SUMMARY

Electronic devices have found use in a variety of flexible form factors such as structural health monitors, wearable human health monitoring devices, and body suits. These form factors expose the electronic components (printed traces, passives, active devices, etc.) to a wide range of mechanical strains that are not typically seen in traditional rigid electronic systems. This is because the utility of the flexible wearable electronic systems depends on their ability to stretch, bend, and twist. With such stretching, bending, and twisting, the electrical conductance and thus, the overall performance of the flexible wearable electronics will change, and a clear understanding of the relationship between applied loading and the evolution of damage as well as the change in electrical properties is lacking. In this work, printed silver conductors on various flexible substrates such as polyimide and polyethylene terephthalate (PET) are subjected to both monotonic and cyclic stretching while the in-situ DC resistance is monitored. A representative volume element approach is developed to model the piezoresistive response of the strained conductors. The conductors temperature coefficient of resistance is characterized over a multiple temperature cycles. Additionally, innovative test apparatuses are designed and fabricated to apply controlled pure twist as well as combined stretch and twist to printed samples for both monotonic and fatigue testing and different failure mechanisms are explored for these loading modes. In addition to DC measurements, selected high-frequency measurements are also explored to understand the behavior of conductors intended for high frequency applications.