bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Heat Repartition Parameters on High Speed Pin-on-Disc Tribometer by Inverse Heat Conduction Method
Authors: Meresse Damien , Watremez Michel , Harmand Souad , Dubar Laurent
Published: February 2012

The heat transfers are investigated between a phenolic pin sliding against a steel disc. Inverse heat conduction methods are used to identify the temperature fields and the heat fluxes at the contact surface for each part. Experimentals tests are performed on the High Speed Tribometer designed to reproduce mechanical and thermal conditions met in forming and braking applications at reduced scale. It allows to measure temperatures inside rotating part in seven locations with K-type thermocouples sensors connected to a telemetry system. Their positions have been chosen regarding a sensibility analysis performed in expected thermal conditions. The heat distribution on the disc surface, the heat repartition parameter α between the pin and the disc and the sliding thermal conductance hc are discussed regarding the friction conditions during the tribological tests performed. In this tribological system, the temperature and the pressure influences on hc are highlighted. The originality of this work is the possibility to calculate two dimensional transient heat fluxes for sliding speed until 15m.s-1 thanks to several thermocouple measurements.
New Technique to Model the Effect of Intermediate Induction Heat Treatment (IIHT) in Pre-Strained Aluminium Sheets
Authors: Govindarajan Rajarajan , Zubeil Martin , Siefert Kathleen , Kleeh Tobias , Lorenz David , Borrvall Thomas , Ageorges Christophe
Published: February 2012

This paper presents a new technique to model the effect of intermediate induction heat treatment (IIHT) on pre-strained aluminium sheets, predominantly AA5182. IIHT is a heat treatment technique carried out between two conventional cold forming steps, which eventually lead to enhanced formability of aluminium alloys. The aim of IIHT is to alleviate the strain hardening of the material which is introduced in the first cold forming step and there by reducing the yield limit and increasing the hardening modulus for subsequent forming steps. As a result, a remarkable increase in formability can be achieved in the subsequent forming steps at room temperature. The scientific aspect of the IIHT process is demonstrated by defined pre-strained tensile test specimens at different object temperatures to establish a process window. To accurately model the effect of IHTT in simulations, it is necessary for the material model to consider the plastic recovery that the material undergoes during heat treatment. To this effect, material model Mat133 (Barlat_YLD2000) in LS-Dyna has been enhanced to account for the effect of intermediate heat treatment. The numerical simulation is carried out in four steps namely pre-forming, springback simulation to account for residual stresses, thermo-mechanical coupled simulation for heat treatment, and final forming with enhanced material model. To validate this model, experiments have been carried out on a simple cross-die deep drawn cup and compared with simulation results.
The Effect of Temperature, Strain Rate and Strain on the Induced Mechanical Properties of Biaxially Stretched PET
Authors: MENARY Gary , Tan C.W. , Armstrong C.G.
Published: February 2012

The study is focused on the effect of strain rate, temperature and stretch ratio on the room temperature mechanical properties of PET (Polyethylene terephthalate) following biaxial deformation. Specimens were biaxially stretched within a temperature range 80-110°C, a strain rate in the range 1-16/s and stretch ratio in the range 1-2.8. The tensile moduli of the stretched specimens were obtained using tensile testing. Results show that post-stretching room temperature modulus increases with decreasing temperature, increasing strain rate, and stretch ratio.
The Effect of Thermoforming of PLA-PHBV Films on the Morphology and Gas Barrier Properties
Authors: Guinault Alain , Nguyen Anh Son , Miquelard-Garnier Guillaume , Jouannet Denis , Grandmontagne Anne , Sollogoub Cyrille
Published: February 2012

Poly(lactic acid) (PLA) is a biodegradable, thermoplastic, aliphatic polyester derived from renewable resources, which is a potential candidate to replace conventional polymers in food packaging applications.. Other bio-based materials like polyhydroxyalkanoates (in our case PHBV) could be associated with PLA in order to improve its gas barrier properties and/or its mechanical properties. Two processes, classical 3 layer coextrusion and original polymer blending extrusion, have been used in this study to combine PLA and PHBV to obtain films with different PLA-PHBV structures. The aim of this paper is to compare the thermoformability of the different films and to investigate the final structure in relationship with their gas barrier properties. The effect of the thermoforming steep has been studied by separating heating and stretching effects. We show that the blend morphology offers better mechanical and barrier properties than single PLA or 3 layers PLA/PHBV films.
Structure of Polymer – Multiwall Carbon Nanotube Composites
Authors: Adamne Major Andrea , Belina Károly
Published: February 2012

In the last ten years carbon nanotube composites are in the focus of the researchers. Different composition of carbon nanotubes and polymers were produced by IDMX mixer. In the experiments polypropylene, polycarbonate and ABS polymers were used as matrix materials. Nanotube master batches were used to prepare different compositions. Concentration series were manufactured by the dynamic mixer. The prepared materials were characterised by scanning electron microscopy. The carbon nanotubes can be seen on the fractured surfaces. We did not find any sign of agglomerates in the materials. During the investigation of isothermal and nonisothermal crystallization of polypropylene nanocomposites it was shown that the carbon nanotube has nucleating effect on polypropylene. Mechanical properties were determined. It was found that the mechanical properties of the nanocomposites decreased. The flammability of the composites is significantly smaller than the original polymers. Polypropylene nanotube composites above 4% nanotube content were not dripping. It is most probable due to some kind of network structure of the material. We assume that the carbon nanotube creates a physical network in the polymers.
Development of a Process Evaluation System for Wire-EDM Applications Using an Intelligent Process Monitoring Tool
Authors: Klocke Fritz , Schwade Max , Klink Andreas
Published: February 2012

In this paper a first approach is presented to investigate the electrical parameters of the EDM process using an intelligent process monitoring tool to evaluate different technologies and generators. Goal is to characterize every single discharge by extracting relevant data from recorded current and voltage signals using an adequate algorithm. For demonstration purposes a steel material is machined using a corresponding technology recommended by the machine tool supplier as well as a recommended technology for hard metal. In a first step the machining quality is evaluated by the cutting rate and surface roughness which is common practice for EDM. These results are then compared to the data extracted by the process monitoring tool. In the future this tool may be able to accelerate the parameter development for a specific task or material significantly. The effectiveness of the process could be determined directly during the process and no longer indirectly by a quality inspection of the machined part. By investigating the course of each discharge the process parameters can be linked to the actual physical parameters and a direct influence could be identified.
Developments in Wire-EDM for the Manufacturing of Fir Tree Slots in Turbine Discs Made of Inconel 718
Authors: Klocke Fritz , Welling David , Dieckmann Jens , Veselovac Drazen , Perez Roberto
Published: February 2012

This paper deals with developments of Wire-EDM technologies for fir tree slot production. The aim of these developments is to substitute certain conventional processes within turbine manufacturing that have been identified as non-optimal like the critical broaching process. Thereby the negative characteristics like inflexible manufacturing processes, high machine tool investment costs and huge energy consumption can be abolished. The objective targets of the conducted research are to meet all safety requirements of the critical components and get an economic manufacturing process. In the first step a special brass wire technology for cutting Ni-based super alloys was developed. Main focus was to meet the requirements of fir tree production concerning aspects of surface integrity and geometry. To measure these aspects on the one hand non-destructive analyses have been performed to guarantee surface roughness and accuracy. On the other hand destructive analyses in terms of cross section polishing for showing thermal influenced rim zones have been prepared. A capable Wire-EDM process is presented.
Electrode Tool Wear at Electrical Discharge Machining
Authors: Slătineanu Laurenţiu , Schulze Hans Peter , Dodun Oana , Coteaţă Margareta , Gherman Lorelei , Grigoraş (Beşliu) Irina
Published: February 2012

As consequence of the development of electrical discharge machining process, the electrode is affected by wear; knowing the evolution of the electrode wear, a better estimation of its service life is possible. It is expected that the electrode wear depends on the energy of the electrical discharges and the mass of the electrode. It is known also that the nature of the workpiece material exerts influence on the evolution of the electrode wearing process. In the paper, some theoretical considerations are used to highlight the above mentioned aspects. A set of experimental tests was designed and developed in order to highlight the influence exerted by the nature of the workpiece material and by the size of the cross section of the electrode, respectively, on the electrode wear. Empirical mathematical models corresponding to the evolution of the electrode wear were established.
Laser Beam Structured Sheets – A New Potential for Sheet Metal Forming
Authors: Neugebauer Reimund , Ahnert Maik
Published: February 2012

The increasing requirements of car body manufacturers concerning formability and load of sheet metal structures necessitate new approaches in forming technology. Especially the requirements as regards local loads and local forming behaviour of the components vary significantly. In the field of welding technology there is a verified effect of emerging higher strengths in the welding seam. Using a laser, similar effects can be applied to change the material properties locally. In the current investigation the use of a laser beam allows for creating very small heat-affected areas of a width from 0.5 mm up to 5 mm. These areas are characterised by a significantly higher hardness and strength. Depending on the sheet metal material, areas of higher and lower hardness can be produced. Using laser heat-affected zones in sheet metal makes it possible to increase the drawing depth without necking or cracks. The heat-affected zones increased the stiffness in the critical necking area and hence moved the critical strains to the surrounding area. The required formability was guaranteed by the adjacent areas and the draw depth can be increased.
Applications of the Electro-Contact-Discharge Machining (ECoDM) and the Analysis of Different Process Parts
Authors: Schulze Hans Peter
Published: February 2012

The Electro-Contact-Discharge Machining (ECoDM) is a hybrid process composed of Electrical Discharge Machining (EDM), Arc Discharge Machining (ADM), Contact Heating Proc-ess (CoHP), and Mechanical Machining (MM). The article presents a comparison of different ap-plications and the different influence of the machining parts for a necessary result. The application field ranges from ECoDM-Cutting to the cleaning of railway tracks. The analysis of the different processing parts is necessary for monitoring the process parameters (electrical and mechanical). An advantage of the ECoDM is the cutting of electric-conductive and partial electric-non-conductive materials. The application field is not high-precise machining but rather recycling and pre-working processing. The examples show that the focal point is not the process energy source, but the selec-tion of the processing parts through the analysis of the voltage curve and/or the current curve.
Elasto-Plastic Models with Continuously Distributed Dislocations and Disclinations
Authors: Cleja-Tigoiu Sanda
Published: February 2012

The paper deals with a mathematical model able to describe the presence of lattice defects of the crystalline materials, such as dislocation and disclination. Within the constitutive framework of second order plasticity developed by the author, the evolution equations to describe the disclinations that are compatible with the screw dislocations are derived.
Displacement Behavior of Wood in Boss Forming Using Open-Die Wood Forging
Authors: Kajikawa Shohei , Iizuka Takashi , Yamaishi Keisuke
Published: February 2012

Biomass materials such as wood are attracting renewed attention as alternative fuels in order to help resolve environmental resources caused by the use of fossil fuels. In this study, the possibility of products being processed from wood bulk was investigated by means of boss forming using open-die forging. Additionally, the difference in formability and deformation behavior during forging was investigated by changing the experimental conditions, such as the moisture content of the wood billets used, the forming pressure, and the forming temperature. The experimental results showed that wood had enough liquidity to be forged, and that two sudden and large increases in displacement occur during forging. Finally, the conditions governing these displacements were summarized from these results
Material Parameter Identification from Machining Simulations Using Inverse Techniques
Authors: Shrot Aviral , Bäker Martin
Published: February 2012

Machining is a complex process during which the material undergoes large deformations at high strain-rates with large variations in temperatures. One of the difficulties faced during the simulation of machining is that of determining appropriate material parameters which are valid for such large ranges of strains, strain-rates and temperatures. An inverse method of material parameter identification from machining simulations is proposed in this paper. An error function is defined that takes into account the chip overlap error and the cutting force difference at different frames of observation. The two components are suitably weighted so that the contribution of each is rendered almost equally. A two stage optimisation process is employed for the minimisation of the error function where the Levenberg-Marquardt algorithm is used in the first stage for faster convergence and the Downhill Simplex algorithm in the second stage in order to navigate through the noisy error landscape. A wide range of cutting conditions is used and the method is shown to work also for non-adiabatic simulations. However, the converged parameter sets are found to be non-unique.
Hardness-Based Flow Stress for Numerical Simulation of Machining Inconel 718 Alloy
Authors: Umbrello Domenico , Caruso Serafino , Rotella Giovanna
Published: February 2012

The phenomenological models for material flow stress and fracture, typically used in the Finite Element simulations of Inconel 718 alloy during machining processes, are often deemed to represent only certain metallurgical material states. In contrast, these models are not suitable to describe the constitutive behaviour of the workpiece for different metallurgical states (i.e., annealed, aged, etc.) and, consequently, different hardness values. Since the description of the material behaviour requires correct formulation of the constitutive law, new flow stress models which include also the hardness effect should be developed and, accordingly used, for computer simulation of machining Inconel alloy. This paper describes the development of a hardness-based flow stress and fracture models for machining Inconel 718 alloy, which can be applied for a wide range of work material hardness. These models have been implemented in a non-isothermal viscoplastic numerical model to simulate the influence of work material hardness on the chip formation process. The predicted results are being validated with experimental results available in literature. They are found to satisfactory predict the cutting forces, the temperature, the shear angle and the chip morphology from continuous to segmented chip as the hardness values change.
Crack Investigation of the Multilayer TiN/Ti Coatings during the Nanoindentation Test
Authors: Perzynski Konrad , Madej Łukasz
Published: February 2012

Nanoindentation test is one of the most commonly used methods for the strength investigation of the nanomaterials. Information provided from such test gives the possibility to obtain a knowledge about fracture development under the spot hitting tool. However, nano dimensions of the coatings obtained by the deposition method creates problems with exact investigation of this test. Costs of experimental study are very often excessive due to very specialized laboratory equipment. The numerical simulations can be a support for mentioned experimental research as they give possibility of fast and efficient investigation on behavior of different nanolayers dimensions and alignments. The main aim of this work is focused on taking into account real morphology of microstructure of ceramic TiN layers deposited on the metallic Ti layers during nanoindentation test. This combination of layers is widely used in medicine for improvement mechanical properties and biocompatibility behavior of bio elements. Particular attention during numerical simulation is put on influence of columnar structure of these layers on fracture development. Results obtained from the extended finite element model (XFEM) for various nanolayers alignments is discussed according to the fracture initiation and propagation.
Numerical-Experimental Correlation of Distortions Induced by Machining Process on Thin-Walled Nickel Super Alloy Forged Components
Authors: Del Prete Antonio , de Vitis Antonio Alberto , Franchi Rodolfo
Published: February 2012

AeroEngines main components made by nickel super alloys are mainly obtained by machining of large forged components. The work piece machining process generates some distortions that may also be relevant. In this contest, in many cases the removed volume in the machining operations represents a large percentage of the forged component in order to obtain the thin-walled wanted geometry. Due to this reason, the residual bulk stresses induced by the process history can lead to significant 3D geometric distortions in the machined component with unacceptable dimensions and shapes of the obtained product for comparison with the wanted geometry. Moreover, it is a matter of fact how, the final component distortions depend by the cutting strategy adopted in the machining process. The experimental study of such cutting strategies on real components are particularly time consuming and costly and for this reason the chance to study the problem using reliable numerical models it is particularly welcome. In the present work authors reports the numerical model development of the forging and machining processes needed for the production of a aircraft engine component and the comparison of the obtained results with the ones physically measured. The objective is to develop and validate a modeling method able to predicts the shape and the magnitude of the distortion induced by the machining operation on the considered component and to establish a possible strategy to suggest machining working steps able to improve the quality of the manufactured component reducing the needed production time.
Tool Engage Investigation in Nickel Superalloy Turning Operations
Authors: Del Prete Antonio , de Vitis Antonio Alberto , Filice Luigino , Caruso Serafino , Umbrello Domenico
Published: February 2012

This paper reports the results of an experimental study of the tool wear and cutting forces in turning of Inconel 718 with coated carbide inserts. Inconel 718 is a difficult-to-cut nickel-based super-alloy commonly used in aerospace industry. The effects of cutting speed, feed rate and cutting tool geometry on tool wear have been widely analyzed in literature. Turning operations on complex components such as aircraft engines casings require the insert replacement at the end of each geometric feature manufacturing, independently from the actual tool wear level. For this reason, it is important to preserve tool integrity mainly in the most critical phase of operation (i.e., when the tool engages the workpiece). In fact, if the tool is damaged in this stage the quality of the whole operation is compromised. The attention has been focused on engage cutting conditions because the phenomenon that appears in this critical step plays a wide influence on tool integrity and, consequently, on the quality of the operation. For this purpose a nickel-based super alloy ring-workpiece, (Inconel 718), has been machined in lubricated cutting conditions by using a CNC lathe with carbide coated tools. Two variables have been investigated in this study: the Depth Of Cut (DOC) and the approaching Engage angle (En). In the studied working conditions Speed (S), Feed-rate (F) and removed volume (Vrim) were kept constant. Both tool wear and cutting forces evolution during cutting have been analyzed.
Failure Evaluation of Spot Welds for Advanced High Strength Steel Sheets
Authors: Noh Wooram , Yoo Dong Hoon , Koh Young Woo , Chung Kwan Soo , Yang Xin
Published: February 2012

Resistance spot welding (RSW) is commonly employed in the automotive industry to join sheet metal parts, which often involves several thousands of welds for one vehicle. Therefore, the proper evaluation of their formability/failure behavior is so vital to accurately predict overall crash performance of vehicles. In this work, the failure performance of spot welds has been experimentally and numerically analyzed for welds in which the base material is the TRIP (Transformation induced plasticity steel) 980 sheet. The mechanical properties of the base and welds have been characterized utilizing the inverse method based on the standard and miniature simple tension tests along with the lap-shear tests.
Machinability Study Using Chip Thickness Ratio on Difficult to Cut Metals by CBN Cutting Tool
Authors: Thamizhmanii Sivaprakasam , Sulaiman Hasan
Published: February 2012

Machinability is the one of the criteria in determining the life of the cutting tool. In this experiment, hard and difficult to cut materials like hard AISI 440 C stainless steel and hard SCM 440 alloy steels were discussed. However, machinability of the material is considered to be poor due to its inherent characteristics. The machinability studies on AISI 440 C stainless steel and SCM 440 alloy steels had not been carried out by researchers. Machinability indices used in such cases have the characteristics such as cutting force, surface roughness, tool wear etc. In the case of high-speed machining of said materials machinability indices such as chip thickness (RC), shear angle (Ф), surface integrity, and chip analysis are of prime importance. Most of the researchers have not given due consideration to these vital machinability indices necessary for understanding of high-speed cutting of said materials. In this work, an experimental investigation was carried out to understand the behavior of difficult to cut materials, when machined with Cubic Boron Nitride (CBN) insert tool. The results and analysis of this work indicated that the above-mentioned machinability indices are important and necessary to assess the machinability of said materials effectively. The operating parameters used were cutting velocity 100, 125, 150, 175 and 200 m/min with feed rate of 0.10, 0.20 and 0.30 mm rev-1 with constant depth of cut of 1.0 mm. The length of turning was 150 mm and 300 mm. Machinability of both materials and tool was evaluated in terms of roughness, flank wear, cutting force, chip thickness ratio and shear angle.
Cutting Force Prediction in Drilling of Anisotropic Materials
Authors: Matsumura Takashi , Tamura Shoichi , Arrazola Pedro José
Published: February 2012

The paper presents a predictive cutting force model in drilling of anisotropic materials. Three dimensional chip flow in drilling is interpreted as a piling up of the orthogonal cuttings in the planes containing the cutting velocities and the chip flow velocities. The cutting models in the chip flow are determined to calculate the cutting energy using the orthogonal cutting data. Then, the chip flow direction is determined to minimize the cutting energy. The cutting force can be predicted in the determined chip flow model. The cutting force with anisotropy in the material is modeled as the change in the shear stress on the shear plane. The shear stress changes with the rotation angle of the cutter. The cutting force prediction is verified in drilling of a titanium alloy. The anisotropic parameters are identified to minimize the model error between the measured and the predicted cutting forces. The periodical oscillation of the cutting force is also predicted by anisotropy in the shear stress.
Laser Assisted Cutting of Abrasion Resistant Steel
Authors: Kantola Jani , Mäntyjärvi Kari , Karjalainen Jussi A.
Published: February 2012

Abrasion resistant (AR) steels offer excellent hardness and strength properties in applications as mining and earth moving machines. As an outcome of high hardness AR steels can be used to produce durable, light-weight and energy saving products. However, their mechanical processing can be challenging as the hardness of the material approaches the hardness of the tooling used. This places high forces on cutting tools and machines, which, in turn, increases wear and causes early breakdown. This research examines whether the laser treatment of AR steels can be used to aid guillotine shearing. The tested material was abrasion resistant steel with hardness of 400 HBW. Two different laser treatments were examined: local laser heat treatment and laser milling. The aim of laser heat treatment was to change the original martensitic microstructure locally into weaker structure, beneficially for shearing. Narrow grooves were made along the cut line by laser milling, and then the plate cut along them. The effect of local laser heat treatment and the fracture initiating effect of the groove was evaluated from the cutting force. Microhardness tests and micro photos were taken after laser heat treatments. The results indicated that the shearing force of AR steels can be reduced up to 25% with the aid of laser heat treatments. Laser milling had only a slight effect to the shearing force of up to about 8%. In addition, the relative depth of the laser milled groove is estimated at the same range, thus force reduction is mainly due to reduction of material thickness.
A Reliability Study on the Structural Performance Prediction of Reinforced Aluminium Panels with Respect to Variations in Input Parameters of Numerical Simulations
Authors: Paulo Rui Miguel Ferreira , Teixeira-Dias Filipe , Valente Robertt
Published: February 2012

Stiffened panels are composed of a base plate with stiffeners in one or more directions, leading to lightweight structures with high resistance. The structural design, in most cases, focuses mainly on the longitudinal compressive loads that the panels are subjected and can safely withstand. In the present work, a set of Finite Element Method Analyses (FEA) were carried out, using ABAQUS commercial simulation software, and compared with experimental data in order to infer about the sensitivity of the results to the initial geometrical imperfections (either in magnitude and shape). The developments in the present work aim to provide a range of models able to properly reproduce the experimental behaviour of aluminium stiffened panels subjected to compressive loads. It was shown that FEA using shell finite elements were able to obtain accurate predictions of the ultimate load, considering large deformation and elasto-plastic behaviours. The effect of using different shapes and magnitudes of the initial geometrical imperfections on the numerical simulation of the panels was also inferred and tested using previously obtained eigenvalue (EV) buckling modes.
Increase the Deformability of NiCo Single Crystals Using of Electrical Pulse-Like Currents
Authors: Gerstein Gregory , Nowak Marc , Bierbaum Marten Sebastian , Zhuravina Tatjana , Schaper Mirko , Bach Friedrich Wilhelm
Published: February 2012

The effect of short-term electrical pulses on metallic single crystals, with and without the application of external mechanical stresses, was investigated with the aid of deformation reliefs. The nickel-cobalt single crystals were subjected to electrical pulses and subsequently microscopically measured. In doing this, it was established that an electrical pulse without a simultaneously applied mechanical stress, has no influence on the deformation relief. It was possible to show that on loading the single crystal with a mechanical stress, the deformation relief significantly changes even when the stress was markedly below the flow stress.
Microstructural Behaviour in Rotary Forging of Inconel 718
Authors: Mangas Ángela , Santos Maite , San José Juan , Atxaga Garbiñe , Adarraga Olatz
Published: February 2012

In the work developed in this paper, the model of the microstructural behavior of Inconel 718 for the rotary forging process is studied. This process is presented as an alternative to the conventional forging. The window process of Inconel 718 is very narrow, so the requirements for manufacturing Inconel are very restrictive. Optimization of the rotary forging process was carried out in order to manufacture Inconel pieces with good microstructural distribution. Microstructural specification was given by aeronautic sector. Numerical work was done in order to simulate the microstructural behavior during the forming process. This method was used: a) to understand the recrystallization mechanism that take place in rotary forging processes, b) to compare the microstructure between a piece done in conventional forging and another done in rotary forging and c) to study the influence of the initial grain size in the final piece.
Evolution of Microstructure during the Shape Rolling Modeled by Cellular Automata
Authors: Łach Łukasz , Svyetlichnyy Dmytro S.
Published: February 2012

The numerical modeling of microstructure evolution in the forming processes is used different schemes and different tools. One of the methods is cellular automata (CA), and recently an interest in cellular automata for modeling of forming processes is increased constantly. Cellular automata are considered as one of the most optimal tool for microstructure modeling because of the computational effort and the obtained results. The paper presents the use of frontal cellular automata (FCA) for modeling microstructure evolution during the rolling process. The use of frontal cellular automata in combination with other methods is related to the possibility of obtaining more accurate and reliable results and has undeniable advantages. Results of the modeling of the process by finite element method (FEM) are input data for further simulation by FCA. Some examples of microstructure as results of FCA simulation are presented in the paper.
Scale Behaviour and Deformation Properties of Oxide Scale during Hot Rolling of Steel
Authors: Graf Marcel , Kawalla Rudolf
Published: February 2012

This paper describes the possibilities for identifying temperature-dependent mechanical and thermo-physical properties of oxide scale components which are a necessary data input for a numerical simulation. Scale develops on steel surfaces in oxidising atmospheres above 570 °C and influences the surface quality as well as the roughness of semi-finished products. The main components of oxide scale are wustite, magnetite, and hematite. Intermediate layers can be formed depending on the chemical composition of the basic material, which can be assigned at the rolled samples with the help of the optical microscopy. Hence, the mechanical properties and the metal forming relevant properties of the several oxide layers are very different. Owing to these differences the deformation behaviour of the inhomogeneous oxide scale also varies during hot rolling. With this new method is it possible to determine the pure properties of the several oxide scale layers independently from each other. Thereby, the influences of the raw material as well as the alloys are excluded. The pure powder allows to characterising the physical properties by applying compression tests with similar stress condition then during hot rolling. Additionally, the 3 piont-bending tests are conducted in order to describe the fracture toughness of the oxides. The results will be implemented in a new model, which consist of single layers with specific material properties. Based on the new knowledge the forming technology can be managed and controlled to minimise the scale cracks on the surface and thus the resulting roughness as well.
A Simple Discrete Method for the Simulation of the Preforming of Woven Fabric Reinforcement
Authors: Najjar Walid , Legrand Xavier , Pupin Cedric , Dal Santo Philippe , Boude Serge
Published: February 2012

In this paper, a discrete approach for the simulation of the preforming of dry woven reinforcement is proposed. A “unit cell” is built using elastic isotropic shells and axial connectors instead of bars and beams used in previous studies. Shell elements are used to take into account the in-plane shear stiffness and to manage contact phenomenon with the punch and die. Connectors reinforce the structure in the yarn directions and naturally capture the specific behavior of the fabric. To identify the material parameters, uniaxial tensile tests and bias tests have been employed. A numerical algorithm, coupling Matlab and Abaqus/Explicit, is used to determine the shear parameters by an inverse method. The model has been implemented in Abaqus to simulate hemispherical stamping. Experimental results are compared to numerical simulations, good agreement between both results is shown.
Complex Shape Forming of Flax Based Woven Fabrics - Analysis of the Yarn Tensile Strain during the Process
Authors: Ouagne Pierre , Soulat Damien , Tephany Christophe , Moothoo Julien , Allaoui Samir , Hivet Gilles , Duriatti Davy
Published: February 2012

A flax fibre plain weave fabric has been used to form a complex tetrahedron shape. The global shape has been obtained. Even if no apparent defects are visible when observing the yarns, the strain of the tightest yarns of the preform has been measured and compared to the biaxial strains of the fabric determined independently of the process. The results show that the strains in the yarns close to the triple point of the shape (top of the tetrahedron) are higher than the strain at failure. This could lead to local lack of fibre density and to possible zones of weakness for the composite part. It is therefore necessary to increase the tensile performances of the yarns constituting the fabric.
Compression Behaviour of Steel Fibre Knitted Fabrics
Authors: Hanot Frédéric , Vanclooster Kristof , Lomov Stepan
Published: February 2012

Knitted steel fiber fabrics are used in the fabrication of automotive windshields. To obtain the complex window shapes, the leading technology to produce automotive glass is compression molding at high temperatures. Direct contact between the mold and the glass during the forming process would lead to inadmissible defects and optical distortion of the automotive glass. To ensure the quality of the glass, a soft heat resisting separating layer is used. Knitted steel fiber fabrics are draped over the mould prior to production, shown in Fig. 1, and thus the fabric comes in direct contact with the glass playing a primary role in the quality of the formed windshield.
Flow Monitoring and Permeability Measurements in LCM Processes by the Means of a Dielectric Sensor
Authors: Carlone Pierpaolo , Palazzo Gaetano S.
Published: February 2012

Liquid Composite Molding (LCM) processes, widely used to manufacture thermosetting matrix composite materials, are characterized by the impregnation of a dry fibrous perform, by the means of injection or infusion of the catalyzed resin. The increasing industrial application of LCM processes is due to the demand for high performances materials and constant quality productions, combined with the need to reduce human intervention and costs due manufacturing inefficiency. The opportune planning of LCM processes results, however, very complex, being the process characterized by non-stationary multiphase flows in a three dimensional porous domain with anisotropic permeability, by the cure reaction, influencing the temperature, the degree of cure, and the viscosity of the processing resin, and by the elastic deformation of the fiber bundle due to the applied pressure, which affects significantly preform properties. Nowadays, process planning and optimization is mainly based on trial and error procedures or on computational simulations. Although the existing simulation packages, developed thanks to the efforts spent by several research groups, led to a better understanding and more effective application of LCM processes, on line monitoring of resin flow is very desirable to account for unpredicted variations of processing conditions. Moreover, an accurate experimental evaluation of fiber preform properties is crucial for a reliable process simulation. In this paper, a dielectric capacitive system has been designed, realized, and applied to monitor the position of the saturated as well as the unsaturated flow fronts and to evaluate in plane bulk permeability and tow permeability of dual scale fibrous porous media, typically used in LCM processes. The used sensors, analysed and optimized by computational simulations, have been embedded into opportunely designed rigid dies. Several preform impregnation tests have been performed. Good agreement has been found between results provided by the used system and data obtained using conventional techniques, evidencing the capability of proposed method for process monitoring, as well as for material properties evaluation.
Friction Based Solid State Welding Processes
Authors: Fratini Livan , Buffa Gianluca , la Spisa Dario
Published: February 2012

In the last decade the industrial use of solid state welding processes based on frictional forces work decaying into heat is continuously increasing due to their strong advantages with respect to traditional fusion techniques. Several advances have been proposed by the scientific community regarding process mechanics, material flow and also the computer aided engineering of the operation with the aim to maximize the mechanical performances of the welded joints. In the paper Friction Stir Welding (FSW) and Linear Friction Welding (LFW) operations are considered and a review of the most relevant research issues and results is provided.
A Friction-Test Benchmark with Twintex PP
Authors: Sachs Ulrich , Fetfatsidis Konstantine A. , Schumacher Josefine , Ziegmann Gerhard , Allaoui Samir , Hivet Gilles , Vidal-Sallé Emmanuelle , Akkerman Remko
Published: February 2012

This paper presents an update on a friction benchmark, that was proposed during the 13th ESAFORM conference. The goal is to compare different friction test set-ups [1–4] by determining the coefficient of friction (CoF) for Twintex® PP. The benchmark instructions are based on the ASTM standard D1894 [5] but also account for different friction velocities, pressures and temperatures. At the time of writing five research groups contributed to the benchmark, each with a custom designed test set-up, differing in size, mechanism, force control and temperature regulation. All tests will be conducted with woven glass reinforced polypropylene, from the same Twintex® batch. Conclusions will be drawn about the comparability of different testing methods by recognizing and analyzing systematically deviating results.
Friction Measurement on Dry Fabric for Forming Simulation of Composite Reinforcement
Authors: Vidal-Sallé Emmanuelle , Massi Francesco
Published: February 2012

Forming processes are highly influenced by all the interface conditions between the tooling and the workpieces. For thermo-mechanical processes like hot forging or cutting processes friction is widely studied for a long time but for composite parts, it is not the case because the problem is not so crucial: forming forces are generally weak enough to allow the part be realized with any forming device; surface quality is not highly affected by the friction conditions; for pre-impregnated fabrics, the viscous or even fluid matrix acts like a lubricant and avoids defects due to sticking between fibre reinforcement and metallic tools. Nevertheless, friction seems to have an important role when precise simulations are expected. Up to now, few studies have been focussed on friction during composite forming processes. The aim of the present study is to make a contribution on that topic for an experimental point of view using an high precision device able to measure small friction forces. The relative fibre orientations can be monitored in order to explore the whole range of geometrical configurations. The final goal is to develop an efficient tool for finite element simulations of dry and pre-impregnated fibre fabrics accounting for the main specificity of fabrics, that is to say their strong anisotropy.
The Influence of Particle Size on Viscosity in Thixo Material
Authors: Harboe Siri , Modigell Michael
Published: February 2012

In thixo casting and forming processes, the forming alloy is in a semi solid state - a suspension of solid particles in a liquid matrix. As known from suspension rheology, the solid fraction, particle size distribution, particle shape, surface properties, state of agglomeration etc. determine the complex flow behaviour of the material. In thixo forming, the flow behaviour determines the quality of the produced parts, and it is essential to quantify the flow behaviour to optimize the process route. The goal of the present work was to evaluate the effect of particle size and state of agglomeration on the flow properties in a thixo material-analogue suspension, and to establish an easily applicable model to describe the non-Newtonian behaviour of a thixo material. For this purpose, experiments were conducted applying synthetic suspensions (built up of mono-disperse glass spheres in silicone oil) with behaviour analogue to thixo material. The advantage of synthetic suspensions is that parameters such as particle size and shape can be controlled in a simple manner and hence the number of unknown parameters is decreased. The experimental results show influence of shear rate, solid fraction, particle size and liquid viscosity. A model to determine the shear dependent viscosity was set up. This model was based on the Krieger-Dougherty equation for the relation between viscosity and solid fraction, and on the generally accepted theory that the state of agglomerations is influenced by shear. The model could successfully display the degree of shear thinning and takes into account the influence of particle size. However, it was found that the relation of the viscosity of the suspension and the liquid viscosity was non-linear. This does not correspond to the Krieger-Dougherty equation.
Production of Aluminium Matrix Nanocomposite Feedstock for Thixoforming by an Ultrasonic Method
Authors: Kandemir Sinan , Yalamanchili Anurag , Atkinson H.V.
Published: February 2012

Metal matrix nanocomposites (MMNCs) could be strong candidates for use in the automotive and aerospace industry, where the mechanical performance is a crucial factor. This study aims to determine the feasibility of Al/SiC nanocomposite fabrication by the ultrasonic technique for the production of thixoforming feedstock material. Aluminium (A356) matrix composites were fabricated with the addition of 0.2 wt.% SiC nanoparticles using an ultrasonic method. Two different particle feeding mechanisms; the Al foil double capsulate method and the crucible placement approach, were employed. Better results were obtained for the double capsulate method. Also, Ti and Nb probe tips were tried to provide ultrasonic vibration in the melt. It has been shown that Nb is a promising ultrasonic probe tip material to produce MMNCs above 650 °C as it is thermodynamically stable in comparison with Ti.
Effect of Experimental Conditions on 7075 Aluminium Response during Thixoextrusion
Authors: Neag Adriana , Favier Véronique , Pop Mariana , Becker Eric , Bigot Régis
Published: February 2012

The deformation behavior of semi-solid aluminum alloy is strongly dependent on the microstructure. This paper illustrates several experimental research works concerning thixoextrusion of 7075 aluminum alloy which was carried out at “Arts et Métiers ParisTech” of Metz. Inductive re-heating of the aluminum billet is the method used in order to obtain the target liquid fraction for thixoextrusion. To minimize the heat losses, a sample obtained from a direct extruded bar is inserted in a die for reheating in semisolid state and thixoextrusion. During the experimental re-heating process, the temperature was directly controlled by using thermocouples for temperature measurements in the sample and also in the die. The influence of different working ram speeds and reheating temperature on the microstructure evolution was studied by optical microscopy. The experimental results on extrusion load and microstructure evolution of the component are reported.
Thermal Simulation of Laser Surface Modification of H13 Die Steel
Authors: Syarifah Nur Aqida Syed Ahmad , Naher Sumsun , Brabazon Dermot
Published: February 2012

In this study, the effects of laser parameters on the properties of glazed die steel were investigated. A Rofin DC-015 diffusion-cooled CO2 slab laser with 10.6 µm wavelength was used. Die steel sample surfaces were prepared with a 3 µm roughness and chemically treated to improve CO2 laser wavelength absorbance. One set of processing parameters were processed through the thermal simulation program and correlated with physical results determined from actual test samples. Set processing parameters were 1138 W peak power, 2900 Hz PRF, 24% duty cycle and 261 mm/s traverse speed. Scanning Electron Microscopy (SEM) micrographs and micro-hardness properties of the affected surface were measured. An analytical mathematical model of the heat field generated in the laser glazing process was used to predict the nominal temperature distribution in the surface and dimensions of melt pool. A thermal model using point source surface energy inputs was used to predict the thermal profiles in the die steel. This allowed estimation of the depths of microstructurally altered regions. For higher energy absorbance, the depth of the glazed surface increased from 20 μm to 40 μm. At high nominal heating to cooling rate ratios, high micro-hardness values were recorded.