This paper studies the formability of functional composite structures, consisting of a metal substrate, insulating plastic
foils, flat copper conductors and printable conductive polymers. The aim is the production of smart components in a
sheet metal hydroforming process. In addition to their mechanical properties, these components can also transfer energy
and data. Conventional boundaries between mechanics and electronics will be relaxed expediently.
The challenge of this study is the design of the forming process, so that all elements of the multi-layer composites will
withstand the process conditions. In this context, an analytical method for estimating the formability of these smart
components is presented. The main objectives are the definition of basic failure modes and the depiction of the process
limits.
In this paper we present the design and test of printed strain sensors, which can be integrated in light-weight
structures for monitoring purposes. We focus on composite structures consisting of metal substrate as well as
insulating and conductive ink layers for sensing normal strain at the surface. Both, inkjet and screen printing
technology are used to realize resistive topologies that can be evaluated using a Wheatstone bridge configuration.
In a first step, we analyze electrical properties of functional inks: electrical impedance and breakdown electrical
field strength in case of insulation inks, resistance in case of conducting inks. Silver and PEDOT:PSS based
suspensions are printed as sensing layer. To determine the resistance change due to plastic deformation of the
metal substrate, tensile tests are performed up to 30% strain and subsequent resistance change is measured. In
a second step, the sensing effect of printed conductive structures is investigated. Resistive sensing topologies
are designed for detecting longitudinal and transversal normal strain. Meander structures, which form single
resistors as well as bridge configurations, are printed on test specimens and analyzed in a four-point bending set
up. Performing loading and unloading cycles, gauge factor, cross sensitivity, nonlinearity and hysteresis error of
the sensors are measured.
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