Characterization of the damage in nanocomposite materials by ac electricalproperties: experiment and simulation

Evolution of a.c. electrical properties under large strain of random nanoco mposite materials made of a soft thermoplastic insulating matrix and hard c onductive fillers is investigated. The transport properties are directly li nked with the macroscopic mechanical strain on the composites during uniaxi al tensile test or to the time under relaxation, meaning that the method is suitable for monitoring microstructural evolution of such composites. The real part of the conductivity indicated the breaking of the percolating net work, while the imaginary part gave information on the possible "spatial co rrelation" of the damage events. Two different filler shapes were used, i.e . spherical and stick-like (aspect ratio about 15), leading to quantitative ly different results. The microstructural evolution was simulated with the help of a resistance-capacitance (RC) model for the electrical properties a nd with finite element analysis for the mechanical properties. (C) 1999 Kl uwer Academic Publishers.