Analysis of parameters and influence factors on a piezoresistance model of CFRP materials

This paper presents a systematic parameter analysis on the coupled electrical and mechanical piezoresistance model of CFRP materials. The mathematical expression for electrical resistance (R) or fractional change of resistance (ΔR/R0) of CFRP materials has been simplified into a piecewise function in term of axial strain (εx). Three stages observed from tests results on CFRP tendons were used to determine the separation points (ε1 and ε2) of axial strain for the piecewise function. Some influence factors such as epoxy resin content and conductive pathway on piezoresistance performance of CFRP materials were also discussed. Parameter analysis results suggested that the mathematical model could characterize the main piezoresistance performance of CFRP materials. Model fit results agreed well with the tensile test results indicating that the proposed model was feasible and reliable. Three curve patterns inclusive of concave curve, straight Line and convex curve can be observed respectively for single fiber with epoxy resin, factory-made and laboratory-made CFRP tendons. Influence factor analysis results showed that the epoxy resin content is closely related to the concavity of the curves. The specimen with high content of epoxy resin is more likely to be the convex curve while the low content ones fit the concave curve. Particularly, convex curve pattern can be further explained by conductive pathway effect. Conductive pathway will increase with tensile stress since insulation layers of epoxy resin broke at higher stress state. More conductive pathways will result in a reduction of local resistance, which compensate the overall fast growth of total resistance under tension and make convex curve occur.