Electrical Resistance Change of Unidirectional CFRP Due to Applied Load

Abstract

Carbon Fiber Reinforced Plastic (CFRP) is composed of electric conductive carbon fibers and electric insulator resin. Self-monitoring system has been reported utilizing electric resistance change of unidirectional CFRP due to fiber breakages and to applied strain. Piezoresistivity is electric resistance change with applied strain. Many researchers have already reported the piezoresistivity of unidirectional CFRP. There is, however, large discrepancy in the measured piezoresistivity even in the fiber direction during tensile loading: both positive piezoresistivity (electric resistance increase) and negative piezoresistivity (electric resistance decrease) are reported during tensile tests. Electric resistance change at electrodes due to poor electric contacts are reported to be a main cause of this large discrepancy. In the present study, therefore, basic properties of piezoresistivity were measured with specimens made from single-ply and multi-ply laminates using a four-prove method. Many cases of electric resistance changes in the fiber direction transverse direction were measured during tensile loading. Effect of shear loading was also investigated using a shear test. To investigate the effect of poor electric contact at the electrodes, electrodes were made without polishing specimen surface and a tensile test was performed with measuring piezoresistivity. After the test, the specimen surface was polished, and a tensile test was performed again using the identical specimen. As a result, positive piezoresistivity was obtained for both single-ply and multi-ply specimens and negative piezoresistivity is confirmed that it was caused by the poor electric contact at electrodes.

Strain and Damage Monitoring of CFRP Laminates by Means of Electrical Resistance Measurement

“…This complicated electric current path, they argue, is the cause of the apparent negative piezoresistance. They propose a model for apparent negative piezoresistance and test it using irregularly placed dot shaped electrodes; successfully reproducing negative piezoresistance.. Todoroki and Yoshida have investigated the effect of contact at the electrodes in the four-probe method (66) . They conducted tensile tests and measured electrical resistance changes in single ply CFRP specimens using the four-probe method.…”

“…The single ply specimen did not show fiber misalignment between plies although the ply had small fiber undulation. Figure 4 shows the results of the fraction of electrical resistance change during cyclic loading as per Todoriki and Yoshida's study (66) . The figure shows the single ply specimen has positive piezoresistance.…”

“…The figure shows the single ply specimen has positive piezoresistance. Figure 5 shows the results for a unidirectional multi-ply CFRP specimen under cyclic loading (66) . For this test, the specimen surface was not polished before being painted with silver paste to make electrodes.…”

“…Electrical resistance change during cyclic loading was measured again using the identical specimen. Figure 6 shows the results of the cyclic loading test (66) . The results show that the identical specimen has positive piezoresistance after polishing the specimen surface.…”

Smart Textiles for Strengthening of Structures

“…Observations from the solutions tested in Textile Engineering proved that these fibres may be useful for "sensoring". This feature seems to be underestimated by structural engineers, while other branches of industry dynamically use it in multifunctional smart textiles [1][2][3][4].…”