Paper number 975

ELECTRIC RESISTANCE AND ACOUSTIC EMISSION DURING CYCLIC TENSILE LOADING OF CFRP LAMINATES

T. Prasse¹, F. Michel³, G. Mook³, K. Schulte², W. Bauhofer¹

1Microelectronic Materials Section, Technical University Hamburg-Harburg, 21071 Hamburg, Germany
2Polymers and Composites Section, Technical University Hamburg-Harburg, 21071 Hamburg, Germany
3Institute of Materials Engineering and Materials Testing, Otto-von-Guericke-University of Magdeburg, PF 4120, 39016 Magdeburg, Germany

Summary

This paper reports on simultaneous monitoring of electric resistance and acoustic emission (AE) during cyclic tensile loading of cross-ply carbon fibre reinforced plastics (CFRP). The observed electric behavior is dominated by the ohmic resistivity of the carbon fibre network. During loading and unloading the samples the electric measurements show a hysteresis in the corresponding resistance vs. strain plot. When the previous load maximum is exceeded in the subsequent load cycle a characteristic increase in the measured resistance-strain slope appears combined with a sudden rise in the AE (Kaiser effect). After unloading the resistance relaxes to a new equilibrium value. This behaviour is caused by the formation and the growing of cracks in the CFRP samples. The observed time dependence in the resistance hysteresis and relaxation can be attributed to the influence of the stressed polymeric matrix.

Keywords

carbon fibre reinforced plastics, electric properties, acoustic emission, mechanical properties, non-destructive testing.