bluuebunny/crossref_metadata_2025 huggingface dataset:
When Mesoporous Silica Meets the Alkaline Polyelectrolyte: A Controllable Synthesis of Functional and Hollow Nanostructures with a Porous Shell
Authors: You Liang , Wang Tianyi , Ge Jianping
Published: December 2012

An efficient and environment friendly surface‐protected etching method by using mesoporous silica as a template and alkaline polyelectrolyte as both the protecting and etching agent was developed to prepare a SiO2 nanotube with a porous shell. The polyelectrolytes attached to the template not only create a localized alkaline environment, but also effectively protect the silica surface, whereas the mesopore channels accelerate the diffusion of etchant throughout the template, all of which facilitate the formation of hollow structures in a fully controllable way. By tuning the etching power and protecting ability of the polyelectrolyte, the rigidity and porosity of products can be precisely manipulated. It is inspiring that various alkaline polyelectrolytes including polypeptide and dextran derivative can be used for the etching process, so that the porous and hollow nanostructures are born with positively charged and biocompatible surface as well as abundant amino groups for further coupling, which make them potential capsules for drug delivery and probes for imaging and detection. The protective etching process can also be extended to the preparation of yolk‐shell super structures with functional cores, or porous nanoparticle assemblies with their individual characteristics maintained.
Wave‐Mixed and Orbitally Shaken Single‐Use Photobioreactors for Diatom Algae Propagation
Authors: Lehmann Nicolai , Rischer Heiko , Eibl Dieter , Eibl Regine
Published: December 2012

Although vertical column, flat‐plate, tubular, bubble column and airlift photobioreactors are widely used for the cultivation of diatoms, it has been shown that bubble‐induced hydrodynamic stress created in these types of bioreactor can damage cells. Therefore, three single‐use surface‐aerated bag bioreactors, known for their outstanding results in cultivating shear‐sensitive mammalian cells, were for the first time investigated for their suitability in growing the model microalgae Phaeodactylum tricornutum. All of the systems, which were additionally aerated with CO2 and equipped with illumination systems providing different light qualities, guaranteed a 22‐ to 43‐fold increase in cell density within seven days, without any addition of cell protection agents or changes in cell morphology. Maximum cell density and dry biomass were achieved in the orbitally shaken 2D‐bag by using cool‐white fluorescent tubes.
Interlaboratory Test for Detection of Cytotoxic Leachables arising from Single‐Use Bags
Authors: Steiger Nina , Eibl Regine
Published: December 2012

An interlaboratory test for detection of cytotoxic leachables arising from single‐use bags was established and performed. Results from cultivations with two bag materials indicate that leachables influencing cell growth and metabolism were secreted. For the other seven bag materials a migration of leachables can be excluded.
Thiadiazole—a Promising Structure in Medicinal Chemistry
Authors: Li Yijing , Geng Jingkun , Liu Yang , Yu Shenghui , Zhao Guisen
Published: December 2012

Many compounds containing a five‐membered heterocyclic ring display exceptional chemical properties and versatile biological activities. In this Minireview, thiadiazoles are summarized according to their therapeutic potential, highlighting the versatility of this scaffold in medicinal chemistry. The unique properties of thiadiazoles are also discussed in relation to their potential effect on activity. Thiadiazole is a bioisostere of pyrimidine and oxadiazole, and given the prevalence of pyrimidine in nature it is unsurprising that thiadiazoles exhibit significant therapeutic potential. The sulfur atom of the thiadiazole imparts improved liposolubility, and the mesoionic nature of thiadiazoles makes these compounds better able to cross cellular membranes. By summarizing the thiadiazole‐containing compounds reported in recent decades, we aim to give a brief introduction to their synthesis and diverse biological activities, such as anti‐inflammatory, anticancer, antibacterial, antifungal, antiviral, antiparasitic, anticonvulsant, anticoagulant, antidiabetic, and to show the significant utility of the thiadiazole scaffolds in medicinal chemistry.
Facile Low‐Temperature Approach to Tin‐Containing ZnO Nanocrystals with Tunable Tin Concentrations Using Heterobimetallic Sn/Zn Single‐Source Precursors
Authors: Tsaroucha Marianna , Aksu Yilmaz , Epping Jan Dirk , Driess Matthias
Published: December 2012

Stannyl‐substituted [(RZn)4(OR′)4] cubanes with different tin‐containing alkoxy groups [Ph3SnOZnMe] (1), [Ph3SnOZnEt] (2), [Me3SnOZntBu] (3), and [Ph3SnOZntBu] (4) are easily accessible by Brønsted acid–base reaction of the corresponding triorganotin hydroxides with ZnMe2, ZnEt2, and Zn(tBu)2, respectively. All new compounds 1–4 were characterized by various spectroscopic methods and the structures of 1 and 3 were confirmed by single‐crystal X‐ray diffraction analysis. The thermal degradation of the precursors 1–4 under dry synthetic air (20 % O2, 80 %N2) was studied and the final oxide materials were characterized by employing powder X‐ray diffraction (PXRD) analysis, inductively coupled plasma‐optical emission spectrometry (ICP‐OES), transmission and scanning electron microscopy (SEM and TEM), energy dispersive X‐ray spectroscopy (EDX), and atomic force microscopy (AFM). Remarkably, compounds 1 and 2 proved to be suitable as single‐source precursors (SSPs) for the efficient preparation of tin‐doped ZnO nanoparticles with tunable tin concentrations as a promising system for steering and improving the optoelectronic properties of tin‐doped ZnO. Using 3 as SSP furnishes tin‐containing ZnO materials with good electron mobilities at relatively low processing temperatures (350 °C) for thin‐film transistor (TFT) applications. All the thin films of tin‐doped ZnO prepared by spin‐coating on silicon wafers are of great homogeneity and amorphous structure, which is promising for future applications in the field of transparent conducting oxides (TCOs).
Rapid and sensitive microbial analysis by capillary isotachophoresis with continuous electrokinetic injection under field amplified conditions
Authors: Phung Sui Ching , Nai Yi Heng , Powell Shane M. , Macka Mirek , Breadmore Michael C.
Published: December 2012

A highly sensitive capillary isotachophoresis method with LIF detection for microbial analysis was developed. This allowed the reliable analysis of Escherichia coli bacteria with a LOD of 14 cells in a sample volume of 100 μL, or 1.35 × 102 cell/mL, which is 47 times lower than reported by CE‐LIF and 148 times lower than CE‐UV with on‐line concentration. A leading electrolyte of 50 mM Tris‐HCl was used while the cells were diluted in 5 mM Tris HEPES as the terminator. To facilitate detection, cells were stained with the universal nucleic acid fluorophore SYTO 9. Continuous electrokinetic injection of the cells from the terminator under field amplified conditions concentrated cells into a single peak at the leader/terminator boundary allowing quantitation by measurement of peak height. The method was applied to water collected from two local streams, with only filtration through a 5‐μm syringe filter to remove large particulate matter followed by a ten times dilution in terminator, with total analysis time approximately 40 min. The detected cell numbers in the water samples by the isotachophoresis method were 3.70 × 105 cell/mL and 2.62 × 104 cell/mL, which were slightly higher than the 9.50 × 104 cell/mL and 1.96 × 104 cell/mL obtained by conventional microbiological plate counting.
An Evaluation of the Transdiagnostic Cognitive‐behavioural Model of Eating Disorders
Authors: Lampard Amy M. , Tasca Giorgio A. , Balfour Louise , Bissada Hany
Published: December 2012

Objective

To determine if the relationships between additional maintaining factors and core eating disorder maintaining mechanisms outlined in the cognitive‐behavioural model of eating disorders are transdiagnostic.

Method

Patients (n = 1451) diagnosed with anorexia nervosa, bulimia nervosa (BN) or eating disorder not otherwise specified completed the Eating Disorder Examination Questionnaire, Eating Disorder Inventory‐2 and Personality Assessment Inventory prior to entering treatment.

Results

Multi‐group structural equation modelling results suggested that low self‐esteem, overevaluation of weight and shape, and mood intolerance processes were transdiagnostic. However, some differences between diagnostic groups were observed. Dietary restraint was only positively associated with binge eating in BN, interpersonal difficulties were only associated with dietary restraint in eating disorder not otherwise specified and perfectionism was not associated with core eating disorder maintaining mechanisms in BN.

Discussion

A mixture of transdiagnostic and disorder‐specific processes was implicated in the maintenance of eating disorders, although longitudinal research is needed to validate results. Copyright © 2012 John Wiley & Sons, Ltd and Eating Disorders Association.
Degradable magnesium‐based implant materials with anti‐inflammatory activity
Authors: Peng Qiuming , Li Kun , Han Zengsheng , Wang Erde , Xu Zhigang , Liu Riping , Tian Yongjun
Published: December 2012

The objective of this study was to prepare a new biodegradable Mg‐based biomaterial, which provides good mechanical integrity in combination with anti‐inflammatory function during the degradation process. The silver element was used, because it improved the mechanical properties as an effective grain refiner and it is also treated as a potential anti‐inflammatory core. The new degradable Mg‐Zn‐Ag biomaterial was prepared by zone solidification technology and extrusion. The mechanical properties were mostly enhanced by fine grain strengthening. In addition, the alloys exhibited good cytocompatibility. The anti‐inflammatory function of degradation products was identified by both interleukin‐1α and nitric oxide modes. The anti‐inflammatory impact was significantly associated with the concentration of silver ion. It was demonstrated that Mg‐Zn‐Ag system was a potential metallic stent with anti‐inflammatory function, which can reduce the long‐term dependence of anti‐inflammatory drug after coronary stent implantation. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.
Benefits of using algae as natural sources of functional ingredients
Authors: Ibañez Elena , Cifuentes Alejandro
Published: December 2012

Algae have been suggested as a potential source of bioactive compounds to be used in the food and pharmaceutical industries. With the strong development of functional foods as a method to improve or maintain health, the exploration of new compounds with real health effects is now an intense field of research. The potential use of algae as source of functional food ingredients, such as lipids, proteins, polysaccharides, phenolics, carotenoids, etc., is presented, together with the different possibilities of improving valuable metabolites production either using the tools and the knowledge provided by marine biotechnology or improving the different factors involved in the production on a large scale of such metabolites. The bio‐refinery concept is also presented as a way to improve the efficient use of algae biomass while favouring process sustainability. © 2013 Society of Chemical Industry
Anaerobically digested food waste in compost for Agaricus bisporus and Agaricus subrufescens and its effect on mushroom productivity
Authors: Stoknes Ketil , Beyer David M , Norgaard Erik
Published: December 2012

Background

Source‐separated food waste is increasingly being treated by means of hygienisation followed by anaerobic digestion. The fibrous digester residue (digestate) is a potential mushroom substrate, while heat from the biogas can provide steam for the cultivation process. Using bag experiments the present study explored digestate as a full substitute for chicken manure conventionally used in mushroom composts.

Results

After mixing, a rapid temperature development in the compost was stimulated by a small amount of chicken manure, as aerobic microbial seeding. Mechanical elimination of lumps was essential for full mycelial colonisation. Three straw digestate composts had Agaricus bisporus mushroom yields above 370 g kg−1 substrate. The optimal compost water content was 600 g kg−1 at inoculation, and high digestate content (up to 500 g kg−1 by dry weight) did not affect yield for this species. High yields of A. subrufescens (200 g kg−1) were related to drier composts of lower digestate content (more straw) and lower pH values at inoculation.

Conclusion

Digestate successfully substituted chicken manure in straw composts without affecting mushroom yields for both species. There were no clear differences between straw digestate and control composts in terms of mushroom dry matter, size, nitrogen or ash content. © 2013 Society of Chemical Industry
Mucosal changes in laryngopharyngeal reflux—prevalence, sensitivity, specificity and assessment
Authors: Powell Jason , Cocks Helen C.
Published: December 2012

Objectives/Hypothesis:

A literature review regarding the use of laryngopharyngeal mucosal signs in diagnosing laryngopharyngeal reflux (LPR).

Study Design:

Literature review.

Methods:

A search of MEDLINE in February 2012 using the terms laryngopharyngeal reflux, laryngitis, mucosa, appearances, and signs (English language only).

Results:

One or more laryngopharyngeal mucosal signs associated with LPR were identified in 64% to 93% of healthy volunteers (3% >5 signs) and in 17% to 85% of gastroesophageal reflux disease sufferers (Reflux Finding Score [RFS] >7 in 24%). Reinke's edema, pseudosulcus, ventricular obliteration, vocal cord nodules, and granulomas have in some, but not all studies, been shown to be more prevalent in those with pH‐proven pharyngeal reflux. Pseudosulcus, interarytenoid thickening, and Reinke's edema were more prevalent in those symptomatic of LPR than those not. The use of multiple mucosal signs may improve detection of reflux sufferers from asymptomatic controls. The RFS has a sensitivity and specificity of 87.8% and 37.5%, respectively, for picking up pH‐proven pharyngeal reflux individuals. Inter‐ and intrarater reliability for identifying signs is fair to good in most studies.

Conclusions:

The limited evidence for each mucosal finding should be considered in making the diagnosis of LPR. Further quality research in to mucosal findings in LPR is needed.
Cases of Complete Integrability in Transcendental Functions in Dynamics and Certain Invariant Indices
Authors: Shamolin Maxim V.
Published: December 2012

The results of this work appeared in the process of studying a certain problem on the rigid body motion in a medium with resistance, where we needed to deal with first integrals having nonstandard properties. Precisely, they are not analytic, not smooth, and on certain sets, they can be even discontinuous. Moreover, they are expressed through a finite combination of elementary functions. However, the latter circumstances allowed us to carry out a complete analysis of all phase trajectories and show those their properties which have a “roughness” and are preserved for systems of a more general form having certain symmetries of latent type. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure preserving simulation of monopedal jumping
Authors: Koch Michael W. , Leyendecker Sigrid
Published: December 2012

This work considers the structure preserving simulation of three‐dimensional multibody dynamics with contacts. The used variational integrator is based on a discrete version of the Lagrange‐d'Alembert principle, which yields a symplectic momentum method. One of our main goals is to guarantee the structure preservation and the geometric correctness, thus we solve the non‐smooth problem including the computation of the contact configuration, time and force instead of relying on a smooth approximation of the contact problem via a penalty potential. In addition to the formulation of non‐smooth problems in forward dynamic simulations, we are interested in the optimal control of the monopedal high jump. The optimal control problem is solved using a direct transcription method transforming it into a finite dimensional constrained optimisation problem. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Planned contacts and collision avoidance in optimal control problems
Authors: Leyendecker Sigrid , Johnson Gwen , Ortiz Michael
Published: December 2012

In previous works, discrete mechanics and optimal control for constrained systems (DMOCC) has been introduced for the structure preserving simulation of optimal control problems for rigid multibody systems, whereby possible contacts or collisions between the bodies have been disregarded. In the formulation presented here, both collision avoidance as well as explicitly planned collisions between non‐smooth bodies are included. To this end, a subdifferentiable global contact detection algorithm, the supporting separating hyperplane linear program (SSHLP), based on the signed distance between supporting hyperplanes of two convex sets, is used in the simulation of optimal control problems. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Biphasic FEM Model for the Microperfusion in Liver Lobules
Authors: Werner Daniel , Ricken Tim , Dahmen Uta , Dirsch Olaf
Published: December 2012

The here presented 3D‐FEM model describes of microperfusion in liver lobules with the main focus on the remodeling of the microperfusion after a hepato‐venous outflow obstruction caused for example by liver resection. Via a dilatation and reorientation of small vessels within the lobule, the so called sinusoids, a connection between the obstructed and normal drained areas is established. For the remodeling of the microperfusion the phenomenological approach, namely that the reorientation of the sinusoids mainly depends on the blood pressure gradient, is applied. A biphasic homogenized approach within the framework of the theory of porous media (TPM) is chosen for the modeling of the microperfusion. This work sums up the constitutive equations for the biphasic model regarding the filter velocity and transversely isotropic permeability depending on our phenomenological approach. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiphasic modelling of human brain tissue for intracranial drug‐infusion studies
Authors: Wagner Arndt , Ehlers Wolfgang
Published: December 2012

A direct intracranial infusion of a therapeutic solution into the extra‐vascular space of human brain tissue is a promising medical application for the effective treatment of malignant brain tumours [1]. The advantage of this method, compared to an intra‐vascular medication, is the targeted delivery with the circumvention of the blood‐brain barrier (BBB), which prohibits the passing of therapeutic macro‐molecules across the vascular walls into the brain parenchyma.

The prediction of the resulting therapeutical distribution by a numerical simulation is challenging, since the spreading is affected by the complex nature of living brain tissue. For this purpose, a macroscopic continuum‐mechanical model is established within the Theory of Porous Media (TPM), proceeding from a homogenisation of the underlying micro‐structure [5]. The ternary four‐component model consists of an elastically deformable solid skeleton (composed of tissue cells and vascular walls), which is perfused by two mobile but separated liquid phases, the blood and the overall interstitial fluid (treated as a real two‐component mixture of the liquid solvent and the dissolved therapeutic solute). The strongly coupled solid‐liquid‐transport problem is simultaneously approximated in all primary unknowns using mixed finite elements (uppc‐formulation) and consequently solved in a monolithic manner with an implicit time‐integration scheme.

This numerical investigation allows the computational study of several circumstances influencing the irregular distribution of infused drugs, as observed in clinical studies. Therefore, the microstructural perfusion characteristics in the extra‐cellular space of the white‐matter tracts are considered by a spatial diversification of the anisotropic permeability tensors, provided by Diffusion Tensor Imaging (DTI). Furthermore, Magnetic Resonance Angiography (MRA) enables the in vivo location of blood vessels within the brain tissue. Finally, the selection of appropriate material parameters has a crucial influence on the drug distribution profile and further occurring effects beyond. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A geometrical model of skeletal muscle
Authors: Heidlauf Thomas , Röhrle Oliver
Published: December 2012

A multi‐scale and multi‐physics geometrical model of skeletal muscle is presented. Therein, the excitation‐contraction pathway is described by a biophysical cell model of systems biology; the propagation of action potentials along individual muscle fibres is represented by means of the monodomain equation; a continuum‐mechanical description of the mechanical behaviour of the entire muscle is employed that relies on an additive split of the second Piola‐Kirchhoff stress tensor.

Opposed to previous models, the multi‐physics problem is solved simultaneously using a staggered solution scheme that allows for a multi‐directional coupling between the different physical phenomena, and a parallel implementation is used. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A continuum model for free growth in living materials
Authors: Bolea Albero Antonio , Ehret Alexander E. , Böl Markus
Published: December 2012

We focus in this work on isotropically growing materials. An adaptive algorithm is used in order to maintain a stress‐free state during growth if no external loads are applied, but keeping the volume growth defined by a former kinetic. The proposed model is based on a modified multiplicative split of the deformation gradient into a growth part and an elastic part. The growth part will be isotropic if the elastic deformations are favourable, otherwise the growth will find a more comfortable direction. Three‐dimensional examples based on different kinetics are presented and discussed using the numerical model. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A numerical validation approach of a finite element muscle model using optical data
Authors: Sturmat Maike , Weichert Christine , Siebert Tobias , Böl Markus
Published: December 2012

Aim of this work is to obtain a convenient data set for the validation of a recently developed three‐dimensional constitutive muscle model. Therefore, an optical measurement technique is used to reconstruct a geometrical model of a rabbit soleus muscle. Thus, the muscle geometry and also the generated force characteristics are measured. The proposed numerical model is able to reproduce the experimental results in an adequate manner. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling quasi‐static crack growth with the embedded finite element method on multiple levels
Authors: Raina Arun , Linder Christian
Published: December 2012

The current work presents the multilevel approach of the embedded finite element method which is obtained by combining features of the method of domain decomposition with those of the standard embedded finite element method. The conventional requirement of fine mesh in a possible failure zone is rendered unnecessary with the new approach thereby reducing the computational expense. In addition, it is also possible to stop a propagating crack‐tip in the middle of a finite element. In this approach, the finite elements at the failure‐prone zone where cracks or shear bands, referred to as strong discontinuities which represent jumps in the displacement field, can form and propagate based on some failure criterion are treated as separate sub‐boundary value problems which are adaptively discretized during the run time into a number of sub‐elements and subjected to a kinematic constraint on their boundary. Each sub‐element becomes equally capable of developing a strong discontinuity depending upon its state of stress. A linear displacement based constraint is applied initially which is modified accordingly as soon as a strong discontinuity propagates through the boundary of the main finite element. At the local equilibrium, the coupling between the quantities at two different levels of discretization is obtained by matching the virtual energies due to admissible variations of the main finite element and its constituent sub‐elements. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strain induced damage of ductile materials under compression
Authors: Zapara Maksim , Tutyshkin Nikolai , H. Müller Wolfgang , Wille Ralf
Published: December 2012

The problem of ductile damage and failure prediction at the upsetting of cylindrical specimens with artificial voids is solved by taking a change in stress triaxiality into account. It is shown that such a more accurate assessment leads to a greater shift of stress triaxialities into a range of negative values as compared to their averaged values. At such values of stress triaxiality the material can be subjected to compression without failure under arbitrarily large deformations due to healing of micro‐defects. The constitutive equations of a recently developed tensorial framework for ductile damage [5] are applied to modelling. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microcrack Evolution in Functionally Graded Material under Dynamic Loading
Authors: Konchakova Natalia , Müller Ralf
Published: December 2012

The damage process of metal‐ceramic functionally graded material (FGM) is investigated. The microcrack evolution in a layered structure is analyzed using a numerical simulation of stresses and configurational forces. The modelling of an FGM of alumina ceramic and a metallic phase with gradually changing volume fraction of alumina is performed. A structure of two different layers bonded to a substrate is simulated. The stiffness and density of the three materials are varying. The evolution of configurational forces is simulated. The influence of the crack length on the crack driving force is studied for the case of a stress wave loading. The stress loading is applied in the horizontal direction as a dead load. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhancement of the micro mechanical basis for local approach cleavage models
Authors: Hardenacke Volker , Hohe Jörg , Friedmann Valérie , Siegele Dieter
Published: December 2012

The present study is concerned with the investigation of the micro mechanisms of micro defect nucleation in bainitic steels in order to provide an enhanced basis for probabilistic cleavage models. By a micro mechanical modelling of the cleavage initiation process the effects and the interactions of the relevant parameters can be identified. For this purpose Representative Volume Elements (RVE) of the micro structure are utilised, accounting for both, the grain structure as well as the brittle particles at the grain boundaries. The RVE's are loaded based on the local mechanical field quantities determined numerically at the cleavage origins of different fracture mechanics specimens. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
XFEM modeling of inelastic material behavior of composite
Authors: Müller Sebastian , Kästner Markus , Ulbricht Volker
Published: December 2012

In the present contribution the authors applied numerical homogenization techniques to predict the effective material behavior of composite based on the simulation of a representative volume element (RVE) [1]. An enriched displacement approximation (XFEM) is used to describe weak and strong discontinuities within the displacement field, independent from the underlying FE mesh. For the description of curved material interfaces a higher order XFEM formulation based on quadratic shape functions and consisting integration sub domains is developed. In order to incorporate microscopic damage effects, the XFEM approximation has been combined with a cohesive zone approach to model failure of the fiber‐matrix interface. The inelastic properties of the polymeric matrix material are described via constitutive relations of fractional viscoelasticity with process dependent viscous properties. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of deformation and failure in rubber‐toughened polymers – effect of distributed crazing
Authors: Helbig Martin , Seelig Thomas
Published: December 2012

A continuum mechanical model for rubber‐toughened polymers undergoing inelastic deformation solely by distributed crazing is introduced. Scaling relations with regard to microstructural parameters are derived analytically from a simple unit cell model. The constitutive model is calibrated from experimental data for a commercial ABS material and well captures various aspects of its deformation and failure behaviour. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of the local behavior of different cohesive zone models
Authors: Balzani Claudio
Published: December 2012

Cohesive interface elements are well suited for three‐dimensional crack propagation analyses as long as the crack path is known. This is the case e.g. in delamination analyses of laminated composite structures or failure analyses of adhesively bonded joints. Actually, they are widely used in such applications for both brittle and ductile systems.

As long as the strength and fracture toughness of the material are accurately captured it is generally accepted that the shape of the cohesive law has little to no influence on the mechanical behavior of the investigated structures. However, when having a look on the local behavior of different cohesive zone models, such as stress distribution in the fracture process zone, the results exhibit certain differences. These will be studied in the present contribution. Especially the local stress distribution will be investigated and the effect on the computational efficiency will be pointed out. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled multiscale finite element analysis of shell structures
Authors: Hebel Jochen , Gruttmann Friedrich , Wagner Werner
Published: December 2012

In this paper, a coupled two‐scale shell model is presented. A variational formulation and associated linearisation for the coupled global‐local boundary value problem is derived. The discretisation of the shell is performed with quadrilaterals, whereas the local boundary value problems at the integration points of the shell are discretised using 8‐noded or 27‐noded brick elements, or solid shell elements. The coupled boundary value problem is simultaneously solved within a Newton iteration scheme. Solutions for small strain problems are computed within the so‐called FE2 method. In an important test, the correct material matrix for the stress resultants assuming linear elasticity and a homogeneous continuum is verified. Examples show that the developed two‐scale model is able to analyse the global and local mechanical behaviour of heterogeneous shell structures. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of notches and cracks in circular Kirchhoff plates using the scaled boundary finite element method
Authors: Dieringer Rolf , Becker Wilfried
Published: December 2012

A new formulation of the scaled boundary finite element method (SBFEM) is presented for the analysis of circular plates in the framework of Kirchhoff's plate theory. Essential for the SBFEM is, that a domain is described by the mapping of its boundary with respect to a scaling centre. The governing partial differential equations are transformed into scaled boundary coordinates and are reduced to a set of ordinary differential equations, which can be solved in a closed‐form analytical manner. If the scaling centre is selected at the root of an existent crack or notch, the SBFEM enables the effective and precise calculation of singularity orders of cracked and notched structures. The element stiffness matrices for bounded and unbounded media are derived. Numerical examples show the performance and efficiency of the method, applied to plate bending problems. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Efficient Scheme for Stochastic Finite Element Solutions
Authors: Jablonski Philipp‐Paul , Nackenhorst Udo
Published: December 2012

The Polynomial Chaos expansion in Stochastic Finite Element Methods increases the size of the resulting linear systems dramatically. In iterative scheme which takes the underlying statistics into account is suggested for the efficient numerical solution. Additionally, an approach for the solution of von Mises stresses from the Polynomial Chaos representation of the displacement field is outlined. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive FEM with Stabilized Elements for Parameter Identification of Incompressible Hyperelastic Materials
Authors: Widany Kai‐Uwe , Mahnken Rolf
Published: December 2012

This work is concerned with the identification of material parameters for isotropic, incompressible hyperelastic material models. Besides the principal stretch‐based strain‐energy function by Ogden an invariant‐based strain‐energy function by Rivlin/Saunders is considered for which parameter sensitivities are derived. The identification is formulated as a least‐squares minimization problem based on the finite element method to account for inhomogeneous states of stresses and strains in the experimental data which is obtained by optical measurements. For the finite element method low‐order tetrahedral elements in a mixed displacement‐pressure formulation with stabilization are considered. Special attention is payed to an adaptive mesh‐refinement based on a goal‐oriented a posteriori error indicator to gain reliable material parameters. To approximate error terms an element‐wise recovery technique based on enhanced gradients is introduced. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solving hyperelastic problems using mixed LSFEM
Authors: Steeger Karl , Schwarz Alexander , Schröder Jörg , Starke Gerhard , Müller Benjamin
Published: December 2012

The focus of this contribution is the solution of hyperelastic problems using the least‐squares finite element method (LSFEM). In particular a mixed least‐squares finite element formulation is provided and applied on geometrically nonlinear problems. The basis for the element formulation is a div‐grad first‐order system consisting of the equilibrium condition and the constitutive equation both written in a residual form. An L2‐norm is adopted on the residuals leading to a functional depending on displacements and stresses which has to be minimized. Therefore the first variations with respect to both free variables have to be zero. The solution can then be found by applying Newton's Method. For the continuous approximation of the displacements in W1,p with p > 2, standard polynomials are used. Shape functions belonging to a Raviart‐Thomas space are applied for the stress interpolation. These vector‐valued functions ensure a conforming discretization of the Sobolev space H(div, Ω). Finally the proposed formulation is tested in a numerical example. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the coupling effects of the longitudinal and transverse displacements on the deformation and internal forces of functionally graded beams
Authors: Villamil Pedro , Zhang Chuanzeng , Chen Weiqiu
Published: December 2012

Functionally graded beams (FGBs) with an arbitrary gradation of the material properties along the thickness of the beams are analyzed. Such FGBs are of special interest in civil and mechanical engineering to improve both the thermal and the mechanical behaviour of the beams. In [1] and [3] free vibrations of functionally graded Timoshenko and Euler‐Bernoulli beams have been considered. The obtained analytical solutions are based on the work of Li [2], where closed‐form solutions of stress distributions, eigenfrequencies and eigenfunctions have been derived by means of a single differential equation of motion for the deflection. However, these previous works did not take into account the coupling between the longitudinal and the transverse displacements and its effects on the deformation and internal forces of the FGBs. This approach is appropriate only for a symmetrical material gradation but it may not be valid for general cases with an arbitrary material gradation.

In this paper, the coupling effects of the longitudinal and transverse displacements on the deformation and internal forces of FGBs are investigated for different beam support conditions. Analytical solutions of the corresponding boundary value problem are derived. A comparison is also made with the numerical results obtained by the finite element method (FEM). (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stress concentrations at free edges of shear webs
Authors: Kralovec Christoph , Schagerl Martin , Schröder Kai‐Uwe
Published: December 2012

This article analyzes the stress‐state of a shear web with free edges, i.e. a rectangular plate, which is loaded by shear on two simply supported opposite edges whereas the other two opposite edges can move freely and remain unloaded. Considering the plate's plane stress‐state it is obvious that at the corners the maximum equivalent stress occurs. If the plate does not buckle this stress determines its strength. However, the evaluation of the stress‐state at the corners raises some difficulties. As at these points the loaded and unloaded edges meet, the development of stress concentrations is indicated. Here the fundamental question arises if these stress concentrations remain finite or if singularities occur. To analyze this question we use both, analytical and numerical considerations. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shaking table tests of a model‐scale building with 2DOF pendulum mass damper
Authors: Majcher Krzysztof
Published: December 2012

In this paper, the numerical and experimental studies of a tall building's model with 2DOF pendulum mass damper (PMD) are considered. It is assumed that the model excitation is in the form of horizontal and/or torsional motion of the ground caused by earthquake.

The construction consists of the main system (tall building's model) and a double pendulum mass damper, which is attuned to the first (bending) and the second (torsional) eigenfrequencies of the main structure. The analysis focuses on reduction of structure vibration caused by horizontal or torsional component of ground motions. Therefore, results presented in this work show efficiency of 2DOF PMD for vibration reduction.

The numerical analysis of the problem is performed with using COSMOS/M system (a FEM numerical model is defined), while experimental analysis is carried out on a physical model‐scale building with 2DOF PMD. Model consists of twenty five recurrent storeys (height 2.5m) with a PMD located on the highest one. Shaking table device is used to simulate an earthquake excitation in horizontal and torsional component, independently. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material libraries for texturized thin metal sheets in elastic range
Authors: Montalvo‐Urquizo Jonathan
Published: December 2012

An approach for the simulation of the elastic material responses using stochastic generation of material samples and a subdomain‐based FEM simulation is presented. Both the single‐grain geometries and the lattice orientations are stochastically simulated. This simulations can be used to build a Material Library of responses which must be computed only once for a given material. Furthermore, the Library can be used in a fast two‐scale simulation avoiding any detailed computation in the microscale. In this contribution, the basic ideas of the computational algorithm are presented and some results of the material library for Steel DC01 are given. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hysteresis Effects in Abrasive and Frictional Contacts
Authors: de Payrebrune Kristin Miriam , Kröger Matthias
Published: December 2012

Grinding is a very complex and high dynamical material removal process with stochastically distributed grain engagements and strong varying local contact conditions. Over a long time only macroscopic effects are analyzed and predicted by empirical relations. To understand the dynamical behavior also local effects must be considered.

Therefore, the local contact conditions and especially the time‐dependent friction coefficient are analyzed. One detected effect is the dependency of the friction coefficient on the normal forces and on their time history, so a hysteresis loop occurs for increasing and decreasing values. With the force dependent friction coefficient local and dynamic effects are physically interpretable. In contrast, the global mean friction coefficient is constant over the entire force range which describes only quasi‐stationary effects. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Semi‐Analytical Method of Solving the Fokker‐Planck‐Equation for High‐Dimensional Nonlinear Mechanical Systems
Authors: Martens Wolfram
Published: December 2012

Stochastic processes are a common way of describing systems that are subjected to random influences. Technical systems may be excited by road roughness or wind gusts, for example, as well as fluctuating system parameters, which can all be described by stochastic differential equations. In previous works by the author and others (see [1], for example) it has been demonstrated how a Galerkin‐method can be used to obtain global numerical solutions of the Fokker‐Planck‐Equation (FPE) for nonlinear random systems. Computational efforts are reduced by orthogonal polynomial expansion of approximate solutions so that probability density functions (pdfs) for comparably high‐dimensional problems have been computed successfully. Stationary mechanical systems with dimensions up to d = 10 have been investigated, including polynomial as well as non‐smooth nonlinearities. This article presents results for different energy‐harvester‐systems under stochastic excitation, a field of research that has become the subject of increasing attention in the last years. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rotor Stator Interaction with Many Degrees of Freedom
Authors: Alber Oliver
Published: December 2012

A many‐degrees‐of‐freedom model of rotor stator contact is presented. The stability analysis of the synchronous motion of the simple JEFFCOTT rotor contacting a single‐mass stator is extended to systems with many degrees of freedom. The stationary synchronous motion as well as its stability are validated by direct numerical integration of the differential equations. The resulting dynamics is exemplified in two examples, which may be quite different than the dynamics of the simple JEFFCOTT rotor. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of viscous damping on friction induced travelling waves
Authors: Steindl Alois
Published: December 2012

We investigate the influence of viscous damping on the shape and stability of travelling waves induced by Coulomb friction between a rotating rigid shaft and an annular elastic cylinder. As expected, the damping causes the travelling wave solutions to become smoother and more stable. It also decreases the amplitude and range of separation solutions and may destroy the travelling waves by grazing bifurcations at large values of the damping parameters. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Phase Field Model for Martensitic Transformations
Authors: Schmitt Regina , Müller Ralf , Kuhn Charlotte
Published: December 2012

The martensitic transformation is described using a phase field model which is in mathematical terms the regularization of a sharp interface approach. In this work, up to two martensitic orientation variants are considered. The evolution of microstructure is assumed to follow a time dependent Ginzburg‐Landau equation. The coupled problem of the mechanical balance equation and the evolution equations is solved using finite elements and an implicit time integration scheme. In this work, the global energy evolution during the martensitic transformation and the influence of external loads on the formation of the different martensitic phases are studied in 2d. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On two different inverse form finding methods for hyperelastic and elastoplastic materials
Authors: Germain Sandrine , Steinmann Paul
Published: December 2012

This contribution focuses on two different developments of mechanical‐computational methods for the optimal determination of the initial shape of formed functional components knowing the deformed configuration, the applied loads and the boundary conditions. The first method uses an inverse mechanical formulation and can be applied to materials with hyperelastic behaviors. For materials with elastoplastic properties this method is not advocated, without knowing the final plastic strains, due to the non uniqueness of the solution. The second method uses a shape optimization formulation in the sense of an inverse problem via successive iterations of the direct problem. For hyperelastic materials the inverse mechanical formulation is preferred for its velocity and the non exhibition of possible mesh distortions. In the shape optimization formulation mesh distortions can be avoided by an update of the reference configuration of the functional part. Both methods are using a formulation in the logarithmic strain space. A numerical example for materials with isotropic elastoplastic behaviors illustrates the shape optimization formulation. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The boundary value problems of the full coupled theory of poroelasticity for materials with double porosity
Authors: Svanadze Merab
Published: December 2012

In this paper the full coupled quasi‐static theory of poroelasticity for materials with double porosity is considered. The basic boundary value problems (BVPs) of the steady vibrations are investigated. The uniqueness theorems of the internal BVPs of steady vibrations are proved. The basic properties of elastopotentials are established. The existence of regular solutions of the BVPs by means of the boundary integral equations method and the theory of singular integral equations is proved. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of predeformation‐ and frequency‐dependent material behaviour of filled rubber under large predeformations superimposed with harmonic deformations of small amplitudes
Authors: Wollscheid Daniel , Lion Alexander
Published: December 2012

Viscoelastic materials show a significant frequency and predeformation dependent behaviour under loadings consisting of large predeformations superimposed by small harmonic deformations. Based on further material models of Haupt & Lion [1] and Lion, Retka & Rendek [2] we introduce a recently developed constitutive approach of finite viscoelasticity in the frequency domain that is able to describe the frequency and predeformation dependent material behaviour with respect to storage and loss modulus. The constitutive equations are geometrically linearised in the neighbourhood of the predeformation and will be evaluated in the frequency domain. Furthermore a formulation for incompressible material behaviour is introduced and the corresponding dynamic modulus tensors are derived. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface Roughness Effects in Nanoindentation of Soft Polymers
Authors: Chen Zhaoyu , Diebels Stefan
Published: December 2012

In the present paper, the surface roughness effects in nanoindentation of soft polymers are modelled numerically based on the approach utilising the phenomenological concepts. A real surface topography is characterised by using multi‐level of protuberance‐on‐protuberance profiles. Following the real surface topography is simplified by one‐level or multi‐level sine curve profiles. Finally, the surface roughness effects are quantified related to the force‐displacement data as well as to the identified material parameters. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)