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Four Probe Electrical Resistance Characterization of Carbon Fiber and Carbon Nanotube Buckypaper Composites



In this work, the electrical resistance of carbon fiber reinforced polymer (CFRP) and carbon nanotube buckypaper (BP) composites has been studied. The specimens were prepared according to three different layup configurations. Three 16-ply unidirectional carbon fiber (CF) composites IM7/977-3 [0]16T, or CF16, were prepared and used as the baseline for the study. Additional specimens were prepared with the addition of 4 and 7 layers of BP. Experimental measurements of the electrical resistance have been performed using two methods. In the first method, six probes were attached to the top and bottom of the specimens and measurements were performed using the traditional 4-probe electrical resistance method (i.e. the electrodes span the entire width of the specimen) for composite laminates. The second method was based on a modification of the four-point probe method of the Japanese Industrial Standard (JIS) K7194. Results were analyzed in order to observe the effects of the highly conductive buckypaper on the overall resistance of the composite laminates as well as to illuminate any trends between the number of BP layers added and the resulting changes to electrical resistance. The specimens with layers of BP were found to have lower resistance compared to the specimens with no BP. Moreover, as the number of BP layers increased from 4 to 7, the resistance continued to decrease. These results demonstrated two significant findings. First, the current not only flowed through the top CF layer but penetrated through the thickness, as evidenced by the lower resistance measured on the specimens with BP. Second, the decrease in resistance between the specimens with 4 and 7 layers of BP measured by the traditional 4-probe electrical resistance method was greater than predicted by finite element analysis (FEA) due to nonlinear edge effects. The method based on the JIS K7194 was found to reduce the influence of edge and geometry effects on resistance.

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