A new load cell for measuring normal and shear stresses

A special stress measuring device for determining the normal and shear stresses acting on silo walls was developed and tested. The load cell can be used for measuring simultaneously the normal stress as well as the intensity and direction of the shear stress.     

Analyse der Mikrostruktur und des Eigenspannungszustandes seilverstärkter Aluminiumstrangpressprofile

Analysis of the microstructure and the residual stress state of aluminium extrusions reinforced with ropes Closed profiles of the aluminium wrought alloy EN AW‐6060 have been in‐situ‐reinforced during the extrusion process with ropes built by wires drawn of the nickel‐based alloy Inconel 601 (2.4851). These profiles have been investigated with non‐destructive and semi‐destructive testing methods regarding the residual stresses evolving during cooling from extrusion temperature to room temperature. The results obtained via X‐ray diffraction and hole drilling method have been compared with simulations using a simplified model of the compound investigated. Thereby, compressive residual stresses appearing during the cooling process have been detected parallel to the rope axis nearby the rope‐matrix‐interface because of plastic flow of the matrix material. Additionally, the microstructure of the extruded composite has been analysed focussing on the contingent formation of intermetallic phases at the rope‐matrix‐interface and on the influence of the reinforcements on the longitudinal weld.     

Crystallization Kinetics and Properties of Nonstoichiometric Cordierite-Based Thick-Film Dielectrics

Dielectric thick films based on a nonstoichiometric cordierite (2.4MgO·2Al₂O₃·5SiO₂, containing 3 wt% B₂O₃, 3 wt% P₂O₅, and 3 wt% PbO) were investigated, in regard to their microstructure, crystallization kinetics, and properties. A stable glass-ceramic thick-film microstructure that was formed on a 96% alumina substrate was observed after firing at a temperature of 915°C for 30 min in a nitrogen atmosphere. No µ-cordierite was observed in the X-ray diffraction (XRD) patterns of the thick film. The crystallization kinetics were studied via quantitative XRD analysis using the Avrami equation, and the rate constant increased as the temperature increased. The decreasing tendency of the Avrami parameter, relative to temperature, suggested a change in growth directionality during crystallization. The activation energy for crystallization of the thick film was determined to be ~83 kcal/mol (~350 kJ/mol). The coefficient of thermal expansion (CTE) and the dielectric constant of the glass phase were evaluated using the bulk-sample data. For the case of a 3-wt%-PbO sample fired at 950°C for 30 min in a nitrogen atmosphere, the remaining glass was estimated, using the parallel mixing rule, to have a dielectric constant of 15.3 at 1 MHz. The dielectric constant of the remaining glass was dependent on the PbO content and the heat-treatment temperature. The estimated CTE of the remaining glass for the 3-wt%-PbO sample was 19 × 10^-6/°C.     

Characterization of Lead Scandium Tantalate Ceramics Prepared by Precipitation Method

Precipitation and coating techniques that proved successful for lead scandium niobate were tried with lead scandium tantalate. The Ta₂O₅ did not prove to be a useful substrate for the precipitating carbonates, but the resulting fine-particle-size powder lowered the sintering temperature to 1375° with only 0.4 wt% PbO loss. Annealed samples showed shifts in the dielectric response and sharpening of infrared and X-ray diffraction patterns, but little development of super lattice.     

Search beam method

An interactive multi‐objective decision‐making (MODM) model based on the Search Beam Method (SBM) and a finite‐difference groundwater flow model (GWM), is developed for analysing groundwater resources development and management problems. The SBM utilizes one‐dimensional search in the objective space to (systematically) identify the non‐dominated solutions. The steady‐state GWM determines the aquifer response due to well withdrawals. Three competing objectives of maximizing total yield, minimizing maximum compression and minimizing total pumping cost are considered. Applicability of the MODM model is demonstrated on a simplified confined aquifer system resembling one of the water‐bearing layers underlying Bangkok.     

Determining soil physical properties by multi-sensor technique

Plant growth and crop yield can be significantly impeded by a number of soil physical parameters including soil water content, mechanical strength and soil electrical conductivity (EC). Therefore, to simultaneously measure these physical parameters along vertical depths in the field, it has been desired for many years. This study focused on developing a multi-sensor system, which contained a cell with three sensors for measuring soil water content, mechanical strength and EC. Additionally a Hall-current sensor was proposed to measure the operating current of a dc-motor, which generated the penetrating force during operating process. Based on the theoretical analysis of the transformation from electrical to mechanical energy, it was feasible to evaluate the soil mechanical strength from the operating current of the dc-motor. In order to verify the performance of the designed system and the theoretical analysis addressed, relevant calibrations and tests were conducted. The results demonstrate that the multi-sensor system could be beneficial and practical for field surveys.     

Piezoresistivity in PTCR Barium Titanate Ceramics: II, Mathematical Modeling

A modified grain boundary potential barrier model for positive temperature coefficient of resistance (PTCR) barium titanate is developed. It is based on Heywang's double Schottky barrier model, together with Devonshire's thermodynamic phenomenology of polarization behavior. Modifications are made to address the nonlinearity of the dielectric response with respect to electric field in the depletion region adjacent to the grain boundary, and the circular dependence of these quantities with the height of the barrier. Piezoresistivities are calculated for various PTCR compositions and sintering conditions, and these are compared to experimental results from the preceding paper.