02 Fakultät Bau- und Umweltingenieurwissenschaften

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3

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Author: search.filters.author.Steeb, HolgerSubject: search.filters.subject.670

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    ItemOpen Access
    The high cycle fatigue testing of High‐Performance Concretes using high frequency excitation
    (2023) Madadi, Hamid; Steeb, Holger
    The effect of fatigue failure in brittle materials like (ultra) High Performance Concrete (UHPC) due to cyclic loading causes unexpected failure that consequently results in heavy costs in marine and civil structures. To characterize the effect of fatigue, cyclic loading tests are performed, and “the number of cycles to failure” are experimentally determined. One problem with these kinds of tests is that such experimental investigations are potentially expensive, i.e., time‐consuming process since the number of loading cycles could be extremely high. Further, within the different damage phases of the cycling tests, one has no access to the small‐scale, i.e., microscopical evolution of (micro‐)cracks. Additionally, a full characterization of the small‐strain stiffness evolution of the material is challenging. The goal of the research investigation is to combine a (large amplitude) High Cycle Fatigue experiment with a (low amplitude) Dynamic Mechanical Analysis (DMA). Using a setup based on the piezoelectric actuator, the (rate‐dependent) mechanical properties of the material in tangential space, and the failure modes of the material will be examined accurately. The excitation frequency is between 0.01 Hz to 1000 Hz which allows for reducing the experimental investigation time to failure. Further, it allows investigating the effect of frequency on the number of cycles to failure. Firstly, experimental results for HPC and berea sandstone samples will be presented. Harmonic experimental data include (direct) strain measurements in axial and circumferential directions as well as forces in axial directions. In addition, the resulting complex Young's modulus and evolving damage‐like “history” of HPC and berea sandstone specimens will be shown.
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    DLP 4D printing of multi‐responsive bilayered structures
    (2023) Mainik, Philipp; Hsu, Li‐Yun; Zimmer, Claudius W.; Fauser, Dominik; Steeb, Holger; Blasco, Eva
    Advances in soft robotics strongly rely on the development and manufacturing of new responsive soft materials. In particular, light‐based 3D printing techniques, and especially, digital light processing (DLP), offer a versatile platform for the fast manufacturing of complex 3D/4D structures with a high spatial resolution. In this work, DLP all‐printed bilayered structures exhibiting reversible and multi‐responsive behavior are presented for the first time. For this purpose, liquid crystal elastomers (LCEs) are used as active layers and combined with a printable non‐responsive elastomer acting as a passive layer. Furthermore, selective light response is incorporated by embedding various organic dyes absorbing light at different regimes in the active layers. An in‐depth characterization of the single materials and printed bilayers demonstrates a reversible and selective response. Last, the versatility of the approach is shown by DLP printing a bilayered complex 3D structure consisting of four different materials (a passive and three different LCE active materials), which exhibit different actuation patterns when irradiated with different wavelengths of light.
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    Benchmark simulations of dense suspensions flow using computational fluid dynamics
    (2022) Haustein, Martin A.; Eslami Pirharati, Mahmoud; Fataei, Shirin; Ivanov, Dimitri; Jara Heredia, Daniel; Kijanski, Nadine; Lowke, Dirk; Mechtcherine, Viktor; Rostan, Daniel; Schäfer, Thorsten; Schilde, Carsten; Steeb, Holger; Schwarze, Rüdiger
    The modeling of fresh concrete flow is still very challenging. Nevertheless, it is of highest relevance to simulate these industrially important materials with sufficient accuracy. Often, fresh concrete is assumed to show a Bingham-behavior. In numerical simulations, regularization must be used to prevent singularities. Two different regularization models, namely the 1) Bi-viscous, and 2) Bingham-Papanastasiou are investigated. Those models can be applied to complex flows with common simulation methods, such as the Finite Volume Method (FVM), Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Within the scope of this investigation, two common software packages from the field of FVM, namely Ansys Fluent and OpenFOAM, COMSOL Multiphysics (COMSOL) from FEM side, and HOOMD-blue.sph from the field of SPH are used to model a reference experiment and to evaluate the modeling quality. According to the results, a good agreement of data with respect to the velocity profiles for all software packages is achieved, but on the other side there are remarkable difficulties in the viscosity calculation especially in the shear- to plug-flow transition zone. Also, a minor influence of the regularization model on the velocity profile is observed.