Mesut Ibis

Printed resistive strain sensors for monitoring of light-weight structures

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.

Sheet metal hydroforming of functional composite structures

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.

Towards Mass Production of Smart Products by Forming Technologies

In all areas of technology, the demand for high-quality, competitive and more valuable products is rising steadily. One approach to increase the value of manufactured products is the integration of electronic components in load carrying structures. These new products, which combine electrical and mechanical components synergistically, are called smart products. They consist of a passive structure and integrated electronics or smart materials. In addition to their mechanical properties they are also able to sense, to actuate or to transmit energy or data. The resulting product architecture requires both a mechanical and an electronic design in order to save subsequent assembly costs. Since further components are required to evaluate and control as well as to supply energy, all of those components need to be connected and integrated into the smart product. However, the main prerequisite for the marketability is the possibility of low-cost manufacturing and a robust mass production. Nowadays processes for the manufacturing of smart products do not fulfill the requirements for a sustainable mass production in a satisfying way as long as metallic structures are used. The authors deploy the forming technologies roll forming and sheet metal hydroforming to form sheets with applied flat electronics. Since the components are applied prior to the forming process, small and difficult to access installation spaces can be used effectively in the product architecture. The incremental bulk forming process rotary swaging is employed to integrate piezoceramics during the forming procedure without any additional joining elements. Challenges resulting from the chosen integrative manufacturing approach are the prevention of new kinds of failure modes and additional requirements for defined residual stress states. These challenges lead to extended process design requirements, which will be discussed in the paper in detail.