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Tailoring flow behavior and heat transfer in tempering channels for high-pressure die casting—analysis of potentials of commercial static mixers and prospects of additive manufacturing
(2023-02-16)
Additive manufacturing (AM) opens up manifold possibilities to influence the heat transfer between fluid and die in high-pressure die casting (HPDC), eventually allowing to minimize the total cycle time of the process. AM already has been exploited to establish near-contour temperature control systems in industrial applications. However, AM not only allows to influence the position of tempering channels in dies but it also allows to influence the fluid dynamics itself, e.g., by imprinted static mixers. Up to now, ...
Aufsatz
Weathering of a Polyurethane-Based Gel Electrolyte
(2023-03-14)
A recently described flexible polyurethane electrolyte was artificially weathered at 25/50 °C and 50% r.h. in air and at 25 °C in a dry nitrogen atmosphere, each with and without UV irradiation. Different formulations and the polymer matrix, used as a reference, were weathered in order to investigate the influence of the amount of conductive lithium salt and the solvent propylene carbonate. The complete loss of the solvent at a standard climate was already observed after a few days, strongly influencing the ...
Aufsatz
Study of Dynamics in Metallic MEMS Cantilevers - Pull-In Voltage and Actuation Speed
(2023-01-13)
For different metals and varying geometries, this paper presents simulations of electrostatically actuated MEMS cantilevers regarding their influence on pull-in voltage and actuation speed. Three-dimensional electromechanical modeling including many non-linearities has been performed to study some static but mainly dynamic features. The results show that the involved parameters have different influences on the actuation speed and pull-in voltage: lower length, higher thickness as well as lower density and higher ...
Aufsatz
Potential of Fe-Mn-Al-Ni Shape Memory Alloys for Internal Prestressing of Ultra-High Performance Concrete
(2023-05-18)
Prestressing of concrete is a commonly used technique in civil engineering to achieve long spans, reduced structural thicknesses, and resource savings. However, in terms of application, complex tensioning devices are necessary, and prestress losses due to shrinkage and creep of the concrete are unfavourable in terms of sustainability. In this work, a prestressing method using novel Fe-Mn-Al-Ni shape memory alloy rebars as a tensioning system in UHPC is investigated. A generated stress of about 130 MPa was measured ...
Aufsatz
Measurement and analysis of residual stresses and warpage in fiber reinforced plastic and hybrid components
(2021-02-16)
Glass/carbon fiber reinforced plastic (GFRP/CFRP) and hybrid components have attracted increasing attention in lightweight applications. However, residual stresses induced in the manufacturing process of these components can result in warpage and, eventually, negatively affect the mechanical performance of the composite structures. In the present work, GFRP, CFRP, GFRP/steel and CFRP/steel hybrid components were manufactured through the prepreg-press-technology always employing the same process parameters. The residual ...
Aufsatz
Growth of C-S-H phases on different metallic surfaces
(2022-02-21)
The influence of reinforcement, especially fibre reinforcement in ultra-high performance concrete is strongly dependent on the bonding (adhesive, shear and friction bond) between metallic surface and cementitious matrix. As usually straight fibres are used for fibre reinforcement and, thus, no significant mechanical bonding is existent, the adhesive bond is particularly important. Previous studies stated that the adhesive bonding behaviour between metallic materials and cementitious matrix strongly depends on the ...
Aufsatz
Lifetime Prediction with Combined Hygro-Thermo-Mechanical Influences on Thick Layer Adhesives
(2023-05-31)
Semi-structural bonded joints of steel components are exposed to long-term stresses in addition to water diffusion, temperature changes and varying external forces during operation. These hygro-thermomechanical loadings lead to successive degradation of stiffness and strength due to damage resulting from chemical aging and fatigue processes, causing failure of the bonded joint when its service life is reached. In the following contribution, a methodology is presented to predict the service life of hygro-thermo-mechanically ...
Aufsatz
Modeling and numerical simulation of flow processes of wood-polymer composites
(2023-05-31)
The combination of natural fibers and polymers is finding expanding application in a range of industrial branches, and knowledge of the material behavior is essential for further improving the products and the processing procedure. In this work, the material behavior of wood-polymer composites (WPC) will be modeled and numerical simulations will be used to investigate the flow behavior. By means of rheological measurements, a shear thinning flow behavior of the composite can be determined, which is also often taken ...
Aufsatz
Internal prestressing of ultra-high performance concrete using shape memory fibers
(2023-05-31)
Using shape memory fibers to reinforce concrete is a novel concept in civil engineering. Pre-stretched fibers are brought into concrete and after activating the shape memory effect, a compressive prestress state is introduced. The present work investigates this method numerically. A brief introduction to the relevant behavior of shape memory alloys is given. Fiber activation is modeled by an empirical phase transition model. Simulations are carried out by applying the Finite Element Method to solve the CAUCHY-FOURIER ...
Aufsatz
Optimal attitude maneuvers in the presence of prohibited directions
(2023-05-31)
We consider the problem of realigning a space telescope from one observation target to the next in the presence of prohibited directions. More specifically, we want to steer the space telescope – modelled as a gyrostat – from an initial attitude at rest to a final attitude at rest within a fixed time interval. During the motion, the line of sight of the telescope must be kept away from forbidden directions towards bright objects like the sun, moon or earth due to power or thermal requirements. The kinematics of the ...