bluuebunny/crossref_metadata_2025_split huggingface dataset:
Constitutive modeling of dynamic recrystallization coupled to viscoplasticity
Authors: Westermann Hendrik , Mahnken Rolf 
Published: January 2021

AbstractDuring thermomechanical processing the microstructure is subject to drastic changes. These changes relate to various physical mechanisms such as recrystallization, recovery, grain growth and phase transitions, heavily affecting material properties in engineering components. This enables the targeted adjustment of microstructures and the gradation of macroscopic mechanical properties. During thermomechanical processing the modeling of dynamic recrystallization is of major importance. Thus, we present a thermodynamically consistent framework based on an existing continuum mechanical model. Major improvements, including derived recrystallization volume fractions and clean distinction of true microstresses and nominal microstresses, have been made in comparison to the original model.
Studies on the validity of the reduced bending stiffness method for eccentrically stacked laminates
Authors: Schilling Jakob C. , Mittelstedt Christian 
Published: January 2021

AbstractThe reduced bending stiffness method is used in the framework of computational models for stringer stiffened panels. Here, the stringer foot is often stacked on top of the skin of the panel and leads to a stacked laminate with extensional bending stiffness coupling. The validity of the reduced bending stiffness method for the mentioned laminate type is investigated and assessed, as only unsymmetrical laminates without eccentricity have been considered in existing literature. In exemplary studies, the influence of the coupling effects is shown, which allows drawing conclusions on the error that is introduced in, e. g. closed‐form analytical approximate solutions for the buckling of stringer stiffened panels.
Porosity analysis in SiC/SiC ceramic matrix composites
Authors: Rauscher Sophie-Maria , Kaleel Ibrahim , Raina Arun 
Published: January 2021

AbstractCeramic matrix composites made of silicon carbide fibers embedded in silicon carbide matrix (SiC/SiC CMCs) are widely recognized as excellent replacements for denser superalloys such as Nickel based super alloys for high‐temperature applications in aero engines. During the manufacturing process with chemical vapour infiltration, large amount of pores are introduced in the CMC and their presence can have considerable impact on the structural performance of a component. In this work, we analyze the pore size and spatial distribution in SiC/SiC CMCs for different geometrically‐identical specimens. Porosity within specimens are quantified through computed tomography (CT) scans. Different statistical approaches are utilized for describing the amount of pores, their size and spatial distribution within each specimen.
Phase‐field Fracture with Representative Crack Elements for Non‐linear Material Behaviour
Authors: Storm Johannes , Kaliske Michael 
Published: January 2021

AbstractThe mechanical energy potential of phase‐field fracture models is subdivided into a portion which (actively) drives the crack and a passive portion. This decompositions depends further on the crack state (opened, closed) in order to consider the re‐contact of the crack surfaces. The identification of the crack state and the decomposition is mostly approximated based on splits of the deformation or stress tensor. Stobel and Seelig [1], and Steinke and Kaliske [2] have shown unrealistic predictions for the crack kinematic for those models in quasi‐static and dynamic analyses. The approach proposed by these authors allows to predict the crack kinematic consistently. Nevertheless, this model is restricted to linear, isotropic elasticity and small deformations.In Storm et al. [3], the underlying concept is generalised. The crack kinematics is consistently obtained from a representative, discrete crack model and coupled to the phase‐field model by means of a variational homogenisation formulation. Thus, the crack driving force is a unique result of the framework of Representative Crack Elements. Analytical solutions for the mechanical problem of the representative crack element applied to linear, anisotropic elasticity and linear thermo‐elasticity at small deformations are presented there.In the current contribution to the method of phase‐field fracture, the framework for Representative Crack Elements is applied to non‐linear bulk materials. The iterative solution scheme for the representative crack element is presented and applied to elasticity with crack surface friction, visco‐elastic and elasto‐plastic materials.
Rate dependent free energy formulations for dynamically excited superelastic SMA wires
Authors: Kaup Andreas , Altay Okyay , Klinkel Sven 
Published: January 2021

AbstractSuperelastic shape memory alloys (SMAs) are metallic two‐phase polycrystal alloys. The transformation between austenite and martensite phases allows superelastic SMAs unique hysteretic energy dissipation capacity, which is particularly interesting for the development of new‐type of intelligent vibration control systems for structures. However, in structural control, most of the vibrations occur in high strain rate regimes, which interfere the release of self‐generated heat and cause atomic lattice destabilization and thus influence the hysteretic dissipation. The present work proposes two different strain rate dependent free energy formulations and aims to improve the accuracy of existing one‐dimensional macroscopic models of SMA wires. The approaches are developed and implemented in different continuum thermomechanical frameworks, without impairing the simplicity and robustness of the solution process. The first approach introduces an additional control variable for the entropy evolution. The second approach uses a phenomenological formulation of the latent heat evolution. The proposed formulations are validated by cyclic tensile tests conducted on SMA wires. The results show that the calculations using the new formulations can represent the superelastic SMA wire response more accurately.
Semi‐analytical assessment of free‐edge stress fields in cylindrically curved cross‐ply laminated shells
Authors: Kappel Andreas , Mittelstedt Christian 
Published: January 2021

AbstractThe present work deals with the semi‐analytical assessment of the three‐dimensional stress fields in cylindrically curved symmetrically and unsymmetrically cross‐ply laminated shells subjected to bending load. The developed approach incorporates a layerwise plane‐strain analysis in the innermost regions of the shell. The closed‐form ‘inner solution’, further on, is upgraded by a displacement‐based approach that enables an adequate depiction of the interlaminar stresses at the free edge. This so‐called ‘free‐edge solution’ employs a discretization scheme of each lamina into a number of numerical plies with respect to the thickness direction. Herein, the displacement field of each layer is specified via a priori unknown displacement‐ and Lagrangian interpolation functions. By applying the principle of minimum elastic potential, the governing equations can be derived in an exact manner and further on can be solved by employing the state space approach. The results of the higher‐order analysis method are verified through comparison with highly detailed finite element simulations and it is found that the semi‐analytical approach works with comparable accuracy, however, only at a fraction of the required computational effort.
A comparative study of an isotropic and anistropic model to describe the micro‐indentation of TWIP steel
Authors: Sridhar Praveen , R.G. Prasad Mahesh , Bilz Raphael , W. Klein Matthias , Vajragupta Napat , M. de Payrebrune Kristin , Smaga Marek 
Published: January 2021

AbstractIn grinding, the crystal grain size of the workpiece material is relatively same range compared to the removal depth. This raises a question if an anisotropic material model, which considers the effect of the crystal grain size and orientations, would better predict the process forces when compared to an isotropic material model. Initially, a simple micro‐indentation process is chosen to compare the two models. In this work, a crystal plasticity model and an isotropic Johnson‐Cooke plasticity model are employed to simulate micro‐identation of a twinning induced plasticity (TWIP) steel. The results of the two models are compared using the force‐displacement curves from the micro‐indentation experiments. In the future, the study will be extended to describe the material removal process during a single grit scratch test.
Multiscale modeling of distributed microcracking in concrete
Authors: Vu Giao , Timothy Jithender J. , Iskhakov Tagir , Meschke Günther 
Published: January 2021

AbstractConcrete is a quasi‐brittle material with a heterogeneous morphology across multiple scales, which also influences the evolution of damage in case of loading. Damage in concrete structures is initiated by growth of diffuse microcracks that is followed by damage localization eventually leading to structural failure. Thus, diffuse microcracking processes can be considered as failure precursors. Identification and characterization of these precursors can be applied in conjunction with structural health monitoring based on diffuse ultrasonic waves to develop early warning systems against catastrophic failure of concrete structures. To this end, a multiscale model for a simulation‐based description of diffuse damage in concrete is proposed. At the scale of the cement paste, microcrack growth is modeled by a combination of continuum micromechanics and linear elastic fracture mechanics [1]. The micromechanics model is incorporated into a reduced‐order Lippmann‐Schwinger based meso‐model for concrete [2], [3]. The mesoscale model is generated using Random Sequential Adsorption of realistic aggregates based on concave slicing of randomly cut polyhedrons. The influence of the microcrack morphology at the microscale on the diffuse microcracking and overall concrete stiffness degradation is presented.
An implicit high order finite volume scheme with a posteriori limiting for advection networks
Authors: Eimer Matthias , Borsche Raul , Siedow Norbert 
Published: January 2021

AbstractIn this paper, we describe an implicit high order finite volume scheme for networks of advection equations. Possible oscillations are eliminated using an a posteriori limiting approach. A continuous transition between the different orders is achieved by a convex combination of the numerical fluxes. The scheme shows accurate results even for large CFL numbers.
Fluid‐Structure Interaction of Slender Continua with 3‐Dimensional Flow: An Embedded Finite Element Approach
Authors: Hagmeyer Nora , Mayr Matthias , Popp Alexander 
Published: January 2021

AbstractThe interaction of slender bodies with fluid flow plays an important role in many industrial processes and biomedical applications. The numerical modeling of problems involving such rod‐like structures with classical continuum‐based finite elements poses a challenge because it promptly leads to locking effects as well as very large system sizes. An alternative approach leading to rather well‐posed problems is the use of 1‐dimensional beam theory. Applications of so‐called geometrically exact beam theories have proven to be a computationally efficient way to model the behavior of such slender structures.This work addresses research questions arising from the application of geometrically‐exact beam theory in the context of fluid‐structure interaction (FSI). In particular, we describe an embedded approach coupling geometrically exact beam finite elements to a background fluid mesh. Furthermore, we elaborate on the conversion between the beam's stress resultants and the 3‐dimensional formulation of the fluid field. A preliminary numerical example will demonstrate the general applicability of the proposed approach for a one‐way coupled problem.
A multiphase model for the cross‐linking of ultra‐high viscous alginate hydrogels
Authors: Diebels S. , Gepp M.M. , Meiser I. , Roland M. , Stracke F. , Zimmermann H. 
Published: January 2021

AbstractIn this study, a model for the cross‐linking of ultra‐high viscous alginate hydrogels is provided. The model consists of four kinetic equations describing the process, including the local accumulation and the depletion of mobile alginate, cross‐linked alginate and cross‐linking cations. For an efficient simulation, finite difference schemes with predictor‐corrector algorithms were implemented.
Framework for modelling the elastoplastic behaviour of friction welded lightweight structures under tension
Authors: Heppner Eric , Glüge Rainer , Weber Martin , Woschke Elmar 
Published: January 2021

AbstractPresent‐day research in the field of product development are increasingly focused on the efficient use of energy and raw material resources. In the light of this context, the design principle of consistent lightweight construction is gaining more and more importance. One possible approach is the targeted combination of different materials with favourable technological properties in hybrid structures. Against this background, the rotary friction welding (RFW), is particularly advantageous allowing the joining of dissimilar materials, like aluminium and steel in order to create such lightweight structures. The purpose of the paper at hand, is to present a framework for modelling the elastoplastic behaviour of those manufactured structures under the assumption of large deformation and non‐linear material behaviour. Moreover, the presented model was implemented into a finite element analysis program (ABAQUS), in order to simulate a tensile test of a friction welded lightweight structure. Subsequently, the simulation results were critically evaluated using experimental data.
Numerical approach for a continuum theory with higher stress gradients
Authors: Ghasemi Seyed Ali , Muench Ingo , Liedmann Jan , Barthold Franz-Joseph 
Published: January 2021

AbstractWe use an extended balance of linear momentum derived from stress field analysis of higher order terms in power series expansion. Thus, the balance equation accounts for higher gradients of stress in the contiguity of continuum points. Interestingly, it does not coincide with the balance of linear momentum from strain gradient elasticity. As shown in [1], it exhibits an inverse sign for the extended term compared to strain gradient elasticity. We are interested in the mechanical interpretation of this inversed sign since it seems to inverse the stiffening effect of strain gradient elasticity. Therefore, we set up the weak form of our extended balance equation by means of Galerkin's approach. Then, we use the Finite Element Method to approximate the weak form with help of different shape functions. In this context we also use Isogeometric Analysis since it is very promising for a numerical model with higher gradients.
Nonlinear coupled consolidation problem with large strains
Authors: Artamonova Nina , Sheshenin Sergey 
Published: January 2021

AbstractThe consolidation problems involve the study of soil compaction under load with the possibility of liquid outflow [1]. A completely physically and geometrically nonlinear formulation of the consolidation problem is given using the Lagrange approach with adaptation for the solid phase and the Euler approach for the fluid under the assumption of quasistatic deformation of the rock skeleton. Some results of numerical simulation are presented and discussed.
Adaptive Particle Finite Element Method (A‐PFEM) in Metal Cutting Processes
Authors: Ye Xialong , Rodríguez Prieto Juan Manuel , Müller Ralf 
Published: January 2021

AbstractMachining is very common in industry, e.g. automotive industry and aerospace industry, which is a nonlinear dynamic problem including large deformations, large strain, large strain rates and high temperatures, that implies some difficulties for numerical methods such as Finite element method. One way to simulate such kind of problems is the Particle Finite Element Method (PFEM) which combines the advantages of continuum mechanics and discrete modeling techniques. In this work we introduce an improved PFEM called the Adaptive Particle Finite Element Method (A‐PFEM). The A‐PFEM introduces particles and removes wrong elements along the numerical simulation to improve accuracy, precision, decrease computing time and resolve the phenomena that take place in machining in multiple scales. At the end of this paper, some examples are present to show the performance of the A‐PFEM.
On the boundary element method for Stokes flow in domains with discontinuous boundaries
Authors: Rajski Michal P. , Harmel Maximilian , Sauer Roger A. 
Published: January 2021

AbstractThe classical boundary element method (BEM) has difficulties capturing the solution accurately in the presence of boundary discontinuities. It exhibits higher error values in the proximity of corners than on the rest of the boundary. In an attempt to remedy this problem a two‐dimensional constant uniform flow across a square domain with an outflow condition on one side is considered and analyzed in depth. This leads to the conclusion that the free term from classical approaches needs to be reformulated for the degrees of freedoms lying at the corner points. This modification improves the accuracy of the BEM up to machine precision, which opens interesting directions for further research.
Unimodular transformations for DAE initial trajectory problems
Authors: Trenn Stephan , Unger Benjamin 
Published: January 2021

AbstractWe consider linear time‐invariant differential‐algebraic equations (DAEs). For high‐index DAEs, it is often the first step to perform an index reduction, which can be realized with a unimodular matrix. In this contribution, we illustrate the effect of unimodular transformations on initial trajectory problems associated with DAEs.
Trajectory Planning for Closed Kinematic Chains Applied to Cooperative Motions in Health Care
Authors: Knoll Carsten , Jia Xuehua , Heedt Robert 
Published: January 2021

AbstractPhysical interaction of humans can be a challenging. For some practically relevant situations a reasonable model is given by a closed kinematic chain of a planar rigid body mechanism. From a control perspective a cooperative motion, e. g. assisted standing‐up, can be seen as an optimal control problem (OCP) with input and state restrictions. Due to the algebraic constraints and the comparably high number of joints involved, proper formulation of such a problem is not trivial. In this contribution we compare two different modeling approaches: discretization of the full dynamical problem and iterative solution of consecutive stationary problems. The latter turns out to be significantly faster while still providing – in some sense – optimal solutions.
Material modeling of ferritic steel on microscopic length scale under cyclic loading
Authors: Ahmed Shahbaz , Loehnert Stefan , Wriggers Peter 
Published: January 2021

AbstractA material model for the polycrystalline microstructure of formable steels is developed to determine the residual stress state resulting from incompatible plastic deformation of individual grains under non‐monotonic loading. The glide of mobile dislocations on a specific slip system mainly governs the shear rates. During the movement, dislocations experience several types of resistance. The existing immobile dislocation structures on non‐parallel slip planes reduce the slip activities. This is reflected in a nonlinear isotropic hardening criterion. Furthermore, piled up dislocations on parallel slip planes also create hindrance to mobile dislocations. This effect creates residual stresses within the material which are taken into account by an additional kinematic hardening law. Residual stresses play a crucial role as well, especially during cyclic loading. Both, nonlinear isotropic and kinematic hardening criteria can define the plastic character of ferritic steel under non‐monotonic loadings.
Two‐Point Velocity Correlations in Fully Developed Turbulent Pipe Flow at Shear Reynolds Number of Reτ ≈ 4000
Authors: Zanoun El-Sayed , Egbers Christoph , Dewidar Yasser 
Published: January 2021

AbstractThe aim of this study is to report about the large‐scale pipe flow structures using the two‐point velocity correlations at a radial location of y/R = 0.5 and 41 azimuthal positions for shear Reynolds number Reτ ≈ 4000. The streamwise velocity component was measured, utilizing two single‐wire probes, simultaneously, based on various azimuthal probe separations. One dimensional pre‐multiplied energy spectra, and two‐point joint statistics were adopted. Both the low and the high wavenumber motions were highlighted using the pre‐multiplied cross‐spectral density. The cross‐power spectral analysis for all the 41 measurement points indicates strong correlation between the hot‐wire signals with small azimuthal separation, on contrary, the peak of the spectrum is getting damped as the azimuthal distance increases. For present shear Reynolds number, the large and the very large scale motions showed wavelengths of ≈ 3R and 14R, respectively, at half of the pipe radius.
Static response of a slightly precurved layered beam with interlayer slip
Authors: Ladurner Dominik , Adam Christoph , Furtmüller Thomas 
Published: January 2021

AbstractThis contribution addresses moderately large deflections of a slightly precurved simply supported beam composed of three layers symmetrically disposed about the central axis. The elastic beam layers are flexibly bonded and thus exposed to interlayer slip. Since the displacements of the supports are fully restrained, the static response is geometrically nonlinear. The results of an application example demonstrates the grave effect of interlayer slip on the nonlinear deflection of slightly precurved layered beams.
How the mathematical understanding of the theory of dynamical systems can be improved with computer‐assisted experimentation
Authors: Gunesch Roland 
Published: January 2021

AbstractThis article presents several examples of how the theory of dynamical systems can be studied by exploration (in particular, by using computer simulations), shows typical cases where the inclusion of computer tools is useful for learning and understanding these dynamical systems, and also points out typical difficulties and limitations of this approach.The application of computer simulations to the study of the theory of dynamical systems is a particularly interesting case of seamless learning.