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Fracture behavior of ultra-high performance lightweight concrete: In situ investigations using μ-CT
(2023-12-06)
In various research projects at the University of Kassel, the concept of lightweight concrete has been combined with that of ultra-high performance concrete (UHPC). Due to the high performance of the UHPC matrix, lightweight concretes (UHPLC) with strengths of 60-130 MPa and bulk density of 1.5-1.9 kg/m³ were developed. This material can be used in many applications because of its low thermal conductivity, low weight and thus easy to transport, recyclable and can be prefabricated. Thus, it meets today's multifunctional ...
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Characterization of films and film-forming solutions of chitosan/thermoplastic rice starch associations: Role of starch oxidation and plasticizer type in the molecular interactions
(2023-09-29)
Polysaccharide films are alternative sources to replace fossil-based compounds. This study aimed to use rice starch modified by gelatinization and oxidation processes. Different properties were observed after blending it with chitosan and polyols, as evaluated on the film-forming solutions by rheology. The interaction between chitosan and oxidized starch appeared higher, as the plasticizers exhibited a low effect on the rheological behavior. Polyols played an essential role in chitosan/gelatinized associations, driven ...
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Mechanically induced dye-release from polyurea microcapsules in a rubbery adhesive
(2023-07-13)
Especially in the building industry the demand for in situ monitoring concepts of adhesive joints persists. In a new approach, microcapsules filled with special dyes, are added into a rubbery adhesive. Certain stress levels within the adhesive lead to a breakage of the capsules, which release their liquid cores. This results in a detectable colour change and thus, enables non-destructive condition monitoring of the bond. Dye-filled polyurea microcapsules were produced by interfacial polymerization by varying synthesis ...
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High-Strength Dissimilar Welds Between a NiTi Shape Memory Alloy and Titanium Obtained by Intermixing Niobium Using Pulsed Laser Beam Welding
(2023-11-17)
Joining of NiTi shape memory alloys with commercially pure titanium (Ti) is of great interest for manifold industrial applications. However, dissimilar fusion welding of these materials is associated with the formation of extremely brittle intermetallic compounds, e.g., Ti2Ni and TiNi3, which drastically limit the mechanical properties of NiTi/Ti joints. The present investigation seeks to improve both chemical compatibility and mechanical performance through intermixing of a niobium foil as filler material into a ...
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Analysis of the Machine-Specific Behavior of Injection Molding Machines
(2023-12-22)
The performance of an injection molding machine (IMM) influences the process and the quality of the parts manufactured. Despite increasing data collection capabilities, their machine-specific behavior has not been extensively studied. To close corresponding research gaps, the machine-specific behavior of two hydraulic IMMs of different sizes and one electric IMM were compared with each other as part of the investigations. Both the start-up behavior from the cold state and the behavior of the machine at different ...
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Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe–Mn–Al–Ni Shape Memory Alloys
(2021-07-26)
In situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is ...
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Simultaneous impact modified and chain extended glass fiber reinforced poly(lactic acid) composites: Mechanical, thermal, crystallization, and dynamic mechanical performance
(2021-02-05)
Herein, glass fiber (GF) reinforced binary, ternary, and quaternary poly(lactic acid) (PLA) composites were prepared. Toughening, and chain extension of PLA was achieved through the incorporation of impact modifier and chain extender and their concurrent effects on the spectroscopic, crystallization, mechanical, thermal, and thermomechanical properties of the composites were investigated. High mechanical properties of GF influenced the mechanical performance of the composites. However, GF alone could not restrict the ...
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On the Monotonic and Cyclic Behavior of an Al-Mg-Zn-Cu-Si Compositionally Complex Alloy
(2023-08-03)
In present work, the monotonic and cyclic properties of a novel Al-Mg-Zn-Cu-Si compositionally complex alloy (CCA) are investigated. Microstructural studies reveal that a eutectic phase and fishbone-type structures are embedded in the Al-matrix. The mechanical properties of this CCA obtained under compressive loading are found to be promising. However, low ultimate strength and brittle behavior are seen under tension. The fatigue performance of the alloy in the low-cycle fatigue (LCF) regime is poor. Microstructural ...
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Liquid Silicone Rubber Foams Made with Water as Blowing Agent
(2021-08-18)
Liquid silicone rubber (LSR) is primarily used in injection molding. Foamed molded parts made of LSR are almost nonexistent because the process reliability of LSR foam injection molding is currently not given. It makes sense to have suitable foaming processes for this material as well, because the density of this elastomer is about 1.15 g cm−3. With the injection molding process presented herein for foaming LSR, density reductions of up to 40% can be achieved. In this process, up to 3% by weight of water is added to ...
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Hot Sheet Metal Forming Strategies for High-Strength Aluminum Alloys: A Review—Fundamentals and Applications
(2023-05-17)
In the past decade, aluminum alloys have become important structural materials in the automotive industry, thanks to their low density, high strength, high fracture toughness, and good fatigue performance. However, an important limitation of aluminum alloys is their poor formability at room temperature; as a result, numerous studies have been conducted with the aim of developing forming techniques to overcome this and facilitate the forming of more complex-shaped components. Following an overview on the metallurgical ...