bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated Micro-Sensor Detection System of Meteorological Information
Authors: Liu Hui Chao , Lou Wen Zhong , Hong Rong Sen , Zu Shao Peng
Published: February 2012

This paper describes a meteorological detection system integrating a variety of micro-sensors. Carried by shrapnel, this system is adaptable to complex environment and can gather long-range meteorological information of the region concerned. Basic work process is as follow, the information acquisition module is delivered by shrapnel to the designated area. In the process of falling, meteorology, location and time data is obtained through the micro-sensors and GPS receiver. After analyzing and calculating by the Micro Control Unit, the information received will be transmitted to the user terminal by wireless transmission module. Thus the information collection is completed. The use of micro-sensor makes this system compact, stable and less energy consumption, so the system is worth high practical value.
A Monolithic Integrated Pressure Sensor
Authors: Zhang Zheng Yuan , Yang Cao , Mei Yong , Feng Zhi Cheng , Li Xiao Gang , Li Jian Gen , Hu Guo Xiang
Published: February 2012

pressure sensor, CrSi resistor networks, temperature compensation. Abstract. In this paper, focused on especial requirement monolithic integrated resistance pressure sensor, pressure structure, signal processing circuits and process compatible technology of sensor and IC were studied. The feebleness pressure signal monitoring circuits was designed, high precision CrSi resistor networks was used for temperature compensation of resistance pressure sensor, and a monolithic integrated pressure sensor only 2.3×2.3mm2 was obtained. The measuring results are as follows, measurement range is 5-115kPa, the maximum Vout is more than 4.5V, sensitivity is 1.2%.
Failure Prediction in Sheet Metal Forming Depending in Pre-Straining and Bending Superposition
Authors: Denninger Ralf , Liewald Mathias , Sindel Manfred
Published: February 2012

The automotive industry nowadays, uses numerical simulation systems to determine process safety of car body parts. Forming simulations are usually used to predict local necking and cracks during the deep-drawing operation or to calculate the spring-back behaviour. Furthermore, FEA is also used for optimizing the hemming process. In this contribution, further development and the use of an enhanced failure criterion for the evaluation of flanging and hemming processes are shown. This criterion describes material failure caused by incipient surface cracks on the bending edge keeping the predominant bending load conditions in consideration. The investigations of the bending conditions in this criterion include loads from previous forming operations and geometrical aspects, such as bending radii. The approach presented in this contribution can deliver a more reliable prediction regarding the expected material failure.
Using Image Analysis Techniques for Single Evaluation of the Chip Shrinkage Factor in Orthogonal Cutting Process
Authors: Batista Moises , Calamaz Madalina , Girot Franck , Salguero Gómez Jorge , Marcos Mariano
Published: February 2012

The forces involved in a cutting process are related, for example, with the power consumption, with the final quality of the workpiece and with the chip geometry obtained, since these forces determine the compression experimented by the chip and therefore its final geometry. The orthogonal cutting process assisted with a High Speed Filmation (HSF) permit obtains a digital filmation of the process with high magnification. This filmation permits to obtain a measurement of the longitudinal changes produced in the chip. This deforms are related with the Shrinkage Factor, ζ. And in this case the Stabler hypothesis is enabled, by that using the shear angle and the rake angle is possible obtain a value of the Shrinkage Factor in a different conditions.
White and Dark Layer Analysis Using Response Surface Methodology
Authors: Ambrogio Giuseppina , di Renzo Serena , Gagliardi Francesco , Umbrello Domenico
Published: February 2012

This paper presents a study of the influence of cutting conditions on the finished surface obtained after an hard turning process, in particular a case study is presented where AISI 52100 bearing steel is machined under different cutting conditions. An analysis carried out using Surface Response Methodology has been developed in order to study the influence of the main cutting parameters such as cutting speed, feed rate and workpiece initial hardness on white (WL) and dark layer (DL) thickness. The whole experimental campaign has been performed using a chamfered PCBN tool inserts without any cutting fluid. Results show an evident influence of cutting speed and feed rate on both white and dark layer thickness while less relevant is the contribute given from the workpiece hardness on defining WL and DL depth. Finally, a model to find the optimal process conditions to minimize white and dark layer thickness is developed.
Coupled Thermo-Mechanical Analysis of Process-Integrated Powder Coating by Means of Hot Rolling
Authors: Kebriaei Reza , Frischkorn Jan , Reese Stefanie , Moll Heiko , Theisen Werner , Husmann Tobias , Meier Horst
Published: February 2012

In this paper, a new hybrid production technique is presented. It exploits the advantage of high temperatures and high forces in the ring rolling process. This manufacturing technique is not only suitable to increase the ring’s diameter but also to apply and compact powder metallurgical multi-functional coatings onto solid substrate rings with the same process. In order to design this new process parameterized 2D and 3D FE models are created in ABAQUS/EXPLICIT on the basis of a viscoplastic material model formulation. The control capability of the conventional control mechanisms are based on the assumption of volume consistency. However, this assumption is not well applicable for a ring furnished by multi-functional surfaces with non-isochoric plastic deformation behavior. Therefore, this paper deals with the implementation of a new control mechanism. Finally the paper is concluded with the integration of heat treatment of the rolled ring into the subsequent cooling process.
3D Hyperelastic Constitutive Model for Yarn Behaviour Description
Authors: Charmetant Adrien , Vidal-Sallé Emmanuelle , Boisse Philippe
Published: February 2012

The preforming stage of the LCM composite manufacturing processes lead to fibrous reinforcement deformations which may be very large especially for double curvature shapes. Those deformations have significant influence on the second stage of the process, i.e. the injection of the resin. A way to predict accurately the spatial distribution of the permeability tensor consists in simulating for various configurations, the deformed shape of the reinforcement at the scale of the yarns. Mesoscopic scale analyses of textile reinforcements generally consider the yarns as a continuous material despite their fibrous nature. In order to have an accurate simulation tool, it is necessary to build up a constitutive law which accounts for the physical specificities linked to the microstructure of the yarns. Several models exist with reasonable accuracy. The present paper proposes a new approach in the hyperelasticity framework. The proposed model is based on the definition of mathematical invariants linked to the four main deformation modes of the yarn material: tension, compaction, longitudinal shear and transverse shear. The strain energy potential build up with those invariants is identified using classical fabric material tests: uni- and bi-axial tension and compression. The model has been validated on laboratory tests such as bias extension tests and gives promising results.
Influence of Processing Parameters on Bonding Conditions in Backward Extrusion Forged Bonding
Authors: Yoshida Yoshinori , Matsubara Takamasa , Yasui Keisuke , Ishikawa Takashi , Suganuma Tomoaki
Published: February 2012

In this study, conditions of metallurgical bonding between steel and aluminum in cold forging process is investigated. Two-layered cylindrical cup of the materials is produced in cold backward extrusion in five processing velocity conditions. Small tensile test specimens are cut off at the bonding boundary in the product using a wire-cutting machine and the bonding strength on the boundary is measured in tensile test using the specimens. Fractured contact surfaces are observed with an electron microscope for investigation of bonding. Finite element analyses for the backward extrusion are conducted and surface expansion ratio and interface pressure on the boundary are calculated. The influence of process conditions, extrusion velocity and surface expansion ratio and boundary pressure, on the bonding are investigated.
An Investigation of the Material Flow in a Screw Extruder of Aluminium Using Contrast Material
Authors: Widerøe Fredrik , Welo Togeir
Published: February 2012

The material flow in a screw extruder of aluminium was investigated. Screw extrusion of aluminium is a new solid state process where granulate aluminium is consolidated and extruded in a single continuous process using a rotating screw as the pressure generating device. Understanding the material flow is vital for predicting the consolidation and welding process thereby making it possible to optimize screw and container design to increase the capacity, ekstrudate quality and process stability. Using a prototype screw extruder, aluminium alloy AA6060 was extruded together with contrast material using different feeding schemes to visualize the material flow. Material left in the extruder was inspected visually, sectioned and etched in NaOH to reveal the interaction between the contrast material and the AA6060. It was found that newly fed contrast material primarily displaced material in the centre of the screw channel and the extrusion chamber hereby revealing the main paths of the material flow. Areas of sticking friction, material dead zones and zones of slow material displacement rate were effectively identified using this method.
On the Fundamental Mechanism of Seam Welding in Extrusion of Aluminum Alloys
Authors: Valberg Henry , Khan Yawar Abbas
Published: February 2012

In extrusion of hollow Al-profiles two kinds of pressure welds are present inside the extrusion. One is called the charge weld (CW) and forms across the boundary interface between two billets extruded in sequence. The other is the seam weld (SW) which extends longitudinally along the extruded profile and the extrusion metal behind each die bridge. It is considered to form because of the splitting of the extrusion metal over the die bridge into metal streams which flow past the bridge and rejoin as they encounter behind the bridge. Over the time attempts have been made to explain the mechanics of extrusion welding for both the CW and the SW. Still there is lack of understanding of how these welds form, the main reasons for this is that the deformation conditions around a die bridge are complex and difficult to investigate. Because of the recent advancement of two technological fields, experimental grid pattern analysis and simulation of metal flow by FEA; new tools for analysis of the mechanics of formation of the SW and the CW are now available. The simplest possible case of 2D-extrusion seam welding is considered here and an attempt is made to describe the fundamental deformation mechanisms present when this weld forms behind a butt-ended die bridge.
Dynamic Characteristics of a Micro-Sheet-Forming Machine System
Authors: Qin Yi , Razali Akhtar Razul , Zhou Mei , Zhao Jie , Harrison Colin , Wan Nawang Wan Adlan
Published: February 2012

Dynamic characteristics of a micro-forming machine system are of significant importance to be considered if high-precision micro-parts are to be produced. This is because forming tolerances may be within a range of sub-microns up to 5-15% of the thickness of a thin sheet-metal (e.g. <100µm) being used in micro-sheet-forming. Achievability of the quality parts often vary with the machine-system performance and process parameters being set, and it largely depends on the understanding of the machine and tool system’s dynamic characteristics and effectiveness of the control of the machine and the process. Nevertheless, there has been lack of the effort in this field of research. Significant number of the efforts in this field were focused mainly on discrete and/slow processes where the dynamic characteristics of the forming systems were often neglected. This paper presents the dynamic characteristics of an autonomous micro-sheet-forming machine system and its effect towards the produced parts’ quality. These have been studied by combining finite element analysis and forming experiment, with a particular focus on the combined effects from the machine, tooling system and the sheet-metal feeding system (the strip feeder). The results showed that, besides importance of the dynamic performance of the machine and the tool-system, dynamic characteristics of the material-feeding plays an important part in determining the parts’ quality produced.
Using Cross Stamping to Test Zinc Sheets Formability
Authors: Jansen Yann , Logé Roland E. , Milesi Marc , Manov Stephan , Massoni Elisabeth
Published: February 2012

Sheet metal formability has been studied for a half century. The sheet formability is mostly described by the Forming Limit Diagram (FLD). A prediction of this FLD is a source of interest for industrial companies. Indeed knowing the FLD of a material allows optimization of the production processes which leads to money saving. Nevertheless, the formability tests (tensile, bulge and Nakazima tests) which give the experimental FLD do not really represent the process that the sheet will undergo in industrial conditions. The paper therefore focuses on a cross stamping test. The material of interest is a Zinc sheet. FLD prediction is reported for a wide variety of metals [1] but literature about Zinc is nearly non existent. The studied Zinc sheets exhibit a highly anisotropic mechanical behaviour due to the hcp lattice structure and the inherited rolling texture. This anisotropic behaviour results in an anisotropic formability. The Zinc sheet FLD is influenced by the orientation of the rolling direction during the process. Experimental cross stamping of this material allows describing the studied material behaviour in a large range of mechanical solicitations from tensile to biaxial tension. The experimental results are compared with the finite element simulation and permit to understand where and why failures appear, which leads to a better understanding of Zinc anisotropic formability.
Compartmentalized Model for the Mechanical Behavior of Titanium
Authors: Tabourot Laurent , Balland Pascale , Raujol-Veillé Jonathan , Vautrot Mathieu , Déprés Christophe , Toussaint Franck
Published: February 2012

As close as you watch them, the materials (especially metals) present discontinuities that can easily be qualified as strong. Dislocations, structures formed by these dislocations, phases and grains are all discontinuities, also sources of heterogeneity, with effects on material behavior that are not really well reproduced by a model based on a continuity assessment. Consequently, the materials should be considered as a set of compartments with different behaviors. This promotes an alternative way to define models. A coherent modeling process is probably the integration of the different behaviors of the material compartments within the global model. The objective is here to build an efficient elasto(visco)plastic model of the mechanical behavior of titanium combining compartmentalized behaviors. After setting the frame of the study, which is of primary importance, the proposed modeling process is running as follows (i) choose a local behavior, (ii) identify the parameters of crystalline texture that must be integrated into the simulation and (iii) finally formulate a way of combining local compartments behaviors. The intrinsic properties of Finite Element codes are used to achieve the integration of the whole system.
Implementation and Validation of a Gurson Damage Model Modified for Shear Loading: Effect of Void Growth Rate and Mesh Size on the Predicted Behavior
Authors: Achouri Mohamed , Germain Guenael , dal Santo Phillippe , Saidane Delphine
Published: February 2012

The optimization of automotive security components requires good knowledge of the material state after fabrication, particularly with respect to damage that may have been done to the material by the manufacturing process. To achieve this, numerical simulation of the fabrication process is often undertaken. However, classical continuum damage models, like the Gurson [3] model, are not appropriate for the simulation of the blanking by punching operation because the material damage is primarily the result of shear stresses. This work is focused on the use and validation of a modified Gurson type damage model capable of modeling this process, which has recently been proposed by Nahshan [7]. After a brief description of the modification, the implementation and the validation of the modified Gurson model is detailed. A comparison between the original Gurson model and the modified model is presented in order to highlight the importance of the modification for a pure shear stress state and to show that the two models are equivalent for a purely hydrostatic stress state. It is also shown that the results from the modified model are dependent on the finite element mesh size.
Anisotropic Plastic Behavior of TRIP 780 Steel Sheet in Hole Expansion Test
Authors: Panich Sansot , Uthaisangsuk Viton , Suranuntchai Surasak , Jirathearanat Suwat
Published: February 2012

Plastic behavior of advanced high strength steel sheet of grade TRIP780 (Transformation Induced Plasticity) was investigated using three different yield functions, namely, the von Mises’s isotropic, Hill’s anisotropic (Hill’48), and Barlat’s anisotropic (Yld2000-2d) criterion. Uniaxial tensile and balanced biaxial test were conducted for the examined steel in order to characterize flow behavior and plastic anisotropy in different stress states. Additionally, disk compression test was performed for obtaining the balanced r-value. According to the different yield criteria, yield stresses and r-values were calculated for different directions and then compared with experimental data. To verify the modeling accuracy, a hole expansion test was carried out experimentally and numerically by FE simulation. Stress-strain curve from the biaxial test was described using voce and swift hardening models. Punch load and stroke, final hole radius, and strain distribution on specimen surface along the hole circumference and the specimen diameter in rolling and transverse directions were determined and compared with the experimental results. It was found that the simulations applying Yld2000-2d yield function provided an acceptable agreement. Consequently, it is noted that the anisotropic yield potential significantly affects the accuracy of the predicted deformation behavior of sheet metal subjected to hole expanding load.
Evaluation of the Enhanced Assumed Strain and Assumed Natural Strain in the SSH3D and RESS3 Solid Shell Elements for Single Point Incremental Forming Simulation
Authors: Guzmán Carlos Felipe , Ben Bettaieb Amine , de Sena José Ilídio Velosa , de Sousa Ricardo J. Alves , Habraken Anne Marie , Duchêne Laurent
Published: February 2012

Single Point Incremental Forming (SPIF) is a recent sheet forming process which can give a symmetrical or asymmetrical shape by using a small tool. Without the need of dies, the SPIF is capable to deal with rapid prototyping and small batch productions at low cost. Extensive research from both experimental and numerical sides has been carried out in the last years. Recent developments in the finite element simulations for sheet metal forming have allowed new modeling techniques, such as the Solid Shell elements, which combine the main features of shell hypothesis with a solid-brick element. In this article, two recently developed elements -SSH3D element [1, 2] and RESS3 element [3]- implemented in Lagamine (finite element code developed by the ArGEnCo department of the University of Liège) are explained and evaluated using the SPIF line test. To avoid locking problems, the well-known Enhanced Assumed Strain (EAS) and Assumed Natural Strain (ANS) techniques are used. The influence of the different EAS and ANS parameters are analized comparing the predicted tool forces and the shape of a transversal cut, at the end of the process. The results show a strong influence of the EAS in the forces prediction, proving that a correct choice is fundamental for an accurate simulation of the SPIF using Solid Shell elements.
Acquisition of Heuristic Knowledge for the Prediction of the Frictional Behavior of Surface Structures Created by Self-Excited Tool Vibrations
Authors: Breitsprecher Thilo , Hense Rouven , Hauer Franz , Wartzack Sandro , Biermann Dirk , Willner Kai
Published: February 2012

The selective control of the frictional behavior (tailored friction) in metal forming processes is of high importance with regard to technical and economic aspects. This applies especially for the sheet-bulk-metal forming process. Milling with intentionally invoked regenerative tool vibrations can be applied in order to generate structured surfaces with tailored friction properties on the forming tool. These structures affect the formation of lubrication pockets during the forming process which determine the local frictional properties exceedingly. The full potential of this emerging technology can, however, only be revealed if the heuristic and design-relevant knowledge is acquired and provided to the tool-designer already in the early phases of process development. One thing the tool-designer has to specify is the local frictional behavior on the tool surface. But, however, he does not know which milling parameters lead to the necessary surface structures because in most cases he has no expert knowledge in milling, tribology and forming tools. In this paper data mining is used to determine the frictional behavior based on these parameters. The potential of this method in the described context is revealed by the application on data derived from simulation results, both from milling simulations and contact simulations. The latter are performed by using a Halfspace model for rough surface contact. Both approaches for these simulations, the data mining process and the results are explained to the reader.
Processing and Characterization of Al-Cu-Li Alloy AA2195
Authors: Nayan Niraj , Murty S.V.S. Narayana , Sharma S.C. , Sreekumar K. , Sinha P.P.
Published: February 2012

The objective of the present study was to melt and cast AA2195 alloy in Vacuum Induction Melting (VIM) under dynamic inert atmosphere. These billets were homogenized and subsequently hot forged and rolled to sheets. The products in the form of sheets were subjected to T8 (Solution Treatment +WQ+CW+Aging) temper condition. Mechanical properties were evaluated at room temperature and correlated with microstructure. Highest mechanical properties obtained in T87 temper have been reported.
Effect of Process Parameters on Splat Formation during Impingement of Liquid Metal Droplets over a Cold Substrate
Authors: Kumar Amitesh , Sahoo Seshadev , Ghosh Sudipto , Dhindaw Brij Kumar
Published: February 2012

Molten metal droplet impingement is an integral part of droplet based manufacturing processes like spray casting and sprays coating. In these processes, in a single operation, a liquid metal stream is atomized into fine droplets, which impact on a substrate to form a bulk deposit. The properties of casting or coating strongly depend on the shape of splats formed by individual droplets after impingement and solidification. Therefore, considerable research studies have been carried out to characterize individual droplet impact, usually driven by an interest in a particular process. These studies include extensive modeling of droplet deposition, some of which are supported by experimental studies. Most of these modeling activities have focused on the impingement of a droplet on to a surface to predict quantities such as the extent of maximum spread and the final equilibrium diameter, the rate of heat transfer to the substrate, and the solidification rate. Due to interaction of several complex phenomena, comprehensive modeling of the droplet deposition is a challenging task. The flow of liquid droplet upon impingement is itself a complex phenomenon. Heat transfer and solidification occurring concurrently with the flow adds further to the complexity. Thus the present study aims at the development of a comprehensive mathematical model of impingement of liquid metal droplet upon a substrate to understand the effect of process parameters such as initial temperature of droplet, size of droplet and velocity of droplet.
High Strain Rate Superplasticity in an Al-Mg-Sc-Zr Alloy Produced by Equal Channel Angular Pressing and Subsequent Cold and Warm Rolling
Authors: Avtokratova Elena , Sitdikov Oleg , Mukhametdinova Oksana , Markushev Michael
Published: February 2012

Superplastic (SP) properties of an Al−5%Mg−0.2%Sc−0.08%Zr alloy subjected to equal channel angular pressing (ECAP) at T=325°C with an effective stain of ~ 8 and subsequent rolling at the same and ambient temperatures were studied. It has been shown that the formation of ultrafine grained (UFG) structure with the grain size of about 1 μm and the volume fraction 0.6-0.7 under ECAP resulted in exceptionally high SP ductilities in a wide temperature - strain rate range. Maximum elongations ~3300% appeared at 475°C and the strain rate () of 5.6×10-2s-1. Subsequent warm rolling with a total reduction of 86% led to increased to 0.8-0.85 volume fraction of ultrafine grains with no changes in grain size. Cold rolling with reduction of 80%, in contrast, provided a heavily deformed structure with high dislocation density. In spite of the difference in the alloy microstructures, the SP properties in both rolled conditions were close to similar. The both states exhibited SP behavior with maximum elongation of ~ 2800% at 520°C and = 1.4 ×10-2s-1.
Structural and Mechanical Behaviour of Severe Plastically Deformed OFE Copper Processed by Constrained Groove Pressing Technique
Authors: Kumar S.S. Satheesh , Raghu T.
Published: February 2012

Oxygen free electrolytic (OFE) grade copper sheets (5mm thick) are severe plastically deformed by constrained groove pressing technique (CGP) at room temperature up to three passes thereby imparting a total plastic strain of 3.48 throughout the sheet material. The revelation of significant grain refinement investigated by light microscopy in constrained groove pressed sheets markedly signifies the ability of CGP technique for processing fine grained sheet materials. Relatively higher grain refinement rates are observed during initial passes. Deformation homogeneity evaluated from Vickers microhardness measurements indicated inhomogeneous deformation behaviour during early stages of straining; however enhancement in deformation homogeneity is observed later. CGP processed sheets subjected to room temperature tensile tests showed significant increase in strength associated with drop in ductility. Marginal gain in ductility coupled with slight decrease in strength attributed to the dominance of dislocation recovery is observed after third pass.
Strengthening Behavior of Bulk Ultra Fine Grained Aluminum Alloys
Authors: Manna R. , Mukhopadhyay N.K. , Sastry G.V.S.
Published: February 2012

Billets of aluminum and aluminum alloys have been deformed at room temperature using a die having equal channels of 10 mm diameter intersecting at an inner angle of 120° and outer arc of 60° by equal channel angular pressing (ECAP) to ultra fine grain (UFG) size level, adopting route Bc. Mechanical properties were evaluated by tensile testing and microhardness measurement. Effects of alloying elements on strengthening were explored. The strengths increase rapidly at first few passes and then reach to a saturation level. The improvement in strength at initial passes of ECAP is due to work hardening and subgrain or dislocation cell formation. However, strengthening at large number of passes is due to the grain refinement alone. The rate of strengthening as a function equivalent strain decreases to a minimum. The strengthening level of bulk UFG alloys is about 3.5 to 4.5 times to that of starting materials. The major cause of strengthening is grain refinement apart from solute strengthening. Among Mg, Zn and Ag alloying elements, the strengthening effect is highest for Mg and lowest for Ag. Ductility is regained without affecting the strength after sufficient number of passes when microstructure becomes equiaxed and ultra-fine in size. However, ductility of UFG Al alloys is lower than that of their coarse grained counterpart.
Cobalt and the Toughness of Steel
Authors: Garrison Warren M.
Published: February 2012

In developing compositions for new ultra-high strength steels it is important to understand the effects of alloying additions on the microstructure, strength and fracture resistance. Cobalt has been widely used in the development of high toughness ultra-high strength steels and the effects of cobalt on the strength of steels has been studied extensively but there is remarkably little known about how cobalt influences toughness. In this article are reviewed the effects of cobalt on the toughness of steel. The literature suggests that cobalt in solid solution will act to raise the ductile-to-brittle transition temperature but that it can act to increase the upper-shelf toughness of steel.
Densification of γ-TiAl Powders by Spark Plasma Sintering
Authors: Kennedy Sarangapani , Kumaran S. , Rao T. Srinivasa
Published: February 2012

The superior thermo-physical properties of γ–TiAl alloys like low density, good oxidation resistance and high strength retention at elevated temperature makes it a suitable material for high temperature structural applications. However they have poor low temperature ductility and poor creep resistance at service temperatures. It is expected that nanocrystalline γ–TiAl alloys can overcome this difficulty with improved mechanical properties. Spark plasma sintering (SPS), one of the novel powder metallurgy techniques offers the advantage of manufacturing nanostructured materials. The present paper reports on the basic investigation of densification behaviour of nanostructured γ–TiAl alloy consolidated by spark plasma sintering. As received prealloyed γ–TiAl powder was milled in a high energy ball mill with optimized parameters for 20 and 40 hours. The structural transformations of these powders were studied by X-ray diffraction (XRD) and electron microscopy (SEM). These milled powders as well as unmilled powders were consolidated by spark plasma sintering with varying temperature. The density of these sintered samples was measured by Archimedes principle. The density of spark plasma sintered samples were 92%, 96% and 98% for unmilled, 20hrs and 40hrs, respectively. The densification behavior of these powders with respect to temperature has been studied by measuring the instantaneous linear shrinkage of the specimen that was indicated by the z-axis displacement. It was observed that 60% of densification occurred at temperature range of 700-1000°C .
Challenges in Characterization and Acceptance of Metal Matrix Composite “Carrier Plate” Material for Space Applications
Authors: Shah A.K. , Thaker M.H. , Vyas K.B.
Published: February 2012

In space applications, day by day, the electronic devices are becoming compact with increase in operating frequencies and high power requirements posing challenges in design and selection of materials for high thermal dissipation requirements. In order to achieve optimum performance from thermal management material, engineers have to focus on high reliable, cost effective alternatives. Such materials need to demonstrate excellent thermal conduction to minimize thermo-mechanical stress and fatigue due to operations like soldering, thermal cycling and severe operating conditions. The paper describes a new family of thermal management composite material called “SILVAR”.
Fracture Mechanics of Conventional and Narrow Groove Pulse Current Gas Metal Arc Welds of HSLA Steel
Authors: Kumar Ravi Ranjan , Ghosh P. K.
Published: February 2012

Mechanical and fracture properties of 20MnMoNi55 grade high strength low alloy (HSLA) steel welds have been studied. The weld joints were made using Gas Tungsten Arc Welding (GTAW), Shielded Metal Arc Welding (SMAW) and Pulse Gas Metal Arc Welding (P-GMAW) methods on conventional V-groove (V-Groove) and Narrow groove (NG-13). The base metal and weld metal were characterised in terms of their metallurgical, mechanical and fracture toughness properties by following ASTM procedures. The J-Integral fracture test was carried out using compact tension C(T) specimen for base and weld metal. The fracture toughness and tensile properties of welds have been correlated with microstructure. In conventional V-groove welds prepared by P-GMAW shows the improvement in initiation fracture toughness (JIC) as compared to the weld prepared by SMAW. Similar improvements in tensile properties have also been observed. This is attributed to reduction in co-axial dendrite content due to lower heat input during P-GMAW process as compared to SMAW. In the narrow groove P-GMA weld prepared at f value of 0.15 has shown relative improvement of JIC as compared to that of the weld prepared by SMAW process.
Comparative Study on Tempering Response of Martensitic Grade AISI-420 Stainless Steels with Varying Carbon Content
Authors: Kumar Anil , Kumar Gupta Rohit , Karthikeyan M.K. , Ram Kumar P. , Sinha Parameshwar Prasad
Published: February 2012

Martensitic grade stainless steels are being extensively used in aerospace, defence and nuclear sectors for structural applications. Specialized applications require close control in chemistry and heat treatment parameters. Control of carbon in AISI-420, alloying content has typical service advantages. To study the effect of tempering temperature with carbon content on mechanical properties, various heat treatment cycles were devised, avoiding the regime of temper embrittlement. This paper presents the tempering response of medium carbon stainless steel AISI-420 grade with respect to change in carbon content from 0.2% to 0.3%. It is observed that, by varying the tempering temperature, the grade can be tailored to obtain wide range of mechanical properties. With increasing carbon content, martensite is found to be changing in morphology from lath to lath & plate (mixed) and the amount of retained austenite also increases. An attempt has been also made to arrive at a structure-property correlation in this grade of stainless steel.
Microstructural Characterisation of AA2219 Weldments
Authors: Swathi Kiranmayee M. , Jha Abhay Kumar , Manwatkar Sushant K. , Ramesh Narayanan P. , Sreekumar K. , Sinha Parameshwar Prasad
Published: February 2012

Aluminium alloy AA 2219 has been selected for fabrication of both earth storable and cryogenic propellant tanks of launch vehicles due to its high specific strength, compatibility with liquid propellants, good resistance to stress corrosion cracking (SCC), excellent properties at cryogenic temperatures and good fabricability including weldability. Propellant tanks are fabricated by welding sheets in T87 and rings in T851 temper conditions. Microstructural characterization was carried out on the weldments with sheet-sheet and sheet-forge configuration using optical microscopy and electron microscopy with energy dispersive spectroscopy. Microstructure of weld pool had dendritic pattern, typical of weld cast structure. Fine recrystallised grains were observed near fusion line. Heat affected zone on either side of the weld revealed thickened grain boundaries. EDS on these thickened grain boundaries indicated composition of eutectic. Microhardness and tensile strength for both the configurations was evaluated. Fractures surface of tensile tested specimens were examined for fracture morphology and to understand the role of eutectic film in fracture. Presence of the eutectic film along the grain boundaries was explained with the help of liquation mechanism and Al-Cu phase diagram. This paper brings out details of the investigation carried out.
Preparation, Characterization and Nox Sensing Characteristics of Sensor Grade CuInO2 Thin Films
Authors: Prabhu E. , Gnanasekar K.I. , Jayaraman V. , Gnanasekaran T.
Published: February 2012

CuInO2phase, a p-type semi-conducting oxide was successfully stabilized in thin film form by pulsed laser deposition technique and the deposition parameters were optimized. The gas sensing studies carried out on thin film of CuInO2for different concentrations of NOxexhibited a decrease in resistance, a characteristic of p-type semiconductor. The thin film responded to 4 vppm of NOxin air. The CuInO2thin film did not respond to trace levels of hydrogen, ammonia and petroleum gas at this operating temperature and thus offering selectivity to NOx.
Electroless Coating of Silver on Multiwall Carbon Nanotubes
Authors: Nayan Niraj , Murty S.V.S. Narayana , Sharma S.C. , Sreekumar K. , Sinha Parameshwar Prasad
Published: February 2012

Silver reinforced with carbon nanotubes, instead of graphite, would increase both the electrical conductivity, hardness and wear resistance of the electrical brush materials. The effective utilization of carbon nanotubes in the Ag/CNT composite depends strongly on its uniform distribution and strong interfacial adhesion to the silver matrix and thus demands for its surface modification. In order to carry out the surface modification of carbon nanotubes, electroless coating was given to them after liquid phase oxidation, sensitization and activation process. The room-temperature chemical treatment results in a nominally complete coating over the entire outer surface of multiwall carbon nanotube. The surface morphology of the carbon nanotubes after each step has been studied using TGA, DSC, XRD, FTIR and SEM.
The Influence of Gate Material, SiO2 Fabrication Method and Gate Edge Effect on Interface Trap Density in 3C-SiC MOS Capacitors
Authors: Gutt Tomasz , Malachowski Tomasz , Przewlocki Henryk M. , Engström Olof , Bakowski Mietek , Esteve Romain
Published: February 2012

This paper reports on results of interface trap analysis of 3C-SiC MOS capacitors fabricated using four different gate materials and two SiO2 oxide preparation methods. The results indicate that post-deposition annealing in wet oxygen of PECVD deposited SiO2 samples increases the near-interface or slow trap densities, compared with wet oxygen thermally oxidized samples. It has also been found that the energy distribution, Dit, of electron states at the oxide/SiC interface of MOS capacitors with different sizes depend on the factor R=P/A, where P stands for the gate perimeter and A for the gate area, which is related to the amount of stress under the edge of the metallic gate.
Parallel and Serial Association of SiC Light Triggered Thyristors
Authors: Dheilly Nicolas , Pâques Gontran , Scharnholz Sigo , Planson Dominique
Published: February 2012

This paper demonstrates the parallel and serial association of two SiC light triggered thyristors. Such systems are needed to increase the power handling capacity of SiC switches. The devices and their fabrication are presented. The experiments and their results are detailed, addressing particularly the problem of voltage and current sharing during the switching of the thyristors.
Dose Influence on Physical and Electrical Properties of Nitrogen Implantation in 3C-SiC on Si
Authors: Song Xi , Biscarrat Jérôme , Bazin Anne Elisabeth , Michaud Jean François , Cayrel Frédéric , Zielinski Marcin , Chassagne Thierry , Portail Marc , Collard Emmanuel , Alquier Daniel
Published: February 2012

In this paper, we studied the influence of nitrogen implantation dose on both physical and electrical properties in 3C-SiC grown on Si (100) substrate. Scanning Transmission Electron Microscopy characterizations prove that high dose is responsible for amorphization of the implanted layer and the high defect density after annealing. A high V-shape defect density is still found in the implanted layer after an annealing at 1350°C. By lowering the dose, the layer is less damaged and no amorphization is observed. For the different doses, low Specific Contact Resistances are measured using Ti/Ni contacts. The Specific Contact Resistance value decreases from 8x10-6 Ω.cm2 for the high dose to 3.2x10­6 Ω.cm2 with decreasing the dose. Furthermore, the dopant activation ratio, evaluated by quantitative SSRM measurements, is improved at the same time from 17% (for the high dose) to 60% (for the low dose). This work demonstrates that high activation ratio can be achieved consecutively to a nitrogen implantation at reasonable implantation fluence.
Barrier Inhomogeneities of a Medium Size Mo/4H-SiC Schottky Diode
Authors: Zaman Muhammad Yousuf , Perrone Denis , Ferrero Sergio , Scaltrito Luciano , Naretto Marco
Published: February 2012

Forward current-voltage characteristics of a medium sized (3.05mm2)Mo/4H-SiC (molyb-denum on silicon carbide) Schottky diode|fabricated for high power applications | are analysedwithin a temperature range of 125-450 K. Accurate theoretical modeling is carried out using Tung'smodel in which it is considered that numerous low barrier nanometer size patches, present in uniformhigh barrier, are responsible for the inhomogeneities in the Schottky barrier of SiC-based electronicdevices. A significant difference is observed between the effective area involved in the current trans-port and the geometric area of the Schottky contact along with a dependence of the ideality factor andhe barrier height on temperature. The obtained values of uniform Schottky barrier and Richardson'sconstant are seen to be in accordance with previous works. It is concluded that the above mentionedmodel can be used to describe the electrical behaviour of Mo/4H-SiC Schottky diodes.
Si+ Implantation and Activation in GaN Comparison of GaN on Sapphire and GaN on Silicon
Authors: Bazin Anne Elisabeth , Cayrel Frédéric , Lamhamdi Mohamed , Yvon Arnaud , Houdbert Jean Christophe , Collard Emmanuel , Alquier Daniel
Published: February 2012

In this paper, we evaluated gallium nitride heteroepitaxially grown on sapphire (GaN/Sa) and grown on silicon (GaN/Si) faced to implantation doping. Si+ was implanted on low doped n-type epilayers in order to create a plateau around 1020at.cm-3. All the samples were capped with a silicon oxide and annealed between 1000°C and 1150°C. The surface quality was evaluated in terms of roughness, pit density and maximum pit diameter using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Finally, the dopant electrical activation was studied with Ti-Al contacts using the circular Transfert Length Method (c-TLM). This study shows that low Specific Contact Resistance (SCR) values of 8x10-5Ω.cm2 and 6x10-6Ω.cm2 are respectively obtained on GaN/Sa sample annealed at 1150°C-2min and on GaN/Si sample annealed at 1150°C-30s, proving that good ohmic contacts are obtained on both materials. Nevertheless, a compromise has to be done between the low SCR values obtained and the GaN surface degradation, observed by AFM and SEM after the different annealing treatments and which could affect the good behaviour of the GaN devices.
Comprehensive Analysis of Process Variability on AlGaN/GaN HEMTs through TCAD Simulations
Authors: Miccoli Cristina , Cinnera Martino Valeria , Rinaudo Salvatore
Published: February 2012

AlGaN/GaN high electron mobility transistors (HEMTs) have shown outstanding improvements in performance and reliability, becoming the leading option for power applications in the 1-40 GHz range. However, the presence of traps and defects in the hetero-structure are strongly correlated to the tolerance of the fabrication process. New powerful models designed to overcome limitations associated with the Process Variability (PV) may be part of the exploitation outcome. This work describes a methodology useful to characterize the effects of PV on AlGaN/GaN HEMTs performance, by deriving Process Compact Model (PCM) from systematic TCAD simulations. The device under examination is an Al0.26Ga0.74N/GaN HEMT and the selected critical process parameters are: molar fraction of the first AlGaN layer, AlGaN layer thickness, source-gate and drain-gate distance, field plate extension, gate height and width, recessed effect under the gate contact.
GaN-on-Silicon Evaluation for High-Power MMIC Applications
Authors: Pantellini Alessio , Lanzieri Claudio , Nanni Antonio , Bentini Andrea , Ciccognani Walter , Colangeli Sergio , Limiti Ernesto
Published: February 2012

Today microwave market has identified GaN-HEMT technology as a strategic enabling technology for next generation MMICs to be implemented in high performance RF sub-assemblies such as T/R Modules, Solid State Power Transmitters, Compact Receivers, High Speed Communications. To allow commercial market entry of GaN technology, a tradeoff between high RF performance and low cost is mandatory and a possible solution is represented by GaN-on-Silicon substrate. In this scenario the evaluation of FETs RF performance and losses of passive components are demanding to understand the feasibility of GaN MMIC on Si. Following such approach, in SELEX Sistemi Integrati a 4 inches GaN-on-Si wafer containing discrete active devices and passive components has been fabricated with the 50μm Si thickness. RF FETs performance demonstrates an output power of 4W/mm @ 3GHz, while passive components characterization exhibits similar behavior of GaN SiC passive elements up to C Band.
Almost Free Standing Graphene on SiC(000-1) and SiC(11-20)
Authors: Jabakhanji Bilal , Camara Nicolas , Caboni Alessandra , Consejo Christophe , Jouault Benoit , Godignon Philippe , Camassel Jean
Published: February 2012

We present the growth and characterization of epitaxial Graphene on the (000-1) and (11-20) planes. In both cases, the growth was carried out in a RF furnace, by implementing our technique of confined atmosphere, covering the SiC substrate with a graphitic cap during the growth. The grown material was investigated by means of AFM, SEM, Raman spectroscopy and magneto transport. Contrary to the (0001) face, in both faces (000-1) and (11-20), almost free standing Graphene monolayers of very high quality are grown. These Graphene sheet are uniform, continuous, almost strain-free and lightly doped. In both faces, Hall bars were fabricated and Shubnikov-de Haas oscillations typical of Graphene, as well as the Half Integer Quantum Hall Effect are observed.
Graphene Nano-Biosensors for Detection of Cancer Risk
Authors: Guy Owen James , Burwell Gregory , Tehrani Zari , Castaing Ambroise , Walker Kelly Ann , Doak S.H.
Published: February 2012

Biosensor diagnostics based on bio-functionalized semiconductor devices are an important development in ultrasensitive sensors for early detection of disease biomarkers. Electrochemical devices using chemically modified graphene (CMG) channels are excellent candidates for nanobiosensors. This paper presents the development of novel antibody functionalized epitaxial graphene devices for bio-sensing applications. Epitaxial graphene has been grown on silicon carbide (SiC) substrates under high vacuum and high temperature conditions (1200 – 1700°C). A generic electrochemical surface functionalisation chemistry, which can be used to attach a variety of “bio-receptors” to graphitic surfaces, has been developed. The attached bio-receptors are capable of specific and selective interaction with disease biomarkers. When a target biomarker molecule interacts with the “bio-receptor” functionalized surface, the charge density at that surface is affected. This change can be detected as an electrical signal from the biosensor, enabling highly sensitive (nM) detection of biomarker analytes. This paper reports the fabrication of graphene channel sensors for detection of disease biomarkers.