Abstract
The change in the electric resistance in CFRP due to mechanical loading and thermal history was experimentally investigated. First, the surface electric resistivity and piezoresistivity in the linear region were measured for unidirectional laminates. Secondly, quasi-static tensile tests as well as loading/unloading tensile tests were conducted for on-axis and off-axis unidirectional specimens to measure the change in the resistance together with strain up to failure. Finally, the resistance change in the transverse direction of unidirectional laminates during thermal history was measured to monitor the shrinkage due to post-cure. In order to predict the piezoresistance response in the linear region, a two-dimensional model was proposed. It was found that the electric resistance-strain curves during quasi-static tensile loading exhibit nonlinear behavior after linear region, especially in the off-axis specimens. The permanent change in the electric resistance was observed in all the specimens after loading/unloading. During the thermal cycle, both the transverse strain and the resistance varied with temperature and time and they showed permanent change at the end of the cycle. Thus, post-cure behavior can be monitored by measuring the electric resistance in the transverse direction.
