Measurements and analysis of the dielectric properties of aramid/epoxy composites based on free space method under stress conditions

Aramid/epoxy composites are widely used to fabricate wave-transmitting components in modern aircraft. The composites not only possess excellent dielectric properties but also bear mechanical loads. In this paper, a coupled dielect-mechanical testing method based on the free space method and a mechanical testing machine (MTM) was established and verified. The dielectric parameters of the unidirectional and quasi-isotropic aramid/epoxy composite, epoxy resin and glass fiber/epoxy composite were measured under varying strains. In addition, the coupled processes were simulated by the finite element method (FEM) using ANSYS software. The results show that the dielectric constants of the aramid/epoxy composites increase with the increase of strain while the dielectric loss tangent did not show a clear trend, and the dielectric properties of the pure epoxy resin and glass fiber/epoxy composite remain broadly stable when being stretched. Moreover, the changing mechanism of the dielectric properties of the aramid/epoxy composite under stress conditions has been analyzed according to the experimental and simulation results.