## 4 Results and Discussion  
Figure 6a,b show \(V_{DC}\) versus \(I_{DC}\) curves in wrap and thickness directions, respectively. The linear relationship between \(I_{DC}\) and \(V_{DC}\) for both directions is revealed from 17 different \(I_{DC}\) values. The gradients of the regression curve of the results represent \(R_{Total}\) values of the woven CFRP, which are then plotted against \(L_{c}\), the distance between the two electrode points, as depicted in Figure 7. Note that the \(R_{Total}\) measured here uses the four-wire method, and the woven CFRP specimen was not imposed by tensile loading. Figure 5: Schematic electrical circuit installed during tensile tests. For the wrap direction, the \(R_{Total}\) values can be plotted against \(L_{c}\) as shown in Figure 8. The \(R_{Total}\) increased proportional with \(L_{c}\) which indicates the geometry and electrical properties of the woven CFRP were relatively uniform. Linear regression can then be drawn from the five plotted points. The \(L_{c}\) equals to zero gives \(R_{Total}\) of 0.0019 \(\Omega\) which equals to \(2R_{c}\). Thus, the \(R_{c}\) of 0.00095 \(\Omega\) was obtained. This \(R_{c}\) value was relatively small which indicates the attachment method of the electrode to the woven CFRP surface was effective. For thickness direction, the \(R_{Total}\) of 0.2357 \(\Omega\) was measured. Considering that the woven CFRP has sid laminae and the appearance of \(R_{c}\), the \(R_{t}\) of 0.039 \(\Omega\) was obtained by calculating Equation (3). Furthermore, by calculating Equation (2), \(R_{w}\) with a distance of 70 mm, can be obtained, i.e., 0.307 \(\Omega\). Electrical resistivity (\(\rho\)) can then be calculated by using Equations (4) and (5). The values of \(\rho_{w(6)}\) and \(\rho_{t(6)}\) are shown in Figure 9. The experiment for the wrap direction was conducted for five different electrode distances. The span of \(\rho_{w(6)}\) values was relatively small with an average value of 10.1 \(\mu\)m. In thickness direction, \(\rho_{t(6)}\) of 43.8 \(\mu\)m was obtained. The results show \(\rho_{t(6)}\) was four times higher than \(\rho_{w(6)}\). This occurs because in the thickness direction, there were five interfaces that only contain epoxy resin. However, in wrap direction, the carbon fiber acts as an electric conductor with relatively small resistance. After the specimens have been tested and the results calculated using collected data, it was found that the contact resistance of CFRP will decrease in accordance with its polishing treatment, as we can see from Figure 9. The higher the grit number of the polishing paper used, the surface roughness decreases, and the contact resistance also decreases. High grit number in the polishing paper used makes the surface of the specimen smoother and increases the contact area of electrode and carbon fibers in the specimens, where high contact area decreases contact resistance in CFRP. Lower contact resistance is better for resistance measurement of the CFRP because if the contact resistance is high, it can hinder the total resistance measurement of the CFRP that are very small. For the tensile test, based on the data acquired as depicted in Figure 9b, it may be inferred that the polishing process did  
Figure 6: Voltage to current curves in woven CFRP for (**a**) wrap direction and (**b**) thickness direction. Figure 7: Relationship between total electrical resistance and two electrodes distance for 6 laminas of plain-woven composite. not significantly affect CFRP strength. The above remark is supported by the fact that the unpolished specimen is not necessarily stronger than the polished specimens. Tensile tests are conducted for specimens installed electrical circuit shown in Figure 5. In the tensile tests, the specimen is loaded and unloaded for seven times. The example voltage signals (\(V_{m}\) and \(V_{e}\)) obtained for one cycle loading and unloading can be seen in Figure 10. The vertical axis in Figure 10 shows the \(V_{m}\) and \(V_{e}\) obtained from the data recorder.