bluuebunny/crossref_metadata_2025 huggingface dataset:
Research and Implementation of Image Rotation Based on CUDA
Authors: Liu Zhi Yuan , Zhao Xue Zhang
Published: March 2011

GPU technology release CPU from burdensome graphic computing task. The nVIDIA company, the main GPU producer, adds CUDA technology in new GPU models which enhances GPU function greatly and has much advantage in computing complex matrix. General algorithms of image rotation and the structure of CUDA are introduced in this paper. An example of rotating an image by using HALCON based on CPU instruction extensions and CUDA technology is to prove the advantage of CUDA by comparing two results.
A Novel English Teaching Model Based on Web Environment
Authors: Ma Li Juan
Published: March 2011

This paper concentrates on a new way in higher education English teaching. The paper takes up the new view as the thesis that teachers should adopt pupil-centered teaching methodology and employs every means of teaching. This paper puts forward a novel English teaching model based on Web environment. The conclusion restates the thesis of the paper explicitly stated in the introduction and then highlights the new way in elementary school English teaching.
A Novel Heuristic PageRank Algorithm in Web Search
Authors: He Yan Li
Published: March 2011

With the booming development of the Internet, web search engines have become the most important Internet tools for retrieving information. PageRank computes the principal eigenvector of the matrix describing the hyperlinks in the web using the famous power method. Based on empirical distributions of Web page degrees, we derived analytically the probability distribution for the PageRank metric. We found out that it follows the familiar inverse polynomial law reported for Web page degrees.
Multi-Agent Reinforcement Learning Based on K-Means Clustering in Multi-Robot Cooperative Systems
Authors: Liu Chang An , Liu Fei , Liu Chun Yang , Wu Hua
Published: March 2011

To solve the curse of dimensionality problem in multi-agent reinforcement learning, a learning method based on k-means is presented in this paper. In this method, the environmental state is represented as key state factors. The state space explosion is avoided by classifying states into different clusters using k-means. The learning rate is improved by assigning different states to existent clusters, as well as corresponding strategy. Compared to traditional Q-learning, our experimental results of the multi-robot cooperation show that our scheme improves the team learning ability efficiently. Meanwhile, the cooperation efficiency can be enhanced successfully.
A Parallel Data Mining Method Based on Complex Network
Authors: He Yan Li
Published: March 2011

This paper addresses the well-known classiﬁcation task of data mining, where the objective is to predict the class which an example belongs to. a complex network is a networkwith non-trivial topological features—features that do not occur in simple networks such as lattices or random graphs but often occur in real graphs. We present results evaluating the performance of the hybrid method based on complex network.
A Novel Marketing Strategy Based on Information Technology
Authors: Zhang Xiao
Published: March 2011

Marketing is the process of performing market research, selling products and/or services to customers and promoting them via advertising to further enhance sales. It generates the strategy that underlies sales techniques, business communication, and business developments. Information technology is the acquisition, processing, storage and dissemination of vocal, pictorial, textual and numerical information by a microelectronics-based combination of computing and telecommunications.
Media Access Control Protocols in Multimedia Wireless Sensor Networks: A Survey
Authors: Li Zhe Tao , Pei Tingrui , Yang Shu
Published: March 2011

Multimedia wireless sensor networks (MWSN) have outstanding ability of acquiring and processing information. Media access control is a research hotspot in MWSN. Many MAC protocols with different objectives for wireless sensor networks have been proposed by researchers, however, few of them suit for MWSN. This article presented an overview of characteristics and challenges of MAC in MWSN. We firstly overviewed of the research effort; then we compared different protocols; finally we point out some possible directions of future research on MAC layer design.
Primary Resonance and Bifurcations in Damped and Driven Duffing-Van der Pol System
Authors: Zhang Shu Guang , Zhu Zhi Yong , Guo Zhi
Published: March 2011

In this paper, by using second-order averaging method, damped and driven Duffing-Van der Pol system is investigated in detail. The conditions for the existence and the bifurcations of harmonics are given.
The Cause and Treatment Strategy on Thrashing
Authors: Zhang Tie Nan , Liu Tie Wu
Published: March 2011

Producing in the multiprogramming systems of the demanding paging style ,thrashing is an extreme status coming from doing page replacement. Based on some research results, the cause of thrashing is discussed with describing the feature of it. A policy of "preventing first" is presented to hold on to refrain from the thrashing ,which sets forth the concrete method of preventing and ending the thrashing. Some relating conclusions are also fit for page replacements of the computer designing in other fields.
Finite Element Analysis of Interfacial Stress for Fiber Reinforced Composite Cable Wire Based on FBG
Authors: Li Jian Zhi , Du Yan Liang , Sun B.C.
Published: March 2011

Whenever embedded in materials, optical fibers can be regarded as foreign entities to host structure, which inevitably perturbs instinct structural morphology in a local continuum. This work reports a set of finite element analysis (FEA) on an intelligent hybrid fiber composite cable wire with embedded fiber Bragg grating (FBG). The authors tend to provide a comprehensive investigation on interfacial stress of intelligent hybrid fiber composites wire embedded FBG sensor during their working period.
Effect of Diffusion Induced Driving Forces on Interdiffusion - Stress Development/Relaxation and Kinetics of Diffusion Processes
Authors: Beke Dezső L. , Erdélyi Z. , Parditka B.
Published: March 2011

General description of the interplay between the Kirkendall shift (as a special way of relaxation) and diffusion induced driving forces in diffusion intermixing of binary systems is given. It is shown that, if the Kirkendall shift is negligible, a steady state Nernts-Planck regime is established with diffusion coefficient close to the slower diffusivity, independently of the type of the diffusion induced field and also independently whether this is a single field or a combination of different fields (e.g. stress field and extra chemical potential of non-equilibrium vacancies). Deviations from parabolic kinetics are expected only before or after this steady state stage. Using the results of our previous paper, on development and relaxation of diffusion induced stresses, it is illustrated that the setting of time of the Nernst-Planck regime is very short: intermixing on the scale of few tenths of nanometer is enough to reach it. It is also illustrated that this stage is realized even in the case of asymmetric interdiffusion (in one side of the diffusion zone the diffusion is orders of magnitude higher than in the other), when the stress distribution has a more complex form (having a sharp peak at the interface). Surprisingly the steady state is longer than it would be expected from the relaxation time of Newtonian flow: This is so because the composition profile is not static but changes fast in the timescale of the stress relaxation, and thus the stress re-develops continuously.
Models of Interdiffusion in a Polycrystalline Alloy: Kirkendall Effect versus Non-Equilibrium Vacancies and Backstress
Authors: Gusak Andriy , Storozhuk Nadiya , Tu King Ning
Published: March 2011

In order to study evolution of the concentration profiles and markers velocities in various time and space scales quasi-one-dimensional model of interdiffusion in a polycrystalline alloy is proposed considering non-equilibrium vacancies and the Kirkendall effect. Sinks/sources of vacancies are assumed to be concentrated mainly at the moving grain boundaries. This model simultaneously takes into account the movement of grains and changes of grain sizes.
Diffusion in Point Contact Reaction
Authors: Gusak Andriy , Kovalchuk A.O. , Tu King Ning
Published: March 2011

Recently) the point contact reactions between silicon nanowires (covered by natural oxide) and nanowires or nanodots of metals (nickel, cobalt, platinum) were discovered and studied. These reactions have at least three remarkable characteristics: (1) the reaction product phase is quite different from thin film or bulk reactions (for example, in Ni-Si reaction the appearing phase is Ni1Si1 or Ni1Si2, depending on the orientation of Si, instead of common Ni2Si phase); (2) Phase is formed not in the contact zone but, instead, near the wire tip or between two point contacts; (3) Subsequent phase growth of silicide inside silicon nanowire is a “stop-and-go” process consisting of waiting time before formation of critical island of each new atomic layer and then the fast filling of this new layer (mechanism suggested in 30-s for ideal crystals) Models of surface diffusion along and penetration through silicon oxide are presented. Nucleation models need more place and will be discussed in subsequent parts
Pre-Stressed Sub-Surface Contribution on Bulk Diffusion in Metallic Solids
Authors: Raceanu Laura , Optasanu Virgil , Montesin Tony , Creton Nicolas
Published: March 2011

Our recent modelling works and corresponding numerical simulations realized to describe the UO2 oxidation processes confirm the theory showing that an applied mechanical strain can strongly affect the local oxygen diffusion in a stressed solid. This result allows us to assume that stress field, previously applied at the surface of a metallic sample on several microns, will delay the degradation during its oxidation. Considering this hypothesis, we implemented a FEM simulation code developed in our laboratory to numerically investigate some different stress fields applied on a sample sub-surface, that might significantly modify the volume diffusion of oxygen during the oxidation process. The results of our simulations are presented and discussed from the perspective to study the consequences of a surface mechanical treatment on the durability of a metallic material.
Diffusion-Induced Recrystallization in Nickel/Palladium Multilayers
Authors: Schmitz Guido , Kasprzak M. , Baither D.
Published: March 2011

Diffusion-Induced Recrystallization (DIR) is investigated in size mismatched thin film interdiffusion couples. New grains formed in the diffusion zone are characterized by distinctive composition levels which seem to be characteristic to the interdiffusing materials. In this paper, we analyzed sputter-deposited Ni/Pd films. The lattice mismatch and the driving force are varied by pre-alloying one side of the diffusion couples. Recrystallization was detected after heat treatment by transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. We determined characteristic concentrations from XRD data. Remarkably, the difference between the concentration inside newly formed grains and that of the parent layers remains practically constant, when initial layer concentration is varied. Also, the characteristic compositions are nearly independent of temperature. A thermo-mechanic model has been derived, which demonstrates that the observed concentration differences are such that the stress in front of the moving grain boundary reaches a maximum close to the ideal strength of the host material.
Segregation and Selective Surface Oxidation at the Intermediate Steps of Recrystallization Annealing
Authors: Swaminathan Srinivasan , Rohwerder Michael
Published: March 2011

High strength steels for automotive industry undergo recrystallization annealing in N2-H2 gas atmosphere prior to hot dip galvanizing. Segregation and selective surface oxidation of the alloying elements (Al, Mn, Si, Cr etc.) depending on their extend, can be a serious problem for subsequent galvanizing as the wettability of these oxides with zinc is poor. Moreover, the H2 uptake from the annealing atmosphere majorly depends on the surface evolution during recrystallization annealing. In order to understand the surface phenomena during annealing of multicomponent alloy (i.e. steel), a systematic approach on model alloys is needed. In this work, selective surface oxidation of Mn, Al and the reduction of native Fe oxides in Fe 2 wt. % Mn and Fe 3 wt. % Al binary model alloys have been investigated by interrupting the recrystallization annealing cycle at the desired temperature. The specimens were annealed to various temperatures (200-800 °C) in N2-5%H2 gas atmospheres with a dew point of 30 °C. It has been found that the segregation and selective oxidation of the alloying elements starts at 300 °C whereas the significant reduction of native Fe oxides takes place at 400 °C. Further increase of temperature, increases the surface coverage by forming the oxide islands.
Critical Embrittlement Temperature for Tube Steels Used at Atomic Power Stations
Authors: Petelina A.A. , Youkhanov V.A. , Shur A.D.
Published: March 2011

During the exploitation of the atomic power stations the tubing metal is exposed to the influence of temperatures in the range of 290-320С. It can lead to thermal ageing and to the decrease of the embrittlement resistance. The critical embrittlement temperature is the main value which is needed to calculate the embrittlement resistance of materials. The metal properties degradation is taking into account by introduction of the shift of critical embrittlement temperature. The presented data ensure the prognosis of tube steels properties and shift of the critical embrittlement temperature for 60 years resource.
The Liquid Bismuth Penetration from Solid Bi2Te3: Grain Boundary Embrittlement and Effect of Impurities
Authors: Zhevnenko Sergei , Vaganov Danil V. , Gershman Eugene
Published: March 2011

The liquid bismuth penetration from solid bismuth telluride (Bi2Te3) into grain boundaries of copper and copper-based solid solutions was studied. The experiments were performed at 570 oC in hydrogen atmosphere. The copper specimens were annealed from 10 to 90 minutes. Solid Bi2Te3 didn’t contact with copper specimens during experiments, so copper was covered by the decay products of Bi2Te3 through the gas phase. Liquid Bi penetration leads to grain boundary embrittlement of copper. We assumed that the depth of penetration is equal to the length of cracks which are formed after sample bending. It was shown that there is only bismuth at the grain boundaries while on the surface tellurium also exists. Bismuth concentration in the grain boundaries measured by Auger spectroscopy was about 10-20 at. % and the width of penetration channel was less then 10 nm. Bismuth covered the grain boundaries uniformly. Time dependence of the penetration depth was approximately parabolic. In the present work the effect of impurities (silver, iron) on grain boundary liquid bismuth penetration was studied also. It was shown that silver accelerates the penetration in contrast to iron. The probable reasons were discussed.
Concentration Profiles for Grain Boundary Diffusion in B-Regime with Regard to the Formation of Atomic Complexes in Grain Boundary
Authors: Esin Vladimir , Bokstein Boris S. , Rodin Alexey
Published: March 2011

Thermodynamics of the atomic complexes formation in a grain boundary (GB) is discussed applying to AB complex. It is shown that the AB complex formation leads to the nonlinearity of segregation isothermes. Consequently, the concentration profiles for GB diffusion are nonlinear. The total (free and bound into complexes) concentration of diffusant B decreases at the given depth as the molar fraction of the complexes increases.
Recent Developments in the Study of Grain Boundary Segregation by Wavelength Dispersive X-Ray Spectroscopy (WDS)
Authors: Nowakowski Pawel , Christien Frédéric , Allart Marion , Le Gall René
Published: March 2011

It was recently shown [1] that EMPA-WDS (Electron Probe MicroAnalysis by Wavelength Dispersive X-ray Spectroscopy) can be used to detect and to accurately quantify monolayer surface and grain boundary segregation. This paper presents the last developments of this application. It focuses on the measurement of sulphur grain boundary segregation in nickel on fractured surfaces. A special attention was paid to the quantification of the sulphur coverage, taking into account the non-normal incidence of the electron beam on a fracture surface. Sulphur grain boundary segregation kinetics was measured at 750°C in nickel to document the quantitative possibilities of the technique.
Self-Diffusion Parameters of Grain Boundaries and Triple Junctions in Nanocrystalline Materials
Authors: Lipnitskii Aleksey , Nelasov I.V. , Kolobov Yurii
Published: March 2011

Suggested methods describe the process of self-diffusion along grain boundaries and triple junctions in polycrystals without using geometric models of the grain boundaries structure. The calculation method introduced diffusion characteristics along grain boundaries derived from the results of molecular dynamic simulations of nanocrystalline materials. The diffusion experiments were imposed to establish relationship between introduced diffusion characteristics and the diffusion parameters along grain boundaries and triple junctions of the Fisher’s grain boundary diffusion model. By the example of copper for the first time the characteristics of self-diffusion along grain boundaries of nanocrystalline materials and coarse grained analog defined in the same temperature range was compared for the first time. It was found that values of the self-diffusion characteristics along grain boundaries in high purity nanocrystalline and polycrystalline copper are equal at the same temperatures.
The Harrison Diffusion Kinetics Regimes in Grain Boundary Diffusion: Lattice Monte Carlo Modelling of the Effect of Segregation
Authors: Belova Irina V. , Murch Graeme E. , Fiedler Thomas
Published: March 2011

The location of the transition points for the three main Harrison’s kinetics regimes (Type-A, B and C) for the measurement of grain boundary diffusivities from tracer concentration depth profiles (self-diffusion) has been extensively studied in (Divinski et al. Zeit. Metallk, 2002, Belova and Murch, Phil. Mag, 2001, 2009; Defect and Diffusion Forum, 2006, 2008, 2009) by making use of the phenomenological Lattice Monte Carlo numerical method. Those locations are mainly dependent on the dimensionality of the problem. For the case of impurity grain boundary diffusion, the segregation effect is very important. In the present study, the influence of segregation on the transition points is investigated for the parallel slab model (2-dimensional) of the grain boundary diffusion problem by making use of the tracer-type solution to the equivalent diffusion problem. It is shown that the Type-B regime is most likely not realized for the cases of fine-grain material with a strong segregation effect present.
Can PAC Measurements be Used to Investigate Defects in Nano-Structures?
Authors: Uhrmacher Michael
Published: March 2011

The PAC-technique always claims to test the micro-surrounding of the probe atoms. Typically, the samples are macroscopic and more or less homogeneous and there is no debate about the usefulness of the method: substitutional sites, trapped vacancies or phase transitions are easily seen. Even the PAC-“fingerprint” of an amorphous material is known. In case of inhomogeneous samples, perhaps made out of different constituents, the question arises whether the PAC can contribute to the understanding of such materials or not. The article will show the different ways to introduce the probe atoms into the samples and discuss then the influence of these histories on the final site of the probe in the sample. In general, diffusion tends to place the probes into grain boundaries, whereas implantation reaches the bulk. This becomes important for nano-materials with their high fraction of internal surfaces. As a second, important difference for possible experiments the spatial distribution of the probes has to be considered. Implantation leads to a Gaussian shaped depth distribution of the probes. This corresponds – in a certain region – to a 3-dimensional distribution of probes in the sample, used e.g. when doping a semiconductor. In the production of special sensors (which apply e.g. the giant magnetoresistance (GMR) effect) one needs a different package, thin films (1-2 mono-layers). To apply PAC here, the probes have to be introduced during the fabrication of such a sensor. In these cases the probes have to be placed within a plane of nano-scale thickness.
Perturbed Angular Correlation Spectroscopy – A Tool for the Study of Defects and Diffusion at the Atomic Scale
Authors: Zacate Matthew O. , Jaeger Herbert
Published: March 2011

This paper provides an introduction to perturbed angular correlation (PAC) spectroscopy in the context of its application in the study of point defects and diffusion. It emphasizes what we anticipate to be of interest to non-PAC specialists who are interested in understanding variations in how PAC results are presented by different research groups and in how physical quantities such as defect formation energies, association energies, and migration barriers can be extracted from analysis of PAC spectra. Numerous citations are included to emphasize the universality of the analysis methods across different classes of materials including metallic, ceramic, and semiconducting compounds.
Impurities in Magnetic Materials Studied by PAC Spectroscopy
Authors: Carbonari Artur Wilson , Mestnik-Filho José , Saxena Rajendra Narain
Published: March 2011

Perturbed gamma-gamma angular correlation (PAC) spectroscopy is a precise and highly efficient tool to follow the temperature dependence of local magnetic fields in any material. Its resolution and efficiency does not depend on temperature and therefore can measure local fields at low as well as high temperature with the same accuracy. Due its versatility in using different probe nuclei it can sense the local magnetic fields at different sites in the crystalline structure of materials. In this review, important results obtained with PAC spectroscopy are shown in two classes of materials: transition metal and transition-metal based compounds and rare earth elements and rare-earth-element based compounds using mainly three different probe nuclei: 111Cd, 181Ta and 140Ce. PAC spectroscopy has contributed to the systematic study of the magnetic hyperfine field in impurities in matrices of Fe, Co and Ni as well as in transition-metal based Heusler alloys. It has also provided important contribution to the investigation of magnetism in rare-earth elements and intermetallic compounds. An still open issue concerning the local fields in metallic magnetic compounds and elements is the exchange interaction between the magnetic ions of the host and a dilute magnetic impurity, which acts as a defect in the magnetic lattice. PAC spectroscopy has been contributing to study this problem with success. Also shown in this review is the crucial role of ab-initio first principle calculations in the interpretation of PAC results.
Forming Behavior of Thin Foils
Authors: Hu Zhen Yu , Wielage Hanna , Vollertsen Frank
Published: March 2011

Due to size effects new challenges are involved in micro deep drawing compared to macro deep drawing. One of these challenges is that the limit drawing ratio in micro deep drawing becomes smaller than that in macro forming, which limits the application potential of micro deep drawing in an industrial context. In order to extend the application possibilities of micro deep drawing, investigations were carried out on this topic. Own previous work showed that the “tribological effect”, the “global flow behaviour effect” and the “local flow behaviour effect” are responsible for the lower forming limit in the micro range. In this paper, the flow behavior of thin foils is further investigated. Forming limit diagrams of Al99.5 and E-Cu foils with different thicknesses ranging from 20 μm to 100 μm were acquired using an optical measurement system. It was found that the forming limit of thin foils is lower than that of thicker foils. Further analysis indicates that this difference is due to the number of grains in the direction of thickness of the material: more grains give more grain boundaries, which allows more strain of the grains.
Adaptive Control in CNC Sheet Metal Processing
Authors: Serruys Wim
Published: March 2011

Three different and complementary ways of adaptive control are presented, each working on a different time scale. All three of them are made possible due to evolutions and developments in CNC controls. The first and most popular way of adaptive control is adaptive process control. Since the process variables in sheet metal equipment change significantly in milliseconds, the control loop must also perform on a sub second time scale. The second adaptive loop is adaptive production control. Modern CNC controls know what they are manufacturing and talk with higher production software. Instead of just executing a planning that came top down, the CNC has enough knowledge of its environment that it can propose an intelligent job sequence and hence react more effectively on unforeseen situations. These adaptive loops perform on a time scale of hours and days. The third adaptive loop is adaptive resource control. To produce sheet metal parts, we need several kinds of resources: human resources, material, consumables, energy and equipment. CNC sheet metal equipment is a considerable investment. However most production managers do not know how effective their resources are being used. By applying the principles of overall equipment effectiveness, we can close the resource control loop. This loop performs on a time scale of weeks and months.
Assessment of Electrical Resistance Heating for Hot Formability of Ti-6Al-4V Alloy Sheet
Authors: Ozturk Fahrettin , Ece Remzi Ecmel , Polat Naki , Koksal Arif
Published: March 2011

Ti-6Al-4V (Ti64) is the most commercially used heat treatable high strength/weight ratio, high corrosion, and thermal resistance alloy in titanium alloys. However, room temperature (RT) formability of this alloy is very poor and springback after forming is very severe due to the high yield strength and low elasticity modulus. In this research, the applicability of electrical resistance heating process which is a new and rapid heating process for hot forming application is investigated in order to improve formability and eliminate springback. The electrical resistance heating method is found to be effective for T64 alloy. Results reveal that the changes in hardness and grain size of the alloy have been found inconsiderable when the method is used. Springback compensation is achieved at high temperatures and springback free part is almost produced.
Analysis of Continuous Bending of Thin Plates in Rubber Pad Bending
Authors: Mehrara M. , Nategh Mohammad Javad
Published: March 2011

In the present work the elastic bending of thin plate resting on rubber pad has been analyzed. The governing differential equations have been derived. An analytical solution to these equations has been presented. In addition numerical solution to these equations has also been worked out by using finite difference method. An equation has been derived to estimate the indentation depth of plate at the onset of plastic bending of the plate in terms of the process parameters. The analytical solution has then been verified by experimental results.
Analytical-Numerical Solution of Bending Problem of Thin Plates in Rubber Pad Bending
Authors: Mehrara M. , Nategh Mohammad Javad
Published: March 2011

The bending of plates on rubber pad is a relatively new method used for roll bending of thin plates in recent years. In the present work the problem of plastic deformation of thin plates was analyzed. The governing differential equations for the plate’s elastic and plastic zones were derived. An analytical-numerical solution to these equations was subsequently presented. In addition, the equations were solved for a given problem and the effect of indentation depth of plate on its bending radius was investigated. A relationship has been proposed to correlate these parameters. This relationship is a powerful tool in controlling the process and process planning. This tool helps the operator set the indentation depth to a predefined amount in order that the plate to be bent by a given radius, without any try and error effort. The results were verified by experiment.
Influence of Die Materials on the Microstructural Evolution of HSS Sheets in Hot Stamping
Authors: Ghiotti Andrea , Bruschi Stefania , Pellegrini Daniele
Published: March 2011

Hot stamping of High Strength Steels sheets is gaining more and more popularity, particularly in the automotive industry, due to the sound microstructures achieved at the end of the process. The significant improvement of the mechanical properties achieved in the process enables to reduce the initial sheet thickness in favour of cost and fuel consumption reduction. However, a martensitic microstructure implies significant drawbacks in final trimming and cutting operations, which becomes more difficult and expensive due to tools wear and high blanking forces. This paper aims at investigating the performances of non-metallic materials to be used in heated dies, in order to inhibit the martensite formation by locally reducing the sheet cooling rate. To analyze the influence of the main process parameters, a new experimental set-up was designed and developed in a laboratory environment that allow applying controlled pressure and temperatures to HSS metal sheets. An analytical model was set-up in order to evaluate the influence of process conditions on the cooling profiles in different areas of the specimen. Accordingly, experiments were carried out to investigate the material behaviour when cooled in the different conditions. The experimentally acquired temperatures were analyzed and evaluated together with hardness measurements of metal sheets in order to assess the feasibility of the proposed approach in producing microstructurally-tailored components.
Development of Bionic Design Concepts for Structure Optimisation of Forming Tools According to Production and Stress Constraints
Authors: Oswald Eugen , Liewald Mathias , Stephan Oliver
Published: March 2011

In the automotive industry, current design and dimensioning of forming tools and bearing tool components occurs according to guidelines. Possible interactions between arising loads as well as dimensioning are empirically estimated. Simulative computations, which are based on CAE-methods, are only realized in special cases. Therefore, most often current standards lead to oversized tools. In consequence, new studies based on CAE-analyses are supposed to investigate new possibilities to design forming tools and components optimized in their structure corresponding to the right distribution of forces and stress. This is made in order to increase reliability during the manufacturing process, as well as the tools’ stiffness and contribute to decrease of investment costs.
Process Design for the Manufacturing of Magnetic Pulse Welded Joints
Authors: Psyk Verena , Gershteyn G. , Barlage Bjoern , Weddeling Christian , Albuja Bibiana , Brosius Alexander , Tekkaya A. Erman , Bach Friedrich Wilhelm
Published: March 2011

When manufacturing joints of dissimilar materials thermal technologies as welding reach their limits. Impact welding by electromagnetic forming is a promising alternative because undesired heating of the parts and related disadvantages are avoided. In this process impact parameters need to be adjusted to each specific joining task, but cannot be settled directly. Thus, a two-step methodology is suggested for the process design: First the influence of the impact parameters and the surface preparation on the joint properties is investigated using a model experiment. Joint properties are characterized by metallographic investigations. Parallel to this, the influence of the adjustable process parameters and the equipment on the workpiece acceleration and the impact properties is analyzed. Then the results of both investigation paths are combined and conclusions regarding a target-oriented adjusting of the impact parameters via the process parameters are drawn. In the paper first results considering the model experiment and the analysis of the electromagnetic expansion process are presented and joints manufactured by electromagnetic expansion are characterized.
The Low-Cycle Fatigue Strength of Laser-Welded Ultra-High-Strength Steel
Authors: Keskitalo Markku , Mäntyjärvi Kari , Kiuru Toni
Published: March 2011

The UUltra -high -strength (UHS) steels are used in booms, transport vechicles and other light weight structures. It is well -known that it is possible to achieve a strong weld statically, as the base material, by using laser welding as a weld method [1]. The design strength of the light weight structure is often rather high. In the case of booms and transport vechilevehicles, there can be very high dynamic forces in the structure. Therefore it is necessary to study how much fatigue stress the weld seam can resist and at the same time find the optimal welding parameters. The 4 mm bainitic-martensitic UHS steel was welded with laser without filler material to lasercut seam edges by using different weld parameters. Argon gas was blown by pipe onr coaxial nozzle near the key hole and through a 60 mm gas nozzle after the keyhole. Also, the root side of the weld was shielded with argon. The welds were tested by using the bending fatigue test. The test stresses were 800 MPa and 700 MPa. The fatigue strength results showed that with the laser welded seams, the number of cycles wereas about three times lower than with the base material. The fatigue strength was slightly better in welds which were welded with lower energy input. In the case of the weld seam which was welded with lowest energy input by using 300 mm optics, there was some incomplete penetration due to tooexcessively high surface roughness ofat the weld seam edges.
Computer Aided Design of an Effective Fixture for FSW Processes of Titanium Alloys
Authors: Buffa Gianluca , Fratini Livan
Published: March 2011

During the last years welded titanium components have been extensively applied in aeronautical and aerospace industries because of their high specific strength and corrosion resistance properties. Friction Stir Welding (FSW) is a solid state welding process, currently industrially utilized for difficult to be welded or “unweldable” aluminum and magnesium alloys, able to overcome the drawbacks of traditional fusion welding techniques. When titanium alloys are concerned, additional problems arise as the need for very high strength and high temperature resistant tools, gas shield protection and high stiffness machines. Additionally, the process is characterized by an elevated sensitivity to temperature variations, which, in turn, depends on the main operative parameters. Numerical simulation represents the optimal solution in order to perform an effective process optimization with affordable costs. In this paper, a fully 3D FEM model for the FSW process is proposed, that is thermo-mechanically coupled and with rigid-viscoplastic material behavior. Experimental clamping parts are modeled and the thermal loads are calculated at the varying of the cooling strategy. Finally, the effectiveness of the cooling systems is evaluated through experimental tests.
The Importance of Governing Metal Thickness for Resistance Spot Welding of Aluminium
Authors: Han Li , Thornton Martin , Boomer Douglas , Shergold M.
Published: March 2011

A study was carried out to investigate the effect of governing metal thickness (GMT) on weld quality and strength of resistance spot welded (RSW) AA5754 aluminium. Quasi-static joint strengths were evaluated for 27 different joint stack-ups in three test geometries: lap-shear, coachpeel and cross-tension; whilst micro examination was conducted on some of the samples to assess weld quality. The results derived from over 1000 samples show the importance of GMT and its various effects: the GMT has a significant effect on welding quality and joint strength by controlling the attainable weld diameter, regardless of stack-ups; depending on loading conditions, its effect may differ.
Optical Measuring Technique for the Investigation of Built-Up Cold-Formed Steel Structural Members
Authors: Georgieva Iveta , Schueremans Luc , De Roeck Guido , Pyl Lincy
Published: March 2011

The construction industry uses cold-formed steel (CFS) sheets in the form of galvanised thin-walled profiles and corrugated sheets. In the past decade, CFS profiles have been competing with their hot-rolled counterparts as primary structural members of industrial halls, office buildings and residential housing of up to 3-4 storeys. The spans and column heights achieved with CFS profiles are ever larger. Due to the large slenderness of these members, adequate strength and stability are necessary, as well as reliability in design. Thin-walled members go through buckling during all stages of their working life. Local buckling appears at loads sometimes much lower than the design load. Distortional buckling seriously reduces the member resistance. It interacts with warping and lateral-torsional buckling, being significant for these asymmetric open sections. To restrict these effects, builders employ double sections - usually two standard cold-formed shapes bolted together to form a built-up section. These sections have the advantages of symmetry, higher stability and strength. The design of built-up members involves many uncertainties - although the European standard includes guidelines on the prediction of local, distortional and global buckling, the partial integrity and interaction between the parts of the composed members is still not studied. To study the actual behaviour, built-up members are tested in bending. An optical device for 3D motion analysis measures the displacement of points of interest on the specimen. Two interacting cameras use parallax to obtain the position of an arbitrary number of reflective markers glued to the specimen. The device tracks the movement of the markers in a 3D coordinate system without any contact with the specimen. Standard displacement transducers measure vertical displacements to validate the results. The paper gives an appraisal of the applicability of the method, a summary of the difficulties faced and the outcome of the test campaign.
Comparison of the Identifiability of Flow Curves from the Hydraulic Bulge Test by Membrane Theory and Inverse Analysis
Authors: Bambach Markus
Published: March 2011

In the hydraulic bulge test, flow curves are determined by applying a hydrostatic pressure to one side of a clamped sheet metal specimen, which bulges freely into a circular cavity under the pressure. The pressure and various data such as bulge height, curvature and equivalent strain at the pole are recorded and used to calculate the flow curve of the specimen material using analytical equations based on membrane theory. In the determination of the flow curve, the elastic behavior of the specimen, the elastic-plastic transition and bending effects are neglected, and the flow curves calculated this way are affected by these simplifications. An alternative to this procedure is an inverse analysis, which proceeds by searching for a flow curve that minimizes the difference between computed and measured data, e.g. bulge height vs. pressure. An inverse analysis based on a finite element model takes into account elastic and bending effects but since it involves the solution of an optimization problem, it is not clear whether it yields more accurate results than membrane theory. The objective of this paper is to compare the ‘identifiability’ of a given flow curve from the bulge test by direct identification based on membrane theory and by inverse analysis with different objective functions to be minimized. Using a re-identification procedure, it is shown that an inverse analysis can improve the results of the direct identification if a suitable objective function is chosen.
Study on Impact Crushing Properties of High Strength Steel Sheets
Authors: Natori Keiko , Watanabe Kenichi , Tanaka Tatsuya , Imaida Yutaka
Published: March 2011

The purpose of this study is to verify the validity of sheet buckling design based on the effective width theory investigation of impact crushing properties in high strength steel sheets. We clarify the need to make full sections effectively without elastic buckling occurring and consider the application of the effective width theory under high speed deformation. We report our findings of our investigation into the sheet buckling phenomenon with numerical simulation by varying deformation strain rate, mechanical property of material and member configuration. The results demonstrate that, with increasing crush speed, the cross section of a steel sheet become effective, while there is a high possibility of the buckling phenomenon that does not function as efficient impact absorption and is not evaluated with the existing theory.
Theoretical and Experimental Evaluation of the Formability of Anisotropic Zinc Sheets
Authors: Jansen Yann , Logé Roland E. , Milesi Marc , Manov S. , Massoni Elisabeth
Published: March 2011

. Formability of metal sheet has been widely studied for the past 40 years. This study leads to the well known Forming Limit Diagram (FLD) proposed by Keeler and Backhofen [1]. Such a diagram needs typical drawing and stretching experiments to be achieved. Lots of different metals have been considered as steel, aluminium, titanium or magnesium alloys [2]. Despite of the large amount of papers about sheet metal forming, few deal with Zinc sheets. The material has an anisotropic mechanical response due to its hexagonal crystallographic lattice and its microstructural texture. In the presented work, Nakazima and tensile tests have been performed for different mechanical orientations (0°, 45° and 90° angle to the rolling direction) in order to characterise this typical response. A high anisotropic behaviour has been noticed for the hardening and for the critical strains. The FLD is therefore a function of the orientation. Moreover thickness sensitivity is observed and leads to some criticisms about the plane stress assumption usually used in the FLD predictive models [3, 4]. The Modified Maximum Force Criterion (MMFC) is evaluated, and discussed. Then, this model is compared to a damage model used in [5] within an FEM formulation.
Fracture Characterization of ST37-2 Thin Metal Sheet with Experimental and Numerical Methods
Authors: Aberkane Méziane , Mohand Ould Ouali
Published: March 2011

In this study we characterize the fracture toughness of ST37-2 thin metal sheet. The toughness of this material is obtained by using the essential work concept on DENT (Double Edge Notched Test) specimens. These tension tests, show the linearity of the maximal force , the maximal displacement and the final displacement versus the ligament length . These results are confirmed numerically using the Gurson, Tvergaard and Needleman (GTN) micromechanical model. The simulations are carried out using Abaqus software package. A good correlation is obtained between the numerical value of and the essential work of fracture .
Experimental Characterisation of Structured Sheet Metal
Authors: Fritzsche Sebastian , Ossenbrink Ralf , Michailov Vesselin
Published: March 2011

Structured sheet metals with regular bumps offer higher bending stiffness compared to flat sheet metals. The application of structured sheet metals requires new investigations regarding their strength and deformation behaviour. Standardised testing methods like the tensile test considering defined specimen geometry and measuring methods exist. Those methods, however, have been developed for plain sheets and cannot be directly transferred to structured sheet metals. The assessment of the strength and deformation behaviour of structured sheet metals needs adapted specimen geometry and measuring methods. In this paper the adaption of the standardised tensile test in accordance with DIN EN ISO 6892-1 to the specific characteristics of structured sheet metals is introduced. In order to determine the appropriate specimen geometry their dimensions were methodically varied and the influence of the structure position on the strength and the deformation behaviour was identified. The analysis of the local strain behaviour was carried out by 3D displacement measurement with the ARAMIS-system. For the derivation of the material properties different analysing methods were developed. The test results were compared to those of flat sheet metals.
The Effects of Notch Manufacturing Method and Tolerance on Impact Test Results of UHS Steels
Authors: Kantola Jani , Mäntyjärvi Kari , Toppila Rauno , Karjalainen Jussi A.
Published: March 2011

The Charpy V-notch test is a standardized high strain-rate test which is used to find out behaviour of materials in different temperatures by measuring the amount of energy absorption of a specimen. As a result of the Charpy V-notch test, one gets brittle-ductile transition of material. This research examines the effects of two different notch manufacturing methods on the results of impact tests performed on ultra-high-strength (UHS) steels. The goal of this study is to establish whether there is any effect on absorpted impact energy when specimens are manufactured differently and by another producer. Tested materials were bainitic-martensitic UHS steel (YS/TS 960/1000), S650MC HS steel and abrasion-resistant steel (ARS) with a hardness of 500 HBW. Impact test samples were manufactured by two different milling tools by another producer. The dimensions of the samples were measured after manufacturing. Impact test samples were tested at +20, -40 and -100 degrees Celsius with a Zwick Roell PSW750 –instrumented impact test hammer. Specimens were made in T-L orientation. Samples were impacted with 450 J. The results show that there was some difference between the used tools in the absorpted energy of the specimens.
Intermediate Heat Treatment – A New Proceeding for Aluminum Alloys Using Forming Limit Diagrams
Authors: Siefert Kathleen , Merklein Marion , Töpperwien Almut , Nester Winfried , Grünbaum Martin
Published: March 2011

This paper presents a new procedure for a heat treatment embedded between two cold forming steps. A first cold forming step induces a defined strain hardening in the material. The following step is the heat treatment which takes place in a furnace at various temperatures and for certain durations. The application of such an intermediate heat treatment reduces the strain hardening of the material and enhances the elongation. This allows a higher degree of deformation in the second cold forming operation. The achievable properties of the aluminum alloy AlMg4.5Mn (AA5182) were discussed in detail. Further investigations using Nakajima test setup revealed an increased formability of the material. First the Nakajima samples were pre-strained along different linear strain paths to a predefined strain value. Afterwards the samples were heat treated without allowing the aluminum alloy to recrystallize. After cooling down the samples to room temperature, the tests are continued until the material’s fracture. As a result heat treatment dependent forming limit curves (FLC) are obtained. In comparison with a measured FLC at room temperature the support of the intermediate heat treatment on enhanced formability were shown. Furthermore the method is not restricted to AA5182 aluminum alloys.