bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulating underactuated multibody dynamics using servo constraints and variational integrators
Authors: Leitz Thomas , Leyendecker Sigrid 
Published: December 2014

AbstractIn underactuated dynamical systems, the number of control inputs nu is smaller than the number of degrees of freedom nq. Real world examples include e. g. flexible robot arms or cranes. In these two exmples the goal is to prescribe the trajectory of an end effector and find the necessary control variables. One approach to model these problems is to introduce servo constraints in the equations of motion that enforce a given trajectory for some part of the system [1]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Usage of systematic multi‐body equations of motion for the design of a nonlinear vehicle dynamics controller
Authors: Nitzsche Gunter , Röbenack Klaus , Wagner Sebastian , Zipser Stephan 
Published: December 2014

AbstractIn this article the authors outline how systematic multi‐body equations can efficiently be used to derive a model for the design of a nonlinear vehicle dynamics controller for truck‐semitrailer combinations, steering the last trailer axle. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Geometric Approach to Actuator Failure in Robotic Manipulators
Authors: From Pål Johan , Pham Cong Dung , Gravdahl Jan Tommy 
Published: December 2014

AbstractThe use of robotic manipulators in remote and sensitive areas calls for more robust solutions when handling joint failure, and the industry demands mathematically robust approaches to handle even the worst case scenarios. Thus, a systematic analysis of the effects of external forces on manipulators with passive joints is presented. In parallel manipulators passive joints can appear as a design choice or as a result of torque failure. In both cases a good understanding of the effects that passive joints have on the mobility and motion of the parallel manipulator is crucial. We first look at the effect that passive joints have on the mobility of the mechanism. Then, if the mobility, considering passive joints only, is not zero we find a condition for which the parallel manipulator is conditionally equilibrated with respect to a specific external force. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modular modelling of a multiple pendulum with a guided box attached to its end
Authors: Weyh Bernhardt , Zwiers Ulrike 
Published: December 2014

AbstractA modular modelling strategy which combines motion equations in generalized coordinates with those formulated in terms of redundant coordinates is presented. The general idea is illustrated by the planar model of a multiple pendulum in the gravitational field whose upper end is spatially fixed, while its lower end is attached to an elastically guided box. It is shown how the governing differential‐algebraic system of equations can be reduced to a system of linear differential equations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropic viscohyperelastic behavior of intervertebral discs: Modeling and experimental validation
Authors: Azarnoosh Marzieh , Stoffel Marcus , Markert Bernd 
Published: December 2014

AbstractBiomechanical investigations of human cartilage, especially intervertebral discs (IVDs), have greatly helped to improve people's health over the last several decades. The study of the underlying biomechanical characteristics of cartilage tissues is a key issue to understand its physiological function and degeneration or damage behavior. The aim of this investigation is to describe the biomechnical behavior of healthy sheep IVDs under various loading conditions. Experimental and cartilage histological data, including fiber orientation, are used to develop a viscohyperelastic material model, which allowed us to numerically study the mechanical behavior of IVDs, consisting of a cartilaginous, fiber‐reinforced ring surrounding a highly hydrated, gelatinous core. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of Optimal Bounds on the Probability of Failure of Soft Biological Tissues
Authors: Balzani Daniel , Schmidt Thomas , Ortiz Michael 
Published: December 2014

AbstractIn this contribution, a methodology for the calculation of optimal bounds on the probability of failure of soft biological tissues is presented. Two potential rupture criteria are considered and an uncertainty quantification method [1] is applied to a virtual experimental data set. The results for both criteria are compared in a finite element example. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micro‐mechanical modeling of anisotropic inelastic response of soft tissues under supra‐physiological loading
Authors: Linka Kevin , Khiêm Vu Ngoc , Itskov Mikhail 
Published: December 2014

AbstractUnder supra‐physiological loading, soft tissues exhibit many inelastic phenomena, such as stress softening, hysteresis and permanent set [1]. Knowledge of the mechanical response of soft tissues under such a large range of deformation is vital for optimizations of vascular medical devices or improvement of injury prevention techniques. In this work, a micro‐mechanical model is proposed for soft collagenous tissues. Besides the anisotropy the model can also describe the aforementioned inelastic effects under extremal loadings. To this end, the dispersion of collagen fibers in the soft tissues is captured by a probability distribution of fiber orientations around preferred directions. The deformation induced damage inside the tissue is assumed to take place between collagen fibrils and is included within a statistical mechanical framework. Finally, the accuracy of the model is assessed by comparison with experimental data available in the literature. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growing between barriers
Authors: Bolea Albero Antonio , Böl Markus 
Published: December 2014

AbstractGrowth in living materials is the result of the changes in volume and mass during their development. If volume expansion occurs in a constrained case, some living materials change its growth behaviour. For example, when growth takes place in an environment with restrictions of volume, living materials will stop their volume expansion under compression due to the high amount of water that makes these bodies nearly incompressible. In case boundary conditions limit the growth of the body, the growth direction changes and gives the body another shape as expected. We present a modelling approach that takes volume and shape restrictions during growth into account. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A mechanical approach to explain cortical folding phenomena in healthy and diseased brains
Authors: Budday Silvia , Steinmann Paul , Kuhl Ellen 
Published: December 2014

AbstractThe development of the human brain with its characteristically folded surface morphology remains an intensively discussed topic. Impressive advancements in different fields of research have enhanced the understanding of the brain. However, the mechanism that underlies the folding process in healthy and diseased brains remains undetermined. Here, we hypothesize that growth induced mechanical instabilities drive folding. Using the nonlinear field theories of continuum mechanics supplemented by the theory of finite growth [1], we model the human brain as a bi‐material with the cerebral cortex, a morphogenetically growing outer layer of gray matter, and the subcortex, a strain‐driven growing inner core of white matter [2]. This approach integrates the two popular but competing hypotheses that cortical folding is either driven by differential growth or by axon elongation. Through systematic sensitivity analyses, we identify the critical process parameters of cortical folding and quantify their impact on brain morphology. We further simulate phenomena causing malformations like lissencephaly and polymicrogyria [3], which are associated with neurological disorders, including severe retardation, epilepsy, schizophrenia, and autism. Understanding the mechanisms of cortical folding during brain development might facilitate the diagnostics and treatment of malformed brains. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐dimensional, mechanical stimulation of cartilage implants
Authors: Fuhrmann‐Nelles Nadine , Rath Björn , Stoffel Marcus , Markert Bernd 
Published: December 2014

AbstractIn biomedical engineering, it is a common practice to replace injured cartilage by implants, which are seeded with human cartilage cells. Before implanting, the implants are cultivated and usually stimulated electrically or mechanically in a bioreactor to initiate cell multiplication and oriented cell growth.A new experimental set‐up is developed leading to the possibility of stimulating such implants in a multi‐dimensional, physiologically consistent way. In cooperation with the University Medical Centre Aachen, a human knee simulator is developed. Cell‐seeded implants are placed in a recreated human environment and stimulated with several load cycles of reproduced walking. After the cultivation period, the implanted material is removed and biologically and mechanically evaluated. The quality of the implanted material as well as the influence of the body‐conformable load on the material is studied.To understand the correlation between tissue remodelling and mechanical load history, the load and movement scenario is also numerically investigated. For this reason, the experiment is transferred to a geometrically realistic FE model of a human knee. As a first approach, an elastic material model is used. The aim is to have a predictive FE model with an optimal trade‐off between accuracy and efficiency using an appropriate material formulation. The results will be compared to experimental data. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiphasic Modelling of the Vertebral Bone for Cement‐Injection Studies
Authors: Bleiler Christian , Wagner Arndt , Stadelmann Vincent , Windolf Markus , Gueorguiev‐Rüegg Boyko , Köstler Harald , Boger Andreas , Ehlers Wolfgang , Röhrle Oliver 
Published: December 2014

AbstractThe stability of the human spine is highly dependent on the cancellous bone structure of the vertebra. In the case of osteoporosis and accompanied weaking of the vertebral structure, compression fractures and other lesions of the affected patient may occur. The reinforcement of the porous cancellous bone by the injection of bone‐cement is a common procedure in order to overcome this issues. The modelling and computational simulation of vertebroplasty, i.e., bone‐cement‐injection into the vertebra, is of major interest to obtain valid and reliable predicitions for this surgery. A detailed micromechanical (and locally single‐phasic) model exhibits the drawback that all geometrical and physical transition conditions of the individual parts and their complex microstructure have to be known. Therefore, this study considers a macro‐scopic (and multi‐constituent) continuum‐mechanical model based on the Theory of Porous Media, where the homogenisation of the underlying micro‐structure results in a model of three constituents. In particular, these are the solid bone skeleton, which is saturated by bone marrow, where the latter may be displaced by the injected liquid bone cement. The micro‐architecture is regarded by heterogeneous and anisotropic permeability tensors and the preferred directions of the trabecular bone structure. The presented strongly coupled macroscopic model offers the opportunity to not only simulate the flow of the pore fluids but also predicts the arising stresses and strains of the solid bone skeleton due to the numerical investigation of the injection process. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and computation of acrylic bone cement injection and curing within the framework of vertebroplasty
Authors: Landgraf Ralf , Ihlemann Jörn , Kolmeder Sebastian , Lion Alexander , Lebsack Helena , Kober Cornelia , Schmölz Werner , Blattert Thomas R. 
Published: December 2014

AbstractThis contribution deals with the simulation based investigation of processes related to the surgical treatment of vertebroplasty. In this regard, a simulation framework has been developed, which includes the generation of microstructural computer models of cancellous bone structures, the simulation of bone cement injection by computational fluid dynamics (CFD) methods and finite element (FE) simulations of bone cement curing processes. The modelling and computation strategy is illustrated and different material modelling approaches for the representation of acrylic bone cements as a non‐linear fluid and a non‐linear viscoelastic solid with curing dependent properties are outlined. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mathematically modelling surface EMG signals
Authors: Mordhorst Mylena , Heidlauf Thomas , Röhrle Oliver 
Published: December 2014

AbstractComprehension and correct interpretation of EMG signals and their generation could still be well improved. Computational models that can predict the EMG signal resulting from realistic motor unit recruitment as well as the underlying biophysical processes of single skeletal muscle fibres are therefore highly desirable. Having such a model available, one can test, verify and improve algorithms determining motor unit recruitment. Here, we present a three‐dimensional, continuum‐based, forward model that is able to produce a virtual EMG signal based on the underlying biophysical principles of skeletal muscle fibre activation. The result is a virtual EMG signal for complex and realistic geometries that may even undergo deformations as in the case of dynamic contractions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational Phase Field Modeling of Fracture Caused by Fluid Transport in Poroelastic Solids
Authors: Ulmer Heike , Mauthe Steffen , Miehe Christian 
Published: December 2014

AbstractThe numerical modeling of failure mechanisms due to fracture based on sharp crack discontinuities is extremely demanding and suffers in situations with complex crack topologies. This drawback can be overcome by recently developed diffusive crack modeling concepts, which are based on the introduction of a crack phase field. Such an approach is conceptually in line with gradient‐extended continuum damage models which include internal length scales. In this paper, we extend our recently outlined mechanical framework [1–3] towards the phase field modeling of fracture in the coupled problem of fluid transport in deforming porous media. Here, extremely complex crack patterns may occur due to drying or hydraulic induced fracture, the so called fracking. We develop new variational potentials for Biot‐type fluid transport in porous media at finite deformations coupled with phase field fracture. It is shown, that this complex coupled multi‐field problem is related to an intrinsic mixed variational principle for the evolution problem. This principle determines the rates of deformation, fracture phase field and fluid content along with the fluid potential. We develop a robust computational implementation of the coupled problem based on the potentials mentioned above and demonstrate its performance by the numerical simulation of complex fracture patterns. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A gradient‐enhanced continuum damage model for fibre‐reinforced materials at finite strains
Authors: Waffenschmidt Tobias , Polindara César , Menzel Andreas 
Published: December 2014

AbstractThe assumption of purely local continuum damage formulations may imply a loss of well‐posedness of the underlying boundary value problem. With regard to numerical methods such as the finite element method, this may lead to mesh‐dependent solutions, a vanishing localised damage zone upon mesh refinement, and hence physically questionable results. In order to circumvent these deficiencies, i.e. to regularise the problem, we, in this contribution, apply a non‐local gradient‐based damage formulation within a geometrically non‐linear setting allowing for large deformations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the gradient enhancement of microplane damage models
Authors: Zreid Imadeddin , Kaliske Michael 
Published: December 2014

AbstractThe microplane model allows for the description of damage induced anisotropy in a natural manner by introducing constitutive laws for quantities on individual microplanes at each material point. However, if damage or other strain softening constitutive laws are used within the microplane approach, the well‐known problem of localization arises leading to pathological mesh dependency. This contribution focuses on the implicit gradient enhancement and its efficient application to regularize microplane damage models. Previous works enhanced the strain tensor, thus resulting in large number of additional degrees of freedom. A new method which enhances the equivalent strain driving the damage on each microplane is introduced. The new method limits the number of additional degrees of freedom to one, while preserving the regularizing effect. The capabilities of the proposed formulation are demonstrated by a numerical example. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of fiber‐reinforced PMMA at different scales
Authors: Díaz Guillermo , Mosler Jörn 
Published: December 2014

AbstractThis paper deals with the modeling of fiber‐reinforced PMMA. Focus is on the macroscopic mechanical response with emphasis on the fracture properties such as the ultimate strength and the fracture energy. In order to capture the macroscopic mechanical response of PMMA, a finite element formulation is presented. While the elastic response of the fibres and that of the surrounding matrix are modelled in standard manner, i.e., by standard bulk material models, the relevant failure modes such as cracking of the fibres are accounted for by means of the so‐called Strong Discontinuity Approach (SDA). Since the fibres are relatively small, their fracture mechanical properties crucially depend on their geometry, i.e., they show a pronounced size effect. Based on numerical analyses of fibres with different geometries, the aforementioned size effect is naturally incorporated into the formulation [1]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Three‐dimensional cell model analysis of ductile damage under dynamic loading condition
Authors: Gerke Steffen , Kuhnt Kevin , Brünig Michael 
Published: December 2014

AbstractThe paper deals with the damage and fracture behavior of ductile metals under dynamic loading conditions. The in [1–3] presented phenomenological continuum damage and fracture model, which takes into account the rate‐ and temperature‐dependence of the material, provides reasonable results of experiments with high strain rates while the identification of the corresponding material parameters results difficult from the available experimental data. This lack of information can be resolved by micro‐mechanical numerical simulations of void containing unit‐cells. In this context results of dynamic micro‐mechanical simulations are presented which can be used to study the damage effects on the micro‐scale and to validate the rate‐dependent continuum damage model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
PROCRACK‐A Software Tool for Finite Element Simulation of Three‐Dimensional Fatigue Crack Growth
Authors: Ludwig Christian , Rabold Frank , Kuna Meinhard 
Published: December 2014

AbstractThe lifetime of structural components is limited by fatigue cracks. After initiation from an existing defect the crack grows subcritically until it reaches a critical size. At this point it becomes unstable and the structural component fails. PROCRACK is a powerful tool that enables the commercial finite element software Abaqus to calculate the crack propagation in pre‐cracked components. The complete capability of Abaqus can be used to simulate nearly arbitrary geometries. Abaqus/CAE is used for the three‐dimensional modeling of the initial crack at a geometrical level by means of points, lines and triangles. The numerical analysis is performed by Abaqus/Standard. PROCRACK automatically generates a tube‐shaped submodel around the crack front to calculate the stress intensity factors with high accuracy. The Paris law or the NASGRO equation can be used to calculate the incremental crack growth. The shape of the crack and the finite element mesh are updated in every crack growth step. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural damage detection strategy using correlation functions under inconsistent excitation
Authors: Zhang Muyu , Schmidt Rüdiger 
Published: December 2014

AbstractStructural damage detection using vibration response signals is appealing in recent years since it does not require the identification of the modal parameters or building the structures' finite element model, among which the correlation‐function‐based damage detection methodologies is a novel topic [1]. Beginning with the introduction of the correlation function theory, this paper proposes a new damage detection strategy using the auto correlation function values of vibration response signals of the structure. The maximum value of the auto correlation functions of the vibration responses from different measurement points are used to form the damage index to locate the damage. Differences of the damage index are used to make the damage location more clearly. As in real world applications, structures may undergo different external excitations [2]. Different external excitations are input into the intact and damaged structure. The results from numerical simulation of stiffness reduction detection of a 12‐story frame structure show that the proposed strategy can locate the damage correctly and has a very good anti‐noise ability under inconsistent external excitations. As only the vibration responses before and after damage are used in this damage detection strategy, it can be a useful tool for structural health monitoring. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Optimization of Slender Reinforced Concrete Columns
Authors: Bekdas Gebrail , Nigdeli Sinan Melih 
Published: December 2014

AbstractSlenderness is an important issue in design of reinforced concrete (RC) columns. Especially for long columns, second order effects may be not so small to neglect, but the calculation of second order effects may take too much time. For that reason, ACI 318 design code includes a simple approach in order to increase the flexural moment of columns according to their slenderness. Thus, second order effects are considered. In optimization, the effect of slenderness can be considered by using the factored design flexural moments. In this paper, harmony search (HS) algorithm is employed to find the optimum design variables of slender RC columns. These design variables are web width, height, diameter and number of reinforcements. The optimization objective is total cost of materials including concrete and steel. The developed method is effective to find the optimal design for axial force, flexural moment and shear force values. As numerical examples, optimum design of columns with different lengths, but with the same loadings and material properties were investigated. Thus, the effect of slenderness was seen on the optimum costs. By the increase of column length, increase of total material cost is more than a linear increase. This situation shows us the effect of slenderness on optimum RC columns (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)