bluuebunny/crossref_metadata_2025 huggingface dataset:
Formability of Ultrafine-Grained AA6016 Sheets Processed by Accumulative Roll Bonding
Authors: Hausöl Tina , Schmidt Christian W. , Maier Verena , Böhm Wolfgang , Nguyen Hung , Merklein Marion , Höppel Heinz Werner , Göken Mathias
Published: February 2012

Aluminium alloy AA6016 was accumulative roll bonded up to eight cycles in order to produce an ultrafine-grained microstructure. The formability of these sheets was investigated by means of bending tests. Furthermore the influence of a local laser heat treatment at the bending edge is observed. The strength of the UFG samples is increased by a factor of around two compared to the conventionally grained T4 condition which also results in up to 50 % higher punch forces needed for bending of ARB processed samples. An anisotropic bending behaviour is observed. By applying a tailored laser heat treatment along the bending edge prior to the bending tests a local recrystallization and recovery at the deformation zone of the samples is achieved. Thus, ductility is increased locally whereby bending to an angle of 80° is possible with lower forming forces compared to the non-heat treated specimens. The results are compared to previous studies on mechanical properties and formability investigations of ARB processed AA6016.
A Comparison between Three Meta-Modeling Optimization Approaches to Design a Tube Hydroforming Process
Authors: Ingarao Giuseppe , Marretta Laura , Di Lorenzo Rosa
Published: February 2012

Computer aided procedures to design and optimize forming processes have become crucial research topics as the industrial interest in cost and time reduction has been increasing. A standalone numerical simulation approach could make the design too time consuming while meta-modeling techniques enables faster approximation of the investigated phenomena, reducing the simulation time. Many researchers are, nowadays, facing such research challenge by using various approaches. Response surface method (RSM) is probably the most known one, since its effectiveness was demonstrated in the past years. The effectiveness of RSM depends both on the definition of the Design of Experiments (DoE) and the accuracy of the function approximation. The number of numerical simulations can be strongly reduced if a proper optimization approach is implemented: one of the main issues about optimization techniques is related to the design necessity of performing either global or local approximation. This paper aims to test the efficacy of some meta-modeling techniques in the optimization of a T-shaped hydroforming process. In this paper three optimization approaches based on different meta-modeling techniques are implemented. In particular, classical Polynomial Regression approach (PR), Moving Least Squares approximation (MLS) and Kriging method are applied. The results showed that, thanks to the peculiarities of MLS and Kriging methods, it is possible to strongly reduce the computational effort in sheet metal forming optimization, particularly in comparison with a classical PR approach. Differences were highlighted and quantified.
Towards Inverse Form Finding Methods for a Deep Drawing Steel DC04
Authors: Germain Sandrine , Steinmann Paul
Published: February 2012

A challenge in the design of functional parts in metal forming processes is the determination of the initial, undeformed shape such that under a given load a part will obtain the desired deformed shape. An inverse mechanical or a shape optimization formulation might be used to solve this problem, which is inverse to the standard kinematic analysis in which the undeformed shape is known and the deformed shape unknown. The objective of the inverse mechanical formulation aims in the inverse deformation map that determines the (undeformed) material configuration, where the spatial (deformed) configuration and the mechanical loads are given. The shape optimization formulation predicts the initial shape in the sense of an inverse problem via successive iterations of the direct problem. In this paper, both methods are presented using a formulation in the logarithmic strain space. An update of the reference configuration of the sheet of metal during the optimization process is proposed in order to avoid mesh distortions. A first example showed the results obtained with both methods in isotropic hyperelasticity. A second example illustrated a simplified deep drawing computed with the shape optimization formulation in isotropic elastoplasticity. From the undeformed shapes obtained with both methods the deformed shapes are acquired with the direct mechanical formulation. Compared to the target deformed shape a minor difference in node coordinates is found. The computation time is lower with the inverse mechanical formulation in hyperelasticity. The update of the reference configuration in the shape optimization formulation allowed to avoid mesh distortions but increased the computational costs.
Assessment of Distinct Algorithmic Strategies in the Implementation of Complex Anisotropic Yield Criteria
Authors: Grilo Tiago Jordão , Valente Robertt , de Sousa Ricardo J. Alves
Published: February 2012

In this work, distinct algorithmic strategies for the implementation of complex anisotropic criteria in finite element codes are presented. Two different algorithm classes are presented: semi-explicit and semi-implicit procedures, trying to conjugate the best of conventional return-mapping techniques, and accounting for sub-incrementation and subdivision procedures to improve the quality of the obtained results. In the present study, two complex (non-quadratic) anisotropic yield criteria were implemented: Barlat et al. 1991 (Yld91) and Barlat et al. 2004 with 18 coefficients (Yld2004-18p). The performance of the developed algorithms is inferred in cup drawing simulations for aluminum alloys, with the convergence rate as well as the quality of the solutions being assessed, when compared to experimental results. As result, an algorithm and programming framework is provided, suitable for direct implementation in commercial finite element codes, such as Abaqus (Simulia) and Marc (MSC-Software) packages.
Constitutive Equation for Description of Metallic Materials Behavior during Static and Dynamic Loadings Taking into Account Important Gradients of Plastic Deformation
Authors: Gavrus Adinel
Published: February 2012

For numerical simulations of rapid forming processes the most used constitutive equations are based on the Johnson-Cook (JC) law and on the Zerilli-Armstrong (ZA) one. Starting from physical points of view, detailed in the first part, the present paper proposes a more general constitutive equation available for both static and dynamic loadings. It is then possible to describe correctly gradients of strain rate, plastic strain and temperature which occur during a complex deformation path of a metal forming process. From this new law, the JC formulation can be easily obtained from an asymptotic variation of the proposed law at high values of strain rates and, in similar way, the ZA formulation is obtained at small values of strain rates. Application to an aluminum alloy AA5083 will be presented to validate the proposed constitutive equation by a Finite Element Model (FEM) of a rapid upsetting test performed with the Split Hopkinson Pressure Bars.
Study of Wavy Interface in Electromagnetic Welds
Authors: Kore Sachin D. , Vinod P. N. , Kumar Satendra , Kulkarni M.R.
Published: February 2012

Wavy interface is a characteristic of an impact weld. Electromagnetic pulse welding is a solid state welding process, which produces a weld between two mating surfaces at high velocity of impact. In this paper studies on metallurgical characterization of electromagnetic welds to find the presence or absence of wavy weld interface, by using optical microscope and scanning electron microscope, are reported. EM welds of Al to Al do not show wavy interface due the low energy of impact. EM welds of Al to Steel show wavy weld interface due to instability at the weld interface. Studies have revealed that discharge energy and critical velocity of impact are the important parameters for creating stronger electromagnetic welds and the wavy weld interface.
Effect of the Constitutive Law on the Accuracy of Prediction of the Forming Limit Curves
Authors: Paraianu Liana , Comsa Dan Sorin , Nicodim Ioan Pavel , Ciobanu Ioan , Banabic Dorel
Published: February 2012

The accuracy of the forming limit curves predicted by the Marciniak-Kuczynski model depends on the type and flexibility of the constitutive equations used to describe the mechanical response of the sheet metal. From this point of view, the yield criterion has the most significant influence. The paper presents a comparative analysis referring to the quality of the forming limit curves predicted by the Marciniak-Kuczynski model for the case when the plastic anisotropy of a DC04 sheet metal is described by the BBC2005 yield criterion. The coefficients included in the expression of the BBC2005 equivalent stress are evaluated using different identification strategies (with 4, 6, 7, and 8 mechanical parameters). The forming limit curves predicted by the Marciniak-Kuczynski model in each of the cases previously mentioned are compared with experimental data.
A New Clinching Process Especially for Thin Metal Sheets and Foils
Authors: Behrens Bernd-Arno , Bouguecha Anas , Eckold Claus Peter , Peshekhodov Ilya
Published: February 2012

A novel clinching process design to join thin metal sheets and foils is proposed. In this process a small cup is first stretched out of the sheet plane. A shape interlock between the two sheets is then created by a movement of the die and blank holder in the sheet plane lateral to the cup wall. Such an approach makes the undesired upsetting of the cup bottom redundant, which promises less energy consumption and a longer tool life when compared to conventional clinching processes. The process principle and its finite element analysis for austenitic steel sheets as well as deep-drawing steel sheets (both 0.3 mm thick) are presented. The numerical results suggest feasibility of the proposed design to produce a good shape interlock between two thin sheets.
Viscoplastic Regularization of Local Damage Models: A Latent Solution
Authors: Niazi M.S. , Wisselink H.H. , Meinders V. Timo
Published: February 2012

Local damage models are known to produce pathological mesh dependence in finite element simulations. The solution is to either use a regularization technique or to adopt a non-local damage model. Viscoplasticity is one technique which can regularize the mesh dependence of local damage model by incorporating a physical phenomenon in the constitutive model i.e. rate effects. A detailed numerical study of viscoplastic regularization is carried out in this work. Two case studies were considered i.e. a bar with shear loading and a sheet metal under tensile loading. The influence of hardening / softening parameters, prescribed deformation rate and mesh size on the regularization was studied. It was found that the primary viscoplastic length scale is a function of hardening and softening parameters but does not depend upon the deformation rate. Mesh dependency appeared at higher damage values. This mesh dependence can be reduced by mesh refinement in the localized region and also by increasing the deformation rates. The viscoplastic regularization was successfully used with a local anisotropic damage model to predict failure in a cross die drawing process with the actual physical process parameters.
FlexDie: A Flexible Tooling-Concept for Incremental Sheet Forming
Authors: Sebastiani Gerd , Wawrosch Arthur , Franzen Volker , Brosius Alexander , Tekkaya A. Erman
Published: February 2012

Forming tasks in Sheet Metal Prototyping are currently a balancing act between part flexibility and accuracy. In view of Asymmetric Incremental Sheet Forming (AISF), the part support is the decisive factor: Die-based processes such as TPIF are restricted to the given geometry of the part. On the other hand, the die-less variant (SPIF) is prone to a much more complex process-layout – once a similar accuracy needs to be obtained. Consequently, this requires a flexible die concept, supporting the part in the critical zones only. Within this article we meet this challenge by introducing the configurable tooling concept "FlexDie". This support tool comprises a construction kit for skeleton dies allowing for an adjustment of its geometry to almost any desired shape. Based on the solar cooker benchmark by Jeswiet et al., we show both the tooling-concept and the feasibility. The latter we discuss, based on the quality features geometric accuracy as well as surface quality. Both features are assessed with respect to the forming results obtained by use of a full-die. The accuracy resulting by applying the FlexDie is only slightly inferior to the parts formed by use of a full-die. However, the FlexDie allows for simple optimization of both, die and part geometry. In addition, compensation strategies by adapting the toolpath are still possible. In summary, the results show the feasibility of the FlexDie concept for industrial ISF tasks - even at very low production volumes.
Improved Tool Surfaces for Incremental Bulk Forming Processes of Sheet Metals
Authors: Sieczkarek Peter , Kwiatkowski Lukas , Tekkaya A. Erman , Krebs Eugen , Biermann Dirk , Tillmann Wolfgang , Herper Jan
Published: February 2012

Sheet-bulk metal forming is a process used to manufacture load-adapted parts with high precision. However, bulk forming of sheet metals requires high forces, and thus tools applied for the operational demand have to withstand very high contact pressures, which lead to high wear and abrasion. The usage of conventional techniques like hardening and coating in order to reinforce the surface resistance are not sufficient enough in this case. In this paper, the tool resistance is improved by applying filigree bionic structures, especially structures adapted from the Scarabaeus beetle to the tool’s surface. The structures are realized by micromilling. Despite the high hardness of the tool material, very precise patterns are machined successfully using commercially available ball-end milling cutters. The nature-adapted surface patterns are combined with techniques like plasma nitriding and PVD coating, leading to a multilayer coating system. The effect of process parameters on the resistance of the tools is analyzed experimentally and compared to a conventional, unstructured, uncoated, only plasma nitrided forming tool. Therefore, the tools are used for an incremental bulk forming process on 2 mm thick metal sheets made of aluminum. The results show that the developed methodology is feasible to reduce the process forces and to improve the durability of the tools.
The Load-Scanning Test – Evaluation of a Universal Tribological Model Test in View of Sheet Bulk Metal Forming
Authors: Hetzner Harald , Tremmel Stephan , Wartzack Sandro
Published: February 2012

Combining the loading conditions of two different classes of forming operations, in sheet bulk metal forming processes, contact pressures ranging from a few hundred MPa up to loads exceeding 2,500 MPa are experienced. With the additional need for an enhanced control of the material flow, which is best implemented by locally adapted frictional properties of the contact tool/workpiece, sheet bulk metal forming represents a challenge to tribology. As a consequence, the evaluation of the friction and wear properties of different surface modifications and lubricants within a variety of loading conditions is required. The load-scanning test is a universal tribological model test. Its most distinctive feature is the ability to assess the friction and wear behaviour of a tribological pairing within a whole range of contact loads in a single test run. The simple and quick test method also allows the investigation of plastic contacts. Due to these features, the load-scanning test is of particular interest with regard to the quantitative and qualitative evaluation of the application potentials and limits of use of tribological measures intended for sheet bulk metal forming. Like any model test, the load-scanning test has also specific drawbacks. In some test setups, the stress distribution in the contact area may be non-uniform. Further, the maximum realizable contact pressure may be limited by low yield strengths of the tested materials in combination with the insufficient flow restriction of the contact geometry and/or the moderate machine force. By comparison to other test methods and by giving examples of its application in different scenarios, the present paper discusses the potentials and limitations of the load-scanning test against the background of sheet bulk metal forming.
Material Model Identification for DC04 Based on the Numerical Modelling of the Polycrystalline Microstructure and Experimental Data
Authors: Lehmann Eva , Schmaltz Stefan , Germain Sandrine , Faßmann Dennis , Weber Christoph , Löhnert Stefan , Schaper Mirko , Bach Friedrich Wilhelm , Steinmann Paul , Willner Kai , Wriggers Peter
Published: February 2012

Sheet-bulk-metal forming processes require an accurate material model which is derived in this contribution. The microscopic model is based on a simulation of a real microstructure. A validation on the macroscopical scale is performed through the reproduction of the experimentally calculated yield surface based on the homogenised structural response of a corresponding deformed representative volume element (RVE). The microstructural material model is also compared with a macroscopical phenomenological model based on logarithmic strains. The homogenised microscopic model and the phenomenological macroscopic model are in good agreement with the evolution of the stresses and strains obtained during the experiments.
Development and Characterization of Ti5Al2.5Sn-ELI Alloy Hemispherical Domes for High-Pressure Cold Helium Tanks
Authors: Singh Satish Kumar , Muneshwar Pravin , Kumar K. Naresh , Pant Bhanu , Sreekumar K. , Sinha P.P.
Published: February 2012

Titanium alloys are used for high-pressure gas bottles / propellant tanks and structural applications owing to their high specific strength, good fabricability / weldability and compatibility with various working fluids. For these applications at ambient temperature, the workhorse Ti6Al4V alloy is extensively used. For the applications at low temperatures, two ELI grades of titanium alloys namely Ti6Al4V and Ti5Al2.5Sn are used as these retain toughness down to 77K and 4K respectively. Due to this inherent advantage, Ti5Al2.5Sn-ELI alloy has been selected as high pressure helium gas bottle submerged in liquid hydrogen (20K temperature). The gas bottle is spherical in shape and is made by electron beam welding of two machined hemispherical shells of 500 mm nominal diameter. The hemispherical shells for the difficult-to-forge Ti5Al2.5Sn-ELI alloy are developed through controlled closed-die forging operations. Shells are subsequently characterized for microstructures and mechanical properties at ambient temperature. Substantial increase in tensile strength with reasonably good ductility with respect to ambient temperature is achieved at 20K temperature. Multi point necking is observed at 20K. The present paper briefly outlines the process control devised for development of these domes and discusses the various characterization results obtained on forged hemispherical shells.
Hot Working of Ti Aluminide Made through Reaction Synthesis
Authors: Gupta Rohit Kumar , Pant Bhanu , Agarwala Vijaya , Sinha Parameshwar Prasad
Published: February 2012

Hot working of titanium aluminide made through reaction synthesis (RS) has been studied. Hot isostatic pressing under argon, isothermal pressing under vacuum, open die forging and pack forging was carried out. Hot worked billet samples were characterized for density and microstructure evolution. Presence of refined grains and dynamically recrystallized grains were observed. In case of open die forging, presence of twins was also found. From the present study, near isothermal working through near conventional processes has been confirmed. However, role of isothermal working in obtaining crack free sound deformed product has also been noted.
Processing of Al-Cu-Mg Alloy (V65 Grade) Bars as Feedstock for Wire Drawing
Authors: Nayan Niraj , Murty S.V.S. Narayana , Jha Abhay Kumar , Sharma S.C. , Sreekumar K. , Sinha Parameshwar Prasad
Published: February 2012

Al-Cu-Mg (Russian grade V65) alloys are used for riveting applications in aerospace industries due to relatively high shear strength of the order of 25 kg/mm2 combined with a high plasticity. The main advantage of using V65 aluminum alloy for rivet application comes from its significantly slower natural aging response, which gives flexibility to carryout riveting operation even after 4 days after solution heat treatment and natural aging at room temperature. This very valuable feature is not found in its counterpart alloy AA2024 where due to rapid aging kinetics of this alloy, the riveting operation must be completed within 30 min of the solution treatment, which is many times impractical. This paper presents the processing of V65 aluminium alloy by Direct Chill (DC) casting followed by subsequent secondary processing through extrusion and forging to realize feedstock for caliber rolling. These ingots were caliber rolled to 12 mm diameter rods at different temperatures and mechanical properties were evaluated in T6 and T4 tempers. Detailed microstructural examination using optical microscopy and fractography of the tensile tested samples using scanning electron microscopy were carriedout to correlate microstructure and mechanical properties.
Microstructure and Properties of Stir Cast AZ91 Mg Alloy – SiCp Composites
Authors: Prasanth Sujayakumar , Ajith Kumar Kumaraswamy Kaliamma , Rajan Thazhavilai Ponnu Deva , Pillai Uma Thanu Subramonia , Pai Bellambettu Chandrasekhara
Published: February 2012

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. Using stir casting process, AZ91 magnesium alloy metal matrix composites have been produced with different weight percentages (5, 10, 15, 20 and 25) of silicon carbide particles (SiCp) addition. Microstructural characterization reveals uniform distribution of SiC particles with good interfacial bonding between the matrix and reinforcement. Electrical conductivity and Co-efficient of Thermal Expansion (CTE) measurements carried out on these composites have yielded better properties. Improved mechanical properties such as hardness, ultimate tensile strength, and compressive strength are obtained. The microfracture mechanisms involved during tensile fracture is analyzed and correlated with the properties obtained.
Role of SiCP on Processing and Physical Characteristics of Al-Si-Mg/SiCP Composite Foams
Authors: Ravi Kumar N.V. , Gokhale Hina , Gokhale Amol A.
Published: February 2012

Metallic foams find specialised applications in industry due to their unique properties such as ultra light weight and high impact energy absorption. When ceramic particles (e.g. SiC, Al2O3) are present, metal matrix composite (MMC) foams can be fabricated. Further it is known theoretically that foam strength is proportional to strength of foam material, and also it has been established that metal matrix composites exhibit better strength vis-à-vis their matrix metal. Accordingly, the present work is undertaken to study the processing of composite foams. Al-Si-Mg/SiCP foams were successfully prepared via liquid metallurgy processing using TiH2. The role of particle size, volume fraction (5 to 20 vol. %), and temperature (640 and 670°C) on foaming tendency were explored using the design of experiments approach. Liquid foams with reasonably good expansions could be achieved for all the combinations of particle size, volume %, and foaming temperature. Temperature has a dominant effect on foam collapse (decay) during solidification, irrespective of the particle size and vol. %. For foams processed at 640°C, the cell size variation is marginal along the foam height, except at the top portion which has finer cells. The evolution of foam, and the role of SiC on foam stability are discussed based on macro and microstructural results.
Processing of Primary Silicon and Mg2Si Reinforced Hybrid Functionally Graded Aluminum Composites by Centrifugal Casting
Authors: Raghunandan S. , Hyder Jasim Akber , Rajan T.P.D. , Prabhu K. Narayan , Pai B.C.
Published: February 2012

In the present investigation, FGMs of mono-dispersed in-situ primary Si and their hybrids with Mg2Si reinforcements have been fabricated by the centrifugal casting process using 390 commercial Al alloy. Hard primary silicon particles are formed during the solidification of the 390 alloy and Mg2Si reinforcements are formed by the addition of varying amount of magnesium into the A390 aluminium alloy. Owing to the difference in density both primary silicon and Mg2Si gets segregated towards the inner periphery during centrifugal casting. The size of the Mg2Siin-situreinforcement phase is relatively smaller and is distributed in the edges of primary silicon particles and also individually in the matrix. Thein-situMg2Si and primary silicon can significantly increase the hardness and strength of the inner periphery of the casting. Higher Mg contents have been observed to introduce significant porosity leading to poor castings. Addition of phosphorous to the melt has led to the modification and refinement of primary Si morphology and also helped in the reduction of shrinkage porosity. Maximum hardness of 167 BHN is observed towards the inner periphery of the 390Al-2.5%Mg added in-situ composite.
Tensile Behaviour of Al-Si Alloy and Al-Si/Graphite Composites at Elevated Temperatures
Authors: Rajaram G. , Kumaran S. , Srinivas Rao T
Published: February 2012

The high temperature tensile behaviour of Al-Si alloy and two of its composite systems with graphite as major reinforcement were investigated. The composites were developed by the stir casting method, wherein a mixture of graphite (3 wt %) and Cu / Ni (2 wt% each) were added into the molten Al-Si alloy to fabricate two systems such as Al-Si-Cu/graphite composite and Al-Si-Ni/graphite composite. The properties of composites were better than that of the matrix alloy. Tensile behaviour of alloy and composites were studied at different temperatures from room temperature to 300°C. It is found that the tensile strength of the alloy and composites were decreasing with increase in temperature. The transition elements (Cu / Ni) have played the key role in improving the ultimate tensile and yield strength of the composites over the alloy. The flow stress of the composite is more than that of the alloy. The strain hardening exponent value continuously drops with the increase of tensile temperature due to the thermal softening effect. The % elongation of the alloy is more than that of the composites. Fracture surfaces of the samples are analyzed by scanning electron microscope to understand the fracture mechanisms. Fractography reveals that the fracture behaviour of the alloy changes from cleavage mode at room temperature to complete ductile mode at high temperature.
Slurry Erosion Response of Heat Treated 13Cr-4Ni Martensitic Stainless Steel
Authors: Amarendra Hassan Jayaraj , Kalhan Pradeep , Chaudhari Gajanan Prabhakar , Nath Sameer Kumar , Kumar Shravan
Published: February 2012

In the present work, effect of various heat treatments on slurry erosion behavior of 13Cr-4Ni martensitic stainless steel (MSS) at different impingement angles has been studied. The as-received cast bars of MSS were given various heat treatments. These heat treatments involved the austenitization of cast steel at temperatures of 950° C, 1000° C and 1050° C for different soaking durations of 2, 4 and 6 h at each temperature. This was followed by oil quenching then tempering for 1 h at a 600° C air cooled. Heat treated MSS samples were characterized for microstructure and mechanical properties viz. hardness, ductility (% elongation), tensile strength (UTS), and toughness. For wear characterization, slurry erosion tests were conducted at different impingement angles for as-received cast and heat treated samples. The heat treated MSS shows approximately 34% lesser weight loss as compared to as-received cast MSS. Increase in toughness of heat treated samples is found to be responsible for the improved slurry erosion resistance. Impingement angle close to 0° showed least wear loss.
Effect of Microstructure on Wear Characteristics of Spray Cast Al-Si Alloys
Authors: Raju K. , Harsha A.P. , Ojha S.N.
Published: February 2012

In the present study, the effect of microstructure on the wear characteristics of spray cast Al-15Si and Al-20Si alloys has been investigated and compared with that of vertical axis centrifugal cast and chill cast alloys. The spray cast alloys have been subjected to Hot Isostatic Pressing for porosity reduction. HIPing has reduced the porosity in the spray cast Al-15Si and Al-20Si alloys from 19% to 8% and 19% to 2% respectively. The microstructures of spray cast alloys consisted of finely divided globular shaped Si particles with sizes varying from 2–10 µm. The Si particles have been distributed uniformly throughout the Al matrix. On the contrary coarse and segregated microstructures have been observed in vertical axis centrifugal cast and chill cast alloys. The sizes of primary and eutectic Si in vertical axis centrifugal cast alloys are smaller than that in chill cast alloys. The wear rates are the lowest for spray cast alloys and highest for chill cast alloys over a wide range of sliding velocity. The reasons for better wear resistance of spray cast alloys have been discussed in the light of the microstructural features evolved during spray casting.
Analysis on Characteristic Features of L-Mode Guided Wave in Tube Testing
Authors: Adalarasu S.
Published: February 2012

Applications of long range ultrasonic testing are on cylindrical products(pipes and tubes) and planar products(plates and sheets).Guided wave testing using circumferential and longitudinal modes are getting more and more importance as there are huge requirements for testing pipes and tubes in power generators, Chemical plants, steam generators etc.. There will be infinite number of modes with charectestic propagation and wave structure. This propagation characteristic and wave structure plays a major role in deciding its suitability for use in specific application. It is highly essential to use mode control and to understand the generated modes and its characteristics based on which only testing adequacy can be evaluated. In this paper the characteristic features of L-mode generated using a source design parameter for tube testing are explained. The dispersion characteristic of L-mode are discussed using constructed Dispersion Curves, phase and group velocity, its multiple defect detection capability, pulse shape and amplitude dynamics with propagation range and inclination. The details of controlled experiment conducted and the observations are discussed. The derived inferences are explained based on the applicable particle displacement equations and dispersion characteristic equations.
Analysis of Trace Additives in Copper Alloys for Space Applications: A Comparison between Graphite Furnace Atomic Absorption Spectrometry and Inductively Coupled Plasma Atomic Emission Spectrometry
Authors: Jayalatha T. , Sivadas Deepthi L. , Dimple Roopa , Jacob Salu , Rajeev R. , Rao V. Lakshmana
Published: February 2012

Cu-Cr-Zr-Ti alloy is a special type of copper alloy being used as thrust chamber material in cryogenic engine, owing to its good thermal conductivity and mechanical properties at high temperature. Presence of alloying elements like chromium, zirconium and titanium in lower percentage has considerable effect on the thermal and mechanical properties of the thrust chamber material. Hence the accurate estimation of alloying elements as well as trace impurities is an important part of the quality control process in the manufacture of these materials. In analytical methods like XRF, F-AAS etc. which are used for chemical analysis of alloys, the intensity of analytical signal is highly dependent on matrix composition and hence precise matching of sample and standard matrices is required for drawing accurate results. ICP-AES is well-established analytical technique offers better detection limit, wide linear dynamic range, high precision, good accuracy, and practically negligible chemical interferences for the estimation of alloying elements. An accurate and precise technique for quantitative estimation of the elements viz. chromium, zirconium, titanium, iron, manganese, nickel, lead etc. in Cu-Cr-Zr-Ti alloy has been successfully developed using ICP-AES and GF-AAS. Merits and demerits of the two analytical techniques are also compared with respect to the result obtained.
Ageing Kinetics in Carbon Nanotube Reinforced Aluminium Alloy AA6063
Authors: Kashyap Kishore T. , Puneeth K. Bagaria , Ram Aniruddha , Koppad Praveenath.G.
Published: February 2012

Multiwalled carbon nanotubes (MWCNTs) were added to Aluminium alloy AA6063 by powder metallurgy route. The samples were compacted, sintered and microhardness was measured on sintered samples. The weight fraction of MWCNTs was varied between 0.5-2.5%. The hardness of the composite has been observed to increase. The ageing curves after solutionizing and artificial ageing have been plotted for various weight fractions of MWCNTs in AA6063 alloy. Electroless copper coating was given to CNTs and the hardness of the samples with Cu coated CNTs in AA6063 showed a higher hardness than the samples without Cu coating on CNTs. Further the ageing curves showed a faster kinetics with increase of MWCNTs in Al6063. This result applied to coated CNTs in 6063 which also showed accelerated ageing kinetics during artificial ageing gives inherent evidence for the Arsenault’s thermal mismatch model of strengthening of MWCNT/Al nanocomposite.
Fabrication and Upconversion Luminescence of Highly Transparent Er:YAG Ceramics
Authors: Qin Xian Peng , Zhang Jian , Yang Hao , Luo De Wei , Ma Jan , Tang Ding Yuan , Wang Shi Wei
Published: February 2012

Highly transparent Er:YAG ceramics with different Er concentration were fabricated by a solid-state reaction and vacuum sintering method. The optical properties, the microstructure and the upconversion luminescence of the Er:YAG ceramics were investigated. For 3 mm thick samples, the in-line transmittances of the as-fabricated Er:YAG ceramics at the wavelength of 1100 nm and 400 nm were about 84% and 82%, respectively, which was very close to the theoretical transmittance of YAG ceramics. The micrograph of the Er:YAG transparent ceramics exhibited a pore-free structure and the average grain size was about 10 μm. The grain boundary of the ceramics was clean and no secondary phase was detected. When pumped by a 980 nm LD, the strong green and red upconversion luminescences in the Er:YAG ceramics were observed. The different upconversion mechanisms depending on Er concentration in the Er:YAG ceramics were also discussed.
Tc99m-HMPAO white blood cell scintigraphy: added value of SPECT/CT for infection diagnosis in cardiothoracic surgery
Authors: Prandini Napoleone , Panareo Stefano , Cultrera Rosario , Peterle Chiara , De Cristofaro Valentina , Roncali Massimo , De Biasi Vincenzo , Badia Lorenzo , Feggi Luciano
Published: February 2012

We report a case of a woman who came to our attention because of fever and a sternal fistula draining purulent fluid. Four years before, she had undergone cardiothoracic surgery to place a patch because of a myocardial rupture. Under suspicion of a deep mediastinal infection, a Tc99m-HMPAO white blood cell (WBC) scintigraphy was performed. The use of planar imaging and single photon emission computed tomography (SPECT/CT) imaging allowed the identification of a sternal infection, which involved the anterior mediastinum up to pericardium and diaphgram. SPECT/CT led to a precise diagnosis of a thoracic infection, providing the location and extent of the disease. This turned out useful to improve therapeutic strategies.
Reflexões sobre a aprendizagem matemática em adultos
Authors: C. O. Freitas Rony
Published: February 2012

This paper presents a reflection about adult workers learning Mathematics, arising from doctoral research. The theme has permeated discussions, productions and research on the Proeja at the Instituto Federal do Espírito Santo. We have focused the discussions only on pedagogical aspects in view of the difficulty to engage in psychological theories to understand the cognitive constructions produced by adults. Some aspects have been more relevant when referring to the adults learning mathematics, from the group interaction, the quest for freedom, educational buildings, instructional materials, curriculum, teacher practice, from own experiences and dialogue. In this paper we deepen the last two, given the importance that we have observed, and the influence we have seen over the others. We use as the theoretical influences of research in Adult Education, Professional Education and bring the Critical Mathematics Education to support our vision and our actions in the context of Mathematics.
Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)
Authors: Day K. A. , Taylor M. J. , Mitchell N. J.
Published: February 2012

Abstract. Atmospheric temperatures and winds in the mesosphere and lower thermosphere have been measured simultaneously using the Aura satellite and a meteor radar at Bear Lake Observatory (42° N, 111° W), respectively. The data presented in this study is from the interval March 2008 to July 2011. The mean winds observed in the summer-time over Bear Lake Observatory show the meridional winds to be equatorward at meteor heights during April−August and to reach monthly-mean velocities of −12 m s−1. The mean winds are closely related to temperatures in this region of the atmosphere and in the summer the coldest mesospheric temperatures occur about the same time as the strongest equatorward meridional winds. The zonal winds are eastward through most of the year and in the summer strong eastward zonal wind shears of up to ~4.5 m s−1 km−1 are present. However, westward winds are observed at the upper heights in winter and sometimes during the equinoxes. Considerable inter-annual variability is observed in the mean winds and temperatures. Comparisons of the observed winds with URAP and HWM-07 reveal some large differences. Our radar zonal wind observations are generally more eastward than predicted by the URAP model zonal winds. Considering the radar meridional winds, in comparison to HWM-07 our observations reveal equatorward flow at all meteor heights in the summer whereas HWM-07 suggests that only weakly equatorward, or even poleward flows occur at the lower heights. However, the zonal winds observed by the radar and modelled by HWM-07 are generally similar in structure and strength. Signatures of the 16- and 5-day planetary waves are clearly evident in both the radar-wind data and Aura-temperature data. Short-lived wave events can reach large amplitudes of up to ~15 m s−1 and 8 K and 20 m s−1 and 10 K for the 16- and 5-day waves, respectively. A clear seasonal and short-term variability are observed in the 16- and 5-day planetary wave amplitudes. The 16-day wave reaches largest amplitude in winter and is also present in summer, but with smaller amplitudes. The 5-day wave reaches largest amplitude in winter and in late summer. An inter-annual variability in the amplitude of the planetary waves is evident in the four years of observations. Some 41 episodes of large-amplitude wave occurrence are identified. Temperature and wind amplitudes for these episodes, AT and AW, that passed the Student T-test were found to be related by, AT = 0.34 AW and AT = 0.62 AW for the 16- and 5-day wave, respectively.
The Konya earthquakes of 10–11 September 2009 and soil conditions in Konya, Central Anatolia, Turkey
Authors: Aksoy R. , Demiröz A.
Published: February 2012

Abstract. Earthquakes registering magnitudes Md = 4.5 and 4.7 struck the city of Konya, Central Anatolia, on 10–11 September 2009, causing very slight damages. The earthquake epicenters were located at the east of Sille District along the Konya Fault Zone, a dip-slip fault. The nature and seismicity of the fault zone indicates that it is capable of producing earthquakes of moderate magnitudes. This paper summarizes the geologic data along the fault zone and documents groundwater conditions and analyzes borehole and geotechnical data of the Konya city. The residential area of the city covers an area of approximately 1150 square kilometers and consists almost entirely of flat land except for a small part of rugged land in the southwestern corner. Groundwater and geotechnical data were collected and analyzed to evaluate the liquefaction potential of deposits under the Konya city. This preliminary investigation indicates that areas for liquefaction are generally limited to the eastern and east central parts of the city.
CORPORATE GOVERNANCE AND FIRM VALUE IN EMERGING MARKETS AN EMPIRICAL ANALYSIS OF ADR ISSUING EMERGING MARKET FIRMS
Authors: Ficici Aysun , Aybar C. Bulent
Published: February 2012

This study explores the value implications of good corporate governance for a sample of 54 ADR issuing emerging market firms (EMFs) from 9 countries primarily located in the regions of Asia, Eastern Europe and Latin America and the and employs recently constructed company composite corporate governance metric along with some alternative corporate governance measures associated with the origin of the issuing firm. Although the ADR literature primarily focuses on the impact of subscription to US disclosure requirements we contend that company and country specific corporate governance standards play a significant role in the risk reduction and ensuing value capture.  The fundamental inquiry in this study has the following foci: The primary focus is on the impact of corporate governance structures on firm performance as to whether adherence to standards creates market value for ADR issuing EMFs.  Do good corporate governance practices affect the value of EMFs? The secondary focus is concerned with whether the impact of corruption level and legal system in a firm’s home country affect the corporate structures of EMFs thus affecting the market value of firms.  In this study, we utilize Tobin’s q as the measure of firm performance/market value.  Our findings suggest that there is a significant correlation between corporate governance structures of ADR issuing EMFs and their market values and/or performances.  The results also indicate that the level of corruption and legal structures in home countries of EMFs strongly impact the corporate governance structures of these firms and sequentially affect their market values. Therefore, this research further contributes to the scholarly findings and suppositions that corporate structures of firms do create consequences on firm value.
SERVANT LEADERSHIP AND ORGANIZATIONAL TRUST: THE MEDIATING EFFECT OF THE LEADER TRUST AND ORGANIZATIONAL COMMUNICATION
Authors: Rezaei Morad , Salehi Sajjad , Shafiei Masomeh , Sabet Somaye
Published: February 2012

The purpose of this paper aims to clarify the relationship between servant leadership and organizational trust, and tries to demonstrate the mediator role of leader trust and organizational communication in this relationship. The study sample included 258 employees of Guilan province Tax Administration and for sampling we used cluster method. Previous studies have also focused on the positive impact of servant leadership in organizational trust and in this article the results show that there is a significant relationship between servant leadership, organizational trust, leader trust and organizational communication.
Study into the Iron Content of Seminal Plasma in Normal and Infertile Subjects
Authors: Skandhan KP , Mazumdar BN , Sumangala B
Published: February 2012

The iron content in seminal plasma of normal (n19), oligozoospermic (n11), azoospermic (n12), oligoasthenozoospermic (n19), and asthenozoospermic (n17) subjects was estimated by using atomic absorption spectrophotometer. The concentration of iron in normal seminal plasma varied from 265 to 365 mg%. The source of iron in seminal plasma seems to be the adnexal glands and not spermatozoa, as azoospermic semen also contained it. A statistically highly significant difference was seen when normal was compared with azoospermia and with asthenozoospermia. The necessary average wastage of iron through semen is calculated as 2.52 mg/day. This value is highly variable according to the seminal volume and frequency of ejaculation.
Public Law: Towards a Post-National Model
Authors: Schuppert Gunnar Folke
Published: February 2012

The enactment and enforcement of law is regarded as one of the most important attributes of sovereign statehood. Traditionally, ‘sovereignty’ has been understood as meaning the special quality of a state expressed in its ability to shape its own legal system and to enforce it within the territorial limits of its jurisdiction. Hence, the question of the extent to which member states of the European Union are still masters of their legal systems turns out to be a crucial test of their sovereignty. This chapter argues that the legal system of Germany is a Europeanized legal system, in terms both of a European modification of national laws and of a Europeanization of legal culture and modes of governance. This argument takes the form of testing the degree of Europeanization in six different cases, including the field of constitutional law. The conclusion is that the legal system of Germany is a Europeanized legal system and that the German legal profession is quite aware of this development.
The Media Agenda: The Marginalization and Domestication of Europe
Authors: Voltmer Katrin , Eilders Christiane
Published: February 2012

This chapter investigates whether the assumption that the media contribute to the communication deficit of the EU is reflected in the empirical pattern of political coverage. In particular, it explores the extent to which German media take a Europeanized perspective on political affairs and whether or not they promote the politics of European integration. The study is based on a content analysis of the editorials of German national quality newspapers covering the period between 1994 and 1998. The findings show that the media under study devote only a very small portion of their attention to European issues, thus marginalizing Europe to an extent that is not warranted by the significance of the European level of governance. If the media do focus on European issues, they predominantly address them in terms of national politics, which is interpreted as a ‘domestication’ of Europe in public discourse. At the same time, the media unanimously support the idea of European integration. This pattern of communicating Europe reflects the élite consensus on European matters in Germany and may have contributed to the alienation of the general public from European politics.
The Puzzling Rise in Childbearing Outside Marriage
Authors: Ermisch John
Published: February 2012

This chapter analyses the rise of incidence in childbearing outside marriage. In the last quarter of the twentieth century, the percentage of births outside marriage rose from 9% in 1975 to 40% in 2000. This chapter shows that the major factor accounting for this change is the dramatic rise of cohabitation among young people. It then analyses why there has been widespread substitution of cohabiting unions for direct marriage in Britain. The chapter concludes with a discussion on the implications for changes in family life.