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Für viskoplastische Stoffgesetze wird das prinzipielle Verfahren der Identifikation von Materialmodell-Parametern für das Spannungs-Verformungs- und Versagens-Verhalten metallischer Werkstoffe am Beispiel von Hochtemperatur-Ermüdung aufgezeigt. Dies betrifft zum Einen die Verwendung geeigneter und auch möglichst weniger Experimente zur Hervorbringung der zu beschreibenden Phänomene des Werkstoffverhaltens und deren gezielte Auswertung sowie zum Anderen die physikalisch kontrollierte Führung einer numerischen Optimierung zur Ermittlung vertrauenswürdiger Materialparameterwerte. Diese Vorgehensweise wurde erfolgreich auf Warmarbeitsstähle sowie poly- und einkristalline Superlegierungen angewendet.
A hierarchy of higher order continua is presented that introduces additional degrees of freedom accounting for volume changes, rotation and straining of an underlying microstructure. An increase in the number of degrees of freedom represents a refinement of the material description. In addition to available nonlinear Cosserat and micromorphic theories, general formulations of elastoviscoplastic behaviour are proposed for microdilatation and microstretch continua. A microstrain theory is introduced that is based on six additional degrees of freedom describing the pure straining of the microstructural element. In each case, balance equations and boundary conditions are derived, decompositions of the finite strain measures into elastic and plastic parts are provided. The formulation of finite deformation elastoviscoplastic constitutive equations relies on the introduction of the free energy and dissipation potentials, thus complying with requirements of continuum thermodynamics. Some guidelines for the selection of a suitable higher order model for a given material close the discussion.
This work deals with the formulation of a three-dimensional crystallographic time-incremental lifetime rule for face-centered cubic (fcc) single crystals used for gas-turbine blade applications. The damage contribution rate of each slip system to the total damage is governed by the current values of the resolved shear stress and the slip rate on the corresponding slip system. The damage rule is combined with a crystallographic viscoplastic deformation model. For the nickel-base single-crystal superalloy CMSX4 at 950 °C, various strain- and stress-controlled uniaxial cyclic tests with and without hold-times can be described for different crystal orientations by one set of material parameters. For verification, simulation results for a single-crystal specimen with a notch have been compared with corresponding experimental results. The predicted lifetime is within the factor of two of the measured one.