Macroscopic simulation model for laser cutting of carbon fibre reinforced plastics

Laser cutting of carbon fibre reinforced plastics (CFRP) has shown promising potential as an alternative to conventional manufacturing processes. Laser cutting has major benefits of contactless and therefore wear-free machining and high automation potential. The main challenge is to reduce the heat input into the material during the process. Excessive temperatures cause damage within the surrounding matrix material and could locally modify the structural properties of the CFRP. For industrial use it is necessary to be able to predict the resulting temperature fields. To gain knowledge of the temperature distribution during the process, a three-dimensional macroscopic finite element model is developed using ANSYS simulation software. Transient-thermal analyses are performed and the material removal process is implemented via the element-death technique. Simulations are run for a unidirectional composite structure and different cutting speeds. The resulting temperatures are compared to experimental data

Development of a laser powder bed fusion process tailored for the additive manufacturing of high-quality components made of the commercial magnesium alloy WE43

Additive manufacturing (AM) has become increasingly important over the last decade and the quality of the products generated with AM technology has strongly improved. The most common metals that are processed by AM techniques are steel, titanium (Ti) or aluminum (Al) alloys. However, the proportion of magnesium (Mg) in AM is still negligible, possibly due to the poor processability of Mg in comparison to other metals. Mg parts are usually produced by various casting processes and the experiences in additive manufacturing of Mg are still limited. To address this issue, a parameter screening was conducted in the present study with experiments designed to find the most influential process parameters. In a second step, these parameters were optimized in order to fabricate parts with the highest relative density. This experiment led to processing parameters with which specimens with relative densities above 99.9% could be created. These highdensity specimens were then utilized in the fabrication of test pieces with several different geometries, in order to compare the material properties resulting from both the casting process and the powder bed fusion (PBF-LB) process. In this comparison, the compositions of the occurring phases and the alloys’ microstructures as well as the mechanical properties were investigated. Typically, the microstructure of metal parts, produced by PBF-LB, consisted of much finer grains compared to as-cast parts. Consequently, the strength of Mg parts generated by PBF-LB could be further increased. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Ludger Gerdes

Refering mainly to Kant, Riegl, and Gombrich, Gerdes defines the conditions favourable to an autonomous art outside the museum's walls. In an interview with Guzman, the artist comments on his developments, his influences, his interest in maquettes as models, and in English landscaping in the 18th century. Biographical notes

Ludger Gerdes : Essays

Raising issues of image, modernism, architecture and design of public places, Gerdes expounds his conception of art in four texts written between 1983 and 1987. Inspired by the writings of Habermas, he examines the impact of art on collective life

The Lectures, Witte de With, 1991

This annual publication of lectures and debates contains an abridged lecture on the relation of cinema and painting (Bellour); a discussion concerning the future of public sculpture (Brouwer, Gerdes and König); an examination of Greenberg's, Poggioli's, and Bürger's views of the avant-garde; an essay on the contemporary art world (Guidieri); a discussion of the "centre and periphery" in the art world today, proposing the non-central model of Portugal (Melo), and an account of death masks, the body and the "monumental face" (Verschaffel). Includes a list of exhibitions held at Witte de With in 1991. 28 bibl. ref

Tests von additiver Fertigung und anderen Prozessen unter Weltraumgravitationsbedingungen im Einstein-Elevator

Material processing and material transport systems on Earth are designed for Earth's gravity and atmosphere. In order to pave the way for the future colonization of space, production technologies and transport systems are an essential factor in reducing costs and logistical efforts, such as in-situ resource utilization (ISRU). Laser-based additive manufacturing methods offer the possibility of a production process independent of environmental conditions and a high degree of adaptability to the objects to be manufactured. These and other processes, e.g. for material handling of powder in microgravity, will be investigated in the Einstein-Elevator in the future. This paper first describes the possibilities for the investigation of large scientific experimental setups under different gravitational conditions. Subsequently, the requirements for the experiments and an exemplary project sequence are described using the example of the MOONRISE project. In addition, first experimental results are presented.Materialverarbeitungs- sowie Materialtransportsysteme auf der Erde sind prozessbedingt auf die Erdgravitation und -atmosphäre ausgelegt. Um den Weg für die zukünftige Kolonisierung des Weltraums zu ebnen, sind Produktionstechnologien sowie Transportsysteme ein essentieller Faktor zur Reduzierung von Kosten und logistischem Aufwand, wie beispielsweise bei der In-situ Resource Utilization (ISRU). Laserbasierte additive Herstellungsverfahren bieten dabei die Möglichkeit eines von Umgebungsbedingungen unabhängigen Verarbeitungsprozesses sowie eine hohe Anpassungsfähigkeit an die herzustellenden Objekte. Diese und weitere Verfahren, z.B. zur Materialhandhabung von Pulver in Schwerelosigkeit, werden im Einstein-Elevator in Zukunft untersucht. In dieser Veröffentlichung werden zunächst die Möglichkeiten für die Untersuchung großer wissenschaftlicher Experimentaufbauten in unterschiedlichen Gravitationsbedingungen beschrieben. Am Beispiel des Projekts MOONRISE werden anschließend die Anforderungen an die Experimente und ein beispielhafter Projektablauf dargestellt. Außerdem werden erste Versuchsergebnisse präsentiert

Thymic B Cells Are Licensed to Present Self Antigens for Central T Cell Tolerance Induction

Thymic antigen-presenting cells (APCs) such as dendritic cells and medullary thymic epithelial cells (mTECs) use distinct strategies of self-antigen expression and presentation to mediate central tolerance. The thymus also harbors B cells; whether they also display unique tolerogenic features and how they genealogically relate to peripheral B cells is unclear. Here, we found that Aire is expressed in thymic but not peripheral B cells. Aire expression in thymic B cells coincided with major histocompatibility class II (MHCII) and CD80 upregulation and immunoglobulin class-switching. These features were recapitulated upon immigration of naive peripheral B cells into the thymus, whereby this intrathymic licensing required CD40 signaling in the context of cognate interactions with autoreactive CD4(+) thymocytes. Moreover, a licensing-dependent neo-antigen selectively upregulated in immigrating B cells mediated negative selection through direct presentation. Thus, autoreactivity within the nascent T cell repertoire fuels a feed forward loop that endows thymic B cells with tolerogenic feature

The Lectures, Witte de With, 1992

The publication of four lectures and two debates presented in conjunction with the 1992 Witte de With exhibition programme includes 14 authors' critical analyzes on the following topics: Brazilian artist Oiticica, representation and history, the depiction of the human figure, the art catalogue, graphic design/typography, and the interests of the centre itself. Contains listing of exhibitions and publications. Biographical notes on authors. 62 bibl. ref