bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Modifications for Optimized Forming Operations
Authors: Bräuer Günter , Paschke Hanno , Weber Martin , Behrens Bernd-Arno , Yilkiran Timur
Published: May 2014

During forming operations the contact conditions relating to the surface of the tools, the intermediate coolant or lubricant and the hot work piece material are determining the material flow and the resulting wear. The possibilities for an optimization of the tool surfaces are aspects of various scientific activities of IST and IFUM and are subject of this paper. Tools typically made of hot working steel can be treated with different technologies in order to achieve wear resistant properties. First of all, the surface is mainly determined by its topography which is defined by the manufacturing method or applied finishing technology. This paper will give an overview to adjustable surface properties with additional conditioning methods like severe shot peening.
The stabilization of the topography is a new approach to enhance the wear resistance of forming tools. Several models like the Abbott-Firestone graph are used in order to obtain suitable describing parameters such as the roughness-parameter sk. The development of sk during the running-in stage has a strong influence on the tool life which can be shown. A stabilization of the topographical conditions can enhance the service life of the tools. It will be shown, that this is possible by applying plasma diffusion treatments and thin film coatings by means of vacuum coating technologies.
An Integral Mesoscopic Material Characterization Approach
Authors: Härtel Frank , Böhler Patrick , Middendorf Peter
Published: May 2014

In several fields of engineering the automation of the CFRP production chain is a major issue. In this production chain the forming plays a key role, as the result of the forming influences everything in the chain from the infusion step until the part mechanics. To understand the influence of the material choice onto the forming process is a task followed by many scientists during the last 20 years. Basic tests for shear characterization like Picture Frame Test (PFT) and Bias Extension Test (BiasExt) were developed and used widely. This work deals with the comparison of the BiasExt to a fiber extraction test. The fiber extraction test is developed and used for the characterization of a woven and two non-crimp fabric material. The results are important for the process information and the judgment of primary deformation mechanisms. The tests are simulated for the unidirectional material in a mesoscopic approach and the results are compared in order to judge the capability of the mesoscopic simulation and its residual limitations.
A Yield Criterion Based on Mean Shear Stress
Authors: Emmens Wilko C. , van den Boogaard A.H.
Published: May 2014

This work investigates the relation between shear stress and plastic yield considering that a crystal can only deform in a limited set of directions. The shear stress in arbitrary directions is mapped for some cases showing relevant differences. Yield loci based on mean shear stress are constructed. The Tresca yield criterion can be improved by averaging the shear stress over directions near the direction of maximum shear stress. Yield criteria based on averaging over crystallographic direction show a clear influence of the actual orientation of these direction, notably in case of few crystallographic directions. The general finding is that the higher the isotropy of a material, the lower the plane strain factor. The shape of the yield loci is comparable to those derived by the Hershey criterion with exponents lower than 3.
Tribological Study of Polymer Composite Forming Using Model Experiments and Real Composites
Authors: Smerdova Olga , Sutcliffe Michael P.F.
Published: May 2014

This experimental study is focused on identification of tribological mechanisms acting during forming of polymer composites. The range of relevant processes includes fibre placement, tape lay-up, moulding, draping, and RTM. Two types of tribological experiments, relying both on simultaneous application of compression and shear loadings, are carried out. Firstly, model macromechanical tests are undertaken on plastic rods of millimetric diameter immersed in a viscous liquid, representing composite fibres and matrix, respectively. By careful simulation of forming conditions, this experiment helps to identify the friction phenomena occurring in real composites. On the other hand, the micromechanics of forming processes is studied through a microscopic experiment on real carbon fabric. This material is clamped between two glass plates and pulled in opposing directions in the plane of the fabric. It is hypothesized that the evolution of contact area due to shearing that can be measured in this experiment is an essential feature of the tribology of forming processes, a topic which hitherto has not been investigated.
Application of a Discrete Mesoscopic Finite Element Approach to Investigate the Bending and Folding of Fiber-Reinforced Composite Materials during the Manufacturing Process
Authors: Dangora Lisa M. , Sherwood James , Mitchell Cynthia
Published: May 2014

During the manufacturing of fabric-reinforced composite parts using a matched-die compression molding process or liquid composite molding, the fabric may experience local in-plane compressive loads that cause out-of-plane deformations. The waves that result from this outofplane motion can lead to the formation of resin rich pockets (during the infusion stage of a dry fabric) or they may be forced down into a fold by the tooling. Defects such as resin-rich pockets and folds compromise the structural integrity of the formed composite part. Therefore, it is valuable to have a simulation tool that can accurately capture the fabric bending properties and predict the locations where waves or folds are likely to occur as a result of the manufacturing process. The tool can then be used to investigate changes in the forming parameters such that the development of such defects can be mitigated.
A hybrid finite element model used with a discrete mesoscopic approach captures the behavior of continuous fiber-reinforced fabrics where the fabric yarn is represented by beam elements and the shear behavior is implemented in shell elements. User-defined material subroutines describe the mechanical behavior of the beams and shells for their respective contributions to the overall fabric behavior. Simulations are used to demonstrate the ability of the modeling approach to predict the amplitude and curvature of out-of-plane waves. The simulation results are compared with experimental data to show the accuracy of the modeling. Additional models are presented to demonstrate the capability of the simulation tool to capture fabric folding.
Investigation of the Mechanical Properties of a Stitched Triaxial Fabric
Authors: Mitchell Cynthia J. , Sherwood James A. , Dangora Lisa M. , Gorczyca Jennifer L.
Published: May 2014

A traxial fabric was investigated for use in composite forming applications. Three stitched layers of fibers, originally oriented at [-60o/0o/60o], comprise the fabric architecture. The mechanical properties of the material are characterized by testing the tensile, shear, and frictional behavior. Conventional shear frame testing methodology assumes that the yarns are originally oriented perpendicular to one another; however, such an assumption is not valid for this particular fabric geometry and must be adjusted. The material behavior is implemented into a discrete mesoscopic finite element model that can predict the response of the material during deformation. Different element types will be investigated to represent the fabric and used to determine the ideal mesh configuration that best captures the fabric behavior. Different modes of deformation will also be studied, and the observed experimental deformation will be compared to the deformation predicted by the finite element model.
Investigation of Fibre Movement in Molten Polymer during Shaping Processes of Thermoplastic Composites
Authors: Engel Bernd , Soemer Evelyne , Foysi Holger , Aldudak Fettah
Published: May 2014

In forming processes of thermoplastic composites, the combined forming behaviour of matrix material and fibre reinforcement determines the resulting geometry and structure. These specific characteristics of the components and their interaction vary during the processing steps, especially for the matrix material with change in temperature. During the forming step, the molten thermoplastic polymer exhibits viscoelastic behaviour. Therefore, the fibres encounter resistance if a forming load is applied. The resulting fibre alignment is dependent on the forming temperature, the forming speed, and the time between the release of load and cooling. An investigation into the specific matrix characteristics during the forming step is presented. In the experiments a representing fibre is drawn through a molten polymer specimen under variation of speed and temperature and the resistance force is measured. The experimental findings are compared to numerical results obtained with a computational fluid dynamics (CFD) package using a finite volume approach and its ability for the prediction of fibre movement in molten matrix during forming processes is evaluated. In addition, a better understanding of the impact of forming speed and temperature during forming processes due to the characteristics of the molten matrix is obtained.
Investigation of Different Techniques to Evaluate the FLC from Experiments and FE Simulations
Authors: Groth Anders , Schedin Erik , Moshfegh Ramin
Published: May 2014

The formability of sheet metal is highly related to the materials resistance to strain localisation and fracture. The Forming Limit Curve (FLC) is one way to evaluate the tendency to instabilities during the forming operation of a material for different strain states. The Nakazima test is a common technique used to experimentally determine the limiting strains. In this paper a slightly modified version of the proposed ISO-standard used at Outokumpu/Avesta Research Centre (ARC) is presented. The method considers the limiting principal strains before and after failure has occurred. The obtained results from the present approach are compared with previous internal methods used at the company. The previous internal methods consisted of evaluating the limiting principal strains at the maximum punch force before fracture or at a set punch distance before fracture. An austenitic stainless steel grade (254 SMO®) is used in the study. The method will in this work be called the Interpolation Method (IM). A Finite Element (FE) model of the Nakazima test is modelled in LS-DYNA® with the goal to be able to simulate the experimental test. In order to compare the FLC between the experimental and the numerical results, one instability indicator is proposed based on the onset of fracture in the FE model.The Barlat YLD2000 model [1] using 6 parameters based on proof stresses and anisotropic values for different material directions is applied as a constitutive model. The Interpolation Method is promising and will be used during a trial period at Outokumpu ARC in the future testing. Further development is needed for the simulation model.
A First Step towards a Tribological Approach to Investigate Cutting Tool Wear
Authors: Axel Giovenco , Valiorgue Frédéric , Courbon Cédric , Rech Joël , Masciantonio Ugo
Published: May 2014

The present work is motivated by the will to improve Finite Element (FE) Modelling of cutting tool wear. As a ﬁrst step, the characterisation of wear mechanisms and identiﬁcation of a wear model appear to be fundamental. The key idea of this work consists in using a dedicated tribometer, able to simulate relevant tribological conditions encountered in cutting (pressure, velocity). The tribometer can be used to estimate the evolution of wear versus time for various tribological conditions (pressure, velocity, temperature). Based on this design of experiments, it becomes possible to identify analytically a wear model. As a preliminary study this paper will be focused on the impact of sliding speed at the contact interface between 304L stainless steel and tungsten carbide (WC) coated with titanium nitride (TiN) pin. This experiment enables to observe a modiﬁcation of wear phenomena between sliding speeds of 60 m/min and 180 m/min. Finally, the impact on macroscopic parameters has been observed.
Establishment of Stress-Strain Relationships of Tailor-Welded Tubes via DIC Method Based on Uniaxial Tensile Tests
Authors: Jia Hui Ji , Yang Lian Fa , Liu Jian Wei
Published: May 2014

Tailor-welded tubes are widespread in aircraft and automotive industries due to their advantages of low cost, reduction in part weight and flexibility in mass production. It is necessary to obtain the stress-strain relationship of tailor-welded tubes to study deformation behaviors of tubes and simulate deformation tests of tubes. Then a method via digital image correlation (DIC) method based on uniaxial tensile test (UTT) is proposed in this paper to establish stress-strain relationship of tailor-welded tubes. Material parameters of tailor-welded tubes obtained from three methods, i.e. the method based on UTT, the iso-strain method based on a rule of mixtures and the proposed method, were compared in this paper. To assess the accuracy of material parameters obtained from these three methods, UTTs were simulated, and load-displacement curves and maximal loads obtained from simulations were compared with those obtained from UTTs. In simulations of UTTs, finite element models of specimens of sole parent metal and mixed specimens were established, respectively. The results show that: When HAZ included in the specimen has large proportion of the specimen, the proposed method is more reliable than the iso-strain method based on a rule of mixtures on determining the material parameters of the weld; load-displacement curve and maximal load obtained from the proposed method are more close to those obtained from UTT than those obtained from the method based on UTT.
Modelling of the Microstructure Evolution Using Cellular Automata Framework and WorkFlow Approach
Authors: Golab Rafal , Sitko Mateusz , Madej Łukasz
Published: May 2014

Development of an efficient and user friendly application (framework) for modelling microstructure evolution during thermo-mechanical processing using Cellular Automata (CA) method and WorkFlow approach is the subject of the present work. Description of the major assumptions and functionality of the developed framework is presented first. Then, major assumptions of the implemented cellular automata models dealing with simulation of phase transformation and static recrystallization are presented. Finally, the idea of the WorkFlow methodology is described and used to join the two CA microstructure evolution models into one complex solution. Examples of obtained results of microstructure behaviour during thermo-mechanical processing are also presented within the paper.
First Steps towards Parametric Modeling of FSW Processes by Using Advanced Separated Representations: Numerical Techniques
Authors: Canales Diego , Cueto Elías , Feulvarch Eric , Chinesta Francisco
Published: May 2014

Friction Stir Welding (FSW) is a welding technique the more and more demanded in industry by its multiple advantages. Despite its wide use, its physical foundations and the effect of the process parameters have not been fully elucidated. Numerical simulations are a powerful tool to achieve a greater understanding in the physics of the problem. Although several approaches can be found in the literature for simulating FSW, all of them present different limitations that restrict their applicability in industrial applications. This paper presents a new solution strategy that combines a robust approximation method, based on natural neighborhood interpolation, with a solution separated representation making use of the Proper Generalized Decomposition (PGD), for creating a new 3D updated-Lagrangian strategy for addressing the 3D model while keeping a 2D computational complexity
Numerical Study of the Impact of Constitutive Modelling on the Evolution of Necking in the Case of a Tensile Test on C68 Grade Steel
Authors: Tabourot Laurent , Balland Pascale , Sene Ndéye Awa , Vautrot Mathieu , Ksiksi Nesrine , Maati Ahmed
Published: May 2014

This article deals with numerical simulation of necking. It draws the attention onto the importance of the description of strain-hardening and the effects on the evolution of necking. In order to compare necking evolution in relation with different plasticity models, a tracking procedure which consists in determining the evolution over time of discharged volumes of the sample is adopted. Models that take into account physical phenomena at the microscopic level and especially the heterogeneities of materials from a mechanical point of view seem well suited to fit experimental evidence connected to necking.
Multiscale Finite Element Simulation of Forming Processes Based on Crystal Plasticity
Authors: Soho Komi , Abed Meraim Farid , Lemoine Xavier , Zahrouni Hamid
Published: May 2014

For the numerical simulation of sheet metal forming processes, the commercial finite element software packages are among the most commonly used. However, these software packages have some limitations; in particular, they essentially contain phenomenological constitutive models and thus do not allow accounting for the physical mechanisms of plasticity that take place at finer scales as well as the associated microstructure evolution. In this context, we propose to couple the Abaqus finite element code with micromechanical simulations based on crystal plasticity and a self-consistent scale-transition scheme. This coupling strategy will be applied to the simulation of rolling processes, at different reduction rates, in order to estimate the evolution of the mechanical properties. By following some appropriately selected strain paths (i.e., strain lines) along the rolling process, one can also predict the texture evolution of the material as well as other parameters related to its microstructure. Our numerical results are compared with experimental data in the case of ferritic steels produced by ArcelorMittal.
Forming Simulation Considering the Differential Work Hardening Behavior of a Cold Rolled Interstitial-Free Steel Sheet
Authors: Ichikawa Kazuhiro , Kuwabara Toshihiko , Coppieters Sam
Published: May 2014

The multiaxial plastic deformation behavior of a cold rolled interstitial-free steel sheet with a thickness of 0.65 mm was measured using a servo-controlled multiaxial tube expansion testing machine for the range of strain from initial yield to fracture. Tubular specimens were fabricated from the sheet sample by roller bending and laser welding. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the contours of plastic work in stress space up to an equivalent plastic strain of 0.289 along with the directions of plastic strain rates. The test material exhibited differential hardening (DWH). A material modeling method for reproducing the DWH in a finite element simulation has been developed. Hydraulic bulge forming simulation results based on the DWH model had a closer agreement with the experimental results than those calculated using the isotropic hardening models with selected yield functions.
Study of Microforging of Parallel Ribs from Metal Strip
Authors: Stellin Tommaso , van Tijum Redmer , Merklein Marion , Engel Ulf
Published: May 2014

The on-going trend in product miniaturization, together with the increasing quality and reduction of costs of micro-components, leads to the need of a robust process design, which might additionally avoid the occurrence of defects in the workpiece. Processes like microforming are affected by variations which can be foreseen but not totally mastered in the design stage. One approach is seen in an adaptive control system based on a metamodel processing the data of online measuring. This approach is grounded on in-depth knowledge based on correct and precise process modelling. This paper presents both experimental and simulative study of a microforging process, part of a more complex forming chain. It consists of six parallel ribs on metal strip. The ribs have a width of 250 µm and are spaced by a gap of 150 µm. The process has been studied by different punch forces, analyzing the final geometry of the workpiece. In particular the rib height is considered as critical to quality parameter. The simulations show reliable results that can be used for the design of the model interfacing measurement and control of the whole microforming process.
The Effect of Initial Grain Size on Formability of AZ31B Magnesium Alloy during I-ECAP
Authors: Gzyl Michal , Rosochowski Andrzej , Olejnik Lech , Reshetov Aleksey
Published: May 2014

The goal of this work was to investigate formability of AZ31B magnesium alloy during incremental equal channel angular pressing (I-ECAP). Square billets were processed using different routes of I-ECAP at temperatures varying from 125 °C to 250 °C. The billets were obtained from commercially available coarse-grained, hot-extruded rod and fine-grained, hot-rolled plate. A strong influence of the initial microstructure on processing temperature was reported. Fine-grained samples were successfully processed at 200 °C, while coarse-grained ones must have been heated up to 250 °C to avoid fracture. A gradual temperature decrease with subsequent passes allowed successful pressing at 150 °C. Processing using various routes of I-ECAP showed that a billet rotation before the last pass had strong influence on mechanical properties. The results of experiments were plotted on the diagram of allowable processing temperature for AZ31B. It was found that the relation between the minimum temperature in I-ECAP and the initial grain size could be described by a logarithmic equation.
Finite Element Analysis of the Effect of Flexible Pad on the Deformation of Metal Foils in Flexible Pad Laser Shock Microforming
Authors: Nagarajan Balasubramanian , Castagne Sylvie , Wang Zhong Ke , Zheng Hong Yu
Published: May 2014

Flexible Pad Laser Shock Forming (FPLSF) is a new microforming process using laser-induced shock pressure and a flexible pad. This process involves high strain-rate (~105 s-1) plastic deformation of metallic foils along with the hyperelastic deformation of the flexible elastomer pad over which the foil is positioned. This paper studies the influence of flexible pad on the shockwave propagation behavior and the plastic deformation of metal foil in FPLSF using finite element analysis. The effect of flexible pad materials such as silicone rubber, polyurethane rubber and natural rubber on the deformation of copper foils has been analysed in detail. An increase in crater depth is observed with the reduction in flexible pad hardness. However, it is found that there exists an optimum hardness of the flexible pad to achieve perfect hemispherical craters on metal foils, as bending of foils at non-deformed region is observed with softer pads whereas flattening of crater surface occurs with harder pads. The effect of flexible pad thickness on the foil deformation was analyzed at six different thickness levels: 300 μm, 600 μm, 900 μm, 1200 μm, 1500 μm, and 2000 μm. Similarly, there exists an optimum flexible pad thickness to maximize the crater depth and achieve the hemispherical shapes. Analysis of flexible pad thickness indicates that the pad thickness influences the elastic recovery of the flexible-pad and hence the plastic deformation of the metallic foils.
Estimation of Material Removal by Profilometer Measurements in Mass Finishing
Authors: Bottini Luana , Boschetto Alberto , Veniali Francesco
Published: May 2014

This paper presents a new procedure to estimate the material removal (MR) in such conditions or operations where small amount of material or wear occur. The monitoring of material removal is essential to understand the machining mechanisms of several processes such as super finishing ones. For example the study of some mass finishing (MF) operations, i. e. the barrel finishing (BF) and the spindle finishing (SF), have been always limited by the difficulty to measure the local surface modification. Thus there is no knowledge about the relationship between process parameters and obtainable surface quality. The procedure is based on profilometer measurements typically used to characterized local surface morphology. An algorithm automatically finds the most representative peak of the profile. The comparison between the Abbot-Firestone curves, related to peaks achieved in different condition, permits to measure the volume of material removed by the operation. This method overcomes the well-known problem to repositioning the instrument in the same place when the part is moved from machining process to measurement one. In the case of BF, experimental demonstrated the reliability of this methodology to provide the evolution of material removed as a function of working time. Moreover the graphical plot of the representative peak at different times gave important information about machining mechanism. In particular it allowed to verify assumptions regarding the plastic deformation and the peak cutting which takes place.
Influence of Titanium Carbide Fraction on Material Properties and EDM of ZrO2-TiC Ceramics
Authors: Landfried Richard , Kern Frank , Gadow Rainer
Published: May 2014

EDM of electrically conductive oxide ceramics with addition of titanium carbide have been successfully applied as wear resistant tool inserts in ceramic injection molding or extrusion. In recent years especially alumina based ceramic composites toughened by zirconia have shown their potential in the field of ED machinable ceramics however revealing some drawbacks resulting from their moderate fracture toughness. This study focuses on the zirconia based ceramics with addition of different amounts of titanium carbide as electrically conductive phase (26-36 vol.-%) in order to improve the toughness of ED machinable ceramics. Additionally the influence of the titanium on removing mechanisms during machining as well as the hardness and strength of the material was investigated. It was found that the use of zirconia as matrix material does improve the toughness and strength compared to alumina based composites whereas the drawback of zirconia based materials concerning machinability and lower hardness can be only partially compensated by adjusting the titanium carbide content.
Determination of High Strain-Rate Behavior of Metals: Applications to Magnetic Pulse Forming and Electrohydraulic Forming
Authors: Jeanson Anne Claire , Avrillaud Gilles , Mazars Gilles , Cuq-Lelandais Jean Paul , Bay François , Massoni Elisabeth , Jacques Nicolas , Arrigoni Michel
Published: May 2014

The design of processes like magnetic pulse forming and electrohydraulic forming involves multiphysical couplings that require numerical simulation, and knowledge on dynamic behaviour of metals. The forming process is completed in about 100 μs, so that the workpiece material deforms at strain-rates between 100 and 10 000 s-1. In this range, the mechanical behaviour can be significantly different than that in quasi-static conditions. It is often noticed that the strength and the formability are higher.
The main goal of this study is to use an electromagnetically driven test on tubes or sheets to identify the constitutive behaviour of the workpiece material. In the case of tube, an industrial helix coil is used as inductor. Simulations with the code LS-Dyna® permit to find a configuration where the tube deforms homogeneously enough to allow axisymmetric modelling of the setup. The coil current is measured and used as an input for the simulations. The radial expansion velocity is measured with a Photon Doppler Velocimeter.
The parameter identification is lead with the optimization software LS-Opt®. LS-Dyna axisymmetric simulations are launched which different set of parameters for the constitutive behaviour, until the computed expansion velocity fits the experimental velocity. The optimization algorithm couples a gradient method and a global method to avoid local minima. Numerical studies show that for the Johnson-Cook constitutive model, two or three experiments at different energies are required to identify the expected parameters.
The method is applied to Al1050 tubes, as received and annealed. The parameters for the Johnson-Cook and Zerilli-Armstrong models are identified. The dynamic constitutive behaviour is compared to that measured on quasi-static tensile tests, and exhibits a strong sensitivity to strain-rate. The final strains are also significantly higher at high velocity, which is one of the major advantages of this kind of processes.
Influence of Plasma Channel Change on the Surface Topology in the Electrical Discharge Machining
Authors: Schulze Hans Peter , Mecke Katharina
Published: May 2014

For the EDM, it is important that the surface topology can be determined for given process parameters in advance. Simulations with constant plasma channel radius are very inaccurate and only give a limit of thermally-influenced zone to. Many functional relationships of the temporal change of the plasma channel are only for small time periods and do not reflect properties of the dielectric. In the paper is shown how various properties of the dielectric, contribute to the change of the plasma channel and the plasma channel as different behaviors can be treated with one simulation program. The maximum thermal load may be calculated by selective application of simulation, but also the topologies through moving or split plasma channels. This extended simulation is important because in the micro-EDM process instabilities leading to the splitting of the plasma channels. The simulations are reviewed on the basis of individual discharges and corrected corresponding weighting factors.
Direct Molding of Polymers for Biomedical Applications
Authors: Santo Loredana , Bellisario Denise , Quadrini Fabrizio
Published: May 2014

. Direct molding is a simple molding process to produce small parts at low costs. A single pellet or few pellets are directly molded into a transparent mound by means of an IR lamp. A new micro-molding machine has been developed for this study and used to mould polymers for biomedical applications (PCL and PHBV). Due to the small amount of molded material, the proposed process is particular suitable for biomedical applications which are characterized by small numbers of parts and high costs of the raw materials. Moreover, direct molding is able to reduce material degradation and frozen stresses. The new machine has been used to mold small disks from single pellets. This way, the effect of the main process parameters on the molded polymer density has been evaluated. Moreover, DSC analyses have shown the effect of the molding process on the polymer properties. In conclusion, the micro-molding system has been used to produce small components which were tested in terms of dimensional stability and mechanical performances.
Influence of the Identification Procedure of the Yield Criterion on the Thickness Prediction of the Square Cup
Authors: Paraianu Liana , Comsa Dan Sorin , Banabic Dorel
Published: May 2014

The accuracy of the forming limit curves reported by the Marciniak-Kuczynski model as well as the quality of the predictions provided by the FE programs depend on the yield criterion that describes the anisotropic plastic behavior of the sheet metal. Two identification procedures of Barlat89 and BBC2005 are used in this paper. The first procedure is a conventional one well described in the literature [, while the second approach is developed by adding an experimental parameter determined in plane-strain state that allows establishing the exponent of the yield criteria. The mechanical response of the IF steel shows that the limit strains are strongly influenced by a small alteration of the yield surface. The influence of the yield criterion on the thickness predictions obtained in the simulation of a square cup deep drawing simulation is also studied.
The Influence of Process Parameters on the Forming of Riblets during Riblet Rolling
Authors: Pöplau Julia , Stille Sebastian , Romans Thijs , Beck Tilmann , Singheiser Lorenz , Hirt Gerhard
Published: May 2014

In aeronautics, economic and environmental aspects become increasingly important. As those are very much influenced by the frictional drag of the airplane, a reduction of skin friction which causes a major portion of total aerodynamic drag is desirable. One possible approach for passive drag reduction is the application of riblets small longitudinal grooves orientated in flow direction. Through an adapted rolling process, riblets can be brought into metal sheets on a large scale. For this process a thin high-strength steel wire is wound around a work roll to structure it with the negative riblet imprint. In a subsequent step the riblet profile is rolled into the sheet material. Different parameters can influence the process and the quality of the resulting riblet structure. Those parameters that depend on the sheets sheet thickness, material strength, and composition of the sheet are discussed in this paper. Form filling is used as an indicator for riblet quality. It is found that decreasing sheet thickness is beneficial for form filling, but a process dependent minimum sheet thickness exists for which this effect will reverse. Material strength is found to have a much smaller influence on form filling. Nevertheless, harder alloys seem to need a slightly smaller thickness reduction, but higher rolling forces and pressures to achieve desired form filling. Using clad instead of bare materials has a positive influence on form filling and riblet structuring. Furthermore, riblet rolling does not reduce the fatigue strength of the clad material.
Dual Electromagnetic Forming Using Single Uniform Pressure Coil
Authors: Patel Chandrahas , Kore Sachin D.
Published: May 2014

Electromagnetic Forming (EMF) is a high-speed forming process that can be applied for shaping, joining and cutting of workpieces made of electrically conductive material eg. aluminium. This paper proposes a dual electromagnetic forming method. Energy efficiency of the dual electromagnetic forming is compared with the single sided electromagnetic forming using FEM simulations. In uniform pressure rectangular coil, the top layer of the coil assists in the deformation of the workpiece while the bottom layer hinders the workpiece deformation.To make the bottom layer of the coil also to assist in the deformation of the workpiece, a uniform pressure rectangular coil is designed and placed between the two sheet metal workpiece. The efficiency of the two processes are compared by determing the maximum deformation obtained for each case.
Controlling Penetration Depth in Projection Stereolithography by Adjusting the Operation Wavelength
Authors: Lehtinen Pekka , Laurila Santeri , Kaivola Matti , Partanen Jouni
Published: May 2014

In projection stereolithography, the cure depth and thereby the layer thickness in the manufacturing process may be varied by changing the operation wavelength. The change can be made even in the middle of the manufacturing process, which opens up possibilities for additional flexibility and speed-up of the process.In this paper, we investigate how the penetration depth of the curing light in the resin depends on the wavelength. The measurements were performed for wavelengths between 400 nm and 550 nm using a standard commercial resin. The penetration depth was found to almost double when moving from the short wavelengths to the long ones.
Designing and Manufacturing of a Flexible Longitudinally Laminated Sandwich Panel Forming Tool
Authors: Lämsä Janne , Järvenpää Antti , Mäntyjärvi Kari
Published: May 2014

The main aim of the study was to develop forming tools for wide (over 1.2 meter) sandwich panels. Longitudinal laminating technology was selected for tool manufacturing due to its flexibility and cost efficiency. Laminating technology enables easy modification of the tool dimensions afterwards. The function to optimize or vary the dimensions of the tool was set as a secondary objective for the study. Forming tools for sandwich panels are usually complicated structures and joining of the plates can be difficult in some cases. Typically sandwich forming tools are capable to produce only narrow panels (less than 1 meter) and optimization must be done during designing of the tool.
In this study, a rapid designing and manufacturing of a flexible sandwich panel forming tool was investigated. Sandwich panels are usually applied in light structures or voice covers due to their very low weight, high stiffness, durability and production cost savings. Designing of the forming tool was made by using a 3D CAD program. Conventional steel plates were used for the forming tool and the assembly was done by fixing the plate parts longitudinally together (laminating). Most important criterion for the forming tool was its capability to produce high quality geometry for the core. Laser welding assembly showed that the quality of the core was good enough for welding the lap joints properly. Both of the objectives were fulfilled: 1) forming tools were suitable for forming of wide cores (1.2 meter) and 2) the structure of the laminated tool enables to change or add new plate parts to change the dimensions of the final product.
Laser Cutting of Aluminium Sheets with a Superficial Cold Spray Titanium Coating
Authors: Astarita Antonello , Genna Silvio , Leone Claudio , Minutolo Fabrizio Memola Capece , Paradiso Valentino , Squillace Antonino
Published: May 2014

In the manufacturing of metal components both wear and corrosion have to be considered. In particular, corrosion is a primary problem in the aeronautic field, where the aluminium alloys are affected by several corrosion typologies. Furthermore, nowadays carbon fibre reinforced plastics (CFRP) are finding an increasing use, but they can induce galvanic corrosion phenomena when coupled with aluminium alloys. To overcome this problem, corrosion resistant coatings are used on aluminium components. On these premises, the realization of a titanium coating on aluminium components could allow the coupling of CFRP and aluminium alloys, improving the corrosion resistance. Cold Spray Deposition is a recent technology to realize these coatings. This technology allows the production of near fully dense coatings on metallic surfaces. In many applications the coated aluminium sheets have to be machined (cut or drilled). Machining with conventional cutting methods leads to both tool wear and damages in the coating. Laser cutting represents a promising alternative: it does not involve any mechanical cutting force or tool wear and, thanks to the small laser beam spot, it allows to realize complex shapes. In this paper, laser cutting of an Al alloy sheet (0.6 mm thick) coated with Ti Alloy, was studied. The adopted laser source was a 150 W, lamp pumped Nd:YAG, specifically developed for micro-machining operations on metals. During the tests, the process parameters (cutting speed, pulse duration and entrance side) were changed and the kerf geometry was analysed as a function of the process parameters.
A Novel Heat Treatment Line for Processing of Tailored Small Batch Steels
Authors: Järvenpää Antti , Lämsä Janne , Patard Emmanuel , Mäntyjärvi Kari
Published: May 2014

This study describes design and construction of a novel flexible heat treatment line for processing customer-oriented small batch steels. The induction heater (600 kW) developed is suitable for the sheet thickness in the range 3.2 30 mm and the width of 85 1250 mm. Sheets are fed using an electrical motor (1.5 kW) and a chain drive, the speed being in the range 0.3 7 m/min, depending on the power and the sheet dimensions. At this study, 4.5 (WR-1) and 10 mm (WR-2) thick wear resistant steels were tempered at different peak temperatures to compare the effect of rapid tempering on mechanical properties. Results showed that the heat treatment line is capable of producing tempered steel grades with adequate properties at industrial product rate. For example, 4.5 thick WR-1 tempered at 550 oC provided a yield strength (YS) over 1000 MPa with minimum bending radius of 6 mm (in the delivered condition YS = 1605 MPa and Rmin = 12). Tempering of WR-1 at 700 oC provided YS of 762 MPa and Rmin of 1 mm. Results were similar between two test materials, but the enhancement in bendability was slightly more effective with the thinner sheet.
Formulation and Surface Properties of Bio-Based Polymer Films for Pharmaceutical Applications
Authors: Brogly Maurice , Fahs Ahmad , Bistac Sophie
Published: May 2014

Hydroxypropyl methylcellulose (HPMC) constitutes one of the most dedicated polymers used in the production of film coatings for pharmaceutical applications (capsules, tablets …). In order to control the surface properties (adhesion, friction, wear) of HPMC films, additives are frequently incorporated during film formulation: these are in most cases hydrophobic lubricant (like fatty acids) or hydrophilic plasticizer. Hydrophilic plasticizer like polyethylene glycol (PEG) will determine the diffusion properties of water through the film and thus drug release but also its deformability as well as its surface softness. The main objective is to use dedicated analytical tools to access HPMC formulated film surface characteristics in terms of structuration, surface morphologies, surface phase separation, wettability, nano-adhesion and nano-friction properties. At nanoscale, Atomic Force Microscopy (AFM) in contact mode and in friction mode (FFM) is a powerful tool for studying nano-adhesion and nano-friction. The presented paper underlines the strong dependence of film surface properties on additive nature and concentration. It also shows that first the HPMC-additive compatibility seems to be an interesting factor behind the variation of surface properties of HPMC formulated films, and second that formulation is an effective way to tune surface properties of HPMC biopolymer films.
Substitution of Virgin Material by Recycled Material from End-of-Life Vehicle (ELV)
Authors: Epsztein Sophie Rabeau , de Fombelle Marc Antoine Jevardat , Falher Thierry , Jouannet Denis , Gallone Toni , Cauret Laurent
Published: May 2014

The main objective of this study is the substitution of a part of virgin polypropylene with recycled polyolefin from part of End-of-Life Vehicle (ELV) to be used in automobile applications while respecting existing material specifications. First, the recycled plastic sources were characterized by ThermoGravimetric Analysis (TGA), Fourier Transform Infrared Spectrometry (FTIR), Differential Scanning Calorimetry (DSC) and X-ray Fluorescence. As the sources have almost the same properties, the one, with the easiest supply, was selected. During the second step, the study allows comparison of mechanical performance of several formulations with three specific additives made in two injection process conditions. A higher heat temperature and smaller dosage speed reduced the degradation of fibre glass during processing. Moreover, the additive improving the adhesion between the fibre and the polymeric matrix increased by 3% the flexural modulus. This study has enabled the elaboration of a global method coupling sampling methodology, formulation and process optimisation to substitute a virgin material with recycled plastics from ELV.
Performance and Lightweight Thermoplastic Materials for Automotive Application using Hollow Microspheres
Authors: Doumbia Awa S. , Jouannet Denis , Falher Thierry , Cauret Laurent
Published: May 2014

In recent decades, the weight of passenger vehicles has constantly increased. This leads to a rise in fuel consumption and higher CO2 emissions. On this basis, vehicle weight reduction is a privileged research axis to meet regulatory requirements on emissions by 2020. The current study is focused on the development of thermoplastic polymer used in the automotive sector. In fact, thermoplastic polymers allow innovative design and offer the advantage of being recycled for sustainable development purposes. Some lighter fillers were incorporated in this polymer by melt processing for weight saving benefits. We were interested mainly in hollow microspheres which are lower density than conventional mineral fillers (such as: talc, calcium carbonate, glass fibers etc ...). This study explores the impact of pilot-scale melt-processing on six (6) hollow microspheres embedded in high impact polypropylene commonly used for car bumpers. We found that two commercially available microspheres (grades iM30K and K37) withstand melt-processing successfully and reduce the polymer density.
Parameter Identification by Inverse Analysis Coupled with a Finite Pointset Method for Polyurethane Foam Expansion
Authors: Abdessalam Hichem , Abbès Boussad , Li Yu Ming , Guo Ying Qiao , Kwassi Elvis , Romain Jean-Luc
Published: May 2014

This paper deals with the parameter identification for polyurethane foaming process simulation by using an inverse analysis coupled with a Finite Pointset Method. Simultaneous measurements of the foam height rise, the reaction temperature and the viscosity on a cylindrical cardboard test tube are obtained by using the foam measurement system (FOAMAT). The simulation of the foam expansion is obtained by solving unsteady Navier-Stokes equations coupled with the energy equation, the curing reaction (reaction of isocyanate with polyol) and the foaming reaction (reaction of isocyanate with water to emit the CO2 gas) by using a mesh-free method. The inverse identification method consists in determining the parameters by comparing the computed quantities (height rise, reaction temperature and viscosity) computed by the finite pointset method to those measured experimentally.
Formation of the Printing Elements in the Photopolymer Material Used in Flexography
Authors: Mahovic Poljacek Sanja , Tomasegovic Tamara , Cigula Tomislav , Gojo Miroslav , Milcic Diana
Published: May 2014

Starting point of this paper is photopolymer printing plate used for flexographic printing. It is used for transfer of the printing ink onto the printing surface during the reproduction process. Photopolymer printing plate consists of several layers: polyester basis, photo sensitive polymer material and LAMS - Laser Ablation Mask. In the platemaking process the photosensitive material, which will form a printing plate, has to be several time exposed to different radiation in order to obtain a functional printability performance. LAMS layer has a role of masking in the exposure process. Upon pre-exposure, LAMS layer has to be removed by laser ablation only at the surfaces where photopolymer printing plate needs to be exposed. After ablation the exposures to UV lights follows and the plate will be finished with chemical removal of the unexposed parts of the polymer.
Functionality of the finished printing plate has to be characterised and monitored in every procedure step because the formed image element on the printing plate has a major influence on the quality of the finished printed product. In this paper observing of the changes in the polymer material which is caused by exposure through LAMS layer will be performed. The aim is to measure the surface openings on the LAMS mask and to measure surface coverage (image elements) on the polymer material formed by exposure through the LAMS. Measuring will be made by image analysis software based on microscopic images of the control fields of differing halftone values. It is assumed that there will be a correlation between the LAMS openings and formed image elements on the printing plates. Preliminary results indicate that certain differences in image elements can be detected and are probably the consequence of the different amount of irradiated surface of the polymer material. Since the polymer material which forms the printing plate should be stable in the graphic reproduction process, results of the paper will explain the influence of UV exposures on polymerisation process and on the functional printability performance of the plates.