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On a hybrid approximation concept for self-excited periodic oscillations of large-scale dynamical systems
(2021-12-14)
When approximating periodic solutions in the context of large-scale dynamical systems involving strong local nonlinearities, efficiency is of special interest. Hence, the literature suggests a combination of two approximation methods for increasing the ratio of computational cost to accuracy. Within this contribution, a combination of Finite Difference and Harmonic Balance method is proposed. Due to the usage of Harmonic Balance it is shown, that the resulting equations only depend on the degrees of freedom that are ...
Aufsatz
Fully Implicit RUNGE-KUTTA Schemes for Ideal Elastoplasticity
(2021-12-14)
The present paper derives a multifield formulation of ideal elastoplasticity to enable the consistent application of higher order accurate RUNGE-KUTTA schemes. With the help of an axisymmetric model problem the appearing time discretization errors of distinct schemes are determined and compared.
Aufsatz
An auxiliary crack approach for efficient approximative crack tip loading analyses
(2021-10-20)
An efficient approach based on the path-independent interaction-integral (I-integral) is suggested for assessing the crack tip loading in elastic structures without having to geometrically model a physical crack. Exploiting just the elastic solution of the uncracked structure, the I-integral is adapted incorporating the closed formulation of crack tip stress and displacement fields of an auxiliary crack, which in this approach is interpreted as hypothetical physical crack. Different specimens and crack configurations ...
Aufsatz
Identification of a Spatio-Temporal Temperature Model for Laser Metal Deposition
(2021-12-18)
Laser-based additive manufacturing enables the production of complex geometries via layer-wise cladding. Laser metal deposition (LMD) uses a scanning laser source to fuse in situ deposited metal powder layer by layer. However, due to the excessive number of influential factors in the physical transformation of the metal powder and the highly dynamic temperature fields caused by the melt pool dynamics and phase transitions, the quality and repeatability of parts built by this process is still challenging. In order to ...
Aufsatz
On Optimal Test Signal Design and Parameter Identification Schemes for Dynamic Takagi-Sugeno Fuzzy Models Using the Fisher Information Matrix
(2021-11-21)
This paper is concerned with the analysis of optimization procedures for optimal experiment design for locally affine Takagi-Sugeno (TS) fuzzy models based on the Fisher Information Matrix (FIM). The FIM is used to estimate the covariance matrix of a parameter estimate. It depends on the model parameters as well as the regression variables. Due to the dependency on the model parameters good initial models are required. Since the FIM is a matrix, a scalar measure of the FIM is optimized. Different measures and ...
Aufsatz
Multiscale modeling of ferroelectrics with stochastic grain size distribution
(2021-12-20)
Macroscopic properties of ferroelectrics are controlled by processes on the microscale, in particular the switching of crystal unit cells and the movement of domain walls, respectively. Besides these microscopic levels, the grains of a polycrystalline material constitute the mesoscopic scale. Interactions of grains with statistically distributed orientations, as a consequence of mechanical and electrostatic mismatch, give rise to for example, residual stress which in turn affects domain switching. A multiscale modeling ...
Aufsatz
Nonlocal damage modelling for finite element simulations of ductile steel sheets under multiaxial loading
(2021-12-14)
The finite element simulation of forming processes or vehicle crash scenarios involves multiaxial loading conditions in general. Thereby, damage and failure in ductile steel sheets is triggered by void growth under hydrostatic tensile loading or by void elongation within a narrow band under shear dominated loading. These different damage mechanisms are considered by a stress state dependent continuum damage model. The damage initiation and failure are represented by a critical and a failure strain. Both are HOSFORD-COULOMB ...
Aufsatz
IMEX-DG Schemes for Advection-Diffusion Problems using Term-based or Domain-based IMEX Splitting
(2021-12-14)
IMEX partitioning may be based on a decomposition of the computational domain into two subgrids by implicitly discretizing the unknowns on the smallest cells while explicit time stepping is applied to moderately sized elements. Alternatively, advection-diffusion IMEX splitting applies implicit time discretization only to the viscous terms while inviscid terms are discretized explicitly. Analytical investigations have shown that a careful choice of both the specific IMEX scheme and the particular DG approach yield an ...
Aufsatz
Flow and fiber orientation of fresh fiber reinforced concrete
(2021-12-14)
The orientation of the fibers in UHPC is decisive for the tensile strength and failure of the components. The mold filling strategy during casting of structural components dictates the flow routing and thus the fiber orientation. In addition, the orientation of the fibers also affects the flow behavior of the suspension. In measurements of rheological properties in concrete rheometers, strongly scattering measurements often occur. In this paper, a novel fiber orientation model for viscoplastic fluids is investigated ...
Aufsatz
Modelling stress‐state dependent nonlocal damage and failure of ductile metals
(2021-01-25)
Damage and failure of ductile metals is highly influenced by the stress state. In fact, void growth takes place under hydrostatic tensile loading and void coalescence leads eventually to ductile failure. A completely different damage mechanism occurs for shear dominated loading that results in void elongation within a narrow shear band. In order to account for both failure mechanisms, a stress state dependent damage model is proposed. The model is based on a continuum damage mechanics approach, whereby nonlinear ...