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The propagation of mechanical waves in plates of isotropic elastic material is investigated. After a short introduction to the understanding of focussing of stress waves in a plate with a curved boundary the method of characteristics is applied to a plate of hyperelastic material. Using this method the propagation of acceleration waves is discussed. Based on this a numerical difference scheme is developed for solving initial-boundary-value problems and applied to two examples: propagation of a point disturbance in a homogeneously finitely strained non-linear elastic plate and geometrical focussing in al linear elastic plate.
In the presented paper data collected from the field related to damage statistics of electrical and electronic apparatus in household are reported and investigated. These damages (total number approx. 74000 cases), registered by five German insurance companies in 2005 and 2006, were adviced by customers as caused by lightning overvoltages. With the use of stochastical methods it is possible, to reasses the collected data and to distinguish between cases, which are with high probability caused by lightning overvoltages, and those, which are not. If there was an indication for a direct strike, this case was excluded, so the focus was only on indirect lightning flashes, i.e. only flashes to ground near the structure and flashes to or nearby an incoming service line were investigated. The data from the field contain the location of damaged apparatus (residence of the policy holder) and the distances of the nearest cloud-to-ground stroke to the location of the damage registered by the German lightning location network BLIDS at the date of damage. The statistical data along with some complementary numerical simulations allow to verify the correspondence of the Standards rules used for IEC 62305-2 with the field data and to define some correction needs. The results could lead to a better understanding whether a damage reported to an insurance company is really caused by indirect lightning, or not.
7th International Conference on Reliability of Materials and Structures (RELMAS 2008). June 17 - 20, 2008 ; Saint Petersburg, Russia. pp 354-358. Reprint with corrections in red Introduction Analysis of advanced structures working under extreme heavy loading such as nuclear power plants and piping system should take into account the randomness of loading, geometrical and material parameters. The existing reliability are restricted mostly to the elastic working regime, e.g. allowable local stresses. Development of the limit and shakedown reliability-based analysis and design methods, exploiting potential of the shakedown working regime, is highly needed. In this paper the application of a new algorithm of probabilistic limit and shakedown analysis for shell structures is presented, in which the loading and strength of the material as well as the thickness of the shell are considered as random variables. The reliability analysis problems may be efficiently solved by using a system combining the available FE codes, a deterministic limit and shakedown analysis, and the First and Second Order Reliability Methods (FORM/SORM). Non-linear sensitivity analyses are obtained directly from the solution of the deterministic problem without extra computational costs.
Traglast- und Einspielanalysen sind vereinfachte doch exakte Verfahren der Plastizität, die neben ausreichender Verformbarkeit keine einschränkenden Voraussetzungen beinhalten. Die Vereinfachungen betreffen die Beschaffung der Daten und Modelle für Details der Lastgeschichte und des Stoffverhaltens. Anders als die klassische Behandlung nichtlinearer Probleme der Strukturmechanik führt die Methode auf Optimierungsprobleme. Diese sind bei realistischen FEM-Modellen sehr groß. Das hat die industrielle Anwendung der Traglast- und Einspielanalysen stark verzögert. Diese Situation wird durch das Brite-EuRam Projekt LISA grundlegend geändert. Die Autoren möchten der Europäischen Kommission an dieser Stelle für die Förderung ausdrücklich danken. In LISA entsteht auf der Basis des industriellen FEM-Programms PERMAS ein Verfahren zur direkten Berechnung der Tragfähigkeit duktiler Strukturen. Damit kann der Betriebsbereich von Komponenten und Bauwerken auf den plastischen Bereich erweitert werden, ohne den Aufwand gegenüber elastischen Analysen wesentlich zu erhöhen. Die beachtlichen Rechenzeitgewinne erlauben Parameterstudien und die Berechnung von Interaktionsdiagrammen, die einen schnellen Überblick über mögliche Betriebsbereiche vermitteln. Es zeigt sich, daß abhängig von der Komponente und ihren Belastungen teilweise entscheidende Sicherheitsgewinne zur Erweiterung der Betriebsbereiche erzielt werden können. Das Vorgehen erfordert vom Anwender oft ein gewisses Umdenken. Es werden keine Spannungen berechnet, um damit Sicherheit und Lebensdauer zu interpretieren. Statt dessen berechnet man direkt die gesuchte Sicherheit. Der Post-Prozessor wird nur noch zur Modell- und Rechenkontrolle benötigt. Das Vorgehen ist änhlich der Stabilitätsanalyse (Knicken, Beulen). Durch namhafte industrielle Projektpartner werden Validierung und die Anwendbarkeit auf eine breite Palette technischer Probleme garantiert. Die ebenfalls in LISA geplante Zuverlässigkeitsanalyse ist erst auf der Basis direkter Verfahren effektiv möglich. Ohne Traglast- und Einspielanalyse ist plastische Strukturoptimierung auch heute kaum durchführbar.
Abstracts of the ACHEMA 2000 - International Meeting on Chemical Engineering, Environmental Protection and Biotechnology, May 22 - 27, 2000. Frankfurt am Main. Achema 2000 : special edition / Linde. [Ed.: Linde AG. Red.: Volker R. Leski]. - Wiesbaden : Linde AG, 2000. - 56 p. : Ill., . - pp: 79 - 81
A procedure for the evaluation of the failure probability of elastic-plastic thin shell structures is presented. The procedure involves a deterministic limit and shakedown analysis for each probabilistic iteration which is based on the kinematical approach and the use the exact Ilyushin yield surface. Based on a direct definition of the limit state function, the non-linear problems may be efficiently solved by using the First and Second Order Reliabiblity Methods (Form/SORM). This direct approach reduces considerably the necessary knowledge of uncertain technological input data, computing costs and the numerical error. In: Computational plasticity / ed. by Eugenio Onate. Dordrecht: Springer 2007. VII, 265 S. (Computational Methods in Applied Sciences ; 7) (COMPLAS IX. Part 1 . International Center for Numerical Methods in Engineering (CIMNE)). ISBN 978-1-402-06576-7 S. 186-189
Proceedings of the International Conference on Material Theory and Nonlinear Dynamics. MatDyn. Hanoi, Vietnam, Sept. 24-26, 2007, 8 p. In this paper, a method is introduced to determine the limit load of general shells using the finite element method. The method is based on an upper bound limit and shakedown analysis with elastic-perfectly plastic material model. A non-linear constrained optimisation problem is solved by using Newton’s method in conjunction with a penalty method and the Lagrangean dual method. Numerical investigation of a pipe bend subjected to bending moments proves the effectiveness of the algorithm.
In: Technical feasibility and reliability of passive safety systems for nuclear power plants. Proceedings of an Advisory Group Meeting held in Jülich, 21-24 November 1994. - Vienna , 1996. - Seite: 43 - 55 IAEA-TECDOC-920 Abstract: It is shown that the difficulty for probabilistic fracture mechanics (PFM) is the general problem of the high reliability of a small population. There is no way around the problem as yet. Therefore what PFM can contribute to the reliability of steel pressure boundaries is demonstrated with the example of a typical reactor pressure vessel and critically discussed. Although no method is distinguishable that could give exact failure probabilities, PFM has several additional chances. Upper limits for failure probability may be obtained together with trends for design and operating conditions. Further, PFM can identify the most sensitive parameters, improved control of which would increase reliability. Thus PFM should play a vital role in the analysis of steel pressure boundaries despite all shortcomings.