metallic materials, carbon epoxy composites show a series of advantages, among which a high tensile strength, low density and coefficient of thermal expansion, absence of phenomena specific to the fatigue state, possibility of a relative simple manufacturing of large layered structures. The carbon epoxy composites exhibit electric properties that depend on the type of used carbon fibres and on their volume fraction in the materials, having the transverse electric conductivity between 10 and 100S/m and longitudinal conductivity ranging between 5*10 3 and 5*10 4 S/m. In the case of low energy impacts, the composite gets elastically deformed and a local alteration of the electric conductivity occurs. For high energy impacts, the local deformation results in delaminating, deviation or breaking of the carbon fibres. As the carbon fibres, the KEVLAR fibres have different applications, considering the fact that it is 5 time stronger than steel. It is used in bullet-proof jacket worn by Special Forces, Police, etc. The Kevlar body armour has the capability to stop a bullet fired from a 0.45 calibre gun but rarely stops anything more powerful as, for example, a bullet of 7.62mm which is fired from a AK 47 assault riffle. The Kevlar is a poly (p-phenylenterephtalamide) having an electric conductivity between 10 -10 and 10 -14 S/m. At impact with low energy (bullets with small calibre or large distance till target), the fibers that form the texture are open up, and, together with the elasticity of fibres, and these processes absorb the energy of the bullet. At impacts with high energy, the bullet penetrates the first layers 223