Martin Stockmann

Multifunctional nanomembranes self-assembled into compact rolled-up sensor?actuator devices

This paper reports on the functional principle for a rolled-up microdevice family providing the possibility to realise electrical sensor and actuator functions which are applicable to microsystem techniques, in the field of physical measuring techniques, microfluidics and biological?medical analytics. The fabrication of the roll-up devices is based on a strain-driven process converting a planar two-dimensional membrane into a three-dimensional functional element. For the realisation of these roll-up structures a broad spectrum of thin film technological approaches were used, which are well established. The special feature of these advanced microdevices consists in the possibility to design the latters inner surface using established additive or subtractive thin film techniques. The technological route elaborated in the present work could possibly be used to realise a valve for microfluidics thanks to the combined advantages of rolled-up devices and the unique properties of temperature-sensitive hydrogels. Due to the thermal decoupling of the processed microheaters from the supporting substrate the obtained microdevices obtained are superior to conventional miniaturised planar devices in their general performance, especially in respect to the dynamical behaviour of the thermal properties. This is a prospective basis for the conceptual creation of combined sensor/actuator devices with tailored electrical and thermal properties.

Experimental—numerical investigation of the rolling process of high gears

Rolling of high gears into full material is a new and economic way of manufacturing. Such gearings provide a higher surface strength and a better surface quality than conventional gearings. However, higher expenses for tools are disadvantageous. So far, the design of the forming tools follows only geometric requirements and the loads at the tool surface are not considered for designing these tools. To increase the life cycle of the tools, the loads at the tool surface and the stress state at the contact zone have to be taken into account. This paper presents an experimental setup to record strain data at the forming tool during the processing. Results of these measurements are shown for several stages of the process. Numerical simulations, according to the experimental tests, are shown in the second part. A staggered simulation with a two-dimensional model of the forming process is used to identify contact loads at the tool surface. These loads are transferred to a three-dimensional numerical model of the forming tool and the procedure to transfer loads is described in this article. The validation of the numerical results with the measured strain data shows the applicability of the numerical approach for designing tools.

Forging of eccentric co-extruded Al-Mg compounds and analysis of the interface strength

Within the subproject B3 of the Collaborative Research Center 692 it has been shown that Al-Mg compounds with a good bonding quality can be produced by hydrostatic coextrusion. During processing by forging, the aluminum sleeve is thinned in areas of high strains depending on the component geometry. To solve this problem an eccentric core arrangement during co-extrusion was investigated. Based on the results of FE-simulations, the experimental validation is presented in this work. Rods with an offset of 0.25, 0.5 and 0.75 mm were produced by eccentric hydrostatic co-extrusion. Ultrasonic testing was used to evaluate the bonding quality across the entire rods. For the forging investigations the basic process Rising was chosen. The still good bonding quality after forging was examined by dye penetrant testing and optical microscopy. For an optimal stress transfer between the materials across the entire component, a sufficient bonding between the materials is essential. To evaluate the interface strength, a special bending test was developed. For the conception of the bending specimens it was required to analyze the Rising specimens geometry. These analyses were performed using a reconstruction of the geometrical data based on computer tomography (CT) investigations. The comparison with the numerically deter-mined Rising specimen geometry shows good correlation. Parametric Finite Element Analyses of the bending test were used to develop the load case and the specimen geometry. By means of iterative adaption of load application, bearing and specimen geometry parameters, an advantageous stress state and experimentally applicable configuration were found. Based on this conception, the experimental setup was configured and bending tests were performed. The interface strength was deter-mined by the calculation of the maximum interlaminar interfacial tension stress using the experimental interface failure force and the bending FE model.