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This research investigates the quasi-static and dynamic properties of flexible hybrid electronic (FHE) material systems. FHE material systems are multifunctional systems combining tunable mechanical and electrical behavior and are constructed from the combination of FHEs and elastomeric metamaterial inspired geometries. FHEs are composed of conductive flakes embedded within an elastomer matrix such that electrical conductivity is determined by conductive flake proximity in a percolating network. Therefore, FHE conductivity is highly dependent on strain whereby large strains increase electrical resistance through the separation of conductive flakes. On the other hand, elastomeric metamaterials have been leveraged for energy mitigation purposes through control over strain transfer properties. The strain transfer properties of elastomeric metamaterials arise from built-in or applied geometric features, which capitalize on snap-through buckling or gradual collapse behaviors. By the innovative integration of concepts here, FHE material systems control electrical conductivity through the strain-transfer properties of the elastomeric metamaterial inspired geometries. In quasi-static experiments, conductive ink trace path choice within specimen geometry determines FHE electrical behavior through the strain transfer characteristics of the geometry under compression. A strain-sensitivity of FHEs to internal strain transfer is leveraged in a geometry with snap-through buckling features, which reveals electrical behavior useful for load or buckling event detection. On the other hand, FHE ink trace path choices within geometries with gradual collapse behavior can maintain a nearly constant conductivity due to a strain-insensitivity of the FHEs. FHE material systems are then investigated under high frequency dynamic excitations to investigate transient electrical resistance changes. It is found that the static strain within the conductive networks of the strain-sensitive and strain-insensitive geometries determine the dynamic response of FHE material systems through time-dependent stresses and strains. For example, cyclic deformation experiments show that increases in resistance are due to disruptions of the FHE conductive network that occur as a result of thermal stresses and strains. Furthermore, the strain-rate dependence of the viscoelastic elastomer matrix results in increasing stress and strain within the conductive networks of the FHE material systems under increasing frequencies of excitation. Within the strain-sensitive specimen, this results in an increase of electrical resistance with excitation frequency. The strain-insensitive specimen shows nearly constant electrical resistance with excitation frequency. The advancements in knowledge created in this research may inspire future concepts for FHE material systems designed for simultaneous energy absorption and electrical conductivity characteristics in quasi-static or dynamic environments. |
