Modeling and testing of energy absorbing lightweight materials and structures for automotive applications

As a consequence of the increasing demands in automotive industry concerning crashworthiness and passive safety, the concern for energy management and safety demands also increases. The goal of energy management is to reduce the forces and stresses on an occupant or a pedestrian during a crash event; in some cases it may be possible to reduce the forces by a factor of two. This requires usage of new advanced materials in automotive components. Energy absorbing foams and other lightweight materials like plastics and polymer composites are increasingly used in automotive industry. Hence, extensive study of energy absorbing behavior of these materials as well as the automotive components is needed for further improvements in numerical modeling and crash simulations. The paper enlightens recent advances in investigation of mechanical properties and energy absorption ability of the mentioned lightweight materials as well as modeling with finite element codes for crash simulations.     

Reactive Low Voltage Ion Plating (RLVIP). Prozess‐, Plasma‐ und Schichteigenschaften am Beispiel von Ta2O5/SiO2

Reactive Low Voltage Ion Plating (RLVIP) is a process for production of chemical compound films mainly by direct synthesis from the elements. It can be used for deposition of single layer and multilayer oxide coatings onto unheated glass and other unheated substrates. An introduction to the RLVIP process will be given, together with some relevant plasma process data and optical and mechanical film properties of Ta₂O₅ films and Ta₂O₅/SiO₂ multilayers. The process plasma was analysed by plasma monitoring (PPM421), a Langmuir probe system (Smartprobe) and a Faraday Cup System (MIEDA). A correlation between plasma data and optical/mechanical properties will be shown.     

Group Decision Making on Urban Planning Using Desktop Multimedia Conferencing

Recent developments on multimedia systems and networking technology show that using desktop multimedia conferencing for group decision making on wide area networks such as the Internet is possible. In this paper we review the design, hardware and software requirements and organizational issues in a desktop multimedia conferencing system. We draw on our experiences from multiple multimedia conferences on the Internet and in particular we focus on a case study on urban planning using desktop multimedia conferencing on the Internet. Further we discuss implications for further research on desktop multimedia conferencing.     

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of Laser Beam Welded TiAl-based Alloy

Post-weld heat treatment is carried out on the laser beam welded γ-TiAl-based alloy Ti-48Al-1Cr-1.5Nb-1Mn-0.2Si-0.5B (at. pct). The macro/microstructure and mechanical properties of both as-welded and heat-treated specimens are investigated by radiography, SEM, and tensile tests. Moreover, high energy synchrotron X-ray diffraction is performed to measure the residual stresses and evaluate the microstructure evolution. It is found that the residual stresses are distributed in a three-peak shape in the region of the weld zone and heat-affected zone of the as-welded specimen due to the microstructural transformation and heat softening. The residual stresses are largely relieved after the heat treatment. The heat-treated specimens have a near fully lamellar microstructure and show balanced mechanical properties of strength and ductility. The diffraction shows that the phase transformation from α ₂ to γ takes place under tensile load at 1023 K (750 °C), and the grain size and lamellar spacing are refined in the weld zone. Finally, the fracture mechanisms are found to be controlled by the local stress concentration-induced strain misfit between α ₂ and γ phases in the near γ grains and delamination and debonding in the lamellae. Boride ribbons of 5 μm in the near fully lamellar microstructure are found not to be detrimental to the tensile properties.     

Effect of weak and high magnetic fields in longitudinal and transverse configurations on magneto-thermoelectric properties of quantum Bi wires

We report on the magneto-thermopower of single-crystal Bi nanowires with diameters 75 and 250 nm in a longitudinal and transverse magnetic fields of 0–14 T. The temperature range is 1.5–300 K. Bi nanowires in a glass capillary have been prepared by the high frequency liquid phase casting. The temperature dependence R(T) shows the transition from metallic to semiconducting behavior due to quantum size effect, where the Bi-wire diameter is reduced to less than 80 nm. It is for the first time that the effect of the negative magneto-resistance in a transverse magnetic field, due to the quantum size effect on 75 nm Bi wires, has been observed. The thermopower is very sensitive to the wire diameter, up to a change in the sign from negative to positive at low temperatures, and to a significant extent in a weak longitudinal magnetic field. The field dependences of longitudinal and transverse magneto-resistance have features characteristic of the occurrence of the quantum size effect and galvanomagnetic size effect, and provide information on the parameters of the energy spectrum and charge carrier mobility. The enhancement of the thermoelectric figure of merit for Bi nanowires is discussed. We also discuss the power factor α²σ and its dependence on the diameter, magnetic field and temperature.     

A critical review of all-cellulose composites

Cellulose is a fascinating biopolymer of almost inexhaustible quantity. While being a lightweight material, it shows outstanding values of strength and stiffness when present in its native form. Unsurprisingly, cellulose fibre has been rigorously investigated as a reinforcing component in biocomposites. In recent years, however, a new class of monocomponent composites based on cellulosic materials, so-called all-cellulose composites (ACCs) have emerged. These new materials promise to overcome the critical problem of fibre–matrix adhesion in biocomposites by using chemically similar or identical cellulosic materials for both matrix and reinforcement. A number of papers scattered throughout the polymer, composites and biomolecular science literature have been published describing non-derivatized and derivatized ACCs. Exceptional mechanical properties of ACCs have been reported that easily exceed those of traditional biocomposites. Several different processing routes have been applied to the manufacture of ACCs using a broad range of different solvent systems and raw materials. This article aims to provide a comprehensive review of the background chemistry and various cellulosic sources investigated, various synthesis routes, phase transformations of the cellulose, and mechanical, viscoelastic and optical properties of ACCs. The current difficulties and challenges of ACCs are clearly outlined, pointing the way forward for further exploration of this interesting subcategory of biocomposites.     

Design and analysis of UW-OFDM signals

Unique word-orthogonal frequency division multiplexing (UW-OFDM) is a novel signaling concept where the guard interval is implemented as a deterministic sequence, the so-called unique word. The UW is generated by introducing a certain level of redundancy in the frequency domain. Different data estimation strategies and the favourable bit error ratio (BER) performance of UW-OFDM, as well as comparisons to competing concepts have already extensively been discussed in previous papers. This work focuses on the different possibilities on how to generate UW-OFDM signals. The optimality of the two-step over the direct approach in systematic UW-OFDM is proved analytically, we present a heuristic algorithm that allows a fast numerical optimization of the redundant subcarrier positions, and we show that our original intuitive approach of spreading the redundant subcarriers in systematically encoded UW-OFDM by minimizing the mean redundant energy is practically also optimum w.r.t. transceiver based cost functions. Finally, we derive closed form approximations of the statistical symbol distributions on individual subcarriers as well as the redundant energy distribution and compare them with numerically found results.