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Material Models (material + models)
Selected AbstractsProbabilistic yielding and cyclic behavior of geomaterialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2010Kallol Sett Abstract In this paper, the novel concept of probabilistic yielding is used for 1-D cyclic simulation of the constitutive behavior of geomaterials. Fokker,Planck,Kolmogorov equation-based probabilistic elastic,plastic constitutive framework is applied for obtaining the complete probabilistic (probability density function) material response. Both perfectly plastic and hardening-type material models are considered. It is shown that when uncertainties in material parameters are taken into consideration, even the simple, elastic-perfectly plastic model captures some of the important features of geomaterial behavior, for example, modulus reduction with cyclic strain, which, deterministically, is only possible with more advanced constitutive models. Furthermore, it is also shown that the use of isotropic and kinematic hardening rules does not significantly improve the probabilistic material response. Copyright © 2010 John Wiley & Sons, Ltd. [source] Visualization of material stiffness in geomechanics analysisINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2006Donald C. Wotring Abstract This paper presents novel visualization techniques to simplify representation of the fourth-order material stiffness tensor as a set of three-dimensional geometric objects. Stiffness visualization aids in understanding the complex stiffness characteristics of highly non-linear constitutive models including modelled material anisotropy and loading path dependent stiffness variation. Stiffness visualization is relevant for understanding the relationship of material stiffness to global behaviour in the analysis of a boundary value problem. The spherical pulse stiffness visualization method, developed in the acoustics field, is extended to visualize stiffness of geomaterials using three three-dimensional objects. This method is limited to relatively simple constitutive models with symmetric stiffness matrices insensitive to loading magnitude and direction. A strain dependent stiffness visualization method is developed that allows the examination of material stiffness for a range of loading directions and is suitable for highly non-linear and path dependent material models. The proposed stiffness visualization can be represented as 3-D, 2-D and 1-D objects. The visualization technique is used to represent material stiffness and its evolution during simulated soil laboratory tests and deep excavation construction. Copyright © 2005 John Wiley & Sons, Ltd. [source] Template elastic-plastic computations in geomechanicsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2002Boris Jeremi Abstract In this paper we present a new approach to computations in elasto-plastic geomechanics. The approach is based on the object oriented design philosophy and observations on similarity of most incremental elastic,plastic material models. This new approach to elastic,plastic computations in geomechanics allows for creation of template material models. The analysis of template material models will in turn allow for an easy implementation of other elastic,plastic material models based on the object oriented design principles. Furthermore we present some illustrative implementation details. Finally we present analysis results that emphasize features of template elastic,plastic computations in geomechanics. Copyright © 2002 John Wiley & Sons, Ltd. [source] A finite element algorithm for parameter identification of material models for fluid saturated porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2001R. Mahnken Abstract In this contribution an algorithm for parameter identification of geometrically linear Terzaghi,Biot-type fluid-saturated porous media is proposed, in which non-uniform distributions of the state variables such as stresses, strains and fluid pore pressure are taken into account. To this end a least-squares functional consisting of experimental data and simulated data is minimized, whereby the latter are obtained with the finite element method. This strategy allows parameter identification based on in situ experiments. In order to improve the efficiency of the minimization process, a gradient-based optimization algorithm is applied, and therefore the corresponding sensitivity analysis for the coupled two-phase problem is described in a systematic manner. For illustrative purpose, the performance of the algorithm is demonstrated for a slope stability problem, in which a quadratic Drucker,Prager plasticity model for the solid and a linear Darcy law for the fluid are combined. Copyright © 2001 John Wiley & Sons, Ltd. [source] An accelerated algorithm for parameter identification in a hierarchical plasticity model accounting for material constraintsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2001L. Simoni Abstract The parameter identification procedure proposed in this paper is based on the solution of an inverse problem, which relies on the minimization of an error function of least-squares type. The solution of the ensuing optimization problem, which is a constrained one owing to the presence of physical links between the optimization parameters, is performed by means of a particular technique of the feasible direction type, which is modified and improved when the problem turns to an unconstrained one. The algorithm is particularly efficient in the presence of hierarchical material models. The numerical properties of the proposed procedure are discussed and its behaviour is compared with usual optimization methods when applied to constrained and unconstrained problems. Copyright © 2001 John Wiley & Sons, Ltd. [source] An adaptive stabilization strategy for enhanced strain methods in non-linear elasticityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2010Alex Ten Eyck Abstract This paper proposes and analyzes an adaptive stabilization strategy for enhanced strain (ES) methods applied to quasistatic non-linear elasticity problems. The approach is formulated for any type of enhancements or material models, and it is distinguished by the fact that the stabilization term is solution dependent. The stabilization strategy is first constructed for general linearized elasticity problems, and then extended to the non-linear elastic regime via an incremental variational principle. A heuristic choice of the stabilization parameters is proposed, which in the numerical examples proved to provide stable approximations for a large range of deformations, different problems and material models. We also provide explicit lower bounds for the stabilization parameters that guarantee that the method will be stable. These are not advocated, since they are generally larger than the ones based on heuristics, and hence prone to deteriorate the locking-free behavior of ES methods. Numerical examples with two different non-linear elastic models in thin geometries and incompressible situations show that the method remains stable and locking free over a large range of deformations. Finally, the method is strongly based on earlier developments for discontinuous Galerkin methods, and hence throughout the paper we offer a perspective about the similarities between the two. Copyright © 2009 John Wiley & Sons, Ltd. [source] A reduced integration solid-shell finite element based on the EAS and the ANS concept,Geometrically linear problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2009Marco Schwarze Abstract In this paper a new reduced integration eight-node solid-shell finite element is presented. The enhanced assumed strain (EAS) concept based on the Hu,Washizu variational principle requires only one EAS degree-of-freedom to cure volumetric and Poisson thickness locking. One key point of the derivation is the Taylor expansion of the inverse Jacobian with respect to the element center, which closely approximates the element shape and allows us to implement the assumed natural strain (ANS) concept to eliminate the curvature thickness and the transverse shear locking. The second crucial point is a combined Taylor expansion of the compatible strain with respect to the center of the element and the normal through the element center leading to an efficient and locking-free hourglass stabilization without rank deficiency. Hence, the element requires only a single integration point in the shell plane and at least two integration points in thickness direction. The formulation fulfills both the membrane and the bending patch test exactly, which has, to the authors' knowledge, not yet been achieved for reduced integration eight-node solid-shell elements in the literature. Owing to the three-dimensional modeling of the structure, fully three-dimensional material models can be implemented without additional assumptions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Lebensdauerermittlung bei mehrachsigen wechselnden Beanspruchungen im niedrigen und hohen TemperaturbereichMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 9 2003E. Roos multiaxial fatigue; creep fatigue; stress theories; material laws Abstract Zur Berechnung der Dauerfestigkeit von Bauteilen aus duktilen Werkstoffen bei komplexer Schwingbeanspruchung stehen unterschiedliche Verfahren zur Verfügung. Hierbei wird im Wesentlichen zwischen den Festigkeitshypothesen der Integralen Anstrengung und denen der Kritischen Schnittebene unterschieden. Als typische Repräsentanten werden die Schubspannungsintensitätshypothese (SIH) sowie die Methode der kritischen Schnittebene (MKS) ausgewählt und für körperfeste und nicht körperfeste Hauptspannungsrichtungen gegenübergestellt. Für synchrone Beanspruchungen wird darüber hinaus das Berechnungsverfahren mit dem Anstrengungsverhältnis nach Bach verglichen. Die Berechnungsmethodik wird deutlich komplexer, wenn zeitabhängige Werkstoffeigenschaften bei entsprechend hohen Temperaturen mit in die Betrachtung einbezogen werden müssen. Für diesen Fall wird die Anwendung von viskoplastischen Stoffgesetzen erforderlich, die eine Beschreibung von Kriechen und Ermüdung in Kombination ermöglichen. Am Beispiel eines modifizierten Werkstoffmodells nach Chaboche / Nouailhas wird die Berechnung mehrachsiger Kriechermüdungsversuche vorgestellt. Life time assessment on multiaxial cyclic loadings at low and high temperatures For the calculation of fatigue strength of components made out of ductile materials under complex cyclic load different assessments are present. As typical representatives of stress theories the shear stress intensity hypothesis (SIH) as well as the method of critical plane approach (MKS) are considered and compared for rigid and non rigid principle stress directions. Furthermore for synchronous loads the calculation methods are compared with Bach's method. The calculation method becomes more complex, if time dependent material properties at corresponding high temperatures have to be taken into account. In this case the application of viscoplastic material models is necessary, which allows the consideration of combination of creep and fatigue. As an example a modified material model by Chaboche / Nouailhas is used in order to present the calculation of multiaxial creep fatigue tests. [source] Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targetsMETEORITICS & PLANETARY SCIENCE, Issue 12 2008E. PIERAZZO When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS-MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum-on-aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter-code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well-characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter-code variability. [source] | ||||||||||