FEM-aided identification of gauge factors of unidirectional CFRP through multi-point potential measurements

Carbon fiber reinforced plastic (CFRP) has electrical conductivity in both the parallel and transverse directions of the fiber. Because an electrical network may be changed with the applied strain, the electrical conductivity of the CFRP will also be changed for the piezoresistivity. Strain monitoring of CFRP can therefore be conducted, not by using an additional sensor, but by measuring the change in electrical resistance. There have been many studies on the gauge factors of unidirectional CFRPs, although significant mutual differences have been determined in the results reported. It is thought that the differences may be caused by the strong electrical anisotropy and inhomogeneity of the unidirectional CFRP. In this study, a new concept was introduced to precisely measure the gauge factors of a unidirectional CFRP. A finite element analysis was utilized to take into consideration a non-uniform electrical potential field in a unidirectional CFRP. The gauge factors were obtained as a result of minimizing the error sum of the squares of the electrical potentials between the experimental and analytical results. The gauge factor in the fiber direction was affected by this factor in the thickness direction depending on the specimen configuration. The results of the finite element analysis showed the possibility of a unidirectional CFRP showing both positive and negative gauge factors in the fiber direction.