Bayesian Parameter Determination of a CT-Test Described by a Viscoplastic-Damage Model Considering the Model Error

The state of materials and accordingly the properties of structures are changing over the period of use, which may influence the reliability and quality of the structure during its life-time. Therefore identification of the model parameters of the system is a topic which has attracted attention in the content of structural health monitoring. The parameters of a constitutive model are usually identified by minimization of the difference between model response and experimental data. However, the measurement errors and differences in the specimens lead to deviations in the determined parameters. In this article, the Choboche model with a damage is used and a stochastic simulation technique is applied to generate artificial data which exhibit the same stochastic behavior as experimental data. Then the model and damage parameters are identified by applying the sequential Gauss-Markov-Kalman filter (SGMKF) approach as this method is determined as the most efficient method for time consuming finite element model updating problems among filtering and random walk approaches. The parameters identified using this Bayesian approach are compared with the true parameters in the simulation, and further, the efficiency of the identification method is discussed. The aim of this study is to observe whether the mentioned method is suitable and efficient to identify the model and damage parameters of a material model, as a highly non-linear model, for a real structural specimen using a limited surface displacement measurement vector gained by Digital Image Correlation (DIC) and to see how much information is indeed needed to estimate the parameters accurately even by considering the model error and whether this approach can also practically be used for health monitoring purposes before the occurrence of severe damage and collaps

Evolution of nonlocal damage in steel under cyclic straining

For high dynamic excitation, e.g. by earthquakes, the vibrations of steel structures lead to inelastic material behavior. Hystereses, developing under cyclic loading, are responsible for the dissipation of energy. Additionally, stress concentration at small defects results in the nucleation and the growth of microvoids which is referred to as damage, here especially as ultra low cycle fatigue. The material damage influences the stiffness of a structure and its response to dynamic excitation. With increasing load the voids can coalesce and form a macrocrack which destroys the structural integrity and peril the overall safety. A material model is proposed which describes the evolution and distribution of inelastic strains and isotropic ductile damage for mild construction steel by means of a set of internal variables. Viscoplasticity as well as isotropic and kinematic hardening are taken into account. The evolution of isotropic hardening is related to the growth of a strain memory surface which accounts for the strain amplitude history of the material. Under tension isotropic ductile damage develops for significant inelastic strains [1]. The material model is implemented in the frameworks of the finite element method with displacement based ansatz functions. The equation of motion is solved with the Newmark method. To overcome the phenomenon of vanishing dissipation energy in case of mesh refinement due to strain localization a nonlocal extension in the form of an implicit gradient formulation is applied. The presented model is used to analyse 3D structures subjected to seismic excitation

Simulation der aktiven Schwingungskontrolle von Fluid-Struktur Wechselwirkung durch piezoelektrische Materialien

Ein numerisches Modell zur aktiven Kontrolle des dynamischen Verhaltens von Tragwerken unter transienter Windeinwirkung wird vorgestellt. Auf der Oberschicht passiver Tragstrukturen werden piezoelektrische Sensoren und Aktoren appliziert. Die resultierenden adaptierbaren Strukturen sind mit einem Regler gekoppelt. Die Modellierung der elektroelastischen Struktur erfolgt mit der geometrisch nichtlinearen Elastizitätstheorie und der Maxwell–Faraday–Theorie der Elektrostatik. Die Windumströmung der Struktur ist als inkompressibles, Newton'sches Fluid mit den Navier–Stokes–Gleichungen beschrieben. Die Diskretisierung der gekoppelten Modellgleichungen beider Kontinua erfolgt mit finiten Raum–Zeit–Elementen. Zeitliche Änderungen der Zustandsgrößen werden mit dem diskontinuierlichen Galerkin–Verfahren approximiert. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim