bluuebunny/crossref_metadata_2025 huggingface dataset:
Are voiding parameters a marker for the severity of quality of life impairment in women with overactive bladder symptoms?
Authors: Basu Maya , Doumouchtsis Stergios K.
Published: October 2016

Aims

There is evidence of an association between voiding parameters and the presence of overactive bladder symptoms. The aim of this study was to evaluate whether there is any association between pressure flow study parameters and the degree of health related quality of life impairment in women with OAB symptoms. The null hypothesis is that there is no significant correlation between quality of life domain scores and pressure flow study parameters.

Methods

One hundred and sixty‐seven consecutive women with overactive bladder symptoms underwent evaluation with a quality of life assessment plus filling and voiding cystometry. These data were used to evaluate for any correlation between pressure flow study parameters and quality of life domain scores.

Results

Fifty‐six out of 167 women had proven detrusor overactivity (DO). There were no differences in voiding parameters or quality of life scores between women with DO and women without DO. There was no consistent correlation identified between quality of life domain scores and pressure flow variables.

Conclusions

There is no evidence of an association between increasing quality of life impairment and voiding parameters in this cohort.
Test‐retest repeatability of patterns of brain activation provoked by bladder filling
Authors: Clarkson Becky D. , Tyagi Shachi , Griffiths Derek J. , Resnick Neil M.
Published: October 2016

Objective

To assess short‐term repeatability of an fMRI protocol widely used to assess brain control of the bladder. fMRI offers the potential to discern incontinence phenotypes as well as the mechanisms mediating therapeutic response. If so, this could enable more targeted efforts to enhance therapy. Such data, however, require excellent test‐retest repeatability.

Methods

Fifty‐nine older women (age ≥60 years) with urgency incontinence underwent two fMRI scans within 5‐10 min with a concurrent bladder infusion/withdrawal protocol. Activity in three brain regions relevant to bladder control was compared using paired t tests and intra‐class correlation.

Results

There were no statistically significant differences in brain activity between the two consecutive scans in the regions of interest. Intra‐class correlation was 0.19 in the right insula, 0.32 in the dorsal anterior cingulate cortex/supplementary motor area, and 0.44 in the medial pre‐frontal cortex. Such correlations are considered fair or poor, but are comparable to those from studies of other repeated fMRI tasks.

Conclusions

This is the first evaluation of the repeatability of a bladder fMRI protocol. The technique used provides a framework for comparing different fMRI protocols applied to brain‐bladder research. Despite universal patient response to the stimulus, brain response had limited repeatability within individuals. Improvement of the investigational protocol should magnify brain response and reduce variability. These results suggest that although analysis of fMRI data among groups of subjects yields valuable insight into bladder control, fMRI is not yet appropriate for evaluation of the brain's role in continence on an individual level.
Computational Closed‐Loop Control of Fluid‐structure Interaction (FSCI) for Lightweight Structures
Authors: Mini Andreas , Lerch Christopher , Wüchner Roland , Bletzinger Kai‐Uwe
Published: October 2016

This contribution gives a short introduction into the topic of fluid‐structure‐control interaction (FSCI). This is a multi‐field problem, where three fields are coupled, namely a fluid‐flow, structural dynamics and closed‐loop control of structures. The interactions are identified as surface‐coupling of fluid flow and structural dynamics as well as signal‐coupling of structural dynamics and closed‐loop control.

At first a simple model problem is introduced, which allows an efficient investigation of the convergence behavior and stability of such kind of problem. In this context an iterative partitioned approach, using a serial Gauß‐Seidel scheme, is presented. Finally, the insights gained by the model problem are used to set up a multi‐dimensional numerical experiment. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convolution Quadrature based BEM in acoustics for absorbing boundary conditions
Authors: Pölz Dominik , Sauter Stefan , Schanz Martin
Published: October 2016

In many fields of engineering the acoustic behavior has to be determined, e.g. the sound distribution in a room or the sound radiation into the surrounding. Often, the goal is to obtain a sound pressure field such that disturbing noise is reduced to an acceptable level. In room acoustics, sound absorbing materials are often used to obtain this goal. The mathematical description is done with the wave equation and absorbing boundary conditions. The numerical treatment can be done with Boundary Element methods, where the absorbing boundary results in a Robin boundary condition. This boundary condition connects the Neumann trace with the Dirichlet trace of the time derivative.

Here, an indirect formulation, which uses the single layer potential, is used as basic boundary integral equation. The convolution quadrature method is applied for time discretisation, which allows a simple formulation of the Robin boundary condition in the Laplace domain. Convergence studies with a refinement in space and time show the expected rates. A realistic example for indoor acoustics, the computation of the sound pressure level in a staircase of the University of Zurich, show the suitability of this approach in determining the indoor acoustics. The absorbing boundary condition shows the expected behavior. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new approach to the incorporation of servo constraints in multibody dynamics
Authors: Yang Yinping , Betsch Peter , Altmann Robert
Published: October 2016

A new index reduction approach is developed to solve the servo constraint problems [2] in the inverse dynamics simulation of underactuated mechanical systems. The servo constraint problem of underactuated systems is governed by differential algebraic equations (DAEs) with high index. The underlying equations of motion contain both holonomic constraints and servo constraints in which desired outputs (specified in time) are described in terms of state variables. The realization of servo constraints with the use of control forces can range from orthogonal to tangential [3]. Since the (differentiation) index of the DAEs is often higher than three for underactuated systems, in which the number of degrees of freedom is greater than the control outputs/inputs, we propose a new index reduction method [1] which makes possible the stable numerical integration of the DAEs. We apply the proposed method to differentially flat systems, such as cranes [1,4,5], and non‐flat underactuated systems. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cross‐linked actin networks: Micro‐ and macroscopic effects
Authors: Klinge Sandra , Aygün Serhat , Mosler Jörn , Holzapfel Gerhard A.
Published: October 2016

Actin plays a crucial role in the mechanical response of cells. Together with other proteins, it also drives protrusion, motility and cell division. Two important aspects of the mechanical modeling of this kind of protein are considered: its microscopic and macroscopic behavior. At the microscopic level, we start with a model proposed by Holzapfel and Ogden [1] providing a relationship between the stretch of a single polymer chain and the applied tension force. The model is advantageous as it simulates the so‐called ‘exceptional normal stresses’. This effect is typical for biopolymers and contradicts with the Poynting effect typically observed in rubber‐like polymers. The multiscale finite element method (FEM) is applied to simulate the effective mechanical behavior of cell cytoplasm. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling residual stresses in arterial walls based on anisotropic growth
Authors: Zahn Anna , Balzani Daniel
Published: October 2016

With the aim of obtaining a general local formulation for anisotropic growth in soft biological tissues, a model based on the multiplicative decomposition of the growth tensor is formulated. The two parts of the growth tensor are associated with the main anisotropy directions. Together with an anisotropic driving force, the model enables an effective stress reduction by including growth‐induced residual stresses, which is demonstrated in a numerical example of an idealized arterial segment. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigations in structures with imperfect material interfaces and cracks
Authors: Judt Paul , Ricoeur Andreas
Published: October 2016

Natural fiber reinforced bio‐polymers are in the focus of many research projects to understand and improve the mechanical behavior subjected to different process parameters during production. To provide safe and reliable light weight constructions, special interest is directed towards the damage and fracture behavior of such composite materials. Here, the material's behavior at the imperfect material interface between fiber and matrix plays an essential role and governs inelastic effects at the interfaces on the one hand, and the behavior of growing cracks on the other. The reduction of the elastic potential is related to both energy consuming processes in the system and in general is going along with a reduction of the crack tip loading and a shift of the crack growth direction. In this paper, the crack tip loading analysis in structures with perfect and imperfect material interfaces is presented and applied to different specimens. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On nonlinear damage accumulation and creep‐fatigue interaction of a damage model for the lifetime prediction of adhesively bonded joints
Authors: Kroll Ulrich , Matzenmiller Anton
Published: October 2016

Damage accumulation and creep‐fatigue interaction are investigated and depicted for a continuum damage model proposed for the lifetime prediction of bonded steel joints with the structural adhesive BETAMATE 1496V™. The nonlinearity of damage accumulation is caused by the nonlinearity of damage interaction as a result of the identified parameters. In consequence of the nonlinear accumulation, the model allows for the loading sequence effect, which is the influence of the chronological order of the load values on the lifetime. Although the nonlinearity of the damage accumulation is not very pronounced, the model prediction is in good agreement with lifetimes from tests with service loading of the adhesive at hand. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Hertzian cone cracks using a phase field description for fracture
Authors: Strobl Michael , Morand Lukas , Seelig Thomas
Published: October 2016

The present contribution focuses on fracture caused by indentation loading on the surface of a brittle solid. Its theoretical prediction is a challenging task due to the fact that crack nucleation is not geometrically induced, but is caused by the stress concentration in the contact near‐field. The application of the phase field model requires constitutive assumptions to ensure a tension‐compression asymmetric material response and prevent damage in compressed regions. This is achieved at the cost of giving up the variational concept of brittle fracture. We simulate the indentation of a cylindrical flat‐ended punch on brittle materials like silicate glass. In order to reduce the numerical effort, we exploit axisymmetric conditions for the finite element formulation. After crack initiation stable propagation of a cone crack can be observed in good agreement with experiments. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A fracture angle based three‐dimensional damage model for unidirectional fibre‐reinforced plastics
Authors: Szlosarek Robert
Published: October 2016

Since the failure analysis of fibre‐reinforced plastics is not limited to the first‐ply failure, it is mandatory to use adequate damage models to simulate the failure process. The paper describes a damage model for three‐dimensional stress states, which uses the crack orientation of the inter‐fibre fracture (IFF). The fracture angle describes the crack orientation and can be obtained by using Puck's IFF criterion. The fracture angle enables the possibility to take the causal stress situation for the IFF into account. This means that each Young's or shear modulus has its own damage function, which depends on the stress state and the fracture angle. Therefore, the stress‐strain extrapolation method of Schürmann and Weber for two dimensional stress states was advanced and modified for the three‐dimensional stress space. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermally loaded thick‐walled cylindrically curved aluminum/steel‐FGM‐panel
Authors: Haskul Mehmet , Arslan Eray , Mack Werner
Published: October 2016

Subject of the investigation is a thick‐walled cylindrically curved shell guided at the ends which is heated at its inner or outer surface. The material is presupposed to be functionally graded obeying a power law. Both the elastic limits according to von Mises and the stress distributions for different grading exponents are discussed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the acoustics of sonic composites
Authors: Girip Iulian
Published: October 2016

The primary goal of this paper is to propose an alternative method for obtaining the band structures of the 3D sonic composites without/ with point defects. The point defects are vacancies or foreign interstitial atoms which are supported by the interfaces between the hollow spheres and the matrix. The proposed method is used to simulate a sonic plate composed of an array of acoustic scatterers which are piezoceramic hollow spheres embedded in an epoxy matrix. The scatterers are made from functionally graded materials with radial polarization [1, 2]. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Galerkin‐based energy‐momentum time‐stepping schemes for anisotropic hyperelastic materials
Authors: Groß Michael , Ramesh Rajesh , Dietzsch Julian
Published: October 2016

This paper is motivated by dynamic simulations of fiber‐reinforced materials in light‐weight structures, and has two goals. First of all, the introduction of energy‐momentum schemes for nonlinear anisotropic materials, based on GALERKIN approximations in space and time, assumed strain approximations in time and superimposed algorithmic stress fields (compare [1]). Second, to show a variationally consistent design of energy‐momentum schemes using a differential variational principle. We develop a discrete variational principle leading to energy‐momentum schemes as discrete EULER‐LAGRANGE equations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isogeometric Reissner‐Mindlin shell analysis ‐ employing different control meshes for displacements and rotations
Authors: Kikis Georgia , Dornisch Wolfgang , Klinkel Sven
Published: October 2016

The main purpose of this paper is the development and implementation of a method for the reduction of the so‐called locking effect in the isogeometric Reissner‐Mindlin shell formulation. In [1] an isogeometric Reissner‐Mindlin shell formulation with an exact interpolation of the director vector based on continuum mechanics was introduced. The numerical examples showed that the accuracy and efficiency increased. However, there are only few effective concepts for the prevention of locking effects for low polynomial degrees. In the work of Beirão da Veiga [2], shear locking is prevented for a Reissner‐Mindlin plate formulation by using suitable solution spaces. Here, the method is extended to the Reissner‐Mindlin shell formulation. Different control meshes are used for displacements and rotations. Furthermore, the basis functions in the direction of the relevant rotation are one degree less than the ones which are chosen for the displacements. That leads to control meshes with different number and location of the control points. The aim is to avoid shear locking due to the coupling of shear strains and curvature since the compatibility requirement for pure bending is then fulfilled. The accuracy and efficiency of this method are investigated for different examples. In addition, the results are compared to the analytical solutions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solids in boundary representation ‐ a NURBS based Galerkin formulation
Authors: Klinkel Sven , Chen Lin , Simeon Bernd
Published: October 2016

The present approach deals with a numerical method for the static analysis of solids in boundary representation. A formulation is derived where the geometrical description of the boundary is sufficient to define the elastic boundary value problem for the complete solid. The interior of the domain is described by a radial scaling parameter. Following the idea of the scaled boundary finite element method [1] the scaling of the boundary with respect to a specified scaling center provides a representation for the complete solid. This concept fits perfectly to the boundary representation modeling technique, which is frequently used in CAD to define solids. In CAD the boundary of the solid is described by employing NURBS basis function. In the isogeometric analysis methodology, [2], a trivariate tensor product structure is used to analyze solids. In the present approach, the tensor‐product structure of the solid will be reduced by one dimension to parameterize the physical domain, i. e., the three‐dimensional solid exploits only two‐dimensional NURBS objects, which parameterize the boundary surfaces. Hence, the present approach represents perfectly the isoparametric paradigm, see [3]. However, in [3] the weak form of equilibrium is enforced on the boundary surface. This leads to an ordinary differential equation (ODE) of Euler type, which could be solved by applying a collocation scheme. In the present approach the weak form is employed on the boundary and in scaling direction. The displacement response in the radial scaling direction is approximated by one‐dimensional NURBS. Finally, the Galerkin projection of the weak form yields a linear system of equilibrium equations whose solution gives rise to the displacement response. In conclusion, the presented method is able to analyze solids, which are bounded by an arbitrary number of surfaces. Numerical examples will show the capabilities of the presented method. The accuracy of the method is investigated by comparison to the analytical solution. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of the temperature and wear behaviour of a disc brake
Authors: Lamjahdy Abdelkrim , Ali Jawad , Markert Bernd
Published: October 2016

Aerosols are defined in the simplest form as a mixture of solid or liquid particles suspended in a gas [1]. Brake dust is an aerosol, generated as a result of erosion between brake disc and brake pad. The aerosols can cause visual disorder, heart and lung diseases, short term acute symptoms like asthma, bronchitis and long term chronic irritation and inflammation of the respiratory track, which can lead to cancer. Therefore, it is important to know which factors are affecting the erosion rate of brakes. The main objective of this work is to measure the erosion rate of brake discs and brake pads, depending on temperature changes and deformation by performing experiments and simulations at varying velocities and load conditions. The general purpose, commercially available finite element solver Abaqus is used for performing the thermomechanically coupled simulations. Archad's Wear Law is used for the wear calculation. Experiments are conducted by using a pin on disc test bench. Temperature changes are measured by using thermocouples and erosion rates by measuring the total volume loss. At the end, relationships between erosion rates and temperature changes for different brake disc velocities and load conditions are investigated and experimental and simulation results are compared and discussed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A three‐dimensional discrete element model for heterogeneous solids under mechanical loading
Authors: Ockelmann Felix , Dinkler Dieter
Published: October 2016

The Discrete Element Method (DEM) is used to model solids under quasi‐static and dynamic loading. In order to model elastic bodies, a microscopic model must be able to represent the macroscopic properties of the material. An energy‐based approach to determine the model parameters is presented for an unit cell assemblage of 13 particles in the hexagonal close packing of spheres. The stored strain energy in the unit cell is added up and the specific strain energy expression is derived with respect to the macroscopic strains. The resulting stress‐strain relations can be compared to the constitutive equations of the elastic continuum. To avoid cubic anisotropy for Poisson's ratios above zero, an advanced octahedrongap‐filled hexagonal close packing of spheres is presented and validated.

This approach for regular lattices can be transferred to heterogeneous materials with the goal of describing porous media such as cement stone. Therefore it is possible to use the presented regular lattices with statistically distributed properties or to investigate irregular distributions of particles. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibrations of a beam‐string complex system under a moving force
Authors: Rusin Jarosław
Published: October 2016

In this paper, the dynamic response of an Euler‐Bernoulli beam and string system traversed by a constant moving force is considered. The force is moving with a constant velocity on the top beam. The complex system is finite, simply supported, parallel one upon the other and continuously coupled by a linear Winkler elastic element. The classical solution of the response of a beam‐string system subjected to a force moving with a constant velocity has a form of an infinite series. The main goal of this paper is to show that in the considered case the aperiodic part of the solution can be presented in a closed, analytical form instead of an infinite series. The presented method of finding the solution in a closed, analytical form is based on the observation that the solution of the system of partial differential equations in the form of an infinite series is also a solution of an appropriate system of ordinary differential equations. The dynamic influence lines of complex systems may be used for the analysis the complex models of moving load. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Particle Finite Element Simulations of Cutting Processes in Manufacturing
Authors: Sabel Matthias , Sator Christian , Müller Ralf
Published: October 2016

The cutting of metals is an important process in manufacturing and challenges established methods in the field of computational mechanics. The particle finite element method (PFEM) combines the benefits of particle based methods and the standard finite element method (FEM) to account for large deformations and separation of material. In cutting simulations the workpiece is realised as a set of particles, whose boundary is detected by the α‐shape method. After the boundary detection, the particles are meshed with finite elements. Since metals show a plastic behavior under large deformations, a suitable material model needs to be considered. Numerical examples show the effect of the choice of the parameter α on the cutting force. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermodynamically consistent integration of coupled thermoelastic systems
Authors: Schiebl Mark , Betsch Peter , Hesch Christian
Published: October 2016

This work deals with the energy‐momentum‐entropy consistent integration of thermoelastic systems. While energy‐momentum preserving integrators are well‐known for conservative mechanical systems, Romero recently introduced in [6] a thermodynamically consistent (TC) integrator for coupled thermomechanical systems. TC integrators also respect symmetries of the underlying coupled system and are therefore capable of conserving associated momentum maps. A first step towards the systematic design of a TC integrator is to cast the evolution equations into the GENERIC framework. GENERIC stands for General Equation for Non‐Equilibrium Reversible‐Irreversible Coupling and has been originally proposed by Grmela and Öttinger for complex fluids [3]. As a second step applying the notion of a discrete gradient in the sense of Gonzalez [2] leads to a TC integrator. The GENERIC‐based framework reveals additional underlying physical structures of the thermodynamical system due to the separation of irreversible and reversible driving forces. Using the entropy as the thermodynamical state variable as in [4,6] the GENERIC framework yields an easy structure. However, this choice of thermodynamical state variable leads to a restriction in the material model and, more importantly, only allows to prescribe entropy Dirichlet boundary conditions. This drawback can only be compensated by using Lagrange‐multipliers to be able to handle temperature Dirichlet boundary conditions, which unfortunately extends the system of algebraic equations to be solved (see Krüger et al. [5]). Alternatively, the present contribution uses the temperature as the thermodynamical state variable (see also the recent work by Conde Martín et al. [1]). This temperature‐based approach allows to set Dirichlet boundary conditions directly. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of different least‐squares mixed finite element formulations for hyperelasticity
Authors: Schwarz Alexander , Steeger Karl , Igelbüscher Maximilian , Schröder Jörg
Published: October 2016

The main goal of this contribution is the solution of geometrically nonlinear problems using the mixed least‐squares finite element method (LSFEM). An investigation of a hyperelastic material law based on logarithmic deformation measures is performed. The basis for the proposed LSFEM is a div‐grad first‐order system consisting of the equilibrium condition and the constitutive equation, see e.g. Cai and Starke [1]. For the interpolation of the solution variables vector‐valued Raviart‐Thomas functions for the approximation of the stresses and standard Lagrange polynomials for the displacements are used. In order to show the performance of the presented formulations a numerical example is investigated, where we compare the different interpolation combinations used. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational integration in endochronic theory for small strain elastoplastodynamics
Authors: Bär Sebastian , Groß Michael
Published: October 2016

This paper presents a basic endochronic plasticity model with isotropic hardening for small strain theory according to Valanis. The key point of this model is a convolution integral over an intrinsic time scale involving past values of the strain measure and a so‐called memory kernel which leads to a smooth evolution equation for the internal variable. For the temporal discretization of the underlying constitutive equations and the resulting evolution equation we use higher order accurate variational integrators (VI). The remarkable feature is the fact that we approximate the position vector in terms of velocities according to partitioned Runge‐Kutta methods (pRK). As a representative model problem serves a quasistatic, uniaxial tensile testing as well as a dynamic, elastoplastic cantilever beam with a smooth plasticity model according to the Valanis framework. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bifurcation behaviour and limit cycles of a compliant seal‐rotor system
Authors: Baeuerle Simon , Hetzler Hartmut
Published: October 2016

This contribution discusses the non‐linear dynamic behaviour of a rotor system equipped with a compliant seal. The investigated model consists of a Laval‐Rotor and a stiff seal ring which is visco‐elastically supported. The fluid forces stemming from the turbulent incompressible lubricant film are accounted for by the non‐linear Muszynska model. The added compliance leads to an improved stability behaviour of the steady state. Within the post‐critical regime the additional compliance gives rise to bifurcations of the stationary vibration: Hopf bifurcations lead to limit cycles which can loose their stability via Neimark‐Sacker bifurcations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conditions for the existence and stability of the regime of type 0/1 for an excited unbalanced rotor
Authors: Bartkowiak René
Published: October 2016

Stationary regimes of motion of an unbalanced rotor with harmonic base excitation are investigated. The equation of motion of the rotor can be transformed into integro‐differential equations for the so called slow and fast motions of these regimes using the method of direct separation of motion. The existence and stability conditions of special regimes of motion then can be derived by introducing the approximate solutions of the fast equation into the slow equation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulating a variable displacement vane pump
Authors: Köster Marius , Fidlin Alexander , Schröders Simon
Published: October 2016

Variable displacement vane pumps are used in a variety of applications, most prominently in the context of modern automotive vehicles. Minimal models capturing the main dynamic effects of such pumps have remained scarce. In this contribution, a minimal model taking into account the force effects from line pressure exposure and dead volume compression and expansion is presented. The pump model is autonomous and allows for a simple integration in simulation models for which an example in the form of a non‐smooth hydraulic circuit is given. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Validation of the applicability of a creep model for directionally solidified eutectics with a lamellar microstructure
Authors: Albiez Jürgen , Sprenger Ioannis , Weygand Daniel , Heilmaier Martin , Böhlke Thomas
Published: October 2016

Depending on the process parameters, the directional solidification (DS) of eutectic alloys leads to a fibrous or lamellar microstructure. A physically motivated creep model which was evaluated for a DS‐eutectic with a fibrous microstructure is applied to a DS‐eutectic with a lamellar microstructure. Creep curves are simulated and compared to experimentally measured ones. It is shown, that the simulation is in good agreement with the experiment. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐quadratic defect energy: A comparison of gradient plasticity simulations to discrete dislocation dynamics results
Authors: Bayerschen Eric , Stricker Markus , Weygand Daniel , Böhlke Thomas
Published: October 2016

A small‐deformation strain gradient plasticity (GP) model for single‐crystals has been proposed in [1], including a grain boundary (GB) yield condition without hardening. It has been extended by a hardening term for the GBs after a comparison to discrete dislocation dynamics (DDD) results in [2]. Differences between the strain gradients of the GP results and the DDD results motivate the consideration of a non‐quadratic defect energy [3] in the GP model. It is shown that the gradients in the GP model can be improved using an exponent different from two. Remaining discrepancies in the strain profiles, compared to the DDD results, are attributed to the neglect of the individual gradients of plastic slip and due to the lack of a mechanism for the misorientation‐dependent elastic interactions of dislocations across GBs [4] in the GP model. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient Finite Element Simulation of the Temperature Field during Cryogenic Turning of Metastable Austenitic Steel AISI 347
Authors: Becker Steven , Mayer Patrick , Kirsch Benjamin , Aurich Jan C. , v. Harbou Erik , Müller Ralf
Published: October 2016

The process chain in manufacturing often consists of many steps. As part of current researches the possibility of combining two process steps, turning and hardening, is investigated to optimize the manufacturing time and to decrease the energy consumption of the process. For metastable austenitic steels, deformation induced hardening during turning can be used to achieve surface hardening [1] and thus to increase the wear resistance [2] as well as the fatigue strength [3], by applying high passive forces onto the workpiece. This enables an austenite‐martensite phase transformation, for which it is necessary to maintain low process temperatures, typically below room temperature. Thus, cryogenic coolants are applied [4].

For a better understanding of the influence of cutting parameters on the process temperatures and thus martensite formation, knowledge of the exact temperature distribution in the workpiece and in the contact zone between workpiece and tool is essential. Since the experimental determination of the temperature field is hardly possible, an inverse determination of the process temperatures via transient finite element simulation is performed.

The present finite element approach only takes thermal loads into account. The simulations are performed in the finite element program FEAP (Finite Element Analysis Program) with an Eulerian mesh, which requires special consideration of the rigid body rotation of the workpiece. In order to prevent unphysical oscillations in the solution, introduced by the convective time derivative, a streamline upwind / Petrov–Galerkin stabilization scheme is utilized. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Discussion of Different Model Approaches for the Flow Behavior of Ice
Authors: Christmann Julia , Rückamp Martin , Müller Ralf , Humbert Angelika
Published: October 2016

Ice of Antarctic ice shelves is assumed to behave on long‐term as an incompressible viscous fluid, which is dominated on short time scales by the elastic response. Hence, a viscoelastic material model is required. The thermodynamic pressure is treated differently in elastic and viscous models. For small deformations, the elastic isometric stress for ν → 0.5 gives similar results to those solving for pressure in an incompressible laminar flow model. A viscous model, in which the thermodynamic pressure is approximated by an elastic isometric stress, can be easily extended to viscoelasticity. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An experimentally validated rod model for soft continuum robots
Authors: de Payrebrune Kristin M. , O’Reilly Oliver M.
Published: October 2016

Soft robots are bio‐inspired, highly deformable robots with the ability to interact with workpieces in a manner that complements their hard robot counterparts. To develop practical applications and reproducible designs of soft robots, new models are necessary to describe their kinematics and dynamics. In the present work, we describe experimental and numerical investigations of a popular pneumatically‐actuated soft continuum arm. These works enable us to derive constitutive relations and develop a rod model for large deformations of the arm that faithfully describes its bending behavior. We show how the resulting non‐classical constitutive relation can be defined either through experiments or through quasi‐static finite element simulations. With the help of this relation, the resulting rod model can be used to study the dynamics of the soft robot arm in a fast and tractable manner. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A laminate‐based framework for switching and microstructure evolution in polycrystalline ferroelectrics
Authors: Dusthakar Dinesh K , Menzel Andreas , Svendsen Bob
Published: October 2016

This contribution deals with the numerical modelling of polycrystalline ferroelectric materials considering a sequential laminate‐based approach established for tetragonal single‐crystal ferroelectrics. The particular model [1] is considered and extended to predict the material behaviour of poly‐crystal tetragonal ferroelectric ceramics. The derived laminate‐based model is implemented in a finite element environment to simulate the time‐dependent domain evolution and switching response of a bulk polycrystalline ferroelectric ceramic. © 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large Strain Gradient Plasticity Theory with a Discontinuous Grain Boundary Yield Condition
Authors: Erdle Hannes , Bayerschen Eric , Böhlke Thomas
Published: October 2016

An equivalent plastic strain gradient theory [1] is extended to account for finite strains. The presented model considers discontinuities of the equivalent plastic strain at grain boundaries by using enriched trial functions in the Finite‐Element discretization. As a consequence, a grain boundary flow rule is introduced, depending on both the mean value and the jump of the equivalent plastic strain. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of dilatant plasticity models in application to rubber‐toughened polymers
Authors: Hund Jonas , Naumann Johanna , Seelig Thomas
Published: October 2016

The overall deformation behavior of rubber‐toughened polymers (e.g. PC/ABS blends) exhibits a pronounced plastic dilatancy. As this volume increase results from diverse micromechanisms the appropriate structure of a macroscopic model is not obvious. In this contribution, different material models featuring plastic dilatancy are compared with regard to their ability to capture the deformation behavior of PC/ABS in different loading situations. All models are calibrated to match experimental data under uniaxial tension in terms of true stress‐strain curves and the evolution of volume strain. Afterwards they are employed in finite element (FE) simulations of single‐edge‐notch‐tensile (SENT) tests. Patterns of plastic deformation computed from the different material models are compared to experimental findings. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental investigation, material modeling and parameter identification of a zinc die‐casting alloy
Authors: Martinez Page Maria Angeles , Hartmann Stefan
Published: October 2016

The zinc die‐casting alloy Zamak is widely used in the production of components of cars and machines. Because of its complex highly non‐linear thermo‐mechanical behavior, it is problematic to approximate its response with classical viscoplasticity models, such as von Mises‐viscoplasticity. Based on an extensive experimental investigation on thin‐walled cylindrical specimens, a proposal for the modeling of the rate‐ and temperature‐dependent behavior of the alloy Zamak 5 is presented and its applicability through a numerical example is shown. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of two different modeling approaches to describe the non‐linear viscoelastic behavior of filled rubber material
Authors: Scheffer Tobias , Diebels Stefan
Published: October 2016

This contribution presents the characterisation of an incompressible carbon black‐filled elastomer as one characteristical example for highly filled rubber material. The material model is developed with respect to uniaxial tension data. The experiments show that a strongly pronounced non‐linear viscoelastic material behavior is present and the most important characteristic is the extremely long relaxation time which has to be taken into account. These long relaxation times are also visible in cyclic tests, where a pronounced hysteresis loop appears even for the slowest possible strain rates [1,2].

In the material's characterization two different model approaches are realized. As a first approach the behavior is represented by a pure viscoelastic model. Since all the deformations are reversible for a stress‐free relaxation, no plasticity parts are included in the model. In order to display the non‐linearities process‐dependent material parameters have to be applied. Hence, the resulting coupling of different material parameters yields a complex parameter identification.

For a more effective identification process, a second approach is provided describing the interaction of the filler particles. The friction of the fillers during deformation results in a statical hysteresis, which does not depend on the strain rate. Therefore, special attention is turned towards the behavior of the hysteresis loops that are observed, similar to the description of Vandenbroucke et al. [3]. Therein, in a rheological model, some Prandtl‐elements, consisting of a friction element and a spring are added to the classical viscoelastic model. This results in a model, which does not need any process‐dependency. Hence, the identification process can be simplified. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐resolution simulation of microstructures in dual‐phase steel
Authors: Scherff Frederik , Goldschmidt Florian , Scholl Sebastian , Diebels Stefan
Published: October 2016

Modern dual‐phase (DP) steels are widely used in industry due to their favorable material behavior based on the complex microstructure. In the presented work, a microstructure based FEM model for the elasto‐plastic deformation of DP steels is developed in order to accomplish a deeper understanding of the structure‐property correlation. The underlying microstructure is obtained by serial section tomography. The following contribution deals with a comparison of different approaches to build a FE mesh, which is based on such microstructures. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time and frequency domain finite element implementation of a fully anisotropic linear visco‐elastic model
Authors: Toth Florian , Kaltenbacher Manfred
Published: October 2016

Consistent time and frequency domain formulations for a fully anisotropic, linear visco‐elastic material model are presented. The finite element implementation leads to a complex valued stiffness matrix in the frequency domain. A homogenisation procedure based on unit‐cell analyses in the frequency domain is presented to derive input parameters for the material model. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Digital Rock Physics: A case study of carbonate rocks
Authors: Uribe David , Saenger Erik H. , Steeb Holger
Published: October 2016

Digital Rock physics is a numerical framework applying image‐based methods to determine effective material properties of rock. It is possible to find several of these methods in the literature, but we focused mainly in micro X‐Ray Computed Tomography (µXRCT) to acquire the digital rock samples. After scanning the 3‐D microstructure, morphological filters and numerical simulations were performed to characterize the samples. In particular carbonate rocks present a mismatch in numerical results compared to laboratory experiments. The elastic parameters, the P‐ and S‐wave moduli, respectively,are overestimated when compared to ultrasonic measurements in the laboratory. We describe possible causes of this mismatch and propose a new segmentation technique to improve the correlation between numerical simulations and laboratory data. Furthermore, the workflow proposed for the characterization of carbonate rocks has been applied to different digitized samples from different sources, and a data driven material law has been found that fits better experimental results than the lower Hashin‐Shtrikman bound. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A variational model for the functional fatigue in polycrystalline shape memory alloys
Authors: Waimann Johanna , Junker Philipp , Hackl Klaus
Published: October 2016

Shape memory alloys show a very complex material behavior associated with a diffusionless solid/solid phase transformation between austenite and martensite. Due to the resulting (thermo‐)mechanical properties – namely the effect of pseudoelasticity and pseudoplasticity – they are very promising materials for the current and future technical developments. However, the martensitic phase transformation comes along with a simultaneous plastic deformation and thus, the effect of functional fatigue.

We present a variational material model that simulates this effect based on the principle of the minimum of the dissipation potential. We use a combined Voigt/Reuss bound and a coupled dissipation potential to predict the microstructural developments in the polycrystalline material. We present the governing evolution equations for the internal variables and yield functions. In addition, we show some numerical results to prove our model's ability to predict the shape memory alloys' complex inner processes. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized Interface Models With Damage in Gradient Plasticity
Authors: Wulfinghoff Stephan , Alipour Atefeh , Rezaei Shahed , Kochmann Julian , Reese Stefanie
Published: October 2016

Gradient plasticity can account for experimentally observed size effects. Here, a previously developed gradient plasticity model is extended to account for interface delamination processes. The crystal plasticity model is based on the gradient of an equivalent plastic strain measure. A modification of the related boundary conditions allows for the formulation of a generalized cohezive zone model which can take into account the effect of interface delamination on the gradient plasticity solution. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deformed gap space using macro‐micro FEA model and transferred into a CFD model
Authors: Anwar Ali , Gorash Yevgen , Dempster William , Nash David
Published: October 2016

Using a cylindrical nozzle and seat of a Pressure Relief Valve (PRV) the surface form and waviness is modelled using actual metrological data i. e. average surface form and waviness (Wa and Wsm) in a ${1 \over 4}$ symmetry manner. To model the surface waviness the technique used is based on the summing technique created by Tsukizoe & Hisakado [1, 2] for micro contact analysis. Due to the actual surface form measurements being in the micro‐meter range, the model is required to incorporate micro and macro‐meter dimensions. The material in question is stainless steel. The deformed finite element analysis model is then transferred into a CAD geometry allowing the void space to be meshed and solved using computational fluid dynamics. © 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling Abrasive Wear Caused by Small Solid Particles of Different Sizes
Authors: Beck Florian , Eberhard Peter
Published: October 2016

Abrasive wear is one of the mechanisms which cause the decrease of efficiency of hydraulic machines. The working fluid of a hydraulic machine, e.g., a turbine of a hydroelectric power plant, transports small solid particles of different sizes. Those small particles damage the surface of the hydraulic machine when contacting. In contrast to classical approaches in fluid dynamics, here, we present an approach where only mesh‐free methods are applied. The Smoothed Particle Hydrodynamics (SPH) method is used for modeling the fluid in this study. The SPH method is a mesh‐free method which has its advantages in describing transient fluid flows with free surfaces and large motions. The loading of the fluid consists of small solid particles of different sizes. A coupled approach for describing the loading is used. For the larger abrasive particles the Discrete Element Method and for smaller ones a transport equation is utilized. In doing so it is possible to model a loading of the fluid consisting of small particles of different sizes. The abrasive wear is described with an abrasive wear model. The wear model takes into account different parameters like the size, the velocity of the abrasive particles, and of course material parameters of both the target and the particles. On impact of an abrasive particle, the amount of removed material is stored at the boundary and in doing so the removed material over time is identified.

In this work, a representative numerical example is presented. The simulations were performed with the code Pasimodo, developed at the Institute of Engineering and Computational Mechanics. It is the aim of this work to point out that it is possible to model abrasive wear due to abrasive particles with different sizes with a mesh‐free approach. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)