Parameterization of arbitrary hole shapes using non-destructive testing and resulting stress concentration in a 2D plate with finite dimensions

Air void inclusions are mostly unavoidable in many different materials resulting from manufacturing processes or environmental conditions. In this contribution, non-destructive testing (NDT) like computer tomography (CT) is used for air void detection and quantification. The air voids lead to stress concentrations around them which influence significantly the structural integrity and at worst, lead to structural failure. By nature, air voids exhibit arbitrary shapes on which circular, elliptical, slotted and rounded rectangular holes are fitted by a least-square optimization algorithm to reduce the amount of necessary shape parameters. The mentioned shapes are compared in relation to the arbitrary one and with regard to the resulting stress concentration factor as well as the location of the maximum first principal stress in a 2D plate with finite dimensions under uniaxial tension. Finally, aleatory and epistemic uncertainties are derived from the conducted CT analysis which leads to a problem under polymorphic uncertainties. The problem is solved by a surrogate model based on cubic spline interpolation and points out the importance of the consideration of different hole shapes for analyzing the stress concentration.DFG, 273721697, SPP 1886: Polymorphe Unschärfemodellierungen für den numerischen Entwurf von Strukture

SBML Level 3: an extensible format for the exchange and reuse of biological models

Systems biology has experienced dramatic growth in the number, size, and complexity of computational models. To reproduce simulation results and reuse models, researchers must exchange unambiguous model descriptions. We review the latest edition of the Systems Biology Markup Language (SBML), a format designed for this purpose. A community of modelers and software authors developed SBML Level 3 over the past decade. Its modular form consists of a core suited to representing reaction-based models and packages that extend the core with features suited to other model types including constraint-based models, reaction-diffusion models, logical network models, and rule-based models. The format leverages two decades of SBML and a rich software ecosystem that transformed how systems biologists build and interact with models. More recently, the rise of multiscale models of whole cells and organs, and new data sources such as single-cell measurements and live imaging, has precipitated new ways of integrating data with models. We provide our perspectives on the challenges presented by these developments and how SBML Level 3 provides the foundation needed to support this evolution

Alles nur Spaß? Die Bedeutung des Stjob in den Texten und Auftritten von Graždanskaja Oborona

Ein gut erzogener Mensch spielt so, wie er erzogen wurde. Und wir unerzogenen Menschen können Jazz, Rock und Punk spielen. Wir können minimalistische und lärmende Musik spielen. (Egor Letov) Egor Letov im November 2000 bei einem Konzert in Nürnberg, Foto: Alex Ex, CC BY-SA 3.0, via Wikmedia Commons Egor Letov, der 1964 im russischen Omsk geboren wurde, gilt als Begründer des sibirischen Punkrocks und war bis zu seinem Tod 2008 einer der wichtigsten Musiker im Gebiet der ehemaligen Sowjetunio..

Laser edge forming to increase the bending radius in hemming

Hemming can be used, for example, to join dissimilar materials which cannot be welded by conventional laser or arc based processes. A critical value in hemming is the ratio of outer sheet bending radius and outer sheet thickness because cracks can occur in outer sheets with low ductility due to a small bending radius. In this study, a novel approach is introduced for increasing the bending radius by laser based edge forming. The laser beam melts the edge of the inner sheet prior to the hemming process. In laser edge forming, the edge thickness increases due to the surface tension of the melt. The edge cross-section has typically a nearly circular shape after solidification. Two laser beam irradiation strategies were investigated. In case of the first strategy, a defocused laser beam was applied. The second strategy combined a focused laser beam resulting in the formation of a vapor capillary (keyhole) with sinusoidal beam oscillation transversal to the sheet edge. The results show that the position of the cylindrical edge cross-section according to the sheet plane could be affected by the applied irradiation strategy. The needed laser power was significantly lower when using a focused laser beam due to the deep penetration effect. The potential of the laser edge forming technique for crack-free hemming processes was demonstrated with 1 mm thick aluminum alloy sheets by carrying out stripe tests

Laser edge forming to increase the bending radius in hemming

Hemming can be used, for example, to join dissimilar materials which cannot be welded by conventional laser or arc based processes. A critical value in hemming is the ratio of outer sheet bending radius and outer sheet thickness because cracks can occur in outer sheets with low ductility due to a small bending radius. In this study, a novel approach is introduced for increasing the bending radius by laser based edge forming. The laser beam melts the edge of the inner sheet prior to the hemming process. In laser edge forming, the edge thickness increases due to the surface tension of the melt. The edge cross-section has typically a nearly circular shape after solidification. Two laser beam irradiation strategies were investigated. In case of the first strategy, a defocused laser beam was applied. The second strategy combined a focused laser beam resulting in the formation of a vapor capillary (keyhole) with sinusoidal beam oscillation transversal to the sheet edge. The results show that the position of the cylindrical edge cross-section according to the sheet plane could be affected by the applied irradiation strategy. The needed laser power was significantly lower when using a focused laser beam due to the deep penetration effect. The potential of the laser edge forming technique for crack-free hemming processes was demonstrated with 1 mm thick aluminum alloy sheets by carrying out stripe tests

PolyUQ: framework for solving problems with polymorphic uncertainties

The consideration of aleatory and epistemic uncertainties is an important challenge in structural engineering problems, especially from the viewpoint of realistic analysis. Inaccuracy and variability are always present and have to be quantified by either probabilistic, possibilistic, polymorphic or other uncertainty approaches. Thus, the authors have developed the framework PolyUQ in MATLAB for solving problems in which uncertainties in the fuzzy space, the interval space and the stochastic space can be treated simultaneously. The workflow from defining uncertain input variables to solving the model and up to evaluating the uncertain output is presented in this contribution.DFG, 312928137, Mehrskalige Versagensanalyse unter polymorphen Unsicherheiten für den optimalen Entwurf von Rotorblätter