Christoph Greb - Academia.edu (original) (raw)

Papers by Christoph Greb

CEAS Space Journal

A large deployable reflector antenna (LDA) is comprised of numerous components. One of the key co... more A large deployable reflector antenna (LDA) is comprised of numerous components. One of the key components of this reflector antenna is the reflector surface. Several types of reflector surfaces have been developed and used, namely, metal mesh-based reflector surfaces, membrane-based reflector surfaces, etc. The benefits presented by warp-knitted metal mesh-based reflector surfaces are their foldability and light weight structural characteristics. Typical metal mesh-based reflector surfaces are produced using a warp knitting textile manufacturing process. A warp-knitted metal mesh reflecting surface is an elastic, open structured knit with a low bending stiffness produced on a high gauge knitting machine (E26 or higher gauge) consisting of a compatible metal yarn (typically tungsten or molybdenum). This paper gives an overview about the requirements for mesh reflector surfaces stated in the literature. Afterwards, an overview of different patterns currently investigated by the LDA co...

Materials Science Forum

Fiber reinforced plastics are an essential material for lightweight products. However, their supe... more Fiber reinforced plastics are an essential material for lightweight products. However, their superior mechanical properties compared to traditional materials are only guaranteed, if necessary quality requirements are met (e.g. fiber orientation). One promising approach for detecting quality deviations in image-based monitoring data is to use deep learning models. Nevertheless, these models need vast amounts of labeled training data, which is either not available or expensive to attain. To train deep learning models more data efficiently, a common and intuitive transfer learning approach is applied to detect fiber orientations for two different fiber reinforced plastics. By comparing the similarity between different domains of public datasets with the domain of the materials of this work, the range of optimal hyperparameters were estimated for the transfer learning task at hand. Through a grid search within the estimated hyperparameter range, the best-performing models were identifie...

Journal of Composites Science, 2021

Hybridization of carbon fiber composites can increase the material damping of composite parts. Ho... more Hybridization of carbon fiber composites can increase the material damping of composite parts. However, there is little research on a direct comparison of different fiber materials—particularly for carbon fiber intraply-hybrid composites. Hence, the mechanical- and damping properties of different carbon fiber intraply hybrids are analyzed in this paper. Quasi unidirectional fabrics made of carbon, aramid, Vectran and cellulose fibers are produced, and their mechanical properties are analyzed. The material tests show an increased material damping due to the use of Vectran and aramid fibers, with a simultaneous reduction in strength and stiffness.

Recent developments have demonstrated the challenges and impacts of disruptions in supply chains.... more Recent developments have demonstrated the challenges and impacts of disruptions in supply chains. Current disruptions especially affected procurement and have indicated a lack of resilience. Resilience aims at being prepared, decreasing the impact, and enabling fast reactions and adaption in case of disruptions. The systematic design of resilience in procurement is significantly influenced by proactive and strategic actions before disruptions occur. Thus, the procurement strategy plays a major role when increasing resilience. The procurement strategy is influenced by various factors. Thus, a data-based approach for its systematic design is required. Based on the vision of the Internet of Production (IoP), this paper presents a data-based approach for designing procurement strategies. The IoP is a framework that enables cross-domain collaboration by providing semantically adequate and contextual data from production, development, and usage in real-time at an appropriate granularity. ...

Advances in Intelligent Systems and Computing, 2021

Nowadays, the importance of non-physical goods in traditional production companies is steadily in... more Nowadays, the importance of non-physical goods in traditional production companies is steadily increasing. Accompanying this, companies are confronted with challenges in the area of knowledge transfer and employee support during production processes. Particularly affected are conservative industries such as the textile industry, which rely heavily on implicitly available experience-based (tacit) knowledge. A promising approach to tackle these challenges presents the concept of an "Internet of Production (IoP)". This contribution provides a framework on how the IoP can be conceived and incorporated within the textile industry. Focusing on five textile use-cases, it is described, how know-how transfer and support systems are imminent for the widespread introduction and perpetuation of the IoP.

Towards Sustainable Customization: Bridging Smart Products and Manufacturing Systems, 2021

Object detection has the potential to facilitate the automation of optical quality inspection, ac... more Object detection has the potential to facilitate the automation of optical quality inspection, achieving a significant reduction of human error. However, the gap between needed expertise to understand and integrate complex object detection systems into production environments and the availability of computer scientists, is hindering its use in the manufacturing industry. A support system for decision-makers unrelated to the subject is therefore required to promote industry utilisation of object detection and effectively manage this otherwise unused opportunity of profitable knowledge. Within the Cluster of Excellency "Internet of Production (IoP)", such a support system has been developed. Lowering the implementation hurdle of object detection systems is achieved by translating complex information about existing methods into tangible factors, such as quality and cost. In this work we aim to structure relevant object detection techniques and employ a decision tree to provide a user-support based on a use-case-oriented framework. The use-case's basic conditions and requirements serve as input for the framework. The decision tree gives the suitable object detection method as output, accordingly. For traditional object detection techniques, the characteristics are translated into basic requirements, which are then used as input, e.g., for the template matching method the comparison of a source image with a reference image is translated to the ability to guarantee images for all possible quality deviations. The deep learning (DL) methods are consolidated in the project management triangle consisting of quality, cost, and time. Firstly, an introduction into object detection is given. Secondly, traditional methods are clustered and deep learning methods classified. A description of the decision tree is then presented, before testing results conclude this paper. The developed support system enables decision-makers to evaluate object detection methods for individual use-cases and consequently achieve increased production planning efficiency. The system's universal design allows for application across manufacturing industries and use-cases.

International Journal of Sustainable Manufacturing, 2020

Materials Research Express, 2019

The effect of normal load on the reciprocating sliding behavior of plain weave woven carbon fiber... more The effect of normal load on the reciprocating sliding behavior of plain weave woven carbon fibers (CF) and graphene nanoplatelets (GNPs) coated unidirectional carbon fiber strands (GCF) reinforced polymer (CF-GCF/epoxy) composites was investigated. The normal load was varied from 50 N to 90 N at the interval of 10 N. The high frequency of reciprocating motion (5 Hz) was considered. Nearly 13,500 cycles were employed with a stroke length of 1.5 mm. The tensile behavior of CF-GCF/epoxy composite was also investigated keeping longitudinal direction of GCF along the loading direction. The fractured samples and worn surfaces were analyzed under scanning electron microscopy. It was observed that the surface of GCF was rough which increased its interlocking tendency with the matrix and hence increased the tensile strength. The friction coefficient increased with increase of load up to 80 N and decreased afterward, whereas wear loss exhibited increasing trend with increase in load. However wear loss showed a slight decrease in slope beyond 70 N load. Fiber fragments in wear debris were observed at high loads. Although the friction film was also observed at high loads, the abrasion furrows were not significantly visible. The plasticity of matrix and the formation of friction film depicted the friction and wear behavior of CF-GCF/epoxy composites.

Wireless Power Transfer, 2018

The objective of the presented work is to take advantage of the precision capabilities of tailor-... more The objective of the presented work is to take advantage of the precision capabilities of tailor-fiber-placement (TFP) embroidery processes in order to qualify carbon-fiber parts as viable antennas for wireless power transfer applications in multifunctional carbon-fiber-reinforced plastic (CFRP) composites. The solution comes first from a literature study of electrical, high-frequency, and textile engineering concepts. This review built familiarity with the technological challenges and state-of-the-art of the presented technology. Next step was iterative experimentation of machine capabilities for the production of carbon-fiber antennas. Finally, antenna prototypes were produced and their physical and electrical characteristics were evaluated through several test methods. The results showed that TFP embroidery machines were capable of producing quality, carbon antennas. Induction values of the antennas from 0.5 to 3.5 ‘H were achieved. Signal transfer efficiencies from carbon-antenn...

Journal of Industrial Textiles, 2015

Commingling is a prospective manufacturing process for the production of hybrid yarn in which a r... more Commingling is a prospective manufacturing process for the production of hybrid yarn in which a reinforcement material and a thermoplastic matrix in the form of filaments are mixed to form continuous filament yarn. In this work, hybrid two-component carbon/ polyphenylene sulfide (PPS) yarns designed for high-performance thermoplastic composites were developed. Experiments were carried out to investigate the manufacturing process of commingled yarn and quantify the homogeneity of distribution of carbon and PPS fibers in cross section of commingled hybrid yarns. The effect of process parameters in commingling including degree of overfeeding, production speed, and air pressure on the filament distribution in the cross section of commingled hybrid yarns was investigated. The results show that process parameters play a large part in improving blend uniformity and filament distribution in hybrid commingled yarns. A correlation between the observed homogeneity and the process parameters wa...

ZWF Zeitschrift für wirtschaftlichen Fabrikbetrieb, 2014

Kurzfassung Kohlenstofffaserverstärkte Kunststoffe (CFK) werden zunehmend in Großserienanwendunge... more Kurzfassung Kohlenstofffaserverstärkte Kunststoffe (CFK) werden zunehmend in Großserienanwendungen der Automobilindustrie eingesetzt. Neue Fertigungstechnologien, wie z. B. Faserdirektablagetechnologien, haben ein großes Potenzial, die Herstellkosten von CFK zu senken. Um die Wettbewerbsfähigkeit sicherzustellen, müssen jedoch organisatorische und technische Risiken bewertet werden. Der Beitrag beschreibt daher ein Vorgehen zur technologiespezifischen Anpassung eines bestehenden Reifemodells und wendet dieses auf eine Faserdirektablagetechnologie an.

ATZ - Automobiltechnische Zeitschrift, 2013

Wenn man Bauteile aus endlosfaserverstarkten Kunststoffen (FVK) wie CFK herstellen mochte, muss m... more Wenn man Bauteile aus endlosfaserverstarkten Kunststoffen (FVK) wie CFK herstellen mochte, muss man den Prozess ganzheitlich betrachten. Anhand von lokal angepassten Multiaxialgelegen und biegeschlaffer textiler Preforms zeigt die DFG-Forschergruppe 860 aus IKV und ITA der RWTH Aachen University sowie das Fraunhofer IPT, wie Leichtbau im Automobil kostengunstiger reif fur die Grosserie werden kann. In Zukunft soll so eine Motorhaube aus CFK moglich werden.

Leichtbau-Technologien im Automobilbau, 2013