Influence of Precursor Densification on Strength Retention of Zirconia-Coated Nextel™ 610 Fibers

Strength degradation of Nextel^™ 610 fibers by continuous liquid phase coating was investigated for four different zirconia precursors. The precursors differed regarding their chemical composition (with or without yttrium), phase composition (amorphous or crystalline), and decomposition behavior. Phase transformation and densification of the films were characterized and found to depend on the kind of precursor. Single fiber Weibull's strength was measured for calcination temperatures between 250° and 1150°C for all precursors. Each precursor had an individual degradation behavior. For an annealing temperature of 1150°C highly damaged (∼1600 MPa) and undamaged (>3300 MPa) fibers were obtained depending on the kind of precursor. Fiber degradation could be correlated to mechanical stresses. Stress concentration due to inhomogeneous film thickness distribution is proposed as the cause of fiber strength degradation. Full strength could be retained for porous coatings or coatings where stresses were reduced by phase transformation.     

Modelling of alcohol and water diffusion in fuel cell membranes—Experimental validation by means of in situ Raman spectroscopy

In this work a multi-component transport model has been set up to describe the diffusion driven mass transport of water and methanol in fuel cell membranes. For a membrane in contact with liquid methanol and water on one side and conditioned air on the other, the corresponding differential equations and boundary conditions were derived in a polymer-related coordinate system taking into account the polymers three-dimensional swelling. Phase equilibrium parameters and unknown diffusion coefficients for Nafion^® 117 were obtained by comparing the simulation results to water and methanol concentration profiles measured with confocal Raman spectroscopy. The influence of methanol concentration, temperature and air flow rate was predicted by the model with a maximum relative mean deviation between measurement and simulation of 8.6% for methanol and 3.4% for water.     

Spatially resolved thermal probe measurement for the investigation of the energy influx in an rf-plasma

The total energy influx for a typical radiofrequency process plasma has been measured by means of a simple thermal probe. The procedure is based on the measurement of temporal slope of the substrate temperature during the plasma process. A substrate dummy which is thermally isolated and inserted into the plasma at substrate position served as thermal probe. It can be moved in vertical and horizontal directions in order to measure the different energy influxes and their topology in the reactor vessel. The knowledge of the spatial distribution is important for coating or sputtering processes.Different contributions to the total energy influx can be identified by different orientation of the thermal probe. If the thermal probe is orientated to the rf-electrode (“down”) the energy influx is much higher than in the opposite direction. This difference can be explained by an additional influx due to the secondary electron emission from the powered rf-electrode.     

Thermo-hydro-chemical couplings considered in safety assessment of shallow tunnels subjected to fire load

Fire loading of concrete tunnel linings is characterized by various physical, chemical, and mechanical processes, resulting in spalling of near-surface concrete layers and degradation of strength and stiffness of the remaining tunnel lining. In this paper, the governing transport processes taking place in concrete at elevated temperatures are considered within a recently published fire-safety assessment tool [Savov K, Lackner R, Mang HA. Stability assessment of shallow tunnels subjected to fire load. Fire Safety J 2005; 40: 745–763] for underground structures. In contrast to consideration of heat transport only [Savov et al.], a coupled thermo-hydro-chemical analysis, simulating the heat and mass transport in concrete under fire loading, is performed, giving access to more realistic temperature distributions as well as gas-pressure distributions within the tunnel lining. These data serve as input for the structural safety assessment tool considering, in addition to the temperature dependence of mechanical properties, the effect of the gas pressure on the strength properties of the heated lining concrete. The combination of the two analysis tools (coupled analysis of governing transport processes and structural safety assessment) is illustrated by the fire-safety assessment of a cross-section of the Lainzer tunnel (Austria) characterized by low overburden (shallow tunnel).     

An Adaptive Contact Model for the Robust Simulation of Knots

In this paper, we present an adaptive model for dynamically deforming hyper‐elastic rods. In contrast to existing approaches, adaptively introduced control points are not governed by geometric subdivision rules. Instead, their states are determined by employing a non‐linear energy‐minimization approach. Since valid control points are computed instantaneously, post‐stabilization schemes are avoided and the stability of the dynamic simulation is improved. Due to inherently complex contact configurations, the simulation of knot tying using rods is a challenging task. In order to address this problem, we combine our adaptive model with a robust and accurate collision handling method for elastic rods. By employing our scheme, complex knot configurations can be simulated in a physically plausible way.