Two-dimensional strain sensitivity of epoxy-matrix carbon fiber smart layer

The paper deals with the two-dimensional strain sensitivity of a new type strain sensor named smart layer made of polymer-matrix composites with short carbon fiber mats. A set-up capable to supply unidirectional strain field was used to measure the gauge factors of the square smart layer upon the unidirectional strain parallel to the measuring resistance direction and upon the unidirectional strain perpendicular to the measuring resistance direction. The values of the two gauge factors are approximately equal, indicating the in-plane isotropic property of the carbon fiber smart layer's piezoresistivity. Based on the measured gauge factors, a symmetry piezoresistive matrix considering the effects of the strains in both two directions was proposed to predict the strain sensitivity in the two-dimensional strain state. A shear strain effect was detected in the test. By modifying the piezoresistive matrix with a shear gauge factor, good agreement was obtained between the predicted and the experimental results.