Papers by Author: Jürg Dual

Abstract: A newly developed resonator in combination with a UDS 200 rheometer allows performing different kinds of measurements. The characteristics of the resonator are its resonant frequency slightly above conventional rheometers, the high sensitivity allowing measurement of fluids with viscosities as low as that of water and the very small oscillation amplitudes. The nonlinear behavior of viscoelastic liquids can be analyzed using parallel superposition of shear. It is known that the parallel complex shear modulus differs from the complex modulus of a fluid at rest. First measurements have shown the ability of the instrument to quantify this effect. At the same time, normal force, shear rate viscosity and complex viscosity can be measured on a sample.

Abstract: In recent years there have been vast efforts to establish organic electronic devices. A key property of such devices is the possibility to fabricate them on flexible substrates. As the layers are mechanically stressed during bending, the knowledge of mechanical properties of the materials used will become very important. In this research the mechanical properties of the intrinsically conductive and widely used polymer PEDOT/PSS were investigated using a micro tensile test setup. The tensile tests showed values for Young’s Modulus in the range from 1 GPa to 2.7 GPa, for the tensile strength in a range from 25 MPa to about 55 MPa and for the total strain at break between 3% and 5%, all of them depending on relative humidity.

Abstract: The reliability and optimal design of Micro Electro Mechanical Systems (MEMS) can be achieved only with the determination of material properties at the micro-scale. The major challenges in performing fatigue tests at the micro-scale are related to the accurate measurement of tiny deformations, to the control of very low forces and to the preparation, handling and positioning of μm-sized samples. In order to investigate the fatigue behaviour of MEMS components a new experimental setup based on the Phase Lock Loop (PLL) technique and a continuum mechanical model were developed for the characterization of micro-sized test samples. The main advantage of PLL is the achievable resolution in the crack length measurement, which increases with the decreasing of specimen size. Therefore, micro-beams with notches and without notches were prepared by electroplating Nickel in a SU8 photoresist mold (UV-LIGA). Investigations on the initiation and near-threshold crack growth behavior were performed to improve the understanding of the micro-mechanisms involved in fatigue phenomena.

Abstract: Tensile testing of thin rolled copper foils with thickness ranging from 10 to 250 µm shows a dependence of the fracture strain with respect to the thickness of the foils [G. Simons et al., in Solid Mechanics and its Applications, Vol. 114 (2004), pp. 89-96]. To understand the influence of the microstructure in the foils on this phenomenon the microtexture is investigated by orientation mapping through electron backscatter diffraction (EBSD). As the samples are rather small standard preparation techniques do not apply. Two methods are described which allow the investigation of different section cuts of the samples: Cross sections of the samples were produced by ion beam cutting with a wide beam of 7 keV Kr ions. Internal planes parallel to the specimen surface were made accessible by wet etching. The as-received material possesses a very strong texture consisting mostly of the cube component and some remnants of a previous rolling texture. Specimens tested in a tensile test do not show major microstructural changes compared to virgin samples. After a heat treatment at 300°C the cube texture has significantly weakened in favour of revived rolling components, and the fracture strain increased about ten times relative to the as-is material.