Fraunhofer Institute for Structural Durability and System Reliability


Fraunhofer Institute for Structural Durability and System Reliability

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Kolupaev V.A.,Fraunhofer Institute for Structural Durability and System Reliability
Journal of Engineering Mechanics | Year: 2017

The equivalent stress concept allows the comparison of arbitrary multiaxial stress states with a uniaxial one. Based on this conceptseveral limit surfaces were formulated. The trend in the formulation lies in the generalized criteria that contain classical hypotheses and aresuitable for several materials. In this work, three generalized criteria are discussed. They are rewritten in order to more closely meet a set ofplausibility assumptions. A schematic representation of the unified strength theory (UST) of Yu can be given as a convex combination of theclassical hypotheses (Tresca, Schmidt-Ishlinsky, and Rankine). For this schema a criterion as a function of the stress angle is proposed. Itdescribes a single surface without plane intersecting in the principal stress space. The introduced criterion is similar to the UST and like theUST is C0-continuous. The Podgórski criterion as function of the stress angle is C1-continuously differentiable and can be used as yield andstrength criterion. The parameters of this criterion are real numbers restricted in order to obtain the convex shapes in the π-plane. The sameparameters can be defined as complex numbers. With these complex parameters, this criterion describes an extended region of the convexshapes in the π-plane. The Altenbach-Zolochevski criterion as function of the stress angle will be modified in order to describe additionalconvex shapes in the π-plane. In contrast to the Altenbach-Zolochevski criterion, the modified criterion contains the Schmidt-Ishlinskyhypothesis as extremal yield function. Both criteria are C0-continuous and can therefore be recommended as strength criteria. The suggestedmodifications of the discussed criteria extend their application area and simplify the fitting procedure. Therefore these criteria are recommendedfor practical use. © 2017 American Society of Civil Engineers.

Weidmann F.,Fraunhofer Institute for Structural Durability and System Reliability
2017 12th International Conference on Ecological Vehicles and Renewable Energies, EVER 2017 | Year: 2017

Modern electric vehicle battery thermal management systems provide sophisticated means to control the temperature of its battery cells within the optimal temperature range. This is crucial as Lithium-Ion battery cells result in reduced lifespans if exposed to temperatures above 50°C. On the other hand, temperatures below 10°C lead to a reduced capacity and with respect to electric vehicles in reduced driving ranges. The OPTEMUS project therefore develops a thermal insulating battery module housing that thermally disconnects the battery cells from the ambient temperature, providing a more stable temperature profile and more efficient thermal management of the battery. Different housing materials and designs have been developed to provide thermal insulating properties while also withstanding mechanical forces. Based on a concept module design of Fraunhofer LBF, two different fiber reinforced plastic sandwich structures have been manufactured with insulating foam cores and analyzed with respect to their cellular structures and resulting thermal properties. The cellular structure was detected three-dimensionally via computer tomography analysis. The manufactured sub-module housings were tested in a climatic chamber at-10°C and compared to a benchmark housing design based on aluminum as construction material. Results showed that the cell temperatures decrease 250 to 400 % slower using foam core sandwich structures as housing material compared to an aluminum housing while providing large scale manufacturability via the injection molding process. © 2017 IEEE.

News Article | September 1, 2016

The big container ship slowly departs from the quay. The two-stroke diesel engines boom inside the hull. The powerful 60,000 kilowatt engine makes everything vibrate: the connectors on the engine, the high-pressure pipes for fuel and lubricating oil, the drive train, stairs, steps, floor and ceiling made of steel – everything. The vibrations are transmitted to the entire hull. "A massive problem: The vibrations are not only disturbing; they also damage important components of the ship," says Heiko Atzrodt, researcher at the Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt. Adaptronic systems help to reduce the vibrations. The LBF has written a simulation software with which these systems are developed efficiently. The researchers are presenting the "Mechanical Simulation Toolbox" at the maritime trade fair SMM from September 06 – 09, 2016 in Hamburg."A simulation software for adaptronic systems is available for the first time. To date, there has not been an integrated development process for such systems. Corresponding software has so far only been available as isolated solutions," reports the graduated mechanical engineer. With the development kit, shipbuilders can easily design adaptronic systems step by step on the computer. "This saves the time and costs involved with expensive prototypes. Subsystems are optimally designed from the very beginning," Atzrodt says, identifying one of the advantages. LBF implements the software and is the service provider. The toolbox is a result of the Hessian research promotion program LOEWE (the State Offensive for the Development of Scientific and Economic Excellence). Partners of the LBF in the adaptive systems project LOEWE Center AdRIA (Adaptronic – Research, Innovation, Application) in Darmstadt are the Technical University and the Darmstadt University of Applied Sciences. The virtual simulation environment is not limited to the shipping industry. "It can be used wherever that vibrations occur – and it is available immediately," Atzrodt informs. With the software, passive and adaptronic systems for vibration reduction can be simulated on the computer. In passive systems, no additional electrical energy is added. They work solely through their structure. Springs and additional materials, for example, reduce the vibration of bridges and engine or transmission mounts by modifying the transmission paths. "However, these systems have limits which are set precisely for mobile applications, since they cannot be arbitrarily large and heavy," explains Atzrodt. That is where adaptronic systems come into play. These components convert supplied electrical energy into mechanical energy, thereby actively counteracting the vibrations. This makes them more efficient, despite their lower weight and smaller size. The toolbox of the LBF simulates the vibrating and the required adaptronic system. The simulated system can be started up with simple models and made more complex at a later time. Atzrodt, also the managing director of the Fraunhofer Alliance Adaptronics, in which a total of six Fraunhofer Institutes are organized: "At the LBF, we have been dedicating ourselves for more than 15 years to adaptronic systems and their simulation. We work very closely with the industry. Adaptronics is progressively gaining in importance and the demand for a generally available simulation software has been increasing steadily in recent years. We have therefore used our expertise in the past for developing the required product. Now, it is available on the market."

Sonsino C.M.,Fraunhofer Institute for Structural Durability and System Reliability
International Journal of Fatigue | Year: 2011

The multiaxial fatigue behaviour of components seems to depend mainly on the ductility of the material used determined by applied manufacturing parameters. The ductility steers the damage mechanisms. While, in the case of low-ductility (brittle) materials, the normal stress (strain) is the decisive parameter, in the case of ductile materials, it is the shear stress (strain), and, for semi-ductile materials, a combination of normal and shear stresses (strains). Critical plane oriented hypotheses can consider these different parameters, but the difficulty lies in the definition of ductility and, based on this, the selection of the appropriate hypothesis. Therefore, especially for the evaluation of safety parts, experimental verifications are still necessary, because of the lack of a general multiaxial fatigue hypothesis. © 2011 Elsevier Ltd. All rights reserved.

Kaal W.,Fraunhofer Institute for Structural Durability and System Reliability | Herold S.,Fraunhofer Institute for Structural Durability and System Reliability
IEEE/ASME Transactions on Mechatronics | Year: 2011

Electroactive polymers (EAPs) have been widely employed as smart material for actuators in recent years. Numerous investigations have focused on static or quasi-static applications. For the use as actuators in the field of active vibration control (AVC); however, the dynamic behavior needs to be studied in detail and the inherent nonlinear effects demand new control concepts. Since AVC applications have only recently been considered for EAP actuators, only a few studies have been published in this area so far [1]-[4]. In this paper, the nonlinearities in a dielectric elastomer (DE) actuator and their consequences for dynamic applications are analyzed on a theoretical level first and then shown to be practically relevant in an experimental setup. Afterward, two compensation methods are presented and their improving influence on the dynamic behavior proven. Finally, the DE actuator is included in an active closed-loop control system and its potential for AVC demonstrated. Furthermore, a MATLAB/SIMULINK model of the whole system is presented, its general validity shown, and its potential for future system development processes highlighted. © 2006 IEEE.

Ghareeb H.O.,Fraunhofer Institute for Structural Durability and System Reliability | Radke W.,Fraunhofer Institute for Structural Durability and System Reliability
Carbohydrate Polymers | Year: 2013

A two-dimensional liquid chromatographic method (2D LC) was developed to analyze the heterogeneities of cellulose acetates (CA) in the DS-range DS = 1.5-2.9 with respect to both, molar mass and degree of substitution (DS). The method uses gradient liquid chromatography (HPLC) as the first dimension in order to separate by DS followed by separation of the different fractions by size (SEC) in the second dimension. The 2D experiments revealed different correlations between gradient and SEC elution volume. These correlations might arise from differences in the synthetic conditions. The newly developed 2D LC separation therefore provides new insights into the heterogeneity of CAs. © 2013 Elsevier Ltd. All rights reserved.

Pfaendner R.,Fraunhofer Institute for Structural Durability and System Reliability
Polymer Degradation and Stability | Year: 2013

Flame retarded polymer formulations are mainly used in long-term applications whereas antioxidants, light stabilizers and co-additives provide the requested lifetime of plastic materials. However many flame retardants influence the oxidative and photooxidative stability of polymers often in a negative way resulting in early failure and loss in value. Moreover insufficient (photo)oxidative stability of the flame retardant itself may reduce the flame retardance performance over time. Therefore, there is a need to develop adjusted stabilizer systems considering the type of flame retardant, the polymer substrate and the intended application. Therefore, the influence of flame retardants on the (photo)oxidative stability of selected polymers is reviewed and strategies to extend the lifetime of flame retarded polymers are provided. In addition, the specific requirements of the stabilization of nanocomposites as potential flame retardant components are covered. © 2013 Elsevier Ltd. All rights reserved.

Radke W.,Fraunhofer Institute for Structural Durability and System Reliability
Journal of Chromatography A | Year: 2014

Most heterogeneities of polymers with respect to different structural features cannot be resolved by only size exclusion chromatography (SEC), the most frequently applied mode of polymer chromatography. Instead, methods of interaction chromatography became increasingly important. However, despite the increasing applications the principles and potential of polymer interaction chromatography are still often unknown to a large number of polymer scientists. The present review will explain the principles of the different modes of polymer chromatography. Based on selected examples it will be shown which separation techniques can be successfully applied for separations with respect to the different structural features of polymers. © 2013 Elsevier B.V.

Wilen C.-E.,Åbo Akademi University | Pfaendner R.,Fraunhofer Institute for Structural Durability and System Reliability
Journal of Applied Polymer Science | Year: 2013

Most flame-retarded polymer products need to be highly durable throughout their service lifetime in many demanding applications areas such as construction, transportation, electric equipment, and textiles, where low flammability in combination with high resistance toward oxidative deterioration triggered by the action of light, heat, and/or mechanical stress is a mandatory quality. To achieve this, it is essential to better understand the overall interplay (both physical and chemical processes) between different components such as different flame retardant structures in their respective polymers and in the presence of coadditives such as processing stabilizers, antioxidants, light stabilizers, metal deactivators, filler deactivators, ultraviolet absorbers, and so on, in the flame-retarded polymer product. In this article, the key difficulties in improving weathering resistance of flame-retarded polymers are reviewed. Copyright © 2013 Wiley Periodicals, Inc.

Sonsino C.M.,Fraunhofer Institute for Structural Durability and System Reliability
International Journal of Fatigue | Year: 2012

The structural durability design of complex welded structures should not rely only on one single design method but should apply different methods for assuring the reliability of the assessment. In this context the application of the structural stress (hot-spot), notch stress, notch strain and crack-propagation concepts are discussed through the example of K-nodes used in energetic offshore constructions like oil platforms or wind power plants, presenting the state of the art. While the hot-spot, notch stress and crack-propagation concepts show a good agreement between calculated and experimental results and do not differ significantly from each other, the notch strain concept fails significantly. © 2011 Elsevier Ltd. All rights reserved.

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