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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.

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.

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.

Wilen C.-E.,Abo 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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