Nonlinear anisotropic electrical response of carbon fiber-reinforced polymer composites

Composites materials are often subjected to multi-physics conditions in different applications where, in addition to mechanical loads, they also need to sustain other types of loads such as electrical currents. Composite materials have heterogeneous electrical properties at the local level that can be different at the global level. In this study, electrical response was measured to explore how different lamina orientation and electrical current density affect anisotropic electrical properties of composite. For in-plane study, current was applied up to 80 kA/m(2) for both unidirectional and quasi-isotropic composite. In thickness direction, maximum current density was 6 kA/m(2). As expected, electrical properties are indeed dependent on fiber architecture which acts as conduction path in the laminate, and also depends on progressive increase in current density. Anisotropic electrical behavior was measured experimentally and the threshold of nonlinear behavior due to high current was identified. Threshold current density for unidirectional composite in fiber direction and for quasi isotropic are, respectively, 48.14 +/- 4.3% kA/m(2), 56.06 +/- 4.4% kA/m(2). For off-axis fiber laminates, this threshold limit shifts from 34.36 +/- 5.9% kA/m(2) to a lower value of 17.95 +/- 7.9% kA/m(2) as the fibers are oriented away from the x axis. In thickness direction, this threshold limit is in between 2.56 and 3.80 kA/m(2). The electrical-thermal responses were also studied experimentally with thermography tests and the results were compared to indicate damage. A 3D X-ray microscope has been used to visualize and quantify (down to 1 micron) such local material state changes due to electrical current.