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Leipzig, Germany

Kaseberg S.,HTWK Leipzig
Proceedings of the 6th European Workshop - Structural Health Monitoring 2012, EWSHM 2012 | Year: 2012

The fields of activity in civil engineering are subjected to a constant change. Thereby maintenance, strengthening and monitoring of existing buildings have become more and more important. During the last ten years an increasing amount of Carbon Fiber Reinforced Polymer (CFRP) applications to rehabilitate damaged concrete or steel elements was observed. Thereby some important disadvantages of the brittle materials must be considered, for example the low ductility of the bond between CFRP and concrete and brittle failure of FRP. With embedded sensor systems it is possible to measure crack propagation and strains. In this paper a sensor based CFRP system will be presented, that can be used for strengthening and measuring. The used optical fibers with Fiber Bragg Gratings (FBG) have a large number of advantages in opposite to electrical measuring methods. Examples are small dimensions, low weight as well as high static and dynamic resolution of measured values. A Bragg Grating consists of a periodic sequence of artificial and equidistant refraction switches in the core of an optical fiber. It can be produced over emblazing of an interference pattern of ultraviolet light. The core is surrounded by cladding. The main problem during the investigations was the fixing of the glass fiber and the small FBG at the designated position. In this paper the possibility of setting the glass fiber with embroidery at the reinforcing fiber material will be presented. The direct embroider of the optical fiber (and the FBGS) clearly simplifies the fixing. An embroidery machine, using computerized support, is able to fix the fiber optical system accurately fitting at the carbon fiber material. By using computer-controlled machines it is possible to achieve a very high degree of préfabrication as well as a high productiveness. The economic industrial fabrication of smart structures can be realized. Another possibility is the direct converting at the building site by hand made lamination with an epoxy resign. Source


Sangerlaub S.,Fraunhofer Institute for Process Engineering and Packaging | Sangerlaub S.,TU Munich | Bohmer M.,HTWK Leipzig | Stramm C.,Fraunhofer Institute for Process Engineering and Packaging
Journal of Applied Polymer Science | Year: 2013

The incorporation of salt in a polymer matrix could potentially achieve a humidity-regulating film system of high porosity for packaging applications. In this study, sodium chloride (NaCl) powder was used as a model substance for humidity-regulating fillers in polypropylene films. A polypropylene homopolymer was extrusion-blended with NaCl at concentrations of 0.03, 0.06, 0.12, and 0.24 g NaCl·g film-1. Films were produced and were subsequently oriented mono and biaxially. At stretching ratios (SRs) of between 2 and 25 a porosity of 20% v/v to 50% v/v was achieved. The porosity positively correlated with the SR. An empirical model based on ellipsoids that approximated the correlation between the SR and the porosity was developed. This correlation offers a basis for further studies on other salt-polymer systems that have undergone differing orientation processes. Copyright © 2012 Wiley Periodicals, Inc. Source


Biedert R.,German Research Center for Artificial Intelligence | Dengel A.,German Research Center for Artificial Intelligence | Kading C.,HTWK Leipzig
Eye Tracking Research and Applications Symposium (ETRA) | Year: 2012

In this paper we present an approach to build an eye-tracking based text cursor placement system. When triggered, the system employs a computer vision based analysis of the screen's content around the current gaze position to find the most likely designated gaze target. Eventually it synthesizes a mouse event at that position, allowing for a rapid text cursor repositioning even in applications which do not support eye tracking explicitly. For our system we compared three different computer vision methods in a simulation run and evaluated the best candidate in two double blinded user studies. We used a total of 19 participants to assess the system's objective and perceived end user speed up. We can demonstrate that in terms of reposition time the OCR based method is superior to the other tested methods, it also beats common keyboard-mouse interaction for some users. We conclude that while the tool was almost universally preferred subjectively over keyboard-mouse interaction, the highest speed can be achieved by using the right amount of eye tracking. © 2012 ACM. Source


Finsterbusch M.,HTWK Leipzig | Muller J.-A.,HfT Leipzig
Proceedings - International Conference on Network Protocols, ICNP | Year: 2013

Internet traffic identification and validation has been the subject of intensive study for many years. It is used to provide Quality of Service, to provide security and to implement many other tasks. The reliability of these methods, however, is not proved by formal verification. Therefore, the results of these methods can vary from the lab where these methods were developed and their deployment in real world application. In this paper, we present an idea to overcome this problem in order to guarantee reliability and provide more optimised solutions. © 2013 IEEE. Source


Gorke U.-J.,Helmholtz Center for Environmental Research | Kaiser S.,TU Chemnitz | Bucher A.,HTWK Leipzig | Kreissig R.,TU Chemnitz
European Journal of Mechanics, A/Solids | Year: 2012

This paper presents the theoretical background of a phenomenological biphasic model at large strains based on a generalized material description of the theory of porous media, and its numerical realization within the context of a mixed finite element formulation. The study is aimed at the simulation of coupled hydro-mechanical (HM) problems with special focus on geo- and biomechanics. If, in the sense of an initial approximation, the materials of interest can be considered as a mixture of two immiscible components (solid and fluid phases), they can be modeled as saturated porous media. For the numerical treatment of according problems within a finite element approach, the weak formulation of the balance equations of mass and linear momentum of the overall continuum are developed. Within this context, a generalized material approach is preferred assuming the initial configuration of the solid phase as reference configuration of the overall continuum. The transient problem results in a weak formulation with respect to the displacement and pore pressure fields as well as their time derivatives. Following, time discretization is performed using a generalized single step approach, and a linearization technique based on Taylor series representation is applied. After the usual spatial discretization, a global system for the incremental solution of the initial-boundary value problem within the framework of a stable mixed u/p-c finite element approach is defined. This algorithmic proceeding comprises some different conceptual aspects compared to the known literature, and is characterized by a consistent and comprehensive representation. The presented numerical model was implemented into a scientific in-house finite element code based on hierarchical structures, which support the straightforward use of an iterative solver with hierarchical preconditioning, local adaptive remeshing techniques, and parallelized programming features. The accuracy and the efficiency of the numerical algorithms are demonstrated on typical examples. Therewith, the importance of the consideration of large strains in a consistent and proper way is demonstrated as well as the differences compared to models based on small strains. © 2011 Elsevier Masson SAS. All rights reserved. Source

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