Suche
Anzeige der Dokumente 31-40 von 62
Aufsatz
Influence of Mean Stress on Lifetime Prediction of Adhesive Bonds
(2023-05-31)
The importance of adhesive bonds in the field of joining technology is increasing due to their advantageous properties. One of these attributes is the possibility to reduce the weight compared to welded joints in group of components. For a safe design, the knowledge of the lifetime of these components is essential. Various methods are used for the prediction of the lifetime under cyclic loading. On the one hand there are test-based methods, on the other hand simulation-based approaches. Test-based ones are often ...
Aufsatz
A Stability Analysis of Modified Patankar–Runge–Kutta methods for a nonlinear Production–Destruction System
(2023-03-24)
Modified Patankar–Runge–Kutta (MPRK) methods preserve the positivity as well as conservativity of a production–destruction system (PDS) of ordinary differential equations for all time step sizes. As a result, higher order MPRK schemes do not belong to the class of general linear methods, i. e. the iterates are generated by a nonlinear map g even when the PDS is linear. Moreover, due to the conservativity of the method, the map g possesses non-hyperbolic fixed points.
Recently, a new theorem for the investigation of ...
Aufsatz
Hybrid modeling of viscoelastic and switching–induced heating in ferroelectrics
(2023-03-24)
This contribution focuses on two effects causing a temperature change in electrically loaded ferroelectrics. These materials are often subjected to cyclic loading, where viscoelasticity prevails at lower electric fields, whereas dissipative heating by domain switching dominates above the coercive field. While viscoelasticity is modeled within a phenomenological, rheological framework, the ferroelectric constitutive behaviour is described based on a microphysical model. Merging both approaches results in the hybrid ...
Aufsatz
Benzene Oxidation over Pt Loaded on Fly Ash Zeolite X
(2023-07-20)
In the present study, zeolite X (FANaX) was synthesized from coal fly ash (FA) by a two-step high-temperature method. In order to follow the effect of different contaminants in the starting coal ash, zeolite X was also synthesized from pure chemicals according to a classical recipe (NaX). Iron was loaded on this reference zeolite with the amount which was contained in the coal FA. The final catalytic samples were obtained by wet impregnation of Pt nanoparticles on both types of zeolite crystals. The most active samples ...
Aufsatz
Ultra-high performance alkali-activated slag as a reusable mold for light metal casting
(2023-12-06)
Light metal die casting is usually performed using steel molds. However, these lead to a reduced quality of the casting due to the occurrence of metal corrosion on the surface and the incorporation of hydrogen into the casting as a result of required process chemistry. Ultra-high performance concrete based on alkali-activated slag can be used to produce mineral molds for aluminum casting. The use of reusable mineral molds not only enables the production of various thin-walled geometries. The risk of metal corrosion ...
Aufsatz
Verbesserung der CO₂-Bilanz von Kalksandsteinen durch den Einsatz von Sägeschlamm als Optimierungszuschlag
(2023-12-06)
Rund 20% der aus den Rohstoffen Kalk, Sand und Wasser hergestellten Kalksandsteine (KS) in KS-XL-Formaten werden zur Vorkonfektionierung gesägt. Dabei fallen in den KS-Werken insgesamt rd. 20.000 t Sägeschlämme pro Jahr an, die derzeit keiner gezielten Verwendung zugeführt werden. Allerdings handelt es sich dabei bereits unter Einsatz von CO₂-intensivem Branntkalk gehärtetes Material, welches als Optimierungszusatz genutzt werden kann.
Insgesamt 13 verschiedene Sägeschlämme (SäS) wurden hinsichtlich ihrer Eignung ...
Aufsatz
Latent heat effects in inductive heating of shape memory alloy fibers
(2023-11-23)
Motivation of the present work is an inductive heating process, used in manufacturing a new kind of improved ultra-high performance concrete. In this novel material, fibers made out of shape memory alloys are used to increase the maximum possible fiber volume fraction, or to create an internal state of compressive stress. In contrast to other works, the underlying microstructure transformation from martensite to austenite is highlighted based on thermal analysis. Dynamic scanning calorimetry measurements are adapted ...
Aufsatz
Fibre reinforced ultra-high performance concrete – Rheology, fibre bond strength and flexural strength
(2023-12-06)
Ultra-high performance concrete (UHPC) is characterised by a high compressive strength, high durability, and a dense microstructure. The latter causes UHPC to fail in a brittle and sometimes explosive manner. For this reason, UHPC is reinforced with microfibre reinforcement. On the one hand, these lead to increased tensile and bending loads being able to be absorbed, but above all to ductile post-fracture behaviour. The fibres used are mostly steel fibres.
An essential aspect of the fibre reinforcement is the bond ...
Aufsatz
Funktionalisierung faserverstärkter Hochleistungsbetone mittels Formgedächtnislegierungen
(2023-12-06)
Faserverstärkte (Ultra-)Hochleistungsbetone ((U)HPC) werden bereits seit den 1970er Jahren in großen Mengen für die Herstellung von Betonfertigteilen verwendet. Fasern werden eingesetzt, um die Zugfestigkeit zu erhöhen und sprödes Versagen in duktiles Nachbruchverhalten umzuwandeln. Funktionale Formgedächtnislegierungen (FGL) als Bewehrung haben das Potenzial, in Form von Vorspannelementen im erhärteten Beton zu wirken und die Frischbetoneigenschaften zu verbessern.
FGL haben die Eigenschaft, sich an eine eingeprägte ...
Aufsatz
Spatially resolved in situ analyses of the adsorption behavior of different admixtures on binders
(2023-12-06)
Admixtures play a key role in improving the performance of the cement paste matrix. A more efficient matrix can allow a reduction the binder content while maintaining the same properties. There is currently a lack of knowledge about the spatial distribution of admixtures in situ on binder surfaces which would facilitate the use of admixtures in general in inorganic binder systems. Imaging techniques such as confocal laser scanning microscopy (CLSM) and fluorescence microscopy can be used to study the spatiotemporal ...