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The initial focus of this research was on the development of a general workflow for the documentation and monitoring of historical stained glass windows using structured light scanning.
Therefore windows from different churches, time periods and with different corrosion and damage phenomena were scanned before and after conservation measures.
For many sealing applications rubber O-rings are applied due to their special properties and easy use. In many applications as e.g. in aviation, traffic or process technology the material can be exposed to a variety of conditions during operation as e.g. low temperatures, elevated temperatures and different media. Therefore, it is important to know the material behaviour and the seal performance under those conditions. Additionally ageing of seals is an important factor which has an influence on the long term reliability.
In this contribution we would like to discuss different aspects affecting the seal performance, lifetime estimation and address open questions which should be addressed to come to a deeper understanding of these seals commonly understood as typical machine elements.
Results of running investigations at the Bundesanstalt für Materialforschung und -prüfung (BAM), Division 3.4 “Safety of Storage Containers” are presented and discussed.
Society for Applied Spectroscopy (SAS) Atomic Section Student Award.
Magnesium is a major element in the hydrosphere and biosphere and plays important roles in (bio-) geochemical and physiological cycles. Mg has three stable isotopes, 24Mg, 25Mg and 26Mg. It is due to their relatively large mass difference (~8% between) that isotope fractionation leads to slight variations of isotope amount ratios in biological, environmental and geological samples. Traditionally, isotope ratios are measured by mass spectrometric methods. Their drawbacks include the high costs for instruments and their operation, experienced operators and elaborate time-consuming chromatographic sample preparation.
Recently, optical spectrometric methods have been proposed as faster and low-cost alternative for the analysis of isotope ratios of selected elements by means of high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS), and laser ablation molecular isotopic spectrometry (LAMIS).
For the determination of Mg isotope ratios in selected rock reference materials, the molecular spectrum of the in-situ generated MgF and MgO molecules were studied and their results compared with MC-ICP-MS. By HR-CS-MAS, samples were dissolved by acid digestion and Mg isotopes analyzed with and without matrix. The absorption spectrum was recorded for MgF for the electronic transitions X 2Σ → A 2 Πi, and X 2Σ → B 2Σ+. In the case of LAMIS, we investigated the MgF molecule for the electronic transition A 2Πi → X 2Σ, as well as direct analysis by the MgO molecule for the electronic transition A 1Π+ → X 1Σ. The MgF and MgO spectra are described as the linear combination of their isotopic components or isotopologues: 24MgF, 25MgF, and 26MgF for the MgF and 24MgO, 25MgO, and 26MgO for the MgO. The isotope analysis was done by deconvolution of the MgF spectrum by partial least square regression (PLS) calibrated with enriched isotope spikes. Results were accurate with precisions ranging between 0.2 ‰ and 0.8 ‰ (2 SD, n= 10) for HR-CS-GFMAS. No statistically significant differences were observed for samples w/o matrix extraction. On the other hand, LAMIS allows the direct analysis of solid samples with the extended possibility of direct analysis, however the precision is lower due the lack of solid isotopic calibration standards.
An analysis has been presented pertaining to the use of a convex
bottom tank shape instead of an elliptical, for a road tanker.
Two analyses have been made, concerning the static and the dynamic
relative performance expectations of such tank shape when compared
with the elliptical shape performance.
The outputs of both analyses suggest that the level of average benefit
due to using the proposed shape, is around 10%, with a maximum
benefit observed in the dynamic performance in the case of the
minimum fill level.
Correlation between static and dynamic outputs. Manufacturing.
The weld pool dynamics and shape play a fundamental role in keyhole mode welding. The presented work aims the experimental and numerical investigation of the influence of the weld pool characteristics on the formation of hot cracking. The experimental procedure allows recording the molten pool in the longitudinal section of a butt joint configuration of 15 mm thick structural steel and transparent quartz glass by using a high-speed video camera and two thermal imaging cameras. The observations show that the dimensions of the weld pool vary depending on the depth. The regions close to the surface form a teardrop-shaped weld pool. A bulge-region and its temporal evolution are observed approximately in the middle of the depth of the weld pool, where hot cracking appears. A numerical framework including models for the weld pool dynamics, global temperature field, transient stress state, crystal growth, diffusion and macro-segregation and subroutines for their one-way couplings is developed. The numerically obtained and experimentally observed results are in a good agreement. It is shown that the bulge-region leads to a delay in the solidification behavior, increased temporal tensile stresses and accumulation of impurities in the defect region and hence enhance the probability of hot cracking formation.
The weld pool dynamics and shape play a fundamental role in keyhole mode welding. The presented work aims the experimental and numerical investigation of the influence of the weld pool characteristics on the formation of hot cracking. The experimental procedure allows recording the molten pool in the longitudinal section of a butt joint configuration of 15 mm thick structural steel and transparent quartz glass by using a high-speed video camera and two thermal imaging cameras. The observations show that the dimensions of the weld pool vary depending on the depth. The regions close to the surface form a teardrop-shaped weld pool. A bulge-region and its temporal evolution are observed approximately in the middle of the depth of the weld pool, where hot cracking appears. A numerical framework including models for the weld pool dynamics, global temperature field, transient stress state, crystal growth, diffusion and macro-segregation and subroutines for their one-way couplings is developed. The numerically obtained and experimentally observed results are in a good agreement. It is shown that the bulge-region leads to a delay in the solidification behavior, increased temporal tensile stresses and accumulation of impurities in the defect region and hence enhance the probability of hot cracking formation.
Driven steel piles are commonly used as deep foundations for a wide range of engineering structures, particularly in the offshore branch. They are also an interesting example among the broad spectrum of geotechnical applications where the fluid-solid interaction at the pore-scale can play a major role for the macromechanical behaviour of the whole system.
In the context of the geotechnical practice for offshore wind-farm structures, both the industrial design and the actual dimensions of the large piles used as foundations in the seabed are often driven by factors such as the soil resistance to driving (SRD), which are still not well understood and often estimated based on mere empirical correlations or overly simplified one-dimensional models. In particular, the role of the micromechanical effects during the installation process (e.g. local dilatancy or contractancy) and their consequences on the pore pressure levels at the pile-tip and on the effective resistance to driving, are generally either disregarded or at most assumed to be covered by the simplified engineering “black-box” solutions.
Here, we propose a general framework to address such local aspects of a geotechnical application involving fluid-saturated soils while retaining the focus on the micro-scale phenomena. We advocate for an approach that combines the relative simplicity of the Discrete Element Method (DEM) for the solid mechanics with the capabilities of the Lattice Boltzmann Method (LBM) for the fluid dynamics. In this sense, we aim to compile some useful techniques and practical recommendations for an efficient GPU-based implementation of a micromechanical LBM-DEM simulation tool.
A hyper reduced domain decomposition approach for modeling nonlinear heterogeneous structures
(2019)
Many of today's problems in engineering demand reliable and accurate prediction of failure mechanisms of mechanical structures. Herein it is necessary to take into account the often heterogeneous structure on the fine scale, to capture the underlying physical phenomena. However, an increase of accuracy by dissolving the fine scale inevitably leads to an increase in computational cost. In the context of multiscale simulations, the FE2 method is widely used. In a two-level computation, the fine scale is depicted by a boundary value problem for a representative volume element (RVE), which is then solved in each integration point of the macro scale to determine the macroscopic response. However, the FE2 approach in general is computationally expensive and problematic in the special case of concrete structures. Here rather large RVEs are necessary to sufficiently represent the meso-structure, such that separation of scales cannot be assumed.
Therefore, the aim is to develop an efficient approach to modeling nonlinear heterogeneous structures using domain decomposition and reduced order modeling.
A look inside nanoparticles
(2019)
Small-angle scattering is the method of choice when it comes to obtaining information about the interior of nanoparticles. The aim is to make nanotechnology safer. While the use of small-angle neutron scattering (SANS) is limited to a few instruments in the world, small-angle X-ray scattering (SAXS) is widely accessible, with an upward trend. The example of core-shell particles shows how simple their analysis is with data from an Anton Paar laboratory system. Here, SAXS is a central tool for the development of new reference materials based on poly(methyl) acrylate-PVDF core-shell particles. The dimensions of the cores and shells can be precisely determined. A detailed analysis makes it possible to show that the cores contain fluorinated and nonfluorinated polymers, whereas the shell consist only of PVDF. This core-shell particles with a diameter around 40 nm show a significantly higher PVDF beta phase content than the PVDF homopolymer when using an emulsion polymerization technique. This finding is of importance with respect to applications in electroactive devices.
Compared with the original time-temperature superposition (TTS) principle, an extended non-linear time-temperature equivalent (TTE) principle is suggested in this work. Results shown us, all application of TTS and most of the TTE parameters, for example, the Orr-Sherby-Dorn, Manson-Succop, Larson-Müller, Manson-Haferd, Mendelson-Roberts-Manson parameters and the more general ‘single metamodel’ from Haque–Stewart are special cases of the new suggested principle. The merits of this new method are discussed.
Avoiding road crashes has been the purpose behind many specialized software and hardware systems, involving both active and passive safety principles. Global Positioning technologies were incorporated into the transportation systems with the main purpose of acquiring the position of the vehicle under a continuous basis, for security and economy purposes. However, the GPS data can also be used for assessing the level of safety at which the vehicle is driven. On the basis of the essential data available from commercial GPS devices, in this paper we propose a combined performance measurement to assess the road safety level at which the vehicle is being driven. Such performance measure uses GPS data of the vehicle displacement, including the speed and the acceleration, as well as the course (latitude and longitude coordinates), in an integral driving assessment formulation that can run in real time. Results from the experimental use of this formulation suggest that the level of safety in the driving is time dependent, and that there are risky situations when different factors converge.
Remote gas sensors like those based on the Tunable Diode Laser Absorption Spectroscopy (TDLAS) enable mobile robots to scan huge areas for gas concentrations in reasonable time and are therefore well suited for tasks such as gas emission surveillance and environmental monitoring.
A further advantage of remote sensors is that the gas distribution is not disturbed by the sensing platform itself if the measurements are carried out from a sufficient distance, which is particularly interesting when a rotary-wing platform is used.
Since there is no possibility to obtain ground truth measurements of gas distributions, simulations are used to develop and evaluate suitable olfaction algorithms.
For this purpose several models of in-situ gas sensors have been developed, but models of remote gas sensors are missing.
In this paper we present two novel 3D ray-tracer-based TDLAS sensor models. While the first model simplifies the laser beam as a line, the second model takes the conical shape of the beam into account.
Using a simulated gas plume, we compare the line model with the cone model in terms of accuracy and computational cost and show that the results generated by the cone model can differ significantly from those of the line model.
The propagation of ultrasonic waves in concrete is affected by its micro- and macro-structure, geometry and properties as well as external influences as stress, temperature or moisture. In addition, age and degradation have a strong influence. Therefore, Ultrasound has been used to monitor concrete samples and structures since decades. However, early applications using conventional techniques as time-of flight or changes in amplitudes have been limited to detect changes in a late stage close to serviceability or ultimate load states.
Around 2000, several new, more sensitive techniques adopted from geophysics or other field of material sciences have been introduced to research in ultrasonic monitoring of concrete. The most discussed methodologies are coda wave interferometry, a technique which allows to detect very subtle changes from repeated ultrasonic measurements. Nonlinear acoustic techniques help to identify e. g. cracks even in an inhomogeneous background. Both techniques can be combined.
This paper reviews methods and results achieved so far on the laboratory scale and with full scale models the directions for future research and application is given as well.
Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be observed on almost any material after the irradiation by linearly polarized laser beams, particularly when using ultrashort laser pulses with durations in the femtosecond to picosecond range.
During the past few years significantly increasing research activities have been reported in the field of LIPSS, since their generation in a single-step process provides a simple way of nanostructuring and surface functionalization towards the control of optical, mechanical, biological, or chemical surface properties. In this contribution the mechanisms of formation and current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting properties, the mimicry of the natural texture of animal integuments, the tailoring of surface colonization by bacterial biofilms, the advancement of medical pacemakers, and the improvement of the tribological performance of nanostructured metal surfaces.
The additional element from the filler wire in the laser beam welding is usually distributed inhomogeneously in the final weld due to the high solidification rate of weld pool. It has been found that the electromagnetic stirring produced by an external oscillating magnetic field can enhance the material mixing in the weld pool to achieve a more uniform element distribution. However, the magnetic field has a highly non-linear and multi-coupled interaction with the weld pool behavior, which makes the quantitative explanation of the physical mechanism difficult. In this study, the effect of electromagnetic stirring on the transport phenomena in the wire feed laser beam welding is investigated by a numerical modelling. A 3D transient multi-physical model considering the magnetohydrodynamics, heat transfer, fluid flow, keyhole dynamics and element transport is developed. The multiple reflections and the Fresnel absorption of the laser on the keyhole wall are calculated using the ray tracing method. The numerical results show that a Lorentz force produced by the oscillating magnetic field and its induced eddy current gives significant influence on the transport phenomena in the molten pool. The forward and downward flow is enhanced by the electromagnetic stirring, which homogenizes the distribution of the additional elements from a nickel-based filler wire in a steel weld pool. The numerical results show a good agreement with the high-speed images of the molten pool, the fusion line from the optical micrograph and the element distribution from the energy dispersive X-ray spectroscopy. This work provides a physical base for the electromagnetic-controlled laser beam welding and some guidance for the selection of electromagnetic parameters.
To date, there are only very few technologies available for the conversion of low temperature waste heat to electricity. In this talk, we first describe the principle of thermomagnetic generators. Then we focus on the impact of topology of the magnetic circuit within thermomagnetic generators. We demonstrate that the key operational parameters strongly depend on the genus, i.e. the number of holes within the magnetic circuit.
To date, there are only very few technologies available for the conversion of low temperature waste heat to electricity. In this talk, we first describe the principle of thermomagnetic generators. Then we focus on the impact of topology of the magnetic circuit within thermomagnetic generators. We demonstrate that the key operational parameters strongly depend on the genus, i.e. the number of holes within the magnetic circuit.