bluuebunny/crossref_metadata_2025 huggingface dataset:
Boundary Crossing and Boundary Objects
Authors: Akkerman Sanne F. , Bakker Arthur
Published: April 2011

Diversity and mobility in education and work present a paramount challenge that needs better conceptualization in educational theory. This challenge has been addressed by educational scholars with the notion of boundaries, particularly by the concepts of boundary crossing and boundary objects. Although studies on boundary crossing and boundary objects emphasize that boundaries carry learning potential, it is not explicated in what way they do so. By reviewing this literature, this article offers an understanding of boundaries as dialogical phenomena. The review of the literature reveals four potential learning mechanisms that can take place at boundaries: identification, coordination, reflection, and transformation. These mechanisms show various ways in which sociocultural differences and resulting discontinuities in action and interaction can come to function as resources for development of intersecting identities and practices.
Social-Psychological Interventions in Education
Authors: Yeager David S. , Walton Gregory M.
Published: April 2011

Recent randomized experiments have found that seemingly “small” social-psychological interventions in education—that is, brief exercises that target students’ thoughts, feelings, and beliefs in and about school—can lead to large gains in student achievement and sharply reduce achievement gaps even months and years later. These interventions do not teach students academic content but instead target students’ psychology, such as their beliefs that they have the potential to improve their intelligence or that they belong and are valued in school. When social-psychological interventions have lasting effects, it can seem surprising and even “magical,” leading people either to think of them as quick fixes to complicated problems or to consider them unworthy of serious consideration. The present article discourages both responses. It reviews the theoretical basis of several prominent social-psychological interventions and emphasizes that they have lasting effects because they target students’ subjective experiences in school, because they use persuasive yet stealthy methods for conveying psychological ideas, and because they tap into recursive processes present in educational environments. By understanding psychological interventions as powerful but context-dependent tools, educational researchers will be better equipped to take them to scale. This review concludes by discussing challenges to scaling psychological interventions and how these challenges may be overcome.
Anatomy and palynology of endemic Stachys iberica Bieb. Subsp. Iberica var. densipilosa Bhattacharjee (Lamiaceae) from Turkey
Authors: Erkara Ismuhan Potoglu , Koyuncu Onur , Ardic Murat , Yaylaci Omer Koray
Published: April 2011

Bangladesh J. Bot. 39(2): 131-136, 2010 (December)
Isolation and characterization of bacteria from rusted iron materials
Authors: Khan Muhbubar Rahman , Saha Mihir Lal , Begum Nahmina , Islam Mohammad Nurul , Hoque Sirajul
Published: April 2011

Seventy bacterial isolates were recovered from different rusted iron materials using modified NP glucose, 9K and sulfur oxidizing media. Thirty four isolates were selected after primary screening on the basis of their growth in modified NP glucose medium. Out of 34 isolates 5 belonged to the genus Kurthia, 6 Thiobacillus, 16 Bacillus and remaining 7 were Acidiphilium, Oscillospira, Sulfobacillus, Alicyclobacillus, Neisseria, Pseudomonas and Rahnella. One of the isolated organisms, Bacillus megaterium (F16/2), was found to be thermophilic. The organisms showed better growth in presence of iron salts like ferrous sulfate, ferric sulfate and ammonium ferric citrate. Five isolates were found to transform ferrous (Fe2+) to ferric (Fe3+) of which Bacillus subtilis (F8) was most efficient. A good number of bacteria were associated with oxidation of iron. Key words: Isolation; Bacteria; Rusted iron; Transformation DOI: 10.3329/bjb.v39i2.7479 Bangladesh J. Bot. 39(2): 185-191, 2010 (December)
Effects of soil flooding on roots, photosynthesis and water relations in mungnean (Vigna radiata (L.) Wilczek)
Authors: Islam M Rafiqul , Hamid Abdul , Khaliq Quzi Andul , Haque M Moynul , Ahmed Jalal Uddin , Karim M Abdul
Published: April 2011

Two mungbean (Vigna radiata (L.) Wilczek) genotypes (GK48 - flood tolerant and BARImug5- flood susceptible) were flooded at vegetative and flowering stages for 5 and 10 days, respectively. Flooding damaged the lateral roots of GK48 wholly, but it recovered quickly by forming numerous adventitious roots. Flooding significantly reduced photosynthetic rate (Pn) and leaf water potential (Ψ1) in both the genotypes but GK48 tended to regain Pn and Ψ1 during postflooding phase. It appeared that GK48 withstands flooding to a great extent. Key words: Water potential; Mungbean; Root growth; Photosynthesis DOI: 10.3329/bjb.v39i2.7487 Bangladesh J. Bot. 39(2): 241-243, 2010 (December)
Effects of land ownership on psychological well-being of the poor farmers of the northern parts of Bangladesh
Authors: Huq Md Mozibul , Khan Azad , Jahan Md Sarwar , Haque Md Ariful
Published: April 2011

This study was designed to compare the psychological well-being of three categories of farmers in Bangladesh. They are the landless, Khas land allotees and the share-croppers. Charghat and Puthia Upazilla of Rajshahi District was the study area. Randomly selected 90 (30 from each group) respondents were the subjects of this study. To measure the psychological wellbeing the Bangla version of the MUNSH scale for Measuring happiness (Kazma and Stones 1980) was administered on the subjects. Results revealed that the psychological well-being of the Khas land allotees was best and psychological well-being of the landless was worst. On the other hand, the psychological well-being of the share-croppers was in between of the Khas land allotees and landless farmers. Key words: Psychological well-being; rural poor; landless; owner of the Khas land DOI: 10.3329/jles.v2i2.7496 J. Life Earth Sci., Vol. 2(2) 43-46, 2007
Rimbaud et Corbière se sont-ils lus ?
Authors: Ischi Stéphane
Published: April 2011

Cet article met en avant les nombreuses correspondances qu’entretiennent les poèmes d’Arthur Rimbaud et de Tristan Corbière. Dans la plupart des cas, aucun des deux auteurs n’avait connaissance du travail de l’autre au moment de la rédaction de son texte. Un fait retiendra spécifiquement notre attention : les analogies les plus troublantes avec Les Amours jaunes de Corbière se trouvent dans des œuvres de Rimbaud qui ne nous sont connues que par des manuscrits de la main de Verlaine, peut-être réécrits de mémoire bien après leur date de création. La fiabilité de ces « copies » verlainiennes est incertaine et fait l’objet de débats au sein de la critique rimbaldienne. Dans ce contexte, les « échos » corbiériens, au sein de poèmes de Rimbaud, pourraient être le signe d’une intervention de Verlaine dans les textes qu’il nous transmet. L’article constate à quel point les deux poètes semblent se mêler dans l’esprit de Verlaine, par exemple lorsqu’il les évoque dans ses Poètes maudits .
Interprétations croisées franco-russes du régime politique en Russie
Authors: Lapina Nathalia
Published: April 2011

Résumé Le passé historique peut-il expliquer le présent ? C’est un problème que se posent les spécialistes de la Russie contemporaine tant en France qu’en Russie. Les interprétations du régime politique postcommuniste sont fortement influencées par la lecture de l’histoire russe. Les objections formulées à l’égard de cette approche sont nombreuses : vision droitière lorsque l’histoire se projette sur le présent et même sur le futur, déterminisme, remplacement de la réalité politique et sociale par le passé historique. Une question reste à poser : comment intégrer les connaissances du passé dans la réflexion sur le monde contemporain ? L’approche historique est pertinente à condition que le chercheur ne se concentre pas uniquement sur le passé mais donne une image de la réalité politique, de la situation unique que nous vivons ici et maintenant.
Les socialistes, la Banque de France et le « mur d'argent » (1981-1984)
Authors: Duchaussoy Vincent
Published: April 2011

Résumé Cet article examine l’existence d’une opposition financière à l’exercice du pouvoir par les socialistes en France, pendant les trois premières années du premier septennat de François Mitterrand. Cette idée a déjà été exprimée sous l’expression de « mur d’argent », dont la réalité a été démontrée pour les expériences du Cartel des gauches et du Front populaire. Toutefois, la question restait entière pour la période des années 1980. Vincent Duchaussoy explicite les mythes et réalités de ce « mur d’argent » dans le contexte singulier de ces premières « années Mitterrand ». Une place particulière est accordée à l’étude du rôle de la Banque de France, qui fut dans les années 1920 la figure de proue de cette opposition financière. L’étude des rapports entre la Banque et l’État, principalement à travers la direction du Trésor, est un prisme éclairant pour l’histoire naissante de ces années 1980.
Le moment Allègre (1997-2000)
Authors: Prost Antoine , Bon Annette
Published: April 2011

Résumé Ministre de l’Éducation nationale de 1997 à 2000, Claude Allègre a lancé plusieurs réformes importantes avec un succès inégal. Cet article décrit sa politique et les raisons pour lesquelles elle a suscité une opposition croissante, qui débouche sur des grèves et des manifestations de rue si fortes que le Premier ministre, son ami Lionel Jospin, fut forcé de le renvoyer. Ce fut le premier ministre congédié sous la pression de la rue. Il mobilisa contre lui non seulement les enseignants, mais aussi les élèves et les parents. Les syndicats enseignants étaient divisés, et certains approuvaient ses projets, mais la vague de protestation était si puissante qu’il s’y joignirent. L’analyse des formes de mobilisation contre Claude Allègre montre comment le refus de la mondialisation néolibérale et de la marchandisation du savoir a été renforcé par un nouveau processus de production de l’opinion publique et d’appel aux manifestations par Internet. La mobilisation contre Claude Allègre apparaît ainsi comme l’émergence du mouvement qui, cinq ans plus tard, abat la Constitution européenne.
Secretive Marsh Bird Species Co-Occurrences and Habitat Associations Across the Midwest, USA
Authors: Bolenbaugh Jason R. , Krementz David G. , Lehnen Sarah E.
Published: April 2011

Because secretive marsh birds are difficult to detect, population status and habitat use for these birds are not well known. We conducted repeated surveys for secretive marsh birds across 264 sites in the Upper Mississippi River and Great Lakes Joint Venture region to estimate abundance, occupancy, and detection probabilities during the 2008 and 2009 breeding seasons. We identified species groups based on observed species co-occurrences. Two species, least bittern Ixobrychus exilis and American bittern Botaurus lentiginosus, co-occurred with other species less often than expected by chance, and two species groups, rails (Virginia rail Rallus limicola and sora Porzana carolina) and open-water birds (pied-billed grebe Podilymbus podiceps, common moorhen Gallinula chloropus, and American coot Fulica americana; coots were only surveyed in 2009), co-occurred more often than expected by chance. These groupings were consistent between years. We then estimated the relation of these species and groups to landscape and local site characteristics by using zero-inflated abundance models that accounted for incomplete detection. At the landscape level (5-km radius), the amount of emergent herbaceous wetland was positively associated with least bittern occupancy, whereas the amount of woody wetland was negatively associated with least bittern, rail, and open-water bird occupancy. At the local level, habitat variables that were associated with abundance were not consistent among groups or between years, with the exception that both least bitterns and open-water birds had a strong positive association between abundance and water–vegetation interspersion. Land managers interested in marsh bird management or conservation may want to consider focusing efforts on landscapes with high amounts of emergent herbaceous wetland and low amounts of woody wetland, and managing for high amounts of water–vegetation interspersion within the wetland.
Characterization of Resistivity of Sb2S3 Semiconductor Nanowires by Conductive AFM and In Situ Methods
Authors: Bukins Janis , Kunakova Gunta , Birjukovs Pāvels , Prikulis Juris , Varghese Justin , Holmes J.D. , Erts Donats
Published: April 2011

Conductive AFM and in situ methods were used to determine contact resistance and resistivity of individual Sb2S3 nanowires. Nanowires were deposited on oxidized Si surface for in situ measurements and on Si surface with macroelectrodes for conductive AFM (C-AFM) measurements. Contact resistance was determined by measurement of I(V) characteristics at different distances from the nanowire contact with the macroelectrode and resistivity of nanowires was determined. Sb2S3 is a soft material with low adhesion force to the surface and therefore special precautions were taken during measurements.
Stable Emission Characteristics of Low Work Function Amorphous Carbon Coated Transfer Mold Nickel Field Emitter Arrays in Harsh Environment
Authors: Nakamoto Masayuki , Moon Jong Hyun
Published: April 2011

Low work function amorphous carbon Transfer Mold field emitter arrays (a-C-FEAs) have been fabricated by combining the Transfer Mold emitter fabrication method and the emitter material coating method to realize stable vacuum nanoelectronic devices in harsh environments of aerospace. The emitter tips of a-C-FEAs are extremely sharpened to 26.7-30.7 nm of tip radii. Work function of a-C-FEAs was as low as 3.6 eV compared with those of conventional emitter materials such as carbon nanotube of 5.0 eV. Oxygen radical flux intensity of 1015 atoms/cm2•sec was used for the evaluation of field emission characteristics, whose value is 107-108 times higher than those of 107-108 atoms/cm2•sec in aerospace of satellite orbits. As the oxygen radical treatment time increased, turn-on fields of Ni-FEAs exhibited the 2.2 times degradation from 14.9 V/µm to 32.7 V/µm. Those of a-C-FEAs have been keeping almost the same value of 20.8-23.7 V/µm after oxygen radical treatment. The a-C-FEAs exhibit stable field emission characteristics in harsh environments.
Defect and Structure Engineering – Submicron Technology and Inverse Nanotechnology for Photo- and Ionizing Radiation Detectors
Authors: Vaitkus Juozas Vidmantis
Published: April 2011

A review is given of what kind technological aspects were used for realizing the defect engineering in semiconductor layers or crystals. The possibilities to change the free carrier capture are presented. The effect of Fermi level pinning at the surface levels allow to avoid the influence of barriers on the photoconductivity as well as to increase a role of recombination in the inter-crystalline region. The isovalent doping or the creation of the clusters allows transforming the defect distribution in the crystal bulk. The detector structure using the high electric field can introduce the recombination in at the contacts therefore allow diminishing a role of carrier capture in the bulk of structure. The cluster generation allows to increase the capture rate in the definite volume by a proton irradiation. The experience of different technologies for Si, GaAs, PbS, CdSe are presented.
P-N Junction Formation in ITO/p-Si Structure by Powerful Laser Radiation for Solar Cells Applications
Authors: Medvid' Artur , Onufrijevs Pavels , Dauksta Edvins , Barloti Janis , Ulyashin Alexander G. , Dmytruk Igor , Pundyk Iryna
Published: April 2011

The research report is devoted to the development of a new method of nanostructures formation in ITO/p-Si/Al structure with powerful laser radiation and study of its optical and electrical properties for solar cells applications. It was shown that after the structure irradiation by Nd:YAG laser second harmonic, dark current voltage characteristics become diode-like. Increase of ITO/p-Si/Al solar cell efficiency after irradiation by the laser, using photocurrent voltage characteristic method, was shown.
Application of Titanium Dioxide Nanorods in DSC Using Hydrothermal Method
Authors: Bin Ahmad Mohd Khairul , Murakami Kenji
Published: April 2011

Rutile titanium dioxide nanorods (TNR) were successfully prepared by hydrothermal method. By using hydrochloric acid (HCl) as chelating agent and titanium butoxide (TBOT) as precursor, aligned TNR with titanium nanoflower (TNF) was successfully prepared onto fluorine-doped tin oxide (FTO) at 150°C and 20 h. The influence of TBOT concentration on the surface morphology, structural properties and solar cell efficiency are discussed. The highest light-to-electric energy conversion efficiency, 0.4% is achieved using different concentration under simulated solar light illumination of 100 mWcm-2 (1.5 AM).
Numerical Investigation of the Limiting Sliding Condition of Polyoxymethylene with Various Sliding Geometry
Authors: Takagi Youhei , Sone Akihiro , Mizoguchi Kensaku , Okano Yasunori , Okuizumi Ryo , Kada Masahiro , Hirota Shinichi , Tajima Yoshihisa
Published: April 2011

A numerical simulation code was developed for estimating the surface temperature of POM wear test with different shapes. By using the developed code, the effect of sliding geometry with various contact areas on the surface temperature was numerically investigated. The simulation results show that the limiting sliding velocity depends on contact area and reaches a peak value at a certain geometry. It was also found that the simulation code leads an exact prediction of limiting velocity in the range of small contact area. This is important since the exact temperature measurement is very difficult in this range.
Lidocaine Loaded Ca/P Scaffolds for Bone Regeneration and Local Drug Delivery
Authors: Loca Dagnija , Locs Janis , Gulbis Juris , Salma Ilze , Berzina-Cimdina Liga
Published: April 2011

Local drug delivery devices especially based on osteoconductive porous calcium phosphate ceramics are of clinical importance. However, the brittleness, pore structure, porosity and pore size should be controlled for their wider applications in hard tissue implants and load bearing compartments. An approach to the fabrication of the bone graft exhibiting bone regeneration function as well as the local drug delivery was made. Hydroxyapatite (HAp)/β-tricalcium phosphate (β-TCP) porous scaffolds were prepared and mechanical properties (compression strength 20MPa), porosity (>50%), pore size (60-350µm) and structure as well as interconnectivity of pores were investigated. Porous scaffolds were impregnated with 4-5 mg of lidocaine hydrochloride (LidHCl) and drug release rate was evaluated and compared for scaffolds with and without poly lactic acid (PLA), poly(-caprolactone) (PCL) and polyvinyl alcohol (PVA) coatings. From in vitro dissolution tests it was seen that biopolymer coatings sustained the drug release up to 12h.
Staphylococcus Epidermidis and Pseudomonas Aeruginosa Adhesion Intensity on a TiO2 Ceramic in an in Vitro Study
Authors: Pavlova Agnese , Reinis Aigars , Berzina-Cimdina Liga , Kroica Juta , Burlakova Aleksandra , Rubenis Kristaps
Published: April 2011

Extrusion is a perspective forming technology for obtaining objects with certain profile, important for the TiO2 application as biomaterial. Extruded samples were calcinated at 1100 °C, thermally treated in different atmospheres: at 1450 °C in air and at 1300 °C in vacuum. An approach was made to examine the adhesion and colonization intensity of Staphylococcus epidermidis and Pseudomonas aeruginosa on TiO2 ceramic in vitro. It was found that Ps.aeruginosa demonstrated higher adhesion and colonization intensity as S.epidermidis and TiO2 samples treated in vacuum demonstrated higher attachment of microorganisms as TiO2 samples treated in air. It was supposed that surface charge promoted the bacterial adhesion on the vacuum treated samples.
Gasification and Hydrogen Production from Waste Biomass with High Pressure Superheated Steam
Authors: Okajima Idzumi , Sako Takeshi
Published: April 2011

High pressure superheated steam above the critical temperature (374oC) and below the critical pressure (22.1MPa) of water was used to produce hydrogen gas from waste biomass efficiently. The targets are large amount of waste biomass such as livestock excrement and paper sludge. We investigated the effects of reaction temperature, pressure, time, catalyst and molar ratio of water to carbon in biomass on the decomposition efficiency of waste biomass and the productivity of hydrogen. Almost 100% of the decomposition efficiency and 1350-1550cm3 of hydrogen production per gram of dry biomass were realized in the presence of KOH catalyst at 700oC, 10MPa, 20min and 20 of molar ratio of water to carbon in biomass.
Subdural Electrocorticogram Measurement with a Minimally-Invasive Procedure Using an SMA-Manipulated Microelectrode Array
Authors: Yamakawa Toshitaka , Yamakawa Takeshi , Aou S. , Ishizuka Satoru , Suzuki M. , Fujii M. , Aoki Toru
Published: April 2011

We propose a subdural electrode array guided by a 0.3mm-diamter shape memory alloy guidewire for a minimally-invasive method of electrocorticogram recording. The measured electric characteristics showed that the proposed electrodes are compatible with the application of electrocorticogram recording. Somatosensory evoked potential was measured by the proposed method in the animal test in vivo. The results confirmed that the proposed electrode array is available for the electrocorticogram recording under a minimally-invasive surgery.
PMMA Wettability Caused by Ultraviolet Radiation
Authors: Dekhtyar Yuri , Lancere Linda , Polyaka Natalie , Sudnikovich Aleksander , Tyulkin Fyodor , Valters Valdis
Published: April 2011

Poly methyl metha acrylate (PMMA) is widely in use for eye prostheses and contact lenses. The latter is under ultraviolet radiation of Sun. Therefore the PMMA properties could be influenced and bring the patient to discomfort, because of polymer surface wettability alteration. The latter is under the focus of the present research. Wettability and electron work experiments show similar tendencies, also high correlation has been found between electron work function and absorption minimum area. More interestingly - surface electrical potential depended on exposure under light.
On-Line Monitoring of Random Stocks of Divisible Productions in Interrelated Warehouses
Authors: Guseynov Sharif E.
Published: April 2011

In the given work two stochastic continuous mathematical models for determining the random volumes of current stock are constructed and investigated. This stochastic models describe the dynamics of current stock of divisible homogeneous (the first model) and heterogeneous (the second model) productions at several interconnected warehouses.
Applications of High-Precise Three-Dimensional Measurement System
Authors: Hashimoto Takeshi , Kaneko Mitsuo , Rövid András , Ohta Hiroaki , Fukuda Akira , Aniya Masamu , Naito Nozomu , Enomoto Hiroyuki , Skvarca Pedro
Published: April 2011

To reveal the influence of global warming on glaciers, highly accurate observations of glacier movement must continue every year. It is thought that there is a close relationship between glacier moving speed and global warming. Thus, there have been precise, detailed observations of the movement of the Perito Moreno glacier in Patagonia of the Argentine Republic over the past five years. The measurement method of using GPS and an optical measuring instrument is generally used to monitor glacier movement, but the measurement accuracy attained is not optimal because of the huge size of the glacier. The measurement system used for the Perito Moreno observations, however, could realize high accuracy measurement over long distance. The measurement system is based on the principle of stereo measurement using cameras. This paper describes the results of the Perito Moreno glacier observations of this year and considers the effectiveness of glacier observation using cameras.
Laser Marking in Digital Encoding of Surfaces
Authors: Kanev Kamen D. , Gnatyuk Petro V. , Gnatyuk Volodymyr A.
Published: April 2011

In this work we consider some laser based methods and technologies for surface engraving and layered marking of opaque and transparent materials. Based on that, physical object surface and sub-surface layers can be enhanced with digital codes for augmented security and more advanced human-computer interactions. Laser procedures for creating digitally encoded layers in various materials are investigated and one of the mechanisms of laser-induced formation of marks (micro-cracks) in transparent materials is discussed in more details.
CFRP Drilling Model: Fiber Orientation Influence on Mechanical Load and Delamination
Authors: Bonnet Cedric , Benmohammed Brahim , Poulachon Gérard , Rech Joël , Girard Yannick
Published: April 2011

This paper presents a combined experimental and theoretical investigation and proposes a mechanical load modeling of a multidirectional layer CFRP drilling to avoid fibers delamination by a better choice of their orientations. A first step consists in working with unidirectional CFRP to correlate cutting mode (opening, shear and bending) with force level depending on the angular tool position. The discretisation of the cutting edge is employed to know the exact contribution of each elementary part of the edge, resulting in a complete drill operation modeling (tip penetration, full engagement and exit). A second step consists in using this unidirectional approach to model a multidirectional layer CFRP drilling. In this case, layers are cut simultaneously which induce brutal mechanical load variation. A summation method is used to estimate the force level depending on fiber arrangement. Optimal orientation combinations are underlined by this approach, in order to improve the CFRP design, by considering the manufacturing concerns.
FEM Based Design of a Chip Breaker for the Machining with PCD Tools
Authors: Gonzalo Oscar , Quintana Iban , Etxarri Jon
Published: April 2011

This paper presents a methodology to design and manufacture a chip breaker in a PCD turning tool. The objective is to avoid the surface roughness and chip evacuation problems produced by long chips in turning processes. An analysis of the process is made to design a suitable chip breaker shape for semi-roughing and finishing operations in aluminum turning. FEM simulation and experimental test are used to understand the chip formation and breakage processes leading to improved chip breaker geometry. The new designed geometries are micromachined with laser in the PCD tools, and the improvement in the chip control is proved experimentally.
On Methodologies inside Two Different Commercial Codes to Simulate the Cutting Operation
Authors: Zhang Yan Cheng , Umbrello Domenico , Mabrouki Tarek , Rizzuti Stefania , Nelias Daniel , Gong Ya Dong
Published: April 2011

Nowadays, numerical simulation of cutting processes receives considerable interest among the scientific and industrial communities. For that, various numerical codes are used. Nevertheless, there is no uniform standard for the comparison of simulation model with these different software. So, it is often not easy to state if a given code is more pertinent than another. In this framework, the present work deals with various methodologies to simulate orthogonal cutting operation inside two commercial codes Abaqus and Deform. The aim of the present paper is to build a common benchmark model between the two pre-cited codes which can initiate other numerical cutting model comparisons. The study is focused on the typical aeronautical material - Ti-6Al-4V - Titanium alloy. In order to carry out a comparative study between the two codes, some similar conditions concerning geometrical models and cutting parameters were respected. A multi-physic comprehension related to chip formation, cutting forces and temperature evolutions, and surface integrity is presented. Moreover, the numerical results are compared with experimental ones.
Application of the Nodal Integrated Finite Element Method to Cutting: a Preliminary Comparison with the “Traditional” FEM Approach
Authors: Greco Francesco , Umbrello Domenico , Di Renzo Serena , Filice Luigino , Alfaro I. , Cueto Elías
Published: April 2011

FEM implicit formulation shows specific limitations in processes such as cutting, where large deformation results in a heavy mesh distortion. Powerful rezoning-remeshing algorithms strongly reduce the effects of such a limitation but the computational times are significantly increased and additional errors are introduced. Nodal Integration is a recently introduced technique that allows finite element method to provide more reliable results when mesh becomes distorted in traditional FEMs. Furthermore, volumetric locking phenomenon seems to be avoided by using this integration technique instead of other methods, such as the coupled formulations. In this paper, a comparison between a “classical” FEM simulation and the Nodal Integration one is carried out taking into account a simple orthogonal cutting process.
Simulation of the Temperature Distribution in NC-Milled Workpieces
Authors: Surmann Tobias , Ungemach Eduard , Zabel Andreas , Joliet Raffael , Schröder Andreas
Published: April 2011

In most cases the simulation of temperature distributions in machined workpieces is carried out by moving a heat source along a predefined workpiece model within a commercial FEM-system. For performance reasons, the material removal is often neglected or performed by removing small predefined parts of the workpiece. Furthermore, the heat source often has a constant heat flux and therefore it is not dependent on the current tool engagement. In this paper we present a voxel-based finite difference method for the thermal behavior of the process-state dependent workpiece, which is integrated into the milling simulation system NCChip, developed at the ISF. This simulation is capable of modeling the cutting forces along any arbitrary NC-path. Since the tool rotation and the cutting edges in this time domain simulation are divided into discrete angle steps and cutting wedges respectively, the thermal energy that is applied to the workpiece at each time step and at each cutting wedge can be computed as a fraction of the corresponding cutting work. In this way, the correct heat is introduced to the workpiece exactly at the current contact zone of the tool.
Inverse Flow Stress Calculation for Machining Processes
Authors: Yang Jae Bong , Wu Wei Tsu , Srivatsa Shesh
Published: April 2011

Finite element modeling of the machining process has been quite successful in recent years. The model can be used to better understand the interactions between chip flow, heat generation, residual stress, tool stress, tool wear, tool chatter and dimensional accuracy. One of the key inputs to the model is the high strain rate (>104 1/sec) flow stress data. The split Hopkinson bar test has been commonly used to measure the flow stress at these high strain rates. The method is expensive and typically limited to the strain rate range from 102 to 104 1/sec. To overcome these limitations, an optimization based inverse methodology was developed. In this technique, the measured and predicted cutting forces were matched by iteratively adjusting the coefficients in the flow stress constitutive model. Since the method requires many FEM simulations to reach the final optimal condition, a computationally efficient FEM solver using ALE (Arbitrary Lagrangian Eulerian) method was adopted to make the method practical. The method was validated with experimental data with excellent agreement.
Inverse Identification of Johnson-Cook Material Parameters from Machining Simulations
Authors: Shrot Aviral , Bäker Martin
Published: April 2011

A material model is a prerequisite to the modelling of machining processes. Owing to its versatility, the Johnson-Cook model is commonly used for machining simulations. Determination of the model parameters from experiments is challenging due to the large variations of strains, strain-rates and temperatures which lead to several problems. State-of-the-art experimental methods have to rely on data obtained from much lower strains and strain-rates than those encountered during machining. In this paper, an inverse method of identifying Johnson-Cook parameters from machining experiments is described. A fnite-element model of the machining process was created and a particular Johnson-Cook parameter set was taken from literature for the simulation. The Levenberg-Marquardt Algorithm was used to re-identify the material parameters by looking at the Chip-morphology and the Cutting force evolution. It is shown that the optimisation parameters and error function must be chosen carefully in order to achieve better solutions at lower computational expense.
The Numerical Investigation of Stress Distribution on the Rake Face for Grooved Cutting Tool Inserts
Authors: Kwiatkowska E. , Niesłony Piotr , Grzesik W.
Published: April 2011

The development of an accurate model for the shear and normal stresses on the rake face is very important for modeling of the metal cutting mechanics. It is known that the stresses vary over the contact surfaces of the tool and change substantially with their configurations. On the other hand, the recent attempts were generally addressed to orthogonal cutting process and tools with flat rake faces. At present, grooved tools with complex rake faces are commonly applied in the industry. In this study a plane strain finite element (FEM) program AdvantEdge was used to simulate the cutting process with some disposable grooved cutting tools. Both the reduced von Mises stresses and their components in x and y directions were considered and visualized for appropriate chip formation stages. In particular, the distribution of the contact stresses was revealed when chip breakage occurs. The simulated results were correlated with the geometry of the chip breaker and process parameters.
Strain Rate Effect on the Mechanical Behavior of Austenitic Stainless Steel during Machining
Authors: Barbosa Patrícia Alves , Machado Izabel Fernanda
Published: April 2011

Machining is characterized by a large amount of localized plastic strain on material due to chip formation; hence, there is a commitment among the strain process, strain hardening, and heat softening, generating shear bands. Understanding these shear zones is important because it contains information that can be applied to the improvement of machining techniques related to process optimization, and to materials and tools innovation. In this sense, the aim is to analyze the strain and the strain hardening with the strain rate variation as from the chip formed during the austenitic stainless steel AISI 304 turning. The results showed that the cut type, orthogonal or semi-orthogonal machining, affects the way the material strains, and that the strain rate has no significant effect on the strain and strain hardening of the austenitic stainless steel AISI 304 for the range investigated.
Prediction of Machining Induced Surface Integrity Using Elastic-Viscoplastic Simulations and Temperature-Dependent Flow Softening Material Models in Titanium and Nickel-Based Alloys
Authors: Ulutan Durul , Sima Mohammad , Özel Tugrul
Published: April 2011

In this study, the feasibility of predicting surface integrity and residual stresses by using elasto-viscoplastic finite element simulations and temperature-dependent flow softening constitutive material modeling is investigated. A friction determination method is proposed to identify friction coefficients in presence of tool flank wear. Serrated and cyclical chip formation has been simulated for using tools with and without flank wear. The predicted residual stresses and surface integrity is compared against experimental results from literature. Effect of friction on the residual stress profiles is also investigated. These results are highly essential in predicting machining induced microstructure alterations that are detrimental to fatigue life of nickel and titanium alloy components.
Prediction of Residual Stresses in Turning of Inconel 718
Authors: Torrano Ivan , Barbero Oscar , Kortabarria Aitor , Arrazola Pedro Jose
Published: April 2011

Heat-resistant alloys like Inconel 718 are used in critical components such as aircraft engine turbine discs. Surface integrity is a critical issue in this kind of components and specially residual stresses are a key aspect. Currently, the development and optimization of the machining process with regards to the residual stresses is done through expensive experimental trial and error methods. This article shows the research work made on the development of a machining model in three dimensions with the finite element code Abaqus / ExplicitTM aiming to predict residual stresses. Results obtained in different working conditions are compared with those of commercial programs as DeformTM and AdvantEdgeTM, so as with experimental results obtained in turning. The results obtained show on the influence of working conditions (cutting speed, feed per revolution) on the cutting forces and temperatures and the high degree of qualitative agreement with finite element modeling in the generation of surface residual stress.
Residual Stress Prediction by Means of 3D FEM Simulation
Authors: Attanasio Aldo , Ceretti Elisabetta , Cappellini Cristian , Giardini Claudio
Published: April 2011

In cutting field, residual stress distribution analysis on the workpiece is a very interesting topic. Indeed, the residual stress distribution affects fatigue life, corrosion resistance and other functional aspects of the workpiece. Recent studies showed that the development of residual stresses is influenced by the cutting parameters, tool geometry and workpiece material. For reducing the costs of experimental tests and residual stress measurement, analytical and numerical models have been developed. The aim of these models is the possibility of forecasting the residual stress distribution into the workpiece as a function of the selected process parameters. In this work the residual stress distributions obtained simulating cutting operations using a 3D FEM software and the corresponding simulation procedure are reported. In particular, orthogonal cutting operations of AISI 1045 and AISI 316L steels were performed. The FEM results were compared with the experimental residual stress distribution in order to validate the model effectiveness.
3D-FEM Modeling of Gear Skiving to Investigate Kinematics and Chip Formation Mechanisms
Authors: Schulze Volker , Kühlewein Christoph , Autenrieth Hermann
Published: April 2011

Latest research clearly demonstrates the excellent capability of the gear skiving process. For further improvement of the process and particularly for the enhancement of the process reliability fundamental scientific research is conducted. In this paper the result of investigation of process kinematics and chip formation mechanisms are presented. First the experimental analyses will be described, which represent an essential basis for developing and validating the models. In further experiments the material behavior of the test material SAE 5120 was determined and a material model was developed. The modeling of the process represents a central aspect of the research. This includes the basic modeling of the kinematics in a 3D-model. The simulation enables analysis of the kinematical conditions as well as the chip formation mechanisms and evaluation of the effects on process reliability. The results support the tool and process design and are an important basis for the implementation of the process.
Influence of Hard and Soft Inclusions on the Machinability and Polishability of VP100 Mold Steel
Authors: Zanatta André Marcon , Gomes Jefferson De Oliveira , Bressan José Divo , Barbosa Celso Antonio
Published: April 2011

The aim of this study was to evaluate the influence of the amount and distribution of inclusions of titanium carbonitride and manganese sulfide on the machinability and polishability of Villares VP100 steel which is used in manufacturing polymer injection molds. By means of materials metallography, captured images were processed with image analysis software to characterize the inclusions. Tool life tests were performed in an open cavity in order to approach the real processes situation found in the toolmaking industry. The flank wear and chip formation were evaluated periodically. The cutting forces were also evaluated under the same conditions applied to the tool life test. The polishing tests were performed in a polishing equipment specially developed for this purpose, which allows adjustable rotation speed and pressure load. In the polishing process, abrasives with particle size of 1mm are applied and surface roughnesses of the samples were evaluated according to the polishing time. The results show that the amount of titanium and size of titanium carbonitride hard inclusions are fundamental for good machinability, while the soft sulfides of manganese do not take any effect in the presence of these hard particles. The polishability is worsened by the presence of large inclusions of manganese sulfides, forming pin holes.
Analysis of Surface Integrity for DIN 100Cr6 Steel Conical Bearing Rings after Hard Turning
Authors: Delijaicov Sergio , Salazar Carlos Eddy Valdez , Bordinassi Éd Claudio , Padovese Linilsson Rodrigues
Published: April 2011

This work studies the influence of machining parameters, such as cutting speed and forces, feed rate, cutting depth, and tool flank wear, on the generation of surface residual stresses in DIN 100Cr6 steel conical bearing rings submitted to a hard turning process. A complete factorial planning was used to perform the tests and projected measurement. Cutting forces were measured by a piezoelectric dynamometer and residual stresses were determined by the hole-drilling method using strain gage. Results showed that after 2000 m of tool machining, phase transformations had been observed on sample surfaces, with white layer formation, and deeper, a dark layer whose thickness varied depending on the severity level of turning and the tool wear (in machined distance). Increase in tool wear generated minor values of compressive residual stresses and the surface roughness presented almost the same values in all experiments, except when the bigger parameters were used.
Modeling and Characterization of Surface Structures Produced by Milling
Authors: Borštnik Bračić Anamarija , Surmann Tobias , Govekar Edvard
Published: April 2011

In this paper, a novel method for the modeling and characterization of surface structures is presented. The method is based on the nonparametric statistical modeling of the surface structure, represented as a two dimensional field. Using a sample of a surface structure in question, the model reproduces the structure of the surface and estimates the corresponding machining parameters. The applicability of the method is demonstrated on the modeling and characterization of the functional surfaces generated by intentionally invoked chatter during the milling process. Based on the model of the generated surface structures, the corresponding diameter of the toroidal cutter and spindle speed are estimated using the surface structure data as the input for the model.
Tool Load during Multi-Flank Chip Formation
Authors: Klocke Fritz , Gorgels Christof , Herzhoff Stefan
Published: April 2011

Tools used in cutting processes with multi-flank chip formation like gear hobbing or bevel gear cutting, often reach their tool life due to excessive wear at the tool corner radius. Tool wear depends on the strength of the cutting edge and on the thermal and mechanical load. The objective of this work is to analyze the thermal and mechanical tool load during multi-flank chip formation. As the tool load cannot be measured in the necessary high local resolution, a finite element based machining simulation is used to model the process of chip formation. The simulation is able to calculate the temperature and stress distribution along the cutting edge. For the examinations presented in this report the bevel gear cutting process for ring gears is simulated. The simulation results show a significant thermal and mechanical load maximum at the tool corner, where the maximal wear occurs in cutting.
Modeling and Optimization of Multiple Characteristics in the AISI 52100 Hardened Steel Turning
Authors: Gomes José Henrique De Freitas , De Paiva Anderson Paulo , Ferreira João Roberto , da Costa Sebastião Carlos , De Paiva Emerson José
Published: April 2011

This work aimed to develop a multiple response optimization procedure for the AISI 52100 hardened steel turning process. Optimizing this turning operation is important so that multiple quality characteristics are achieved simultaneously. The considered responses are: total cost, cutting time, total turning cycle time, tool life, material removal rate, and surface roughness. The adjusted process parameters were cutting speed, feed rate and depth of cut. A multi-objective optimization technique based on the Global Criterion Method and Genetic Algorithm were employed to identify the optimal settings for parameters with objective functions built through Response Surface Methodology. This two-fold approach lead up to optimized responses settled near the desired values were obtained with cutting speed = 214 m/min, feed rate = 0.088 mm/rev and depth of cut = 0.33 mm.
Life Prediction of Cutting Tool by the Workpiece Cutting Condition
Authors: Gomes de Mattos de Mesquita Noemia , Ferreira de Oliveira José Eduardo , Ferraz Arimatea Quaresma
Published: April 2011

Stops to exchange cutting tool, to set up again the tool in a turning operation with CNC or to measure the workpiece dimensions have direct influence on production. The premature removal of the cutting tool results in high cost of machining, since the parcel relating to the cost of the cutting tool increases. On the other hand the late exchange of cutting tool also increases the cost of production because getting parts out of the preset tolerances may require rework for its use, when it does not cause bigger problems such as breaking of cutting tools or the loss of the part. Therefore, the right time to exchange the tool should be well defined when wanted to minimize production costs. When the flank wear is the limiting tool life, the time predetermination that a cutting tool must be used for the machining occurs within the limits of tolerance can be done without difficulty. This paper aims to show how the life of the cutting tool can be calculated taking into account the cutting parameters (cutting speed, feed and depth of cut), workpiece material, power of the machine, the dimensional tolerance of the part, the finishing surface, the geometry of the cutting tool and operating conditions of the machine tool, once known the parameters of Taylor algebraic structure. These parameters were raised for the ABNT 1038 steel machined with cutting tools of hard metal.
Stability Analysis of Machining with Spindle Speed Variation
Authors: Otto Andreas , Kehl Gerhard , Mayer Michael , Radons Günter
Published: April 2011

In this paper the chatter stability of turning and full-immersion milling operations with spindle speed variation is studied. We present a method to calculate the stability lobes in the limit of very low and very high frequencies of the delay modulation. These approximations help to classify the results of numerically exact methods, as for example semi-discretization or multi-frequency approaches. For slowly time-varying delay, the position of the stability lobes is understandable from a simple connection between the lobes for constant and time-varying delay. Furthermore, this method can be used to estimate the efficiency of an application of spindle speed variation and helps to find optimal parameters for it.