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Pressure vessels subjected to high mechanical loadings can fail due to microscopic crack growth, i.e., stress corrosion cracking. A popular way to increase the crack resistance of a structure is by autofrettage. The standard approach to obtain a numerical solution for the involved fields is to discretize w.r.t. Cartesian coordinates as implemented in common commercial FE programs. However, this approach is computationally costly in comparison to pure elastic simulations-often rendering this method practically unfeasible. The current work shows that autofrettage can be simulated more efficiently in extensive bodies that can be described by a bijective map where certain symmetries are available in load and form. The discretization and the mathematical formalism of this approach in curvilinear coordinates are described. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A numerical approach simulating the effects of coupled local-global mode interaction on the postbuckling of axially compressed sandwich beam columns is presented. The formulation is based on the weak form of the balance of linear momentum whilst large strains are considered. An open source software is used to solve the formulation and results are presented showing good phenomenological agreement with analytically derived solutions. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In medicine a fundamental understanding for blood flow in human arteries is significantly important. In socalled hemodynamics engineers all over the world simulate blood flows in healthy and diseased vessels. Scientific findings in this area help to improve cardiovascular assisting devices and to plan surgical operations. The difficulty with such simulations is the interaction of the blood flow with the elastic vessel wall, which deforms due to changing flow conditions. We will present a two-dimensional model for blood flowing through an arterial vessel and investigate the balance of mass and the balance of linear momentum. We will adjust these balance equations appropriately and define time dependent boundary conditions. The necessary partial differential equations for the fluid-structure interaction will be solved by using the finite element method in FEniCS [1]. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Oscillatory rheometer measurements are used to determine the material parameters of a NEWTONian fluid model, which can be expressed by a linear constitutive relation. However, rheological materials, such as polymer melts, mixture of oils, or food paste, can only be modeled as non-NEWTONian fluids by using non-linear constitutive relations. Since the rheometer measures the energy loss in the induction motor due to shear loading of the viscous material, this can be used as the objective function for a regression analysis. The dissipated energy will be obtained as outlined in [1]. The goal of this work is to explain how to determine the parameters of a non-linear material model by using the energy loss that is measured in a rheometer. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Ultrasonic wire bonding is a method applied in electronic packaging to fabricate interconnections between two devices at ambient temperature. In order to investigate the material diffusion during this process, the occurring thermal and mechanical mechanisms at and around the interface of the formed bond were studied by means of coupled thermo-mechanical FE simulations. Within the framework of material forces the local jump of the Eshelby tensor was compared with the thickness of the formed intermetallic phase for various bonding parameters. This allows us to predict an effective diffusion constant which takes temperature and mechanical driving forces into account. After this relation has been established a subsequent objective of our investigations is to optimize the growth of the Au8Al3 intermetallic phase in terms of bonding parameters. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Some rheological materials, such as melting polymers, cosmetic creams, ketchup, toothpaste, can be modeled as non-NEWTONian fluids by using a non-linear constitutive relation. An incompressible flow of this kind of amorphous matter can be considered as a thermodynamic process, and a solution for the pressure, velocity and temperature fields describe it fully. Since such flow processes are generally irreversible, entropy is produced leading to dissipation in the system. This energy loss can be measured indirectly in a cone/plate viscometer which is used to determine viscosity of a BINGHAM fluid. While dissipation is an observable quantity we also want to be able to calculate it. Thus the goal of this work is to explain briefly how to compute a transient flow of a viscous fluid in two-dimensional channel under a sinusoidal traction and calculate the dissipated energy for non-NEWTONian fluids. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The nanoindentation technique is established in the field of material characterization at small dimensions. It is daily practice to analyze nanoindentation data with an almost 'classical' formula based on the publications by Oliver and Pharr and Fischer-Cripps. The procedure works well for elastic-time independent plastic material behavior, for example copper and the calibration material fused silica, even at higher test temperatures. However, low melting solder materials are susceptible to creep behavior. For this reason, additional analysis procedures are required to determine the material parameters more precisely. In this paper the authors want to give an introduction to an 'enhanced' analysis of nanoindentation data based on rheological models, which are often used to describe the time-dependence of material response. Two examples of such models are the MAXWELL- and the KELVIN-body. The authors present a rheological model, published by Mencik in 2011 [1], in context with the corresponding equation which is used to extract the material properties from the recorded data. Results of the analysis at the calibration material fused silica are presented and discussed together with the material parameters published in the literature. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A numerical approach simulating the effects of interlaminar defects on the buckling stability of layered composite struts is presented. The formulation is based on the weak form of the balance of linear momentum whilst large strains are considered. First results are presented whilst comparisons are drawn to analytically derived results. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The problem of ductile damage and failure prediction at the upsetting of cylindrical specimens with artificial voids is solved by taking a change in stress triaxiality into account. It is shown that such a more accurate assessment leads to a greater shift of stress triaxialities into a range of negative values as compared to their averaged values. At such values of stress triaxiality the material can be subjected to compression without failure under arbitrarily large deformations due to healing of micro-defects. The constitutive equations of a recently developed tensorial framework for ductile damage [5] are applied to modelling. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]