bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolution of structures with homogeneous equivalent stress
Authors: Muench Ingo , Keller Alexander 
Published: December 2018

AbstractA phase field model is used to evolve structures with almost homogeneous equivalent stress σv. The model combines the sensitivity of a stress‐based and a couple‐stress‐based objective function. Since couple‐stress typically increases at stress‐singularities, it is an efficient parameter to influence the topology of load‐bearing structures facing that problem. Further, it will be shown that this combination yields an increased solution space concerning the topology of the evolving structures. The effect is demonstrated for the topology of a bridge. Whereas traffic load q onto the driving surface prefers to evolve an arch as topology, the self‐weight g of the bridge prefers to evolve a topology similar to a suspension bridge. The couple‐stress‐based objective function evolves the combination of both topologies such that a smooth transition appears between the topology for q/g = 0 and the topology for q/g → ∞.
A comparison of methods for approximating periodic limit cycles in nonlinear systems with joint friction
Authors: Kappauf Jonas , Hetzler Hartmut 
Published: December 2018

AbstractIn this contribution, approximation methods for calculating periodic limit cycles of self‐excited dynamical systems with frictional damping are studied. In industrial application, e.g. the analysis of brake squeal, the so‐called Energy‐Balance has attracted a lot of interest [3], while rather classical Harmonic Balance methods are commonly used in non‐linear analysis. Focussing on the effect of both smooth and non‐smooth non‐linearities, limit cycles were calculated for two minimal models, which are commonly used when dealing with NVH or brake squeal analysis. Moreover these two methods are compared in terms of accuracy and numerical effort.
A variational framework for distance‐minimizing data‐driven method for linear elasticity
Authors: Nguyen Lu Trong Khiem , Rambausek Matthias , Keip Marc‐André 
Published: December 2018

AbstractA variational framework for the distance‐minimizing data‐driven computing method is proposed based on the method of Lagrange multipliers. The data‐driven solution is defined as an optimization solution of a double‐minimization problem. A staggered scheme is employed to decompose the original problem into a sequence of single‐minimization problems. As an advantage, the variational formulation renders straightforward implementation of the high‐order polynomial interpolation. The non‐uniqueness of the data‐driven solution is the consequence of the use of the current solution strategy and non‐convexity of the data function space. A convergence study of the solution with respect to the data size is presented. The decrease of mean values and standard deviations of errors with respect to the reference solution justify the variational formulation.
A consistent multi‐scale derivation of a micro‐plane model within the framework of RVE homogenisation
Authors: Storm Johannes , Kaliske Michael 
Published: December 2018

AbstractThe micro‐plane model is an approach to describe complex anisotropic material behaviour by a set of uniaxial deformation states. The model is widely applied in the context of concrete materials and has various formulations for anisotropic damage, creep and plastic material behaviour. The paper contributes to this class of material models by a consequent multi‐scale derivation of a micro‐plane‐like model within the framework of RVE homogenisation. The new approach preserves the elegant and efficient model structure and yields a thermodynamically consistent scale transition. The model derivation allows to clearly state the conditions on the micro‐structure and thereby to classify the micro‐plane models and the known extensions with respect to their micro‐structural motivations.
A Stochastic Model for Strong Wind Events in Central Europe based on Historical Wind Data
Authors: Niekamp Rainer , Brands Dominik , Götzen Carina , Kiseleva Maria , Niekamp Jana , Schröder Jörg , Siems Onnen 
Published: December 2018

AbstractFor the generation of synthetic storms in order to estimate claims due to storm hazards there exist a couple of commercial tools. They are based on expert's knowledge and physical models of wind appearance or work with distortions of historical hazards. In contrast to these approaches we present a purely data driven model. From the historical data we extracted the hourly wind peaks over the last two decades and derived by algebraic methods a stochastic storm model in form of a polynomial chaos expansion.
Investigation of austenitic TRIP steels by means of a phase field model
Authors: Schmidt Simon , Klein Matthias W. , Boemke Annika , Smaga Marek , Beck Tilmann , Müller Ralf 
Published: December 2018

AbstractAustenitic TRansformation Induced Plasticity (TRIP) steels offer an outstanding combination of formability and strength. Using Electron Backscatter Diffraction (EBSD) technique, the grain orientation and morphology of f.c.c. and b.c.c. phases can be clearly detected in initial state and at definite strains [2]. In order to qualify the driving mechanisms of phase transformations occuring during deformation of metastable austenites, e.g. TRIP steels, a phase field model is used. For the modelling, we follow [6]. The field equations are solved using the finite element method with bi‐linear shape functions and 4‐node elements. Features of this model are demonstrated by illustrative numerical examples.
Micro‐structure related modelling of ultra‐high‐performance fibre reinforced concrete (UHPFRC) subjected to cyclic tensile loading
Authors: Höper Svenja , Kowalsky Ursula , Dinkler Dieter 
Published: December 2018

AbstractUltra‐high performance concrete with a compressive strength of more than 140 N/mm2 reacts very brittle without the addition of fibres. At designing economical and resource‐efficient building components as well as performance‐optimized materials, the supporting effects of the additional microfibres must be considered. Prospectively, cyclic loading and the fatigue behaviour of high performance materials and slim components will come to the fore. Therefore, the influence of cyclic deterioration on the load bearing capacity of the interface transition zone connecting microfibres and the surrounding concrete surface must be investigated. As part of the DFG Priority Programme 2020, the damage mechanisms and processes regarding the deterioration of UHPFRC subjected to cyclic tensile loading are explored in an Experimental‐Virtual Lab. Using the concepts of elasto‐plasticity and continuum damage mechanics, the material models for the components of the composite material UHPFRC are improved and enhanced to be combined on a mesoscale with the help of a non‐linear bond model. This bond model is discretized by interface elements with curved surfaces in 3D space and describes the interaction of fibres and concrete in the bond zone in terms of adhesion and friction effects. For validation and verification, single and multiple fibre pullout tests are simulated in 3D‐finite element analyses. These FE‐simulations and preliminary findings are supposed to provide the essential basis for future numerical degradation prediction.
Oscillations of a visco‐elastic belt drive
Authors: Steindl Alois 
Published: December 2018

AbstractWe investigate the loss of stability of the steady configuration of a planar visco‐elastic belt drive. The belt is considered as a linearly visco‐elastic slender beam with small bending stiffness, which is driven by a steadily rotating drum. For a belt clamped on both ends at different heights no Hopf bifurcation is found, but a perturbed pitchfork bifurcation is observed. For a belt on a drum different Hopf bifurcation points are detected, which depend strongly on the viscous damping.
Micromorphic and micropolar continua: A comparative study based on homogenisation of particle simulations
Authors: Bidier Sami , Ehlers Wolfgang 
Published: December 2018

AbstractExtended continuum‐mechanical theories, such as the micromorphic, the micropolar or the microstrain continuum, are suitable formulations when additional characteristic microstructural deformation modes should be included into macroscopic modelling techniques. This is especially the case when the microscopic view of the considered material reveals a granular or particulate structure. Then, by means of a particle‐centre‐based homogenisation technique, it is possible to link the microstructural information that can be gained, for example, from Discrete‐Element (DE) simulations, to the extended deformation and stress states of the above mentioned extended continua. In this context the present contribution focuses on two main aspects: at first, different granular microstructures, in particular bonded and unbonded granular systems, are investigated using a discrete‐element formulation with the emphasis on the evolution of strain localisation phenomena. Secondly, the obtained results of these initial‐boundary‐value problems are homogenised towards micropolar and micromorphic stress measures. Depending on the microstructural characteristics, the activation and evolution of the extended stress states are compared and evaluated with special emphasis on the size of the chosen homogenisation domain.
An Adam‐Gibbs based model for the temperature behavior of polymers near glass transition
Authors: Wicht Daniel , Kehrer Loredana , Wood Jeffrey T. , Böhlke Thomas 
Published: December 2018

AbstractThe mechanical behavior of polymers and other glass forming materials is strongly time‐ and temperature‐dependent. Based on the rheological Poynting‐Thomson Model and the Adam‐Gibbs equation, a shift function is developed which relates the time constants of a material to temperature. The behavior of this function is compared to the established Williams‐Landel‐Ferry and Arrhenius equations in the glassy and rubbery temperature regimes.
Modeling of anisotropic boundary layer effects in plate theory
Authors: Schneider Patrick , Kienzler Reinhold 
Published: December 2018

AbstractThe modeling of a Reissner‐type plate theory for elastic, monoclinic material is presented. The basic theory is derived using the a‐priori‐assumption free uniform‐approximation approach, which is based upon series expansions of the displacement field and a structured truncation of the elastic potential that gives rise to a hierarchy of approximating theories. An a‐priori estimate for the approximation error shows that higher‐order theories have indeed a higher rate of convergence with respect to the relative slenderness of the plate. Using a pseudo‐reduction approach, the number of PDEs to be solved is reduced significantly. The resulting first‐order theory is the classical monoclinic plate theory, whereas, the second order theory is not determined uniquely by the approach. Uniqueness is achieved by introduction of an orthogonal decomposition of higher‐order gradients of the in‐plane displacements. The final second‐order theory coincides with the Reissner‐Mindlin theory for the special case of isotropic material.
Iterative spectral identification of bone macroscopic properties described by a probability box
Authors: Rosić Bojana , Kumar Shivanand Sharana , Vinh Hoang Truong , G. Matthies Hermann 
Published: December 2018

AbstractThis paper considers Bayesian identification of macroscopic bone material characteristics given digital image correlation (DIC) data. As the evaluation of the full Bayesian posterior distribution is known to be computationally intense, here we consider the approximate estimation in a Newton‐like manner by using the theory of conditional expectation. The approach is extended to include the epistemic uncertainties in the process of modelling the prior.
Fatigue Reliability Analysis and Design for Structural Components in Quasi‐One‐Shot Device
Authors: Wang Haiqiao , Chen Min , Yao Xiaofei , Liu Zhiyuan , Wang Xiang , Tate Derrick 
Published: December 2018

AbstractThe reliability of the quasi‐one‐shot device is a crucial index and hard to predict due to its complexity and cost‐consuming of testing. In this paper, a bi‐directional approach of reliability optimization design (ROD), integrating stress‐strength interference model and fatigue analysis, was proposed to evaluate and optimize the weakest component of the quasi‐one‐shot device. High‐voltage vacuum circuit breaker was used as a numerical validation example.
Semi‐active vibration reduction based on a variable structure controlled serial‐stiffness‐switch‐system
Authors: Min Chaoqing , Dahlmann Martin , Sattel Thomas 
Published: December 2018

AbstractA concept for semi‐active vibration control with a serial‐stiffness‐switch‐system based on vibration energy harvesting was previously presented. This contribution investigates a variable structure control‐based switching law to reduce the settling time of the system response under a nonzero velocity initial condition. The proposed switching law is able to fasten the transformation of initial vibration energy of the system into potential energy stored equally in its two springs. It is characterized, simulated, and proven to be more effective than the old switching law.
Influence of Hemorheology on Nanoparticle Transport in Vessel Bifurcations
Authors: Bavandi Mahrokh , Wünsch Olaf 
Published: December 2018

AbstractThis study presents the effect of hemorheology on nanoparticle transport in the left coronary artery. The flow is considered to be pulsating and particles are modeled by concentration equation. The influence of Newtonian and non‐Newtonian modeling approaches on particle transport is investigated and compared. Three bifurcations are investigated to determine the effect of bifurcation angles. The results show that considering blood as non‐Newtonian in certain configurations is necessary.
Polymorphic Uncertainty Modeling for Optimization of Timber Structures
Authors: Schietzold Friedemann Niklas , Graf Wolfgang , Kaliske Michael 
Published: December 2018

AbstractThe uncertainty characteristics of wood are mainly affected by natural variation. Out of this, the traditional approach of stochastic variables can be expanded to a polymorphic uncertainty model. Therefore, e.g. fuzzy probability based randomness is used by extending stochastic variables with fuzzy variables in parameterization concerning the distribution functions, see [1] and [2]. The coupling of both aleatoric and epistemic uncertainty is involved in the uncertainty analysis.The FEM is applied as basic solution of particular load situations on the focused timber structure. A local orthotropic formulation is used and the properties are evaluated on each integration point with respect to the tree trunk axis.In this contribution, an approach to polymorphic uncertainty modeling for timber structures is introduced. According to [3], models representing the spatial variation and interdependencies of material parameters are necessary for a realistic representation in numerical simulation. For this purpose, on the one hand interactions between fuzzy variables, on the other hand correlations among random variables are considered. Random fields are utilized to capture spatially varying material properties in context with the discretization of FE. Approaches to both spatially and structurally depending autocorrelations along with crosscorrelations based on [4] are presented.The preliminary steps aim at an optimization in design of timber structures, provided that polymorphic uncertain design as well as a priori parameters are considered. The developed tools for uncertainty analysis and the basic FEM solution are prepared as a basis for an automated optimization processing, whereas they are preferably parallelized, incorporating methods for reducing the numerical effort. Results of the uncertainty analysis of a timber structure are shown exemplary.
Low latency output feedback predictive control based on optimality conditions
Authors: Kögel Markus , Findeisen Rolf 
Published: December 2018

AbstractIn output feedback predictive control the control input is calculated by solving an optimization problem at each time instant based on a state estimate obtained by an observer. To efficiently counteract disturbances it is important to reduce the delay/latency due to the solution of the optimization problem. To this end we present an approach splitting the optimization into two phases: In the inter‐sample period a set of control laws parameterized by future measurements is determined exploiting the optimality conditions. Once the new measurement is available, the controller selects the corresponding control law and determines the optimal input, which can be achieved fast and with a low computational demand.
Gradient Approximation in Flexible Multibody Systems Using a Multigrid Approach
Authors: Moghadasi Ali , Held Alexander , Seifried Robert 
Published: December 2018

AbstractThe approximation of gradients with a multigrid approach is presented in the framework of flexible multibody systems, in which the flexible bodies are modeled using finite element method. For the cases where the number of design variables are high, for example, in topology optimization where the density of each element is chosen as a design variable, the gradient computation becomes computationally infeasible. The proposed approximation, in which the gradients are computed simultaneously on a fine grid and a coarse grid, can significantly reduce the computation time without hindering the accuracy of the gradients.
The Influence of Cooling Nozzle Positions on the Transient Temperature Field during Cryogenic Turning of Metastable Austenitic Steel AISI 347
Authors: Becker Steven , Hotz Hendrik , Kirsch Benjamin , Aurich Jan C. , von Harbou Erik , Müller Ralf 
Published: December 2018

AbstractMetastable austenitic steels offer the opportunity of a surface layer hardening integrated in the machining process. The hardening effect is achieved by a deformation induced austenite‐martensite phase transformation, for which high mechanical loads and low temperatures are necessary, typically below room temperature. These conditions can be accomplished during cryogenic turning, allowing a phase transformation in the surface layer of the workpiece. To study the austenite‐martensite transformation behavior, information about the temperatures in the contact zone between tool and workpiece during machining is necessary, which can be hardly measured. Therefore, FE simulations of the process are utilized to calculate the transient process temperatures. In this paper predictive temperature field simulations for different settings of the cooling system, i.e. varying cooling nozzle positions, are performed in order to investigate the influence of the cooling nozzle positions on the temperature distribution during cryogenic turning and to correlate the results with measurements of the martensite content resulting for these cooling setups.
Leakage current and polarization domains in ferroelectric nanogenerators for energy harvesting
Authors: Wöhler Franziska , Muench Ingo , Wagner Werner 
Published: December 2018

AbstractEnergy harvesting based on the transformation of mechanical into electrical energy is under investigation. Mechanical deformations from ambient parasitic vibrations serve as energy source for our nanogenerator concept with barium titanate as ferroelectric material. The energy harvesting process is enabled by the designed polarization domain topology. Due to the deformation in the ferroelectric film, the polarization domains reorder resulting alternating charge density within electrodes. Defects and other impurities in the single crystal turn the ferroelectric film into a semiconductor. We account for leakage current mechanisms in our finite element phase field model phenomenologically. Ohm's law (OL) and space‐charge‐limited‐ current (SCLC) are presented by linear or quadratic functions for the current density, respectively. The distance between the electrodes as well as the ferroelectric film thickness have an immense influence on the leakage current density. Further investigations focus on the influence of polarization domain topology on the leakage current.
Desingularization in boundary element analysis of three‐dimensional Stokes flow
Authors: Harmel Maximilian , Rajski Michał P. , Sauer Roger A. 
Published: December 2018

AbstractThe boundary element method (BEM) is able to solve partial differential equations without volumetric discretization and integration. Therefore, the BEM is able to reduce the compuational as well as the meshing effort compared to volumetric methods like classical finite elements. In this work, a conventional and a nonsingular BEM formulation for Stokes flow are presented and investigated in three‐dimensions, considering rotating spheres within a viscous fluid.
Effect of graphene quantum dots on photoluminescence property of polyvinyl butyral nanocomposite
Authors: Arthisree Devendran Lakshmi , Sumathi Rajappan Radhakrishnan , Joshi Girish 
Published: December 2018

Design and development of new photoluminescence system are much in demand for various engineering and technological applications. The present investigation focused on the influence of graphene quantum dots (GQDs) dispersion in the polyvinyl butyral (PVB) matrix. The structural and chemical interaction of GQD‐dispersed PVB composites was confirmed by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), micro‐Raman spectroscopy, ultraviolet and visible (UV‐Vis), and photoluminescence (PL) techniques. Chemical interaction between the functional groups leads to PL quenching at 455 nm. Changes on crystallite size and interplanar spacing hinders on the structural properties of the nanocomposite. Raman spectroscopy reveals the decrease in D/G intensity ratio influenced by GQD loading wt% in the polymer system. The dispersion and occupied network of GQD in the PVB matrix was confirmed by optical polarizing microscopy (OPM), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Effect of electrical conductivity of composites as a function of temperature has been verified. Decrease in direct bandgap as a function of GQD loading confirms the promising PL properties of the prepared composite system. Thus GQD‐derived composites may further be developed as a membrane for improved PL property.
Copolymerization modification: improving the processability and thermal properties of phthalonitrile resins with novel comonomers
Authors: Liu Yang , Liu Zheng‐zhou , Peng Wei‐feng , Lu Zheng , Hu Jiang‐huai , Zeng Ke , Yang Gang 
Published: December 2018

AbstractTwo novel tetrahydrophthalic anhydride end‐capped imide compounds (THAN and THBN) with high thermal stability were synthesized to promote the curing reaction of 1,3‐bis(3,4‐dicyanophenoxy)benzene (3BOCN), and to study the effects of comonomer structure on the curing behavior and thermal performance of phthalonitrile resins. The curing behaviors of THAN/3BOCN and THBN/3BOCN blends with various molar ratios were investigated using rheological analysis and differential scanning calorimetry, suggesting a wide processing window. Dynamic mechanical analysis and thermogravimetric analysis showed that the cured resins possessed high glass transition temperatures (> 500 °C), and superior thermal and long‐term thermo‐oxidative stabilities with weight retention of 95% ranging from about 544 to 558 °C in both nitrogen and air. All these results indicated that the processability and thermal properties of phthalonitrile resins could be improved further by modifying the structure of comonomer in this kind of curing system. © 2018 Society of Chemical Industry