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Aufsatz
Finding Spaces for Urban Food Production – Matching Spatial and Stakeholder Analysis with Urban Agriculture Approaches in the Urban Renewal Area of Dortmund-Hörde, Germany
(Department of Organic Food Quality and Food Culture at the University of Kassel, Germany and Federation of German Scientists (VDW), 2015-05-20)
Using the case of an economically declined neighbourhood in the post-industrial German Ruhr Area (sometimes characterized as Germany’s “Rust Belt”), we analyse, describe and conclude how urban agriculture can be used as a catalyst to stimulate and support urban renewal and regeneration, especially from a socio-cultural perspective. Using the methodological framework of participatory action research, and linking bottom-up and top-down planning approaches, a project path was developed to include the population affected ...
Aufsatz
Comparative investigation of two-dimensional imaging methods and X-ray tomography in the characterization of microstructure
(2017-10-02)
The microstructural features of three different materials have been quantified by means of 2D image analysis and X-ray micro-computer tomography (CT) and the results were compared to determine the reliability of the 2D analysis in the material characterization. The 3D quantification of shrinkage pores and Fe-rich inclusions of an Al-Si-Cu alloy by X-ray tomography was compared with the statistical analysis of the 2D metallographic pictures and a significant difference in the results was found due to the complex ...
Aufsatz
Effect of Post-Process Machining on Surface Properties of Additively Manufactured H13 Tool Steel
(2018-08-28)
Der Werkzeugstahl AISI H13 zeichnet sich durch einen hohen Verschleißwiderstand und eine gute Temperaturwechselbeständigkeit aus. Hauptanwendungsbereiche des H13 sind Druckguss- und Schmiedewerkzeuge. Die Verarbeitung von H13 durch additive Fertigungsverfahren, wie z. B. dem selektiven Laserschmelzen (selective laser melting, SLM), eröffnet neue Gestaltungsmöglichkeiten, wie z. B. die Integration interner Kühlkanäle, die es erlauben, das Einsatzverhalten der Werkzeuge zu verbessern. Aufgrund hoher Oberflächenrauheiten ...
Aufsatz
A Screening Approach for Rapid Qualitative Evaluation of Residual-Stress States – Application to Laser-Hardened Microalloyed Steel
(2019-06-11)
Surface hardening and compressive residual stresses are keys to superior part performance in numerous applications. In this context the development of advanced laser surface treatments for new materials and complex sample shapes is a time con-suming process. Eventually, determination of residual stress states by means of X-ray diffraction in the whole surface and subsurface region, respectively, is one of the main time consuming facors in terms of characterization. In many applications the provision of an adequate ...
Aufsatz
Martensite aging in ⟨001⟩ oriented Co₄₉ Ni₂₁ Ga₃₀ single crystals in tension
(2018-03-22)
Co–Ni–Ga high-temperature shape memory alloys (HT-SMAs) are well-known candidate materials for damping applications at elevated temperatures. Recent studies showed that upon heat treatment in stress-induced martensite under compressive loads transformation temperatures can be increased significantly, qualifying Co–Ni–Ga for HT-actuation. The increase in transformation temperatures is related to a change in chemical order recently validated via neutron diffraction experiments. Since SMAs show distinct tension–compression ...
Aufsatz
Electron beam welding of Fe–Mn–Al–Ni shape memory alloy: Microstructure evolution and shape memory response
(2017-07-03)
The present study reports on the impact of abnormal grain growth (AGG) on the microstructural evolution following electron beam (EB) welding of Fe–Mn–Al–Ni shape memory alloy (SMA). Polycrystalline sheet-like material was EB-welded and a cyclic heat treatment, studied in previous work, was conducted for inducing AGG and a bamboo-like microstructure, respectively. Optical and electron microscopy were carried out to characterize the prevailing microstructure upon cyclic heat treatment. For characterization of the ...
Aufsatz
Processing effects on tensile superelastic behaviour of Fe43.5Mn34Al15 ± XNi7.5∓X shape memory alloys
(2019)
Fe₄₃.₅Mn₃₄Al₁₅Ni₇.₅ was introduced in the current decade as a new superelastic alloy with great applicative potential due to: (i) superelastic behaviour over a thermal range of 200°C and (ii) recoverable strains up to 9.7 %. One of the key factors in enhancing the superelastic response of several shape memory alloys (SMAs) is the formation of an oligocrystalline structure, i.e. without triple junctions between grains, which is the result of an abnormal grain growth (AGG) process that can be induced by cyclic heat ...
Aufsatz
Design of novel materials for additive manufacturing - Isotropic microstructure and high defect tolerance
(2018-01-22)
Electron Beam Melting (EBM) is a powder-bed additive manufacturing technology enabling the production of complex metallic parts with generally good mechanical properties. However, the performance of powder-bed based additively manufactured materials is governed by multiple factors that are difficult to control. Alloys that solidify in cubic crystal structures are usually affected by strong anisotropy due to the formation of columnar grains of preferred orientation. Moreover, processing induced defects and porosity ...
Aufsatz
Shape memory effect and superelasticity in high-strength FeNiCoAlTi single crystals hardened by nanoparticles
(2019-11-19)
For [001]-oriented single crystals of Fe-28Ni-17Co-11.5Al-2.5Ti (at %) alloy in tension, it was shown that particles of the γ’-phase with a size of 4–6 nm lead to the appearance of superelasticity, with a strain of εSE=4.5% and a shape memory effect of εSME=5.9%. Increasing the particle size to 10–12 nm reduces εSE to 3.6% and εSME to 3.5%. The paper discusses the causes of the influence of particle size on the reversible strain.
Aufsatz
Innovative Materials for Novel Concepts for Internal Heat Exchangers
(2018-07-27)
Internal heat exchangers are often employed in solar thermal applications as well as in many other applications that involve heat, and, for the most part, consist of metallic materials (copper, stainless steel). Corrugated stainless steel tubes are easy to assemble, and are commonly used in various storage geometries. In order to significantly reduce costs, alternative materials, such as plastics, can function as excellent substitutes. Alternative heat exchangers for the following examinations using various materials ...