bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of the Sulfated Zirconia Nanostructure Characteristics on Physicochemical and Electrochemical Properties of SPEEK Nanocomposite Membranes for PEM Fuel Cell Applications
Authors: Mossayebi Zahra , Parnian Mohammad Javad , Rowshanzamir Soosan
Published: March 2018

This study expresses that the characteristics of sulfated zirconia (SZ) nanostructure in sulfonated poly(ether ether ketone) (SPEEK)‐based membranes is the key to optimize their properties for fuel cell applications. Two types of SZ treating in different thermal conditions are produced by precipitation and analyzed by X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, energy‐dispersive X‐ray analysis, and transmission electron microscopy. Sulfate concentration on both types of SZ is changing from 0.54 to 1.45 wt% and thus the SZ samples differ in particle size and sulfate content. The nanocomposite membranes are prepared by incorporating 6 wt% of SZ samples into SPEEK matrix in casting procedure followed by performing electrochemical characterizations and impedance spectroscopy. Moreover, morphology, mechanical, and chemical stability of the membranes are investigated by field emission scanning electron microscopy, stress–strain, and ex situ Fenton's tests. The incorporation of SZ sample having more surface sulfate groups in the SPEEK matrix results in not only excessive oxidative stability and tensile strength but also more acidic sites for ion transport, promoting conductivity. Furthermore, both types of nanocomposite membranes show improved ionic conductivity and water affinity with a lower tendency to swell rather than the plain SPEEK membrane. It is proved that desired consequences of doping SZ into SPEEK matrix can be intensified by changing the physicochemical properties of sulfated zirconia nanoparticles.
Chamber/Capsule‐Integrated Self‐Healing Coating on Glass for Preventing Crack Propagation
Authors: Choung Taedoo , Lim Jongkyeong , Won Dong‐Joon , Kim Joonwon
Published: March 2018

A transparent self‐healing coating incorporating chambers and capsules capable of preventing the propagation of cracks in glass is presented. The main features simultaneously satisfy the requirements of high transmittance (≈90% in the visible region) and the ability to heal random and large‐area cracks in coated‐glass materials (up to 6 cm long, 20 µm wide, and 1 mm deep per chamber). Additionally, the polymerized hydrogel used as the healing agent can stop crack propagation because of its high mechanical strength and good adhesion to glass. Remarkably, the healed glass can withstand a force approximately four times greater than what can be withstood by the unhealed glass after cracking.
A Novel Anisotropic Hydrogel with Integrated Self‐Deformation and Controllable Shape Memory Effect
Authors: Le Xiao‐xia , Zhang Yu‐chong , Lu Wei , Wang Li , Zheng Jing , Ali Israt , Zhang Jia‐wei , Huang You‐ju , Serpe Michael J. , Yang Xi‐tao , Fan Xin‐dong , Chen Tao
Published: March 2018

Although shape memory polymers have been highlighted widely and developed rapidly, it is still a challenging task to realize complex temporary shapes automatically in practical applications. Herein, a novel shape memory hydrogel with the ability of self‐deformation is presented. Through constructing an anisotropic poly(acrylic acid)–polyacrylamide (PAAc–PAAm) structure, the obtained hydrogel exhibits stable self‐deformation behavior in response to pH stimulus, and the shapes that formed automatically can be fixed by the coordination between carboxylic groups and Fe3+; therefore, self‐deformation and shape memory behaviors are integrated in one system. Moreover, the magnitude of auto‐deformation and shape memory could be adjusted with the concentration of corresponding ions, leading to programmable shape memory and shape recovery processes.
Cross‐linked peptide identification: A computational forest of algorithms
Authors: Yılmaz Şule , Shiferaw Genet A. , Rayo Josep , Economou Anastassios , Martens Lennart , Vandermarliere Elien
Published: March 2018

Chemical cross‐linking analyzed by mass spectrometry (XL‐MS) has become an important tool in unravelling protein structure, dynamics, and complex formation. Because the analysis of cross‐linked proteins with mass spectrometry results in specific computational challenges, many computational tools have been developed to identify cross‐linked peptides from mass spectra and subsequently interpret the identified cross‐links within their structural context. In this review, we will provide an overview of the different tools that are currently available to tackle the computational part of an XL‐MS experiment. First, we give an introduction on the computational challenges encountered when processing data from a cross‐linking experiment. We then discuss available tools to identify peptides that are linked by intact or MS‐cleavable cross‐linkers, and we provide an overview of tools to interpret cross‐linked peptides in the context of protein structure. Finally, we give an outlook on data management and dissemination challenges and opportunities for cross‐linking experiments.
The lantibiotic gallidermin acts bactericidal against Staphylococcus epidermidis and Staphylococcus aureus and antagonizes the bacteria‐induced proinflammatory responses in dermal fibroblasts
Authors: Bengtsson Torbjörn , Lönn Johanna , Khalaf Hazem , Palm Eleonor
Published: March 2018

Antimicrobial resistance needs to be tackled from new angles, and antimicrobial peptides could be future candidates for combating bacterial infections. This study aims to investigate in vitro the bactericidal effects of the lantibiotic gallidermin on Staphylococcus epidermidis and Staphylococcus aureus, possible cytotoxic effects and its impact on host‐microbe interactions. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of gallidermin were determined, and cytotoxicity and proinflammatory effects of gallidermin on fibroblasts, red blood cells (RBCs) and in whole blood were investigated. Both MIC and MBC for all four tested strains of S. epidermidis was 6.25 μg/ml. Both MIC and MBC for methicillin‐sensitive S. aureus was 12.5 μg/ml and for methicillin‐resistant S. aureus (MRSA) 1.56 μg/ml. Gallidermin displayed no cytotoxic effects on fibroblasts, only a high dose of gallidermin induced low levels of CXCL8 and interleukin‐6. Gallidermin hemolyzed less than 1% of human RBCs, and did not induce reactive oxygen species production or cell aggregation in whole blood. In cell culture, gallidermin inhibited the cytotoxic effects of the bacteria and totally suppressed the bacteria‐induced release of CXCL8 and interleukin‐6 from fibroblasts. We demonstrate that gallidermin, expressing low cell cytotoxicity, is a promising candidate for treating bacterial infections caused by S. epidermidis and S. aureus, especially MRSA.
Laser doppler imaging as additional monitoring after digital replanting: A prospective study
Authors: Schmid Marc , Seyed Jafari S. Morteza , Haug Luzian , Surke Carsten , Hunger Robert E. , Van De Ville Dimitri , Juon Personeni Bettina , Shafighi Maziar , Voegelin Esther
Published: March 2018

Background

Despite various exisiting monitoring methods, there is still a need for new technologies to improve the quality of post‐operative evaluation of digital replantation. The purpose of the study is using a laser Doppler imaging device (Easy‐LDI) as an additional tool to assess perfusion. In this method, the changes in the frequency of the laser ligth provide information regarding perfusion of the monitored tissue.

Patients and Methods

This study included seven patients (10 fingers; age of patients: 21–57 years) who suffered from a total (n = 6) or subtotal amputation (n = 4) due to accidents. In addition to hourly standard monitoring with clinical evaluation and skin thermometry, revascularized fingers were hourly monitored with Easy LDI for 48 h.

Results

LDI measurement values ranged between 0.8 and 223 (mean 90.62 ± 21.42) arbitrary perfusion units (APU). The mean LDI values before and after revascularization were 7.1 ± 2.85 and 65.30 ± 30.83 APU, respectively. For the successful revascularized fingers (8 of 10 fingers) values from 19 to 223 APU (mean 98.52 ± 15.48) were demonstrated. All of the replants survived, but due to venous occlusion two digits required revision 12 and 35 h after revascularization, respectively. In the two cases, Easy‐LDI also showed a constant and slow decline of the perfusion values. Furthermore, Pearson normalized correlation coefficient showed a positive significant correlation between temperatures of the replants and LDI‐values (P < .001, r = +0.392) and a negative significant correlation between Δtemperature and LDI‐values (P < .001, r = –0.474).

Conclusion

The LDI‐device might be a promising additional monitoring technique in detection of perfusion disturbance in monitoring digital replantations.
Reference dosimetry data and modeling challenges for Elekta accelerators based on IROC‐Houston site visit data
Authors: Kerns James R. , Followill David S. , Lowenstein Jessica , Molineu Andrea , Alvarez Paola , Taylor Paige A. , Kry Stephen F.
Published: March 2018

Purpose

Reference dosimetry data can provide an independent second check of acquired values when commissioning or validating a treatment planning system (TPS). The Imaging and Radiation Oncology Core at Houston (IROC‐Houston) has measured numerous linear accelerators throughout its existence. The results of those measurements are given here, comparing accelerators and the agreement of measurement versus institutional TPS calculations.

Methods

Data from IROC‐Houston on‐site reviews from 2000 through 2014 were analyzed for all Elekta accelerators, approximately 50. For each, consistent point dose measurements were conducted for several basic parameters in a water phantom, including percentage depth dose, output factors, small‐field output factors, off‐axis factors, and wedge factors. The results were compared by accelerator type independently for 6, 10, 15, and 18 MV. Distributions of the measurements for each parameter are given, providing the mean and standard deviation. Each accelerator's measurements were also compared to its corresponding TPS calculation from the institution to determine the level of agreement, as well as determining which dosimetric parameters were most often in error.

Results

Accelerators were grouped by head type and reference dosimetric values were compiled. No class of linac had better overall agreement with its TPS, but percentage depth dose and output factors commonly agreed well, while small‐field output factors, off‐axis factors, and wedge factors often disagreed substantially from their TPS calculations.

Conclusion

Reference data has been collected and analyzed for numerous Elekta linacs, which provide an independent way for a physicist to double‐check their own measurements to prevent gross treatment errors. In addition, treatment planning parameters more often in error have been highlighted, providing practical caution for physicists commissioning treatment planning systems for Elekta linacs.
Incorporating BIRD‐based homodecoupling in the dual‐optimized, inverted 1JCC 1,n‐ADEQUATE experiment
Authors: Saurí Josep , Bermel Wolfgang , Parella Teodor , Thomas Williamson R. , Martin Gary E.
Published: March 2018

1,n‐ADEQUATE is a powerful NMR technique for elucidating the structure of proton‐deficient small molecules that can help establish the carbon skeleton of a given molecule by providing long‐range three‐bond 13C─13C correlations. Care must be taken when using the experiment to identify the simultaneous presence of one‐bond 13C─13C correlations that are not filtered out, unlike the HMBC experiment that has a low‐pass J‐filter to filter 1JCH responses out. Dual‐optimized, inverted 1JCC 1,n‐ADEQUATE is an improved variant of the experiment that affords broadband inversion of direct responses, obviating the need to take additional steps to identify these correlations. Even though ADEQUATE experiments can now be acquired in a reasonable amount of experimental time if a cryogenic probe is available, low sensitivity is still the main impediment limiting the application of this elegant experiment. Here, we wish to report a further refinement that incorporates real‐time bilinear rotation decoupling‐based homodecoupling methodology into the dual‐optimized, inverted 1JCC 1,n‐ADEQUATE pulse sequence. Improved sensitivity and resolution are achieved by collapsing homonuclear proton–proton couplings from the observed multiplets for most spin systems. The application of the method is illustrated with several model compounds.
The ultimate intrinsic signal‐to‐noise ratio of loop‐ and dipole‐like current patterns in a realistic human head model
Authors: Pfrommer Andreas , Henning Anke
Published: March 2018

Purpose

The ultimate intrinsic signal‐to‐noise ratio (UISNR) represents an upper bound for the achievable SNR of any receive coil. To reach this threshold a complete basis set of equivalent surface currents is required. This study systematically investigated to what extent either loop‐ or dipole‐like current patterns are able to reach the UISNR threshold in a realistic human head model between 1.5 T and 11.7 T. Based on this analysis, we derived guidelines for coil designers to choose the best array element at a given field strength. Moreover, we present ideal current patterns yielding the UISNR in a realistic body model.

Methods

We distributed generic current patterns on a cylindrical and helmet‐shaped surface around a realistic human head model. We excited electromagnetic fields in the human head by using eigenfunctions of the spherical and cylindrical Helmholtz operator. The electromagnetic field problem was solved by a fast volume integral equation solver.

Results

At 7 T and above, adding curl‐free current patterns to divergence‐free current patterns substantially increased the SNR in the human head (locally >20%). This was true for the helmet‐shaped and the cylindrical surface. On the cylindrical surface, dipole‐like current patterns had high SNR performance in central regions at ultra‐high field strength. The UISNR increased superlinearly with B0 in most parts of the cerebrum but only sublinearly in the periphery of the human head.

Conclusion

The combination of loop and dipole elements could enhance the SNR performance in the human head at ultra‐high field strength.
Growth of Pacific White Shrimp Litopenaeus vannamei Cultured on Inland Low-Salinity Pond Soils
Authors: Pine Harvey J , Jescovitch Lauren N , Roy Luke A , Boyd Claude E , Davis D Allen , Brown Travis W
Published: March 2018

Low-salinity inland ponds in west Alabama were used to determine whether soil composition and water ionic profiles influenced shrimp growth. Soils from four farms were collected and placed into individual tanks equipped with airlift biofilters and 2.5‰ reconstituted seawater. Pacific white shrimp Litopenaeus vannamei were cultured for 42 d. Growth, survival, water, and sediment ionic profiles were analyzed at the end of the trial. There were no differences in survival among treatments. Shrimp grown on Farm 1 soil had the highest weight gain (4,244%), while shrimp cultured on Farm 3 soil grew the least (3,127%). Water placed in the tanks with Farm 1 soil had a lower calcium concentration (156 mg/L) and higher potassium (58 mg/L) and magnesium (80 mg/L), respectively, than water in the tanks with Farm 3 and Farm 4 soils. Differences were observed in soil pore water for potassium, sodium, exchangeable cations, sand–silt–clay composition, and organic matter. Sand–silt–clay composition indicated that soil from Farm 1 was characterized as sandy clay loam, while soils from Farms 2, 3, and 4 were clay loam. Shrimp growth was higher on sandy clay loam soil.
Effect of Pawpaw Carica papaya Seed Meal on Growth and as a Natural Sex-Reversal Agent for Nile Tilapia
Authors: Ugonna B O , Solomon S G , Olufeagba S O , Okomoda V T
Published: March 2018

This research investigated the use of pawpaw Carica papaya seed meal (PSM) as a natural sex-reversal agent in tilapia production and its effect on growth. Freshly hatched fry of Nile Tilapia Oreochromis niloticus were collected from brooders and randomly distributed (n =50) to 15 aquarium tanks (30 × 30 × 20 cm3). They were fed a commercial diet (35% crude protein) blended with varying levels of PSM (0, 2, 4, 6, and 8 g/kg) for 28 d. Fingerlings were then maintained in outdoor concrete tanks (1 × 1 × 1 m3) and were fed the commercial diet (without the inclusion of PSM) for 140 d. Growth evaluation and sexual phenotype of the fish were recorded during the treatment and recovery periods. The results obtained showed that growth of treated fish was significantly reduced compared to the control group during the treatment period; however, the trend reversed during the recovery period. The optimal PSM inclusion that gave the maximum weight gain (32.65 g) and masculinization percentage (82.19%) was 4.27 g/kg. The female phenotype was not noticed in treatments with inclusion levels greater than 2 g/kg; hence, reproduction was effectively controlled in the treated groups. However, percentages of fish with modified or reduced gonads significantly increased at 4-g/kg and greater PSM inclusion levels. Due to the biodegradable nature of PSM, it could be used as a viable alternative to popular synthetic hormones.
Singular boundary method based on time‐dependent fundamental solutions for active noise control
Authors: Li Junpu , Chen Wen
Published: March 2018

Active noise control is an efficient strategy of noise control. A numerical wave shielding model to inhibit wave propagation, which can be considered as an extension of traditional active noise control, is established using the singular boundary method using time‐dependent fundamental solutions in this study. Two empirical formulas to evaluate the origin intensity factors with Dirichlet and Neumann boundary conditions are derived respectively. In comparison with other similar numerical methods, the method can obtain highly accurate results using very few boundary nodes and small CPU time. These meet the major technical requirements of simulation of active noise control. The subsequent numerical experiments show that the proposed model can shield efficiently from the wave propagation for both inner and exterior problems. By applying the newly derived empirical formulas, the CPU time of the singular boundary method is further reduced significantly, which makes the method a competitive new and efficient meshless method. In addition, the singular boundary method makes active noise control in an online manner via time‐dependent fundamental solutions as its basis functions.
Stable isotope ecology and human palaeodiet in the northern coast of Santa Cruz (Argentine Patagonia)
Authors: Zilio L. , Tessone A. , Hammond H.
Published: March 2018

The aim of this paper is to provide information on the analysis of stable isotopes obtained from bones of marine and terrestrial fauna used as potential food by hunter‐gatherers on the northern coast of Santa Cruz province (Argentine Patagonia). The results from the isotopic ecology are analysed to contribute to dietary interpretations of the human populations who lived in this area. The mean of terrestrial resources is −19.1‰ ± 1.8‰ and 9.2‰ ± 2.6‰ for δ13C and δ15N, respectively. Meanwhile, marine resources recorded a mean of δ13C −12.5‰ ± 1.2‰ and δ15N of 19.4‰ ± 2.4‰. The analysed human samples come from different types of burials dated mainly in the Late Holocene. The δ13C and δ15N isotopic values on human remains suggest the existence of different diets during the Late Holocene, including people who consumed mainly marine, terrestrial, and mixed proteins, with a range between −18‰ to −10.4‰ and 12.4‰ to 23.4‰ for δ13C and δ15N, respectively. Some of these isotopic values, which indicate marine diets, are the highest recorded for Patagonia. The influence of the marine spray on the terrestrial trophic chains is suggested for the Patagonian Atlantic coast, evidenced by higher values in the δ15N of guanacos from the coast in relation to others studied from the hinterland.
Experimental Investigations of Brake Pad Shim Properties
Authors: Schmid Dominik , Gräbner Nils , von Wagner Utz
Published: March 2018

The understanding of NVH problems in brake systems becomes a strongly dominant remit in modern days. Finding solutions is the central task to achieve a calm and smooth system behavior.

Brake squeal on automotive disk brakes represents a high frequency noise phenomenon resulting in potential customer complaints. The avoidance of squeal causes high costs in the automotive industry worldwide. One countermeasure for this disruptive noise issue is the application of thin composites named shims bonded to back plates of brake pads. The selection of appropriate shims is according to the state of the art still mainly based on trial and error. Current approaches seem to map the effects of shims on brake squeal insufficiently. To describe the shim behavior in an improved manner, prior experimental investigations have to be carried out, focusing on the identification of modal damping and stiffness values.

The contribution shows experimental results of shims firmly bonded to brake pads and rectangular steel plates. Temperature variations and the analysis of nonlinearities like various excitation levels are examined in greater detail. As a result, the general influence of shims is presented and compared to measurements without damping materials. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of complex states for friction‐excited systems
Authors: Stender Merten , Tiedemann Merten , Hoffmann Norbert
Published: March 2018

For many engineering structures the dynamical response during operation is rarely stationary or regular. In fact, many studies on measured data reveal the irregular nature of dynamical system responses, for example in the field of research on brake squeal. Therefore, linear measures, such as amplitude and frequency spectra, cannot characterize the core dynamics contained in an irregular time series. Additionally, linear methods for damping extraction from measured signals tend to lose significance when it comes to irregular responses of self‐ excited systems. This work aims at highlighting the need for quantifiers from nonlinear time series analysis to adequately characterize real‐world vibration data. In a first step a minimal model is studied to relate nonlinear time series quantifiers to internal system states and dissipation considerations. The goal of this research is to develop an understanding for the information contained in time series data concerning dissipation mechanisms of complex friction‐excited systems. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal Control of Human Muscle‐Actuated Motion
Authors: Fehr Joerg , Fuhrer Julian , Gong Lulu , Schiehlen Werner
Published: March 2018

The question how the brain controls locomotion is a highly treated one. This topic is taken up in this study by means of human computational models, simulating the human musculoskeletal system actuated by advanced Hill‐type muscle models. A forward dynamic approach is considered allowing to simulate human motion independently from pre‐measured trajectories and enabling to resemble the control of the central nervous system – the motor command selection. It is suggested that movement paths arise implicitly through optimisation [1,4]. Hence, stimulation patterns passing through activation dynamics are determined by means of constrained optimal control problems with physiologically motivated objective functions. One advantage concerning the implementation within Neweul‐M2 is the possibility to apply well‐elaborated and tested optimisation algorithms available with Matlab to solve optimal control problems, enabling to employ the novel non‐linear model predictive control (NMPC). The introduced framework is applied to treat different biomechanical movement scenarios including reaching scenarios of the arm which are validated against experimental data from [2–4]. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Boundary Layer Machine
Authors: Ostermeyer Georg‐Peter , Vietor Thomas , Müller Michael , Inkermann David , Otto Johannes , Lembeck Hendrik
Published: March 2018

In multi‐body systems, friction often occurs as a result of the contact between two bodies. The resulting forces may be desirable or undesirable, depending on the intended function of a technical system. Although a number of different causes of these forces have been worked out, the scientific understanding required for a systematic adjustment of friction towards satisfying given requirements is still incomplete. This makes it difficult for the designer to design an optimal friction contact. This is reflected in a large number of scientific publications in the associated fields. In order to cope with these challenges, a new, holistic approach is required to recognize and describe the general design principles of friction contacts. Based on the understanding of these principles, design guidelines in a design catalog can be formulated to support designers. In further steps, the designer can parametrize the frictional contact based on a catalog of diverse possible solutions. In the future, this tool should help the designer to find a simple, fast, and effective solution. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibration Damping of Flexible Link Robots Using an Eye‐in‐Hand Camera
Authors: Pucher Florian , Gattringer Hubert , Müller Andreas
Published: March 2018

Due to their low weight robots with flexible links are ideal candidates for use in dynamically demanding applications. Since the main goal of the robot control is to achieve precise positioning, the damping of oscillations due to low stiffness is imperative. Furthermore classical PD motor position control is insufficient for vibration damping. This paper presents an approach using an eye‐in‐hand camera for vibration damping of an elastic articulated robot with three actuated joints. The idea is to use the position of feature points in the camera image for generating a feedback signal. The image feature position is transformed into the joint space using the image Jacobian. The PD motor control is augmented by a proportional term w.r.t. a virtual arm angle. Experimental results of a comparison with a control concept based on acceleration sensors are presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Motion by variation of the contact force on an inclined plane
Authors: Schorr Philipp , Zeidis Igor , Zimmerman Klaus
Published: March 2018

This paper describes non‐classical locomotion based on the variation of the contact force. The motion of a locomotion system on an inclined plane is considered. The contact force between the locomotion system and the inclined plane can be influenced by the motion of internal masses. Therefore a mechanical model with two internal masses is introduced. The friction between the locomotion system and the environment is described by COULOMB's law. The motion of this locomotion system is investigated and analyzed by using the averaging method of BOGOLJUBOV and MITROPOLSKI. Furthermore the influence of different parameters on the locomotion characteristics like the direction of movement, the stationary velocity and the maximum inclination angle is shown. A prototype based on this locomotion principle is built up for experimental investigations. Additionally, simulations are used to analyze the locomotion system. The experimental values are compared to the theoretically results and confirm the variation of the contact force as an option to enable a controlled locomotion. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Biomechanical evaluation of a femoral neck fracture implant using a novel test‐stand
Authors: Mundt Marion , Bettag Sebastian , Bamer Franz , Stoffel Marcus , Knobe Matthias , Markert Bernd
Published: March 2018

The ageing society leads to an increased risk of femoral neck fractures. Besides endoprotheses and established head‐conserving implants, the rotation‐stable screw anchor is used for surgical treatment. In this in vitro study, the influence of cemented versus non‐cemented implants is tested. Therefore, a novel test set‐up is used that is capable of simulating the load during gait cycles. Thereby, the transferability to clinical practise shall be increased. Additionally, time‐series data is recorded to evaluate clinically relevant parameters during the applied cyclical load. The results show that the test set‐up enables deeper insight to the implants behaviour during loading, which is of relevance due to the differences that can be observed between the cemented and non‐cemented implant. Additionally, the results are compared to the literature. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Personalized simulation of a bone–implant–system during a step forward
Authors: Roland Michael , Tjardes Thorsten , Bouillon Bertil , Diebels Stefan
Published: March 2018

In this study, a workflow is presented for a personalized simulation of a bone–implant–system of a fractured tibia during a step forward. The workflow is based on routinely acquired tomographic data, segmentation, material assignment, mesh generation, setup of realistic boundary conditions and a finite element simulation (FEM). In the absence of patient–specific monitoring data, a dataset from the OrthoLoad database is implemented as individualized boundary conditions. This allows a simulation of the bone–implant–system close to reality of patient's step forward. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A numerical analysis of the fracture toughness in phase‐field modelling of adhesive fracture
Authors: Hansen‐Dörr Arne C. , Hennig Paul , Kästner Markus , Weinberg Kerstin
Published: March 2018

We propose and analyse a phase‐field model which allows for adhesive interface failure between two materials by a local reduction of the critical fracture toughness over a given length scale in the vicinity of the interface. A parameter study is carried out which reveals a significant dependence of the cracking behaviour on the ratio between the length scale of the crack phase‐field model and the width of the adhesive interface. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Neural network representation of a phase‐field model for brittle fracture
Authors: Koeppe Arnd , Bamer Franz , Hernandez Padilla Carlos Alberto , Markert Bernd
Published: March 2018

Phase‐field models constitute a powerful tool in fracture mechanics. However, the main issues of these types of methods are the selection of the phase‐field model parameters, the numerical requirement of very finely meshed structures, and extremely small integration time steps. The subject of this work is the construction of an artificial neural network representing a finite element model coupled with a phenomenological phase‐field approach for brittle fracture. The approach is demonstrated on a notched plate in 2D. The neural network results and computation time is compared to established phase‐field models. After an initial training process, the neural network is able to predict the response of the complex system in a fraction of the time compared to the non‐local continuum mechanical model. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of Process Parameters on the Interlaminar Fracture Toughness of GF‐PA6‐Tapes
Authors: Schober Michael , Kuboki Takashi , Ameri Ehsan , Hohe Jörg , Peter Gumbsch
Published: March 2018

Interlaminar fracture toughness of consolidated, continuous glass fiber reinforced polyamide‐6 tapes, as well as its sensitivity to process parameters are investigated in this study. Therefore, consolidated plaques are manufactured, varying consolidation temperature and pressure, and their delamination behavior in mode I and mode II is analyzed by means of DCB and ENF tests. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The coupling of plasticity with a relaxation‐based approach to damage modeling
Authors: Schwarz Stephan , Junker Philipp , Hackl Klaus
Published: March 2018

Since damage occurs in context of high stresses that are also related to the development of plastic strains, it is natural to couple damage and plasticity phenomena to achieve a more realistic model. Hereto, the new damage model presented in [2] was used and enhanced with plasticity and isotropic hardening, as first shown in [1]. Thereby, the damage model is based on a new regularization approach and provides mesh‐independent results. In order to achieve mesh‐independence, damage models usually take into account the non‐local behavior by using a field function that couples the local damage parameter to a non‐local level, in which differences between the local and non‐local parameter as well as the gradient of the non‐local parameter can be penalized [3]. In contrast, the new regularization approach no longer needs a non‐local level at the finite element scale but directly provides mesh‐independent results. Due to the new variational approach, we are also able to improve the calculation times and convergence behavior. Furthermore, the enhancement with plasticity and isotropic hardening allows to investigate the influences between damage and plastic strains to each other as well as the resulting influences to the cracks. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of the Presta process – Transfer of deformation history
Authors: Scherzer Robert , Ihlemann Jörn
Published: March 2018

The Presta joining process is the world's leading manufacturing method for assembled camshafts. It is a multi‐stage forming process separated in different steps. First, the rolling of the shaft creates a local widening of the intended cam seat. Within the subsequent joining process, the cam is forced onto the widened cam seat to form a tight fit. The two substeps are modelled and simulated using FEM. Within the process large local deformations occur, which requires an appropriate material model. The phenomenological material formulation of finite strain viscoplasticity implemented in the introduced simulation model enables the transfer of the deformation history to a new reference configuration. Hence, at the change of simulation models this feature is applied by passing the material model's internal state variables of the rolling step to the initial FE‐mesh of the joining step. This work shows the simulation models of the Presta joining process and gives a detailed insight into the change of the reference configuration. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Co‐rotational extension of the Logarithmic finite element method
Authors: Schröppel Christian , Wackerfuß Jens
Published: March 2018

Modeling a plane Timoshenko beam, the approximation space of the standalone Logarithmic finite element (LogFE) method provides good approximations for moderate deformations, but deteriorates for large deformations. A co‐rotational extension of the method significantly improves the quality of the approximation for large deformations. However, due to the inability of the extended method to exactly represent low‐order polynomial deformation, the model does not fully converge with mesh refinement, suggesting the use of additional low‐order deformation functions in the co‐rotational update. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A quasi‐axisymmetric lattice model applied to analyze the vibrational contact between a PTFE shaft seal and a rotor
Authors: Albrecht Florian , Kletschkowski Thomas
Published: March 2018

Shaft seals shall prevent the leakage of oil and the intrusion of dirt particles in rotating machineries. A loss of contact between shaft and seal results in leakage. In order to ensure the functionality of the sealing system, the followability of the seal needs to be ensured. To analyze this problem, a model of a Polytetrafluorethylen (PTFE) shaft seal is coupled with an unbalanced rotor. PTFE has pronounced viscous and plastic characteristics. This leads – combined with other non neglectable nonlinearities – to a numerically challenging problem. To reduce the complexity and to increase the computational efficiency, the PTFE shaft seal is discretized by a quasi‐axisymmetric lattice model. The results show that loss of contact at rotor speeds close to the eigenfrequency of the rotor (high amplitude) and at high rotor speeds (high frequency) is possible and shall be avoided to prevent leakage. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rotor‐systems with compliant seals: A comparison of the rotordynamics using the Muszynska model and Hirs' lubrication equations
Authors: Bäuerle Simon , Hetzler Hartmut
Published: March 2018

This contribution compares two approaches for modelling seal fluid forces in a rotor system with compliant seal support: on the one hand side the non‐linear ODEs of the Muszynska model are used. On the other hand side Hirs' PDEs for turbulent lubrication flow are numerically integrated and an ODE coefficient model is fitted to this data. Simulations are performed with both fluid models and the results are compared: they show not only quantitative differences in the stability behaviour of the rotor‐system but also qualitative differences in the bifurcation behaviour. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the numerical approximation of invariant manifolds for quasiperiodic motions
Authors: Fiedler Robert , Hetzler Hartmut
Published: March 2018

The interference of oscillations with different physical origins with incommensurable frequencies can lead to quasiperiodic motions. Concerning engineering problems, there is a variety of models which exhibit multi frequent oscillations. This contribution proposes a numerical approach approximating stationary solutions by an invariant manifold. To apply the approach a partitioning of the phase variables is necessary, which defines the parametrisation of a dynamical system. In order to demonstrate the applicability of the proposed method, stationary solutions of an unbalanced Laval‐rotor (Jeffcott‐rotor) are calculated and continued under variation of a control parameter. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of Damping for Squeal Avoidance in Disc Brakes
Authors: Jekel Dominic , Hagedorn Peter
Published: March 2018

This paper deals with the optimization of the linear stability behavior of circulatory systems with respect to particularly advantageous damping properties. The technique is demonstrated by applying it to an industrial finite element model of a disc brake in order to reduce the propensity of squeal noise. After decomposing the damping matrix into several component matrices, which may have some special structure or physical relevance, the ratio of these are varied to either stabilize or make more stable the equilibrium state subject to sensible constraints. For the purpose of this study, a system is defined to be more stable if its eigenvalue with largest real part is as negative as possible. For a certain velocity range, it is shown to be beneficial to reduce the material damping in the pads and in the caliper, which might be counterintuitive from an engineer's perspective. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the modelling of curvature effects in fibre‐reinforced nanocomposites
Authors: Asmanoglo Tobias , Menzel Andreas
Published: March 2018

Motivated by the progress in nanoengineering over the past years, novel experimental approaches to characterise the material behaviour on the nanoscale have been developed which indicate that the material response on the nanoscale does not have to be identical with the one observed on the macro scale, i.e. size effects occur. However, experiments at the nanoscale are expensive and difficult to conduct, therefore necessitates the development of sophisticated modelling approaches which allow for predictive simulations at these scales. Regarding experimental findings on one‐dimensional nano‐materials presented in e.g. [1], and adopting the higher‐order gradient based modelling framework proposed in [2], the development of a fibre‐curvature based contribution to the stored energy function which results into well‐interpretable contributions to the stress‐ and to the couple stress tensor is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanical Modeling of the Strain‐Induced‐Crystallization in Polymers
Authors: Aygün Serhat , Klinge Sandra
Published: March 2018

The strain‐induced crystallization (SIC) in polymers is a phenomenon manifesting itself as the natural reinforcement caused by the high deformation or by the reduction of the temperature. It is typical for natural rubber, since this material contains more regularly oriented chains than the other polymers. Most of the models focusing on the modeling of polymers use the Langevin expression for the free energy as a basis [1]. The current work, however, treats a polymer affected by the strain induced crystallization as a heterogeneous medium consisting of regions with a different degree of network regularity. Such a concept allows the depiction of the nucleation and the growth of crystalline regions as well as the change of effective material parameters depending on the level of the strain applied. The model proposed is thermodynamically consistent. It is based on the assumptions for the free Helmholtz energy and dissipation potential. The inelastic deformations and degree of the network regularity are internal variables. Their evolution equations are derived according to the minimum principle of the dissipation potential. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Consistency of dynamic recrystallization models from the perspective of physical metallurgy and continuum mechanics
Authors: Bambach Markus , Klinge Sandra
Published: March 2018

Dynamic recrystallization (DRX) is characterized by the nucleation and growth of new grains, which takes place concurrently to plastic deformation. DRX processes are used in industrial hot forming operations to control the microstructure and properties of the workpiece. Various models have been developed that consider the coupled evolution of microstructure and flow stress during hot deformation processes, some from a perspective of physical metallurgy, some from continuum mechanics. It is widely accepted that the onset of DRX is characterized by an inflection point of the strain hardening rate as a function of stress. This criterion was derived by Poliak and Jonas using results from the thermodynamics of irreversible processes. The present paper analyses the conditions that need to be met by DRX models to be consistent with the criterion by Poliak and Jonas. It is shown that for models which use classical Avrami kinetics to describe the evolution of the recrystallized volume fraction, the Avrami exponent should exceed a value of 3 to ensure that the Poliak‐Jonas criterion is not violated. Based on this observation, a framework for consistent DRX kinetics is presented and discussed. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards a micromagnetics‐inspired framework for the modelling of variant switching in magnetic shape memory alloys
Authors: Bartel Thorsten , Kiefer Björn , Buckmann Karsten , Menzel Andreas
Published: March 2018

This contribution deals with a micromechanical model for the simulation of the magnetomechanical behaviour of magnetic shape memory alloys which captures effects such as martensite variant switching, domain wall motion, and the rotations of local magnetisations. It is revealed, however, that the implementation into micromagnetics‐inspired Finite Element schemes cannot be realized in a standard fashion but requires the treatment of state variables via macroscopic fields. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element modeling of laser beam welding for residual stress calculation
Authors: Herrnring Jan , Klusemann Benjamin
Published: March 2018

Numerous welding processes are used in naval, automotive and aircraft industries for joining structural components. Laser beam welding represents a key technology due to his low heat input and the high degree of process automation. Nonetheless, all welded materials are characterised by a strong change of microstructure in the heat effected and fusion zone. For simulation of residual stress fields the finite element method is the most often simulation tool. Reliable simulations have to take into account the changes in microstructure. Within this work, a viscoplastic material model for welding is presented, accounting for the solid and fluid phase, which is extended later on by a simple kinetic model to model precipitation hardening. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale modeling of thermoplastic PC/ABS blends
Authors: Hund Jonas , Seelig Thomas
Published: March 2018

Rubber‐toughened thermoplastic polymers such as PC/ABS blends exhibit a pronounced plastic dilatancy in their overall deformation behavior which results primarily from damage mechanisms in the ABS phase while PC behaves plastically incompressible, e.g. [1]. In this contribution, two commercial PC/ABS blends of different composition and morphology are approximated through appropriate unit cell models featuring the two constituents PC and ABS as distinct phases. Different visco‐plasticity models are utilized to capture the specific deformation behavior of each phase. Numerical studies of the unit cell models looking at the effect of the blend composition on the overall response are compared with experimental data. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Gold Microbeams with Higher Order Continuum Theories
Authors: Kandaz Murat , Dal Hüsnü , Ünlü Mehmet
Published: March 2018

Microbeams are building blocks for many microstructures as well as microelectromechanical systems (MEMS) and cannot accurately be modelled by classical continuum theories due to size effects based on their micro‐scale. These size effects can be taken into account by the so‐called higher order continuum theories. Modified Strain Gradient Theory (MSGT) and Modified Couple Stress Theory (MCST) are two commonly used theories, which extend the classical local continuum theories of grade one with the introduction of additional length scale parameters. In this contribution, the variational problem governing the elasticity of higher order beam formulation and the finite element implementation based upon, are briefly introduced. To this end, well known Euler‐Bernoulli beam formulation assumptions are used. The size effect for gold‐micro beams is demonstrated and the length scale parameters of gold microbeams for MSGT and MCST are identified form the existing experimental data from literature for the first time. As a novel aspect, significant size effect is demonstrated for the length‐scales associated with the state of the art gold microbeam structures developed for MEMS applications, which reveals the necessity of the use of higher order theories at these length scales. Advantages and drawbacks of these theories are also identified. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A multisurface model for gradient‐enhanced damage coupled to finite plasticity
Authors: Sprave Leon , Menzel Andreas
Published: March 2018

A gradient‐enhanced damage formulation is coupled to isotropic plasticity in the framework of finite strains. Within the finite element method, an additional field variable representing nonlocal damage is introduced and linked to its local counterpart in order to allow a standard local formulation at the material point level. The onset of damage and plasticity is governed by damage and yield criteria respectively. This multisurface approach requires the determination of the two Lagrange multipliers. By using logarithmic strains, a formulation in principal axes in combination with a von Mises yield criterion is implemented. The damage functions are defined by means of exponential functions in order to avoid further constraints on the local damage variable. The model is able to capture a wide range of material responses, ranging from brittle to ductile damage and plasticitiy dominated behaviour. The mesh independence of the model is shown by means of representative finite element examples. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)