bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic Properties of Rhombus Dodecahedron Open-Cell Cellular Materials
Authors: Zhu Hong , Zhang Li Gang , Qi Xiang Dong
Published: June 2013

Based on the principle of pore formation, geometrical model to describe open-cell cellular materials was constructed. The model is rhombus dodecahedron cell shapes with circle-strut and transitional-junction. The dependence of relative density on the microstructure of the model was analyzed; by finite elements method, the relative elastic modulus of the model was calculated, the influence of microstructure and relative density on the elastic modulus was also obtained. The results show that circle-strut radius and transitional-junction curvature radius are the primary factors on relative density increment; nonlinearity of relative density on relative elastic modulus is similar to that of circle-strut radius on relative elastic modulus, is obviously greater than that of transitional-junction curvature radius on relative elastic modulus.
FSW of AA 2139 Plates: Influence of the Temper State on the Mechanical Properties
Authors: Velotti Carla , Astarita Antonello , Buonadonna Pasquale , Dionoro Gennaro , Langella Antonio , Paradiso Valentino , Prisco Umberto , Scherillo Fabio , Squillace Antonino , Tronci Aurelio
Published: June 2013

Nowadays the fiber reinforced materials are finding more and more widespread use in aeronautic field due to their features of lightness, high strength and flexibility of manufacturing systems. The only way for metals to remain competitive for the aerospace applications is to improve new technologies and alloys in order to realize lighter and more resistant structures. The development of new alloys (lighter and stronger) and technologies will allow to use metals also in the future for aerospace applications. In this scenario the research activity has a fundamental importance, and the key point is to work simultaneously on both innovative materials and new technologies that allow to obtain the best performances with the innovative alloys. Welding is nowadays playing a fundamental role in transport industry thanks to the important advantages it allows. Friction Stir Welding (FSW) [1] is one of the most promising welding techniques, particularly suitable for applying to light alloys. FSW in butt joint configuration allows to achieve very high mechanical performances, often absolutely superior to those achievable with all other joining techniques, and lots of researches and results are now available [2]. The AA 2139 is an innovative Al-Cu-Ag alloy that has higher mechanical performances than the conventional 2xxx series aluminum alloys. The AA 2139 is designed to work in service in T8 temper condition, but is simplest to work in T3 temper condition. The aim of this work is to compare the performances of AA 2139 butt joints welded in T8 temper conditions, presented in a previous work [3], with the ones of joints welded in T3 condition and heat treated post welding in order to achieve the T8 temper condition.
Partial Joining of Blanks with Electrochemical Support (ECUF)
Authors: Schmidt Hans Christian , Homberg Werner , Grundmeier Guido , Maier Hans Jürgen
Published: June 2013

Hybrid materials offer great potential for weight and cost reduction, function integration and improved mechanical properties. A whole range of parts or application areas are conceivable (especially in the field of lightweight design). In terms of implementation, it is possible to produce fully or partially joined semi-finished parts from metallic, organic or inorganic materials. Semi-finished parts of this type can be used in applications ranging from simple reinforcements to complex hollow structures in automobiles. Innovative production processes are necessary for the efficient manufacture of these parts. This is why the current research and development work is focused on making complex, hollow work pieces from hybrid semi-finished materials and on manufacturing methods for the partially joined semi-finished parts. A new and innovative incremental joining process with inline electrochemical treatment is opening up interesting perspectives here. For the manufacture of complex work pieces, the use of adapted sheet-metal-forming processes, like deep drawing or working-media-based high pressure forming, is highly promising and will be addressed in the paper.
Characterization and Modeling of the Elastic Behavior of a XC68 Grade Steel Used at High Strain Rates and High Temperatures
Authors: Tabourot Laurent , Balland Pascale , Vautrot Mathieu , Hopperstad Odd Sture , Raujol-Veillé Jonathan , Toussaint Franck
Published: June 2013

This article discusses the characterization and modeling of the elastic behavior of a semi-hard steel used in incremental forming operations which implies great loading speeds at high temperatures and large springback after each passage of the roller. The knowledge of the elastic behavior is essential to correctly predict these springbacks during forming. The objective is therefore on the one hand the characterization of the elastic response of the material under different conditions and on the other hand the definition of a model that describes the material behavior with as much precision as possible. To this end, two models, one phenomenological and the other built on more physical basis, are considered.
On the Study of Distinct Algorithmic Strategies in the Implementation of Advanced Anisotropic Models with Mixed Hardening
Authors: Grilo Tiago Jordão , Valente Robertt , de Sousa Ricardo J. Alves
Published: June 2013

In this study, suitable distinct stress integration algorithms for advanced anisotropic models with mixed hardening, and their implementation in finite element codes, are discussed. The constitutive model studied in the present work accounts for advanced (non-quadratic) anisotropic yield criteria, namely, the Barlat et al. 2004 model with 18 coefficients (Yld2004-18p), combined with a mixed isotropic-nonlinear kinematic hardening law. This phenomenological model allows for an accurate description of complex plastic yielding anisotropy and Bauschinger effects, which are essential for a reliable prediction of deep drawing and springback results using numerical simulations.In the present work distinct algorithm classes are analysed: (i) a semi-explicit algorithm that accounts for the sub-incrementation technique; (ii) the cutting-plane approach (semi-implicit integration); and (iii) the fully-implicit multi-stage return mapping procedure, based on the control of the potential residual. The numerical performance of the developed algorithms is inferred by benchmarks in sheet metal forming processes. The quality of the solution is assessed and compared to reference results. In the end, an algorithmic and programming framework is provided, suitable for a direct implementation in commercial Finite Element codes, such as Abaqus (Simulia) and Marc (MSC-Software) packages.
Asymmetric Yield Locus Evolution for HCP Materials: A Continuum Constitutive Modeling Approach
Authors: Tari Dariush Ghaffari , Worswick Michael J. , Ali Usman
Published: June 2013

A continuum-based plasticity approach is considered to model the anisotropic hardening response of hexagonal closed packed (hcp) materials. A Cazacu-Plunkett-Barlat (CPB06) yield surface is modified to create anisotropic hardening in terms of the accumulated plastic strain. The anisotropy and asymmetry parameters are replaced with saturation-type functions and the new modified model is then optimized globally to fit the material response. Furthermore, the effect of the number of linear stress transformations performed on the deviatoric stress tensor is investigated on the capability of the model to capture the response from the experiments. By increasing the number of stress transformations, more flexibility is obtained. However, increasing the number of stress transformations increases the arithmetic calculations involved in the material model. The proposed approach is an effective and time efficient method to create material models with complex evolving tension/compression behavior.
Hot Deformation Studies of a Low Carbon Steel Containing V
Authors: Poletti Cecilia , Dikovits Martina , Ruete Javier
Published: June 2013

Low alloyed steels produced by continuous casting are thermomechanically treated to achieve final high mechanical properties, meaning a good combination of strength and toughness. The hot deformation mechanisms of a micro-alloyed steel containing up to 0.1wt% of V is studied by means of hot compression tests using a Gleeble® 3800 device. Austenitization of samples is carried out at 1150°C during 2 minutes followed by cooling to the deformation temperature at 1Ks-1 in the range of 750 – 1150°C. The studied strain rate range is from 0.01 to 80 s-1 and the total true strain achieved is of 0.7. In situ water quenching is applied after the deformation to freeze the microstructure and avoid any post dynamic effect. The Ar3 temperature is determined by dilatometry experiments to be 725°C for the used cooling rate. The stress values obtained from the compression tests are evaluated at different strains to determine the strain rate sensitivity and flow instability maps and thus, to predict the formability of the material in the range of studied deformation parameters. These maps are correlated to the microstructure at specific deformation parameters.
Modelling of Polishing Tools for High Spatial Frequency Defect Correction on Aspherical Surfaces
Authors: Goupil Antoine , Iordanoff Ivan , Charles Jean Luc , Rinchet André
Published: June 2013

Nowadays, precision Computer Controlled Optical Surfacing (CCOS) and processes like Ion Beam Finishing (IBF) or Magneto-Rheological Finishing (MRF) allow manufacturing of fused silica optics with nanometer precision. However, High spatial frequency defects remain on the optics and need to be previously smoothed. Full aperture semi-flexible polishing tools can be used, as they can guarantee uniform pressure on low frequency patterns to preserve the pre-formed aspherical shape while maintaining a high pressure differential on high frequency defects, thus smoothing them. That behavior can be obtained with tools that combine a continuous flexible layer for low frequency compliance and a fractionate viscoelastic polishing layer for high frequency defect polishing. The main goals of this study are predicting smoothing efficiency and form control of different tools, and then determining the best tool to achieve a good balance between them. To do this, a multiscale model is developed. First, at the whole tool scale, for a given aspherical shape, the largest misfit between tools and surfaces is mathematically determined, depending on machining parameters. Then a finite-element parametric study is performed and yields for the flexible layer the best mechanical properties and thickness as well as the optimal applied force to achieve pressure homogeneity at the global aspherical shape level. Second, at the viscoelastic polishing layer level, the Discrete Element Method (DEM) is used to investigate the tool – workpiece interface. A model based on the viscoelastic cohesive beam method is developed, thus allowing taking into account the polishing layer’s dynamic response depending on the excitation frequency. The optical surface is also modeled by interpenetrated discrete elements, paving the way for a full-DEM model of the polishing layer – workpiece interface. Smoothing simulations are separated in two steps : the first one is the initial pressure application, leading to an initial state of full tool – surface contact with an homogeneous pressure. Then the tool is moved over the surface and the dynamic pressure is calculated depending on defect and polishing layer properties as well as tool kinematics. By analyzing the pressure differential on defects it becomes possible to calculate the smoothing efficiency of a given polishing layer and therefore optimize its properties depending on the defects that need to be smoothed.
A Theoretical Study of the Effect of the Double Strain Path Change on the Forming Limits of Metal Sheet
Authors: Butuc Marilena , Barlat Frédéric , Grácio José , Vincze Gabriela
Published: June 2013

The present paper aims at a theoretical study of the forming limits of a sheet metal subjected to double strain path changes by using as reference material the AA6016-T4 aluminum alloy sheet. The simulation of plastic instability is carried out through the Marciniak-Kuczynski analysis. The initial shape of the yield locus is given by the Yld2000-2d plane stress yield function. The strain hardening of the material is described by the Voce type saturation law. Linear and several complex strain paths involving single and double strain path changes are taken into account. The validity of the model is assessed by comparing the predicted and experimental forming limits under linear and selected one strain path change. A good accuracy of the developed software on predicting the forming limits is found. A sensitive analysis of the influence of the type and value of the double prestain in the occurrence of the plastic flow localization is performed. A remarkable effect of the double strain path change on the sheet metal forming limits is observed.
Flow Characteristics of New Steel Grades Dedicated to Hot Stamping
Authors: Bruschi Stefania , Ghiotti Andrea , Novella Michele
Published: June 2013

The reduction of the maximum temperature is one of the main goals in the research activities dedicated to hot sheet stamping, thanks to the benefits it can produce in terms of energy consumption and die wear decrease. New steel grades are being expressly developed with the aim of reducing the austenitization temperature without losing the mechanical characteristics and the formability shown by the conventional Usibor 1500P™. In the present work, the flow behavior of four new steel grades is investigated by means of hot tensile tests at varying thermo-mechanical conditions. Results are presented and discussed in terms of obtained mechanical and ductility characteristics.
Reduction of Springback in Hat Channel with High-Strength Steel Sheetby Stroke Returning Deep Drawing
Authors: Geka Taro , Asakura Masayuki , Kiso Takuma , Sugiyama Takashi , Takamura Masato , Asakawa Motoo
Published: June 2013

This study investigated the twisting phenomenon in curved hat channel products made of dual-phase 980-MPa-class high-tensile-strength steel sheets. The stroke returning deep drawing (SRDD) method was proposed to deal with twisting. In this new method, after the punch reaches the bottom dead point, it returns to a certain drawing height without the blank holder being removed. With the application of the SRDD method, twisting hardly occurred, but sidewall curl increased. A two-step SRDD was then proposed to reduce the sidewall curl of SRDD products. In the two-step SRDD method, a stroke returning process is carried out in two steps under different conditions. The results showed that the two-step SRDD method reduced the sidewall curl and twist simultaneously.
Investigation on Effect of Slide Motion Control on Stamping of High Strength Steel Sheets
Authors: Takamura Masato , Nishimura Shigeru , Sunaga Hideyuki
Published: June 2013

High strength steel sheets are increasingly used in automotive body parts with the aim of weight reduction, but their use urgently requires further improvement in sheet forming technology to overcome difficulties such as poor formability, dimensional inaccuracy, etc. On the other hand, servo press facilities are becoming increasingly used in industry and many attempts are being made to bring out their characteristic features for enhancing the formability of high strength steel sheets. Although some of these attempts have been successful in finding the advantages of servo presses for improving formability and dimensional accuracy, the mechanisms of such improvements have yet to be clarified in conjunction with the mechanical properties of the materials used. One of the most remarkable features of the servo press lies in its flexibility in slide motion control. It is thus effective to investigate the relevance of strain rate sensitivity of a material to the mechanism of improvement in formability enabled by the flexible slide motion of the servo press. However, very few studies have been carried out with material testing, material modeling, and numerical analyses combined with experimental verifications. In this study, Norton’s creep model was implemented in the FEM solver in order to take into account visco-elasto-plastic deformation including stress relaxation behavior. Parameters for the visco-elasto-plastic material model were identified through physical measurements and FEM simulations of uniaxial tension and crosshead displacement dwell tests, as shown in Fig. 1. The identified material model was applied to sheet forming simulations of an automotive body part and validity of the model was examined by comparing with stamping experiments using a servo press with a variety of slide motions. Numerical results with the identified material model showed the same tendency with respect to the slide motions as the experimental results. Stress relaxation behavior was found to be an important factor for improving formability enabled by modifying the slide motion.
Determination of Tool Motions in Stretch Forming Process for Aerospace Applications by Using Finite Element Method
Authors: Hatipoglu Hasan Ali , Alkas Celal Onur , Karadogan Celalettin
Published: June 2013

Stretch forming process is commonly used in the aircraft industry for the manufacturing of large sheet panels. The success of this process is highly dependent on the tool motions during forming. These motions are determined by trial - error procedure and it is costly. This study aims to optimize the stretch forming process by determining the necessary tool motions with numerical analysis. For this purpose, finite element model (FEM) of the process is established. Material characterization and friction tests of mostly used aluminum alloys are conducted for input to the model. In order to improve the model and validate the numerical results, experimental work will be performed in which the deformation of the sheet is measured optically.
Experimental Determination of Heat Transfer Coefficients for Forming of Stainless Steel Sheets Considering Process Conditions and Deep-Drawing Film
Authors: Schmid Philipp , Liewald Mathias
Published: June 2013

Heat transfer coefficients are playing an important role in forming of metastable stainless steel sheets. Metastable austenitic stainless steels are highly influenced by heating of forming tools due to generation of latent heat during forming process. Strain-induced martensite formation and hence the TRIP-effect is directly coupled with the temperature development within forming tools as well as the temperature induced by heat controlled tools. Measurements of heat development in serial deep drawing processes are showing the need for an accurate determination of heat transfer coefficients considering actual process conditions. Heat transfer coefficients were determined with a simple and easy applicable measurement device for tool materials AMPCO 25 and cold work tool steel EN 1.2379 in combination with aluminum, austenitic EN 1.4301 and ferritic EN 1.4016 stainless steel grades. Special attention was paid to production-related individual influences such as surface conditions, lubrication and deep drawing film. Experiments were accomplished between 1-15 N/mm² showing high influence of intermediate media on heat transfer between forming tool and part and serve as boundary conditions for fully thermo-mechanical coupled forming simulations. A strong influence of deep drawing film, lubrication and surface pressure on heat exchange could be determined and this basic knowledge is seen as mandatory for dimensioning of heat controlled metal forming tools. Finally the experimental determined results are discussed and compared to common heat transfer models and similar experiments from literature.
Simulations of an Infrared Composite Curing Process
Authors: Nakouzi Sawsane , Berthet Florentin , Le Maoult Yannick , Schmidt Fabrice
Published: June 2013

Epoxy resins have several applications in the aerospace and automobile industry. Because of their good adhesive properties, superior mechanical, chemical and thermal properties, and resistance to fatigue and micro cracking, they produce high performance composites. In the technology presented here, the composite is cured in an IR oven which includes halogen lamps. The liquid resin infusion (LRI) process is used to manufacture the composite, whereby liquid resin is infused through a fiber reinforcement previously laid up in a one-sided mold. These epoxy resins release an exothermic heat flux during the curing process, which can possibly cause an excessive temperature in the thickness. Consequently, for the production of high performance composites, it is necessary to know the thermal behavior of the composite during curing. Therefore, IR interactions with the graphite/epoxy system were modeled as a surface radiation transport. In our work, we have studied IR interactions with the composite, which is placed in an IR oven. Using an IR spectrometer Bruker Vertex 70 (1-27 μm), we measured radiative properties and determined the fraction of IR rays absorbed by the composite. Since it is necessary to optimize the manufacturing time and costs and to determine the performance of these composites, the purpose of this study is to model the IR curing of a composite part (carbon fiber reinforced epoxy matrix) in the infrared oven. The work consists in two parts. In the first part, a FE thermal model based on radiosity method was developed, for the prediction of the infrared incident heat flux on the top surface of the composite during the curing process. This model was validated using a reference solution based on ray tracing algorithms developed in Matlab® (In-lab software called Rayheat based on ray tracing algorithms is used to compute the radiative heat flux that impacts the composite). Through the FE thermal model, an optimization study on the percentage power of each infrared heater is performed in order to optimize the incident IR heat flux uniformity on the composite. This optimization is performed using the Matlab® optimization algorithms based on Sequential Quadratic Programming method. In a second part, the optimized parameters set is used in a three-dimensional numerical model which is developed in the finite element commercial software Comsol Multiphysics ™, where the heat balance equation is coupled with the cure kinetic model of the resin. This numerical model allows calculation of the temperature distribution in the composite during curing, which is a key parameter that affects its mechanical properties. In this model, we can predict also the evolution of the degree of cure as function of time. Experimental measurements were used to validate simulations of the whole infrared composite curing process. Keywords: Curing composite, infrared oven, Radiation, Optimization, Epoxy resin, Carbon fibers.
Influence of the Impact Angle and the Gravity Direction on Heat Transfer during the Cooling of a Cylinder by a Free Planar Subcooled Impinging Jet
Authors: Devynck Sylvain , Denis Sabine , Bellot Jean Pierre , Maigrat Guillaume , Varlez Michel , Benard Thierry , Gradeck Michel
Published: June 2013

Cooling from impinging jet is nearly compulsory in steel industry processing especially in Run Out Table processing and steel tubes production because of the high heat transfer rates provided by the boiling of the subcooled water jet. As far as metallurgical phase transformations, residual stresses and deformations in the workpiece are concerned, the temperature drop during cooling must be perfectly controlled thanks to a fully understanding of the heat transfer mechanisms. In a previous study [1] the effect of surface to jet velocity ratio on heat transfer has been characterized and it has been shown that this parameter has a significant influence on shoulder of flux collapse. In order to understand the effect of more industrial quench process parameters, an innovative experimental quenching device has been designed and built. It allowed us to make heat transfer measurements at the surface of a hot nickel cylinder impinged by a subcooled water jet, according to several angles of impact and three jet directions against gravity. The results clearly highlight an effect of these two parameters on the heat transfer mechanisms at the surface of the tube. These results allow a better understanding of the origins of temperature heterogeneities inside the tube during the quench.
An Original Model Experiment Designed for High-Pressure Crystallization with a Polymer Processing Concern
Authors: Boyer Severine A.E. , Haudin Jean Marc
Published: June 2013

A comprehensive understanding of the inherent link between in-situ growth kinetics of a polymer spherulite and high-pressure constraints under controlled temperature is concerned. As a matter of fact, while the link with temperature is well illustrated, little comprehensive study has been conducted to quantify the effect of pressure. This is yet required to model ‘extreme’ polymer processing conditions.Mainly, the experimental set-ups developed to reproduce the pressure effect can be classified into four families: “simple” cells, dilatometric set-ups, differential thermal analysis and diamond anvil plus in-situ measurement. In this context, an original model experiment, named CRISTAPRESS, has been constructed. The cell design exploits the optical properties of semi-crystalline spherulites. Time-resolved light depolarizing microscopic observations are conducted concomitantly with a fine PVT control, for high pressure up to 200 MPa and temperature up to 300 °C. The physical analysis of isothermal and isobaric holding of a model polymer shows the influence of temperature and pressure on the key kinetic parameters of crystallization, i.e., the growth rate and the number of activated nuclei, as well as on the subsequent morphologies. Simple modeling dealing with the Avrami equation and the Hoffman & Lauritzen theory is established.
Material Efficient Manufacturing of Three-Dimensional Components Using Metal Knitting
Authors: Sagström Elisabeth , Persson Nils Krister , Lundevall Åsa
Published: June 2013

The high investment cost and long lead-time to design and manufacture a forming tool is a major obstacle for local manufacturing of products in sheet metal. To minimize resource consumption large efforts are put into increase material efficiency by reducing the thickness of the sheet and move towards production methods with less scrap percentage. Nevertheless, the scrap portion is still high, in the automotive industry often as high as 50%. This paper discuss the possibilities of introducing knitting of metal wire into metal engineering industry to manufacture scrap free, light-weight three dimensional components in metal. Knitting could be a way of obtaining material efficient production within metal engineering industry especially for small and medium sized enterprises, SME. A knitting machine is able to produce large amounts of products at low price with moderate investments costs. For certain products knitting offer a simplified production of ready formed, 3D components. Experiments with knitting stainless steel wire were performed in order to establish the possibilities and limits of knitting today as well as identify development possibilities. The experiments covered improving the stiffness of the metal knit-wear by using different knitting techniques as well as introducing subsequent manufacturing steps such as surface treatment and joining. Demonstrators where produces for a number of geometries; squares, rectangles, boxes, hour-glass like in 2D and tubular, conical and T-tube shaped in 3D. For two geometries produced with knitting and sheet metal forming the material efficiency was compared. The first geometry used 32 % less material in the knitted product compared to the sheet metal component. The second geometry used 72 % less material in the knitted component compared to the sheet metal component. However, properties like strength and stiffness will be considerable less for a knitted component than for a sheet metal component. Today applications for the knitted materials have to be chosen carefully to take advantage of the potential of the material. With further development of both the knitting technique and subsequent operations the process will open new possibilities of material efficient and light-weight manufacturing.
Influence of Process Parameters on Surface Hardening in Hammer Peening and Deep Rolling
Authors: Scheil Jan , Müller Clemens , Steitz Manuel , Groche Peter
Published: June 2013

This paper focusses on the statistical evaluation of process parameters in the mechanical surface treatments deep rolling (DR) and machine hammer peening (MHP) on the hardness increase. In MHP process a spherical hard metal tool is repeatedly accelerated onto the material surface. Just as the shot peening process MHP is an impact treatment although in MHP the impact area can be controlled, leading to the desired impact density. In DR the contact between spherical tool and work piece is quite different to MHP as the spherical is in sliding contact as it is moved along the surface. Although the material loading of both surface treatments vary, the resulting surface structure is the same. Both lead to a cold worked, smooth surface including compressive residual. Technically DR and MHP parameters have been part of researches but there still is a lack of statistical validation of every single process parameter leading to a hardened surface. This paper tries to close this gap. DR and MHP are conducted on different materials, containing tool steel 1.2379 and grey cast iron EN-JS-2070. Using a fractional factorial test design an experimental matrix was created able to examine the influence of every single process parameter. Which were for DR: rolling pressure, line spacing between hammer traces, diameter of roller ball and the travelling speed. For MHP the influence of the following process parameters was investigated: angle between hammering direction and surface normal, line spacing between hammering traces, diameter of hammering ball, hammering energy, travelling speed and hammering frequency. On every single sample ten Brinell hardness indents are made which give the statistical coverage needed to calculate the effect of every single process parameter within a confidence interval of at least 95 %. For all mentioned materials the effect of every single process parameter has been calculated with respect to hardening. It could be shown that especially the loading of the cast iron is quiet complex as a high amount of impact energy (MHP) or contact pressure (DR) can lead to overloading of the material leading to a degradation of the surface. At least an explanatory approach which describes the different influence of the tool diameter on the surface hardness is given using FEM simulations. These FEM simulations contain an advanced material model in which the Bauschinger-effect of 1.2379 is implemented. It can be clearly shown that a larger tool diameter in DR produces a higher amount of cold working in the material surface leading to harder surfaces compared to the smaller tool diameter. In contrast to DR the contact pressure in MHP is determined by the Hertzian pressure distribution. Here smaller tool diameters create larger Hertzian pressure and therefore a higher amount of cold working.
Experimental Investigation on Dry Electrical Discharge Drilling
Authors: Coteaţă Margareta , Besliu Irina , Schulze Hans Peter , Pop Nicolae , Slătineanu Laurenţiu
Published: June 2013

The electrical dischargemachining (EDM) is known as the machining method in which the material removalis the result of developing electrical discharges having certain energetic andtemporal characteristics between the workpiece and the active surface of thetool electrode, while a dielectric liquid is circulated in the gap, essentiallyin order to remove debris. The last decades showed that in certain conditions,the dielectric liquid could be replaced by gaseous dielectric fluids, theprocess being named dry EDM. In the paper, some preliminary considerations areformulated about the material removal process for dry EDM drilling. Experimental researches were developed byconsidering the modifying of the values of some electrical characteristics(peak current, on time, off time and applied voltage) and determining thequantity of material removed from the test piece and the wear of the toolelectrode. The experimental results were mathematically processed and empiricalrelations were determined; these mathematical relations highlight the influenceexerted by the input parameters on the material removal rate.
A Roll Caster to Cast Clad Strip
Authors: Haga Toshio , Tsuge Hiroshi , Kumai Shinji , Watari Hisaki
Published: June 2013

A tandem-type roll caster that can cast a three-layered clad strip was developed by mounting one twin roll caster on another twin roll caster. In this caster, the base strip is cast by the upper twin roll caster, and the overlay strips are cast by the lower caster. The three strips are metallurgically bonded by the lower caster. This study investigated three aspects of this caster. First, the clad ratio could be controlled by the solidification lengths of strips from the upper and lower twin roll casters, and a clad ratio of 1:8:1 was attained. Second, although it is known that fabrication of clad strips from Al-Mg alloy and other Al alloys is very difficult, the clad strip with the Al-Mg alloy as the base strip or the overlay strip could be cast. Finally, by adding scrapers, the caster could cast the clad strip with a base strip having a lower melting point than the overlay strip. Element strips of the clad strip are made by many processes, such as direct chill (DC) casting, scraping of the ingot surface, heat treatment, hot rolling, and cold rolling. Typically, surface treatment and hot rolling are used to clad the strips. Since many processes are required, clad strips require consume much energy. Therefore, producing clad strips is expensive. A vertical-type tandem twin roll caster was developed to cast clad strips. This caster has the advantages of process saving and energy saving, and so can fabricate economical clad strips. In the fabrication of clad strips, control of the clad ratio is very important. In the brazing sheet for automobile radiators, the base strip is made from AA3003 and the overlay strips are made from AA4045, and the clad ratio is usually 1:8:1. In the present study, a clad strip with a clad ratio of 1:8:1 was attained. The cladding by hot rolling of Al-Mg and other aluminum alloys, which is considered to be a very difficult process, was also investigated. Clad strips with either a base strip or an overlay strip of an Al-Mg alloy were cast by the roll caster. Although the cladding was not easy, the Al-Mg alloy could be cast into the clad strip. In addition, a clad strip with a base strip having a lower melting point than that of the overlay strip was investigated. Such cladding cannot be cast by the vertical-type tandem twin roll caster as mentioned above because the base strip is re-melted from the heat of the overlay strips. In the present study, a scraper was developed and adopted to cast a clad strip with a base having a lower melting point than that of the overlay strips. This type of clad strip could be cast because the scrapers prevented the re-melting of the base strip. In this paper, these three aspects of fabrication are reported.
Modelling and State Estimation in Pulsed ECM with Variable Electrolyte Conductivity
Authors: Boxhammer Markus , Lu Jin Ming
Published: June 2013

In Pulsed Electrochemical Machining the control of the size of the process gap is necessaryto achieve process stability. However, the gap size cannot be measured directly during the machiningprocess. Based on an equivalent circuit, a process model has been derived for plane electrodes andconstant conductivity. In a previous study, an approach to controlling and estimating the gap size hasbeen introduced. By input-output-linearisation, a linear system was found, making it easier to controlthe gap size and current flow simultaneously.In this work the existing model is revised for its applicability to the conductivity change duringeach pulse resulting from heat and gas bubble generation. Depending on the particular moment of thecurrent measurement, the value of the conductivity in the electrolyte reservoir cannot be used for thegap size estimation directly. Three different approaches to overcome this problem are reviewed. Themost promising approach was implemented on a real-time platform and optimised for execution time.
Forming of Shape Memory Composite Structures
Authors: Santo Loredana , Quadrini Fabrizio , De Chiffre Leonardo
Published: June 2013

A new forming procedure was developed to produce shape memory composite structures having structural composite skins over a shape memory polymer core. Core material was obtained by solid state foaming of an epoxy polyester resin with remarkably shape memory properties. The composite skin consisted of a two-layer unidirectional thermoplastic composite (glass filled polypropylene). Skins were joined to the foamed core by hot compression without any adhesive: a very good adhesion was obtained as experimental tests confirmed. The structure of the foam core was investigated by means of computer axial tomography. Final shape memory composite panels were mechanically tested by three point bending before and after a shape memory step. This step consisted of a compression to reduce the panel thickness up to 60%. At the end of the bending test the panel shape was recovered by heating and a new memory step was performed with a higher thickness reduction. Memory steps were performed at room temperature and 120 °C so as to test the foam core in the glassy and rubbery state, respectively. Shape memory tests revealed the ability of the shape memory composite structures to recover the initial shape also after severe damaging (i.e. after room temperature compression). Compressing the panel at a temperature higher than the foam resin glass transition temperature minimally affects composite stiffness.
A Study of the BTA Deep Drilling Process through a Quantitative and Qualitative Analysis of the Chip Formation Process
Authors: Haddag Badis , Thil Julien , Nouari Mohammed , Barlier Claude
Published: June 2013

This paper deals with the analysis of the cutting process in the BTA (Boring Trepanning Association) deep hole drilling. The process is a major technique of drilling when the machining with a conventional tool is not possible. Poor training and/or poor chips evacuation often cause a temperature rise and excessive wear detrimental to the tool life and the dimensional stability of machined parts. The process is relatively not explored enough, because it is difficult to instrument experimental tests (measurement of forces acting at each insert of the BTA drilling tool, temperature at each cutting edge…). Moreover, the thermomechanical phenomena related to the cut are localized at the end of the BTA drilling head and confined in a zone inaccessible to the observation. Hence, a study of this process based on a scientific approach has been proposed. The evaluation of the chips morphology has been performed. Indeed, it is a good indicator of the stability of the cutting process and it can therefore be a serious help in the selection of optimal cutting parameters. Adequate parameters are proposed to highlight the impact of cutting conditions on the cutting process. Macro and microscopic observations of generated chips under several cutting conditions are performed. Fragmentation and segmentation of chips are some examples of analysed phenomena. In this sense, experimental tests have been conducted. The chips have been sorted according to their morphology and identified according to their origin and then proposed physical parameters are assessed. The quantitative and qualitative analysis of chips allowed identifying the impact of the cutting speed and feed rate on the cutting process.
Development of an Optimized Loading Path for Material Parameters Identification
Authors: Ferreira Elisabete , Pinho-da-Cruz Joaquim , Andrade-Campos António
Published: June 2013

Nowadays, the characterization of material is becoming increasingly important due to ma\-nu\-fac\-tu\-ring of new materials and development of computational analysis software intending to reproduce the real behaviour which depends on the quality of the models implemented and their material parameters. However, a large number of technological mechanical tests are carried out to characterize the mechanical properties of materials and similar materials may also have properties and parameters similar. Therefore, many researchers are often confronted with the dilemma of what should be the best set of numerical solution for all different results. Currently, such choice is made based on the empirical experience of each researcher, not representing a severe and objective criterion. Hence, via optimization it is possible to find and classify the most unique and distinguishable solution for pa\-ra\-me\-ters identification. The aim of this work is to propose a methodology that numerically designs the loading path of multiaxial testing machine to characterize metallic thin sheet behavior. This loading path has to be the most informative, exhibiting normal and shear strains as distinctly as possible. Thus, applying Finite Element Analysis (FEA) and Singular Value Decomposition (SVD), the loading path can be evaluated in terms of distinguishability and uniqueness. Consequently, the loading path that leads to the most distinguish and unique set of material parameters can be found using a standard optimization method and the approach proposed. This methodology has been validated to characterize the elastic moduli for an anisotropic material and extrapolated for an hyperelastic material.
Numerical Optimization of Selective Superplastic Forming of Friction Stir Processed AZ31 Mg Alloy
Authors: Paradiso Valentino , Astarita Antonello , Carrino Luigi , Durante Massimo , Franchitti Stefania , Scherillo Fabio , Squillace Antonino , Velotti Carla
Published: June 2013

Superplastic forming is a near net shape process used to produce various items with complex geometry. However in many cases, only some portions of the workpiece undergo superplastic deformation. In these cases, instead of choosing expensive starting sheet material with superplastic properties, a low-cost conventional material can be chosen and a grain refinement process can be performed in the selected regions to enhance superplastic properties locally [1]. This process is known as “selective superplastic forming” [R.S. Mishra, M.W. Mahoney, US Patent 6,712,916, 2002]. In some previous works the use of Friction Stir Processing (FSP) was used to obtain locally a microstructure with ultrafine grains in the AZ31 magnesium alloys [2, 3]. In this study a modeling approach was adopted thanks to a commercial FE code and different simulations were conducted in order to correlate the experimental and numerical results for the model optimization [4, 5]. Free bulge forming tests of friction stir processed AZ31 sheets, in conjunction with numerical simulations, were used to evaluate the proposed optimization approach, with the aim to reduce the time and costs in the design of components with complex geometry.
Development of Adapted Material Testing for Cold Pilgering Process of ODS Tubes
Authors: Mocellin Katia , Vanegas Esteban , de Carlan Yann , Logé Roland E.
Published: June 2013

Development of fast-neutron sodium-cooled Generation IV reactors is resulting in extremely severe environment conditions for cladding tubes [1]. Both temperature and irradiation level will increase compared to the nowadays conditions. Due to their characteristics in irradiated environment, the oxide dispersion strengthened (ODS) ferritic and martensitic steels are natural candidate cladding materials[2]. However, they exhibit low deformation capabilities at room temperature, leading to problematic issues for forming such as pilgering. In order to improve the fabrication route for tubes, both metallurgical and numerical approaches can be conducted [3,4,5]. To reach predictive description of damage location and evolution, an adapated Latham and Cockoft model has been developed. This model is, of course, highly depending on the stress and strain prediction of the numerical model which itself is linked to the behavior law. In this work, we will describe an adapted material test developed in order to reproduce the cyclic, non uniform loading of the material during pilgering. An advanced cyclic beahvior law is introduced in the software. The model of Chaboche using 2 isotropic and 2 kinematic variables is chosen[6]. An inverse analysis procedure is used to identify both isotropic and kinematic hardening parameters. The results obtained using the identified behavior law are compared to both experimental observation and to other models including monotonic or cyclic laws identified on traditional test.
Prediction of Springback in Unconstrained Bending by a Model for Evolving Elastic and Plastic Anisotropy
Authors: Vladimirov Ivaylo N. , Reese Stefanie
Published: June 2013

Sheet metals exhibit anisotropic plastic behavior due to the large plastic deformations that occur during the rolling of the sheet and which induce texture and are responsible for the initial anisotropy. There exist various possibilities to introduce plastic anisotropy into the finite element modelling of sheet metal forming. The initial yield anisotropy can be incorporated either through an anisotropic yield surface or directly by means of a crystallographic texture model. Here, one basically differentiates between empirical and phenomenological anisotropic yield function equations, where the anisotropy coefficients can be obtained from mechanical tests, and texture-based models the coefficients of which are directly determined based on experimentally obtained orientation distributions. Another type of anisotropy that can be usually found in anisotropic materials is the elastic anisotropy. In metal plasticity one often considers the effect of elastic anisotropy significantly smaller than the effect of plastic anisotropy. Consequently, elastic isotropic expressions are often used for elastic stored energy functions with anisotropic yield criteria. However, the influence of elastic anisotropy in the elastoplastic behavior can be very important especially during elastic recovery processes during unloading after forming and springback. This research focuses, therefore, on the study of the influence of elastic anisotropy on the amount of springback in bending processes such as e.g. unconstrained bending. We discuss a finite strain material model for evolving elastic and plastic anisotropy combining nonlinear isotropic and kinematic hardening. The evolution of elastic anisotropy is described by representing the Helmholtz free energy as a function of a family of evolving structure tensors. In addition, plastic anisotropy is modelled via the dependence of the yield surface on the same family of structure tensors. Exploiting the dissipation inequality leads to the interesting result that all tensor-valued internal variables are symmetric. Thus, the integration of the evolution equations can be efficiently performed by means of an algorithm that automatically retains the symmetry of the internal variables in every time step. The material model has been implemented as a user material subroutine UMAT into the commercial finite element software ABAQUS/Standard and has been applied to the simulation of springback of unconstrained bending.