Electrical anisotropy of unidirectional glass fiber reinforced composites containing carbon black

This investigation concerns the tailoring of electrical anisotropy of unidirectionally reinforced glass fiber reinforced epoxy (GFRP) composites for the purpose of matrix damage detection by the electrical resistance method. The current objective is to maximize the conductivity in the through-thickness direction so that delaminations can be most easily detected. Carbon black (CB) particles were aligned in the through-thickness direction with the application of AC electric field. Different CB amounts and AC voltages were evaluated. Electrical anisotropy was analyzed in three directions: Through thickness, in-plane longitudinal and in-plane transverse. With no applied field, DC conductivities of unidirectional glass fiber reinforced composites with 0.5% CB by matrix weight were 7.53E-12 S/m, 1.74E-09 S/m and 1.90E-07 S/m in the throughthickness, in-plane-transverse and in-plane-longitudinal directions respectively. With 800 V/cm peak-to-peak AC voltage at 1 kHz frequency, the respective DC conductivities were 2.01E-07 S/m, 2.94E-07 S/m and 7.27E-07 S/m. Thus, a factor of 10 5 increase in the through-thickness conductivity was realized, with relatively small changes in the other directions.