bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi-Resolution Transforms Based Robust Image Enhancement for High Frequency Colour Images
Authors: Menakadevi T. , Arivudainambi J. , Sulochana M.
Published: May 2014

An Image Resolution Enhancement Technique based on Interpolation of the high frequency sub-band of colour images obtained by Discrete Wavelet Transform and the input colour image is proposed in this paper. Interpolation determines the intermediate values on the basis of observed values. One of the commonly used interpolation technique is Bicubic Interpolation. The edges are enhanced by introducing an intermediate stage by using Stationary Wavelet Transform. It is designed to overcome the lack of Translation-Invariance of Discrete Wavelet Transform. This is widely used in Signal Denoising and Pattern Recognition. Discrete Wavelet Transform is applied in order to decompose an input colour image into different sub-bands. Then the high frequency sub-bands as well as the input colour image are interpolated separately. The interpolated high frequency sub-bands and the Stationary Wavelet Transform high frequency sub-bands have the same size which means they can be added with each other. The new corrected high frequency sub-bands can be interpolated further for higher enlargement. Then all these sub-bands are combined with interpolated input image for new high resolution image by using Inverse Discrete Wavelet Transform. This has been done by MATLAB. The Peak Signal-Noise Ratio was obtained upto 5dB greater than the conventional and state-of-art image resolution enhancement techniques.
An Application of IPA to Analyze Numeracy of Statistics and Mathematics of Employment-Required Knowledge of University Students
Authors: Ma Hsiu Lan , Jen Chin I , Lin Szu Hsing , Wu Der Bang
Published: May 2014

This study used Importance-Performance Analysis (IPA) to analyze statistics and mathematics employment-required knowledge of university students.
Reliability Evaluation of the Crew Organization of High-Speed Railway
Authors: Wang Yang , Zhu Xiao Ning
Published: May 2014

This paper analyzes the factors which influence the reliability of the crew operation of high-speed railway. With Analytic Hierarchy Process, this paper calculates the effect degrees of these factors. The form of the level of the factors is established. This paper formulates the mathematical methods that can evaluate the reliability of the crew organization of high-speed railway.
Study on the Gaming-Oriented Competition Relationship between Independent E-Retailers and Product Suppliers
Authors: Lei Jiang , Zhao You Gui
Published: May 2014

A with the rapid development of e-commerce, the influence of online retailers gradually increased, vendors sell their products through online retailers have become an inevitable choice in the era of e-commerce. Vendors and online retailers have fundamental differences in the channel control, distribution of benefits, resulting in the presence of both cooperation and competition between the two sides. In this paper, using replicator dynamics model, combined with non-symmetric matrix, analysis of evolution trend between independent Internet retailers and suppliers cooperation competition game, and proposes relevant suggestions accordingly trend.
Living Radical Polymerization of Methyl Methacrylate Mediated by Tris-(4-Acetyphenyl)Methane
Authors: Xu Yuan Qing , Ding Tao , Fang Xiao Min , Xu Hao , Ren Yan Rong
Published: May 2014

Pseudo-living radical polymerization and reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) were reported, utilizing tris-(4-acetyphenyl) methane (TAcPM) as the thermal iniferter and initiator, respectively. The polymerization of MMA using TAcPM as thermal iniferter possesses pseudo-living characteristics: Mnincreases with conversion in a certain range, and the resulted polymer can be used as the macro-initiator for chain extension. The RATRP using TAcPM as the initiator shows linear kinetic plot, linear increase of Mnwith conversion and narrow polydispersity indice (PDI) of the resultant polymers.
Research on Automatic Stacking and Loading System in Major Logistics
Authors: Wei Ze Feng , Ju Hui , Qin Dong Xing , Yan Han Bing , Wang Zhi Hong , Li Guang Xu
Published: May 2014

This document introduces the current status of the stacking and loading technology in major logistics. It introduces the development of a kind of automatic stacking and loading system in major logistics from Chengdu University of Information Technology, including the function, composition, characteristics, key technology of structure design for Non bulk cargo object, automatic extract, automatic loading and stacking. Then the main technical parameters are put forward. It is pointed out that the system has a good social, economic significance.
Drying of Industrial Ceramic Bricks: An Experimental Investigation in Oven
Authors: Almeida G. Silva , Fernandes M.A.F. Barbosa , Fernandes J.N. Ferreira , Neves Gelmires Araújo , Barbosa de Lima W.M.P. , de Lima Antônio Gilson Barbosa
Published: May 2014

The purpose of this paper is to present an experimental study of clay brick drying. For the drying experiments, industrial holed bricks were dried in an oven under controlled conditions of velocity, temperature (constant and variable) and relative humidity of air. The continuous drying experiments ended when the mass reached constant weight. Experimental tests were performed under atmospheric pressure. Results of the drying and heating kinetics and volume variations during the process are shown and analyzed. It was verified that the drying process happens in the falling drying rate period, and air temperature has large influence in the drying rate during process. It was verified that the largest temperature, moisture content and stress gradients are located in the vertexes of the brick.
Effect of Intermetallics on Pt-Al Surface Coatings Colour
Authors: Topic M. , Vinci Richard P. , Khumalo Zakhelumuzi , Mtshali C.
Published: May 2014

We investigated two coatings, Pt:Al and Pt3:Al, deposited onto pure Al substrates. After annealing at 500°C for 2 hours in vacuum, the Pt:Al coating became “matt silver” while the Pt3:Al colour was “old gold”. Although the deposited coatings were relatively smooth, rope-and ridge-like morphologies were observed in the annealed Pt:Al and Pt3:Al coatings, respectively. X-ray diffraction analyses revealed the presence of Al21Pt6and Al2Pt intermetallics in annealed Pt:Al while only the Al2Pt intermetallic phase was observed in the annealed Pt3:Al coatings. RBS spectra showed an increase of coating thickness by four times in the Pt:Al whilst the coating thickness was doubled in the Pt3:Al coatings. The changes to color, surface morphology, and thickness caused by thermal annealing were attributed to the structural characteristics of the most dominant phases.
Determination of Sorption Isotherm Based on the Measured Bottom Contaminant Flux
Authors: Minár Jozef , Kačur Jozef
Published: May 2014

We determine the sorption isotherm in the infiltration model of contaminated water into porous media. We assume that the contaminated water infiltrates into the dry porous media, flow through the sample and flows out at the other side of the sample. We suppose that the contaminant dissolved in the water reversibly adsorbs into the porous media. We use the Richards equation with van Genuchten relation between effective saturation and pressure head. Further, we use Fick’s law to model the contaminant transport in the water and arbitrary adsorption isotherm to model the evolution of the adsorption. By running the direct problem simulation, we obtain the “measurements” of the expelled water mass and its concentration. Then we “forget” the adsorption isotherm function. We solve this inverse problem by evaluating the gradient of the distance function (between “measured” and computed bottom contaminant flux) in an iterative way. We construct the gradient (variation) of the distance function by solving the corresponding dual system of partial differential equations.
Resin Transfer Molding Process: A Numerical Analysis
Authors: de Oliveira Iran Rodrigues , Amico Sandro Campos , Souza Jeferson Avila , de Lima Antônio Gilson Barbosa
Published: May 2014

This work aims to investigate the infiltration of a CaCO3filled resin using experiments and the PAM-RTM software. A preform of glass fiber mat, with dimensions 320 x 150 x 3.6 mm, has been used for experiments conducted at room temperature, with injection pressure of 0.25bar. The resin contained 10 and 40% CaCO3content with particle size 38μm. The numerical results were evaluated by direct comparison with experimental data. The flat flow-front profile of the rectilinear flow was reached approximately halfway the length of the mold. It was observed, that the speed of the filling decreases with increasing CaCO3content and,the higher the amount of CaCO3in the resin, the lower the permeability of the reinforcement that is found. The reduction in permeability is due to the presence of calcium carbonate particles between the fibers, hindering the resin flow in the fibrous media. The computational fluid flow analysis with the PAM-RTM proved to be an accurate tool study for the processing of composite materials.
Characterization of Gamma Irradiated PP/LDPE Blend
Authors: Moori Tatiana Mayumi , Terence Mauro Cesar , Pereira Nilson Casimiro , Faldini Sonia Braunstein , de Miranda Leila Figueiredo
Published: May 2014

This study analyzed nine polypropylene (PP) and low-density polyethylene (LDPE) blends where the mass concentrations of each sample were changed, proportionally. The aim was to investigate the tensile strength by means of these polymers best combination, before and after its exposal to gamma rays. The results showed that the 20/80 - PP/LDPE blend had a better performance concerning mechanical properties after irradiation, where the maximums tensile stress had an average increase of 30% in 30 and 50 kGy doses and 33% in the 200 kGy dose. On the other hand, it was verified that the higher blend's PP concentration, the higher its tensile strength will be (except for 100 kGy and 200 kGy doses which PP concentration over 70% can cause eventual degradation in the polymeric chains of the blend).
Metal Flow Conditions in Porthole Channels of Different Size
Authors: Valberg Henry , Nolte Dirk , Yawar Khan
Published: May 2014

Finite element analysis (FEA) is applied to study metal flow in an asymmetric porthole
die with two ports where one port is bigger than the other. It is shown how FEA predicts the
velocity differences between the two ports to depend on applied extrusion velocity, i.e., the ram
speed, and in addition, how increasing size difference between the ports changes the flow balance
between the ports. Two of the simulations have been validated by experiments in previous work, so
the trends shown by FEA have also been confirmed experimentally.
In long billet extrusion metal flow through the two die channels is predicted stable throughout the
major part of the extrusion stroke. However, in the end stage of the process, there is predicted a
shift in metal flow. Now the velocity in the small channel is speeded up on the expense of that in
the big channel. In short billet extrusion the same shift in metal flow is also confirmed towards end
of extrusion. An explanation is given why the metal flow in the small channel speeds up towards
end of extrusion. In the article it is also quantified (in a diagram) how big the shift in flow balance
between the two ports is as the size difference between the ports increases.
Roller Hemming Simulation: State of the Art and Application Limits
Authors: Neugebauer Reimund , Drossel Welf Guntram , Rössinger Markus , Eckert Alexander , Hecht Benjamin
Published: May 2014

The presented study applied the state of the art in roller hemming simulation on a car body assembly. Corner areas with changing flange lengths are always challenging in case of reaching the quality demands. Thus, the numerical results like e.g. springback, hem thickness, roll-in and hemming geometry are compared to experimental results. It is shown that the quality of prediction depends on the system stiffness of the roller hemming device, the geometrical contour of the car body assembly and the consideration of steps in the process chain like stamping and flanging. Finally, the gained cognitions point out challenges for future research in this topic.
Hot Single Point Incremental Forming of Ti-6Al-4V Alloy
Authors: Ortiz Mikel , Penalva Mariluz , Puerto Mildred J. , Homola Petr , Kafka Václav
Published: May 2014

The lightweight metal alloy Ti-6Al-4V is widely used in the aeronautical industry due to its excellent mechanical properties. However, it is known the difficulty to deform Ti-6Al-4V sheets at room temperature because of its microstructure conditions. The present work focuses on the evaluation of formability of Ti-6Al-4V sheets using hot single point incremental forming (SPIF) process which it seems appropriate to produce small batches of parts due to its flexibility as it allows a significant reduction of costs and lead times. In order to characterize the SPIF of Ti-6Al-4V under hot forming conditions, a set of forming trials evaluation tests was carried out. The obtained results have allowed identifying the key process features and have demonstrated the potential of the proposed approach to hot form of small amounts of Ti-6Al-4V parts.
Electromagnetic Formability of an Aluminium Ice Tray
Authors: Doley Jyoti Kumar , Kore Sachin D.
Published: May 2014

Electromagnetic forming (EMF) is a typical high speed forming process using the energy density of a pulsed magnetic field to form work sheets made of metals with high electrical conductivity like aluminium alloys, which have low formability at low strain rate. Under high velocity forming, metallic materials exhibit an increase of flow stress and ductility with increasing deformation rate. Therefore, materials of lower ductility can be deformed to higher strains using high strain rate deformation processes such as electromagnetic or explosive forming techniques. In this paper analysis of an electromagnetic sheet metal forming process is carried out by using commercial finite element software LS-DYNA®, which incorporates a sequential coupling method involving electromagnetic field, structural and thermal solutions. Study of process parameters for forming aluminium ice tray (used in refrigerator) by Electromagnetic forming process has been carried out, simulation was done involving a die, Al worksheet and a spiral coil.
Numerical and Experimental Study of Preforming Stage in Tube Hydroforming
Authors: Mojarad Farimani Saeed , Gholipour Javad , Champliaud Henri , Savoie Jean , Wanjara Priti
Published: May 2014

The preforming stage in hydroforming of an aerospace generic shape was investigated using a combination of experimentation and numerical modeling. The preform die was manufactured using a rapid prototyping method, namely the selective laser sintering (SLS) process. The preforming experiments were conducted on 0.9 mm and 1.2 mm thick stainless steel 321 (SS321) tubes. To evaluate the preforming process, an automated deformation measurement system, ARGUS®, was used to measure the 3-dimensional (3D) strains on the deformed tubes. Data collected from the experiments were used to validate the simulation of the preforming stage. The simulation and experimental results were found to be in good agreement, indicating that the preform model can be used as a starting point for simulating the tube hydroforming (THF) process. In addition, the SLS approach was found to be very promising, as it reduced greatly the lead time and cost of process development for THF.
Punch Wear in the Forming of Deep Holes with Pulse Ram Motion on a Servo Press
Authors: Matsumoto Ryo , Utsunomiya Hiroshi
Published: May 2014

For the fabrication of lightweight components such as hollow components, we proposed a cold extrusion method for forming of deep holes that utilizes a punch with an internal channel for the supply of liquid lubricant using a servo press. The relationship between the punch ram motion and the punch wear in the proposed forming method is investigated by the finite element analysis in this study. The punch wear is determined by using the Archard’s equation. Although low friction at specimen–punch interface realizes in the forming with pulse punch ram motion (proposed forming method), the punch wear in the backward extrusion with pulse punch ram motion is 1.1–2.4 times larger than that with no pulse punch ram motion (conventional forming method). The influence of punch ram motion and friction on the punch wear is discussed.
Elastic-Plastic Reduced Order Modelling of Sheet and Profiles Bending-under-Tension
Authors: Aguado Jose Vicente , Leygue Adrien , Cueto Elías , Chinesta Francisco
Published: May 2014

The aircrafts fuselage structure is usually composed of an assembly of stringers and frames made of cold-worked aluminium profiles. In particular, frames need of a forming process that shapes the profile into the frame’s curved shape. To do this, both profile ends are clamped, and then the profile is simultaneously stretched and pressed against the mould so that the material is plastically deformed. Industrial experience shows that most of times the resultant frame does not fulfil neither curvature nor planarity tolerances. These defects are mainly due to spring-back, residual stresses, and some technologic restrictions related to the machinery. The lack of understanding has led industry to reduce the automation level, and thus the forming process is frequently interrupted to perform verifications and adjustments that make the process to be time-consuming and very much dependent on the know-how of the machine operator. Aiming to improve the frame’s industrialisation, this work first analyses the influence of several parameters in the final shape. Then, we propose a computer-aided forming process based on the concept of Computational Vademecum (CV), which is also introduced in this work. It allows reducing the dependence on the operator know-how, while reliability and repeatability of the process can be improved.
Influence of the Process Temperature on the Properties of Friction Stir Welded Blanks Made of Mild Steel and Aluminum
Authors: Mertin Chris , Naumov Andreas , Mosecker Linda , Bambach Markus , Hirt Gerhard
Published: May 2014

Hybrid components made of steel and aluminum sheet metal are a promising approach for weight reduction for automotive applications. However, lightweight components made of steel and aluminum require suitable joining technologies, particularly if forming operations follow after the welding process. Friction Stir Welding (FSW) is a promising solid-state welding technology for producing dissimilar joints of steel and aluminum. Within this work dissimilar butt joints were produced using sheet metals of mild steel DC04 and the aluminum alloy AA6016 with a thickness of about 1 mm. The FSW joints show approximately 85 % of the tensile strength of the aluminum base material. In metallographic investigations of the produced FSW blanks it was found that the microstructure in the area of the weld seam changes in the aluminum alloy due to the process temperature and plastic deformation. Due to temperature dependent changes of precipitations of the aluminum alloy, temperature measurements have been carried out during the welding process. To find an explanation of the reduction in tensile strength of the FSW joints, short time heat treatment experiments in the temperature range between 250 °C and 450 °C were performed using the aluminum base material. Heat treatments in the temperature range of the measured process temperature result in a reduction of the tensile strength of about 20 % regardless the annealing time.
Friction Stir Welding of Aluminum Metal Matrix Composite Containers for Electric Components
Authors: Pakkanen Jukka , Huetter Andreas , Poletti Cecilia , Enzinger Norbert , Sommitsch Christof , Niu Ji Tai
Published: May 2014

For aerospace applications, light-weight boxes to protect and carry electronic equipment need to be sealed. The main requirements on the components are low thermal expansion and gas tightness. The common material for such an application is a metal matrix composite (MMC). The MMC suggested here consists of A356 aluminum alloy matrix with 15 vol.% SiC particle reinforcement. A safe limit for the electronic component inside the boxes during sealing is determined to be 180°C. Due to the boundary conditions gas tightness and low heat input, Friction Stir Welding (FSW) might be an alternative to the employed joining techniques. For the FSW process the T-Joint is the most appropriate joint geometry in respect to the box design. The geometry of the lid has to ensure the backing system for the stir zone inside the box. A successful welding of the box was done after a joint geometry optimization. The examination of the welded box concerns material characterization with microscopic methods, measuring thermal expansion in base material and stir zone and temperature measurement while FSW.
Forming of Automotive Parts with Nuts Clinch Process in Comparison to Welding of Nuts
Authors: Balon Pawel , Świątoniowski Andrzej
Published: May 2014

In this paper authors present joining by forming method for screws and nuts. Self-clinching nut process was compared to a traditional nut welding method after drawing the requested shape in order to analyse quality of junction. That process is very often carried out for High Strength Steels which usually contain decreased plastic properties and increased strength. It usually causes a problem to set up the self-clinching process. Currently, there are a few companies specialising only in this kind of processes, however correct designing of such tool requires taking into account many factors such as choose of joining method by forming and proper connector type. Despite many difficulties, this method allows for joining hard welded steels and most of all for minimization of operations amount in mass production. Operations of joining by forming of nuts and screws, gives significant savings of anticipated costs with simultaneously guarantees high static and dynamic strength.
Experimental and Numerical Study on Linear Friction Welding of AA2011 Aluminum Alloy
Authors: Buffa Gianluca , Campanella Davide , D'Annibale A. , di Ilio Antoniomaria , Fratini Livan
Published: May 2014

Linear Friction Welding (LFW) is a solid-state joining process used for non-axisymmetric components. LFW involves joining of materials through the relative motion of two components undergoing an axial force. In the process, the heat source is given by the frictional forces work decaying into heat and determining a local softening of the material and eventually the needed bonding conditions. In the paper, an experimental and numerical campaign is proposed for AA2011 aluminum alloys welding. Different case studies are considered with fixed oscillation frequency and varying pressure at the interface between the specimens. Constant oscillation amplitude and specimens geometry is used. The calculated results permitted to highlight the effects of the process parameters on the material flow determining the soundness of the weld.
Hierarchical Metamodeling: Cross Validation and Predictive Uncertainty
Authors: Colosimo Bianca Maria , Pagani Luca , Strano Matteo
Published: May 2014

At Esaform 2013 a hierarchical metamodeling approach had been presented, able to combine the results of numerical simulations and physical experiments into a unique response surface, which is a “fusion” of both data sets. The method had been presented with respect to the structural optimization of a steel tube, filled with an aluminium foam, intended as ananti-intrusion bar. The prediction yielded by a conventional way of metamodeling the results of FEM simulations can be considered trustworthy only if the accuracy of numerical models have been thoroughly tested and the simulation parameters have been sufficiently calibrated. On the contrary, the main advantage of a hierarchical metamodel is to yield a reliable prediction of a response variable to be optimized, even in the presence of non-completely calibrated or accurate FEM models. In order to demonstrate these statements, in this paper the authors wish to compare the prediction ability of a “fusion” metamodel based on under-calibrated simulations, with a conventional approach based on calibrated FEM results. Both metamodels will be cross validated with a “leave-one-out” technique, i.e. by excluding one experimental observation at atime and assessing the predictive ability of the model. Furthermore, the paper will demonstrate how the hierarchical metamodel is able to provide not only an average estimated value for each excluded experimental observation, but also an estimation of uncertainty of the prediction of the average value.
Influence of a Tensile Pre-Strain on Bending of Aluminium Alloy
Authors: Thuillier Sandrine
Published: May 2014

The mechanical behavior of thin sheets of aluminium alloy 6016, of thickness 1.14 mm, was investigated in unconstrained bending, with or without a tensile pre-strain. In the case of bending without pre-strain, no rupture was observed. Therefore, a tensile pre-strain, ranging from 0.19 up to 0.45 (longitudinal strain), was applied prior to bending. The highest pre-strain values were reached within the necking area. Tensile tests on rectangular samples were performed, then reduced samples were cut out and submitted to bending. A Digital Image Correlation (DIC) system was used to measure the maximum local strains reached during both tests. The evolution of the applied load on the bending tool versus its displacement showed that a rupture in bending was obtained for tensile pre-strains higher than 0.25, as evidenced by a load drop. These results showed that very high strains can be reached in bending, which is consistent with previously obtained numerical results.
Constitutive Modeling Based on Evolutionary Multi-Junctions of Dislocations
Authors: Pham Minh Son , Rollett Anthony D. , Creuziger Adam , Iadicola Mark , Foecke Tim
Published: May 2014

A latent hardening model based on binary junction-induced hardening can effectively describe the anisotropy measured in multiaxial tests. However, this approach still has some descriptive and predictive limitations. Recent findings show that binary junctions generated by interactions of pairs of dislocations can only induce short-term hardening effect due to the unzipping process of binary junctions. By contrast, multi-junctions, which are formed via multiple interactions of dislocations, can exert a strong and enduring influence on the hardening of polycrystals. In this study, we extend the modeling of dislocation junctions from the binary to multi-junctions, and implement this evolution into a self-consistent visco-plastic model. An application of this model for predicting the yield surface and texture evolution of AA5754 during uniaxial and plane strain loadings is given as a demonstration of the capabilities of the evolutionary binary-multi junction approach.
The Effect of Mandrel Configuration on the Warpage in Pultrusion of Rectangular Hollow Profiles
Authors: Baran Ismet , Hattel Jesper , Akkerman Remko
Published: May 2014

Thermo-mechanical process simulation of an industrially pultruded rectangular hollow profile is presented. Glass/polyester is used for the continuous filament mat (CFM) and the uni-directional (UD) layers. The process induced residual distortions together with the temperature and degree of cure are predicted using a three dimensional (3D) thermo-chemical model sequentially coupled with a 2D quasi-static generalized plane strain mechanical model. The predicted deformation pattern at the end of the process is found to agree quite well with the one observed for the real pultruded parts in a commercial pultrusion company. In addition, the predicted warpage behaviour is further analysed by adjusting the mandrel length as well as including the mandrel heating. Using the proposed process model, the effect of the mandrel configurations on the quality of the pultrusion is investigated in terms of temperature, degree of cure and distortions.These unwanted residual distortions may lead to not meeting the desired geometrical tolerances e.g. warpage of pultruded window frames and hollow profiles as well as spring-in of L-shaped profiles, etc.
Investigation of the Spring-In of a Pultruded L-Shaped Profile for Various Processing Conditions and Thicknesses
Authors: Baran Ismet , Hattel Jesper , Akkerman Remko
Published: May 2014

In this study, a thermo-mechanical finite element model is developed to predict the spring-in of an industrially pultruded L-shaped profile made of glass/polyester composite. The resin curing kinetics are obtained from the differential scanning calorimetry (DSC) experiments. The development of the resin modulus is derived using the dynamic mechanical analysis (DMA) tests and the effective mechanical properties of the processing composite are calculated using a micromechanical model. The temperature and degree of cure distributions are obtained in a three dimensional (3D) thermo-chemical anlaysis using the finite element method (FEM). The process induced distortions are then calculated using these distributions in a 2D quasi-static mechanical analysis in which generalized plane strain elements are utilized. The predicted spring-in pattern at the end of the process is found to agree quite well with the one observed for the real pultruded parts in a commercial pultrusion company. In addition, the effects of the pulling speed and the part thickness on the spring-in formations are investigated using the proposed numerical simulation tool. It is found that the magnitude of the spring-in increases with an increase in the pulling speed and part thickness.
Analysis of Composite Reinforcement at Mesoscopic Scale from X-Ray Microtomography
Authors: Naouar Naim , Vidal-Sallé Emmanuelle , Schneider Julien , Maire Éric , Boisse Philippe
Published: May 2014

During the pre-forming stage of the RTM process, large deformations can occur, especially for double-curved shapes. Knowing the mechanical behaviour and the actual geometry of fibrous reinforcements at the mesoscopic scale is of great importance for several applications like permeability evaluations. As such, forming modeling is particularly demanding on the quality of geometric modeling and of the mesh associated. Indeed, analysis of the internal structure of materials in general, and woven materials especially, recently led to major advances. X-ray Micro Tomography (XRMT or μCT) allows detailed and accurate 3D observations inside the sample, which is not possible with the standard microscopy techniques restrained to surface observations. It distinguishes the yarns and even the fibers that define the directions of anisotropy of the material. A FE model is generated from the processed tomography images. It has been chosen in this study to use hypoelasticity behaviour law. Indeed, the yarns are submitted to large deformations, so that the orientation of the material is significantly modified and the fiber direction has to be strictly followed in order to fulfil the principle of objectivity. A way to retrieve the neutral composite reinforcement axis by skeletonization is proposed in order to know the privileged direction of the yarn and thus implement it in the constitutive law. A comparison between experimental and simulations obtained from μCT and idealized geometry of a transverse compression test on the G0986 is presented.
Analyses of Textile Composite Reinforcement Compaction at the Mesoscopic Scale
Authors: Nguyen Q.T. , Vidal-Sallé Emmanuelle , Boisse Philippe , Park C.H. , Saouab Abdelghani , Bréard J. , Hivet Gilles
Published: May 2014

Mesoscopic simulations of the transverse compression of textile preforms are presented in this paper. They are based on 3D FE models of each yarn in contact with friction with its neighbours. The mesoscopic simulations can be used as virtual compression tests. In addition they determine the internal geometry of the reinforcement after compaction. The internal geometry can be used to compute the permeability of the deformed reinforcement and to calculate the homogenised mechanical properties of the final composite part. A hypoelastic model based on the fibre rotation depicts the mechanical behaviour of the yarn. The compression responses of several layer stacks with parallel or different orientations are computed. The numerical simulations show good agreement when compared to compaction experiments.
Modelling and Simulation of the Coupling of Normal Pressure and Shear Force in Plain Woven Fabrics
Authors: Döbrich Oliver , Gereke Thomas , Cherif Chokri
Published: May 2014

In textile engineering, simulative methods are used more frequently due to their advantages in material and process design. Finite element models were developed for simulating the mechanical and the draping behaviour of fabrics. For large deformation analysis of textile forming, macro mechanical models are employed that use continuum mechanical approaches for matters of reduced computation time. The material data that is required as model input, such as tension and shear properties, can either be obtained by experimental or virtual tests. In such virtual tests the deformation behaviour of fabrics can be determined by deforming the structure on the meso level.
Microstructure Prediction during Hot Deformation Using New Dynamic Recrystallization Model and Finite Element Analysis
Authors: Lee Ho Won , Lee Young Seon , Kang Seong Hoon
Published: May 2014

In this study, dynamic recrystallization during nonisothermal hot deformation was numerically simulated by finite element analysis and new physically based dynamic recrystallization model. The dynamic recrystallization model was developed based on mean field approach by assuming grain aggregate as representative volume element. For each grain aggregate, changes of state variables such as dislocation density and grain size were calculated using three sub-models for work hardening, nucleation, and nucleus growth. The developed dynamic recrystallization model was validated by comparing with isothermal hot compression of pure copper. Finally, developed dynamic recrystallization model was combined with finite element method to predict the local changes of microstructure and average grain size during nonisothermal hot compression of pure copper and hot tube extrusion of austenitic stainless steel. The simulation results were in reasonably good agreement with experimentally determined microstructures.
Development of Formability, Microstructure and Martensite Reversion during Intermediate Annealing of Metastable Austenitic Stainless Steel
Authors: Schmid Philipp , Liewald Mathias
Published: May 2014

Intermediate annealing is a widely used process to recover formability in multi-stage deep drawing of austenitic stainless steel sheets. A special ability of metastable austenitic stainless steel is the so called strain-induced martensite formation, which causes the TRIP-effect (TRansformation Induced Plasticity). Major issues of intermediate annealing in serial production processes are long annealing times and high costs for annealing equipment and consumed heating energy. One suggestion for optimization of this process made in this paper is to anneal austenitic material only in regions of the part where it is required and to use suitable annealing parameters. This annealing parameters need to be optimized to requirements of follow-up forming processes. Therefor, basic intermediate annealing experiments were accomplished for austenitic grade EN 1.4301 within temperature range of 100-1100°C. Measurements of mechanical properties by uniaxial tensile tests, martensite contents measured by Feritscope and micrographs are showing the development of martensite reversion as well as reconstitution of austenitic phase. Especially 400°C, 600°C and 1000°C were identified as most interesting annealing temperature levels due to formation of carbides and recrystallization. This knowledge can be used as base for further local heat treatment concepts and may enhance, simplify and save costs of intermediate annealing process of deep draw components made of stainless steel.
Applications of Multi-Scale Models to Numerical Simulation and Experimental Analysis of Anisotropic Elastoplastic Behavior of Metallic Sheets
Authors: Nasri Walid , Gavrus Adinel , Kouadri-Henni Afia , Sai Kacem
Published: May 2014

In this paper anisotropic mechanical behavior of AA2024 aluminum and Ti6Al4V titanium alloys were studied using three different approaches: unified, multi-mechanism and polycrystalline. The theoretical formulations of studied elastoplastic models are first described. Thereafter, some numerical results concerning the simulation of a uniaxial tension test applied to thin metallic sheets are presented. Comparison between experimental results (taken from the literature) and numerical simulations shows that the multi-mechanism and polycrystalline models describe slightly better the anisotropy when considering all the directions. Finally, numerical simulations of a deep drawing test of AA2024 aluminum thin sheets will be analyzed.
Validation of a Multi-Scale Model for Shear Deformation of an Aluminium Sheet Alloy
Authors: Shore Diarmuid , Toledo Miguel Angel Ramirez , Gawad Jerzy , Schouwenaars Rafael , Roose Dirk , van Bael Albert
Published: May 2014

Aluminium is a potential light weight alternative to steel for deep drawn sheet components, but generally does not compare well to steels in terms of formability. Research in polycrystalline plasticity indicates applying shear to rolled fcc alloys improves their deep drawability by favourably modifying their crystallographic texture. Such processing could be realised industrially by cold asymmetric rolling (ASR), but in order to gain detailed understanding of the influence of process parameters on the evolution and through thickness homogeneity of the texture a validated full field multi-scale model of the process is required. This study examines the ability of a hierarchical multi-scale approach to predict evolved textures for aluminium sheet subjected to a mechanical test exhibiting a deformation mode relevant for ASR, namely simple shear. The homogeneity of the deformation field is assessed with full field strain measurement by digital image correlation, and macrotexture is measured by x-ray diffraction. The discrepancies are discussed and further work to validate the modelling approach for simulation of texture evolution in the ASR process is briefly outlined.
Using FEA in Assessing Backward Extrusion of Multiple Micro-Pins
Authors: Salamati Mohammad Reza , Rosochowski Andrzej
Published: May 2014

FE analyses of backward extrusion of multiple micro-pins have been conducted to examine the effects of pin geometry, layout and spacing. The effect of friction on material flow and accuracy of pin geometry has been investigated. FE analysis was performed for a commercial grade Al1050 as well as its ultrafine grained version produced by severe plastic deformation allowing a comparison to be made. Pin layout plays a large role in achieving uniformity of pin height. Material starvation resulted in the central pins being shorter than the surrounding pins. Simulations without the centre pin were conducted, which resulted in increased pin height uniformity. Simulations with friction resulted in a greater uniformity of pin height but required a greater load. Using stronger ultrafine grained material increased the load and reduced the pin height uniformity.
Increasing Performances of En AB-46000 by Squeeze Casting
Authors: Boschetto Alberto , Bottini Luana , Costanza Girolamo , Tata Maria Elisa , Quadrini Fabrizio
Published: May 2014

The evolution of the mold temperature during squeeze casting of EN-AB46000 aluminum alloy has been correlated with the final mechanical performances of cast ingots. Starting from a material model which expresses hardness and yielding stress of cast aluminum alloys as a function of the cooling rate during the melt solidification, an experimental approach has been used to provide a useful tool for process monitoring. As a result, the mold temperature increase during the melt squeezing phase is directly correlated with the main mechanical and microstructural parameters. Experiments were made by squeeze cast small cylinders (14 mm in diameter and 18 mm height) at different values of squeezing pressure, mold pre-heating temperature, and melt temperature. Microscopic observations of the sample sections were made as well as hardness measurements and indentation tests. In conclusion, because of the material solidification, a temperature gradient has been observed in the sample which can be directly related with the aluminum alloy dendrite size and, in turn, with microhardness and yielding stress.
Small Diameter External Cylindrical Surfaces Obtained by Ram Electrical Discharge Machining
Authors: Slătineanu Laurenţiu , Coteaţă Margareta , Schulze Hans Peter , Dodun Oana , Besliu Irina , Gherman Lorelei
Published: May 2014

Electrical discharge machining uses the pulse electrical discharges generated between the closest asperities existing on the workpiece surface and the active surface of the tool electrode in dielectric fluid. Essentially, some distinct electrical discharge machining schemas could be used in order to obtain cylindrical external surfaces; within this research, one preferred a machining schema based on the use of a cooper plate in which there were small diameter holes, by taking into consideration the existence of a ram electrical discharge machine. The results of the machining process analysis were presented. A thin copper was considered to be used as tool electrode, in order to diminish the spurious electrical discharges, able to generate shape errors of the machined surface. Some experimental researches were developed by changing the sizes of the process input parameters. As output factors, the test piece and tool electrode masses decreases were considered. Power type empirical mathematical models were determined, in order to highlight the influence exerted by the pulse on time, off time and machining process duration on the output parameters values.
Numerical Simulation of Laser Forming of Aluminum Sponges: Effect of Temperature and Heat Treatments
Authors: Quadrini Fabrizio , Bellisario Denise , Ferrari Daniele , Santo Loredana , Santarsiero Anna
Published: May 2014

Laser forming ofopen-cell aluminum foams can be modeled by means of 3D thermo-mechanical models but the correct evaluation of the alloy material properties is a key-factor for obtaining good predictions. In order to increase the model predictability from a quantitative point of view, further information about the material behavior under laser exposure is necessary. In this study the effect of the temperature on the mechanical properties of a commercial aluminum sponge has been evaluated in terms of yielding stress and tangent modulus. Experimental tests have been performed by compression and used to infer mechanical properties by means of a 3D FE model. The same approach has been used also to evaluate the effect of a heat treatment of the sponge on the material behavior during forming. In conclusion numerical simulation of laser heating has been used to show the effect of the laser-material interaction on the final homogeneity of processed foams.
Qualification of ECM-Processes by Electro Impedance Spectroscopy
Authors: Labusch Lutz , Müller Claas , Reinecke Holger
Published: May 2014

Electrochemical machining (ECM) is an appropriate technology for structuring a wide range of metals and alloys independent of their mechanical properties. Further advantages the occurence of no tool wear and almost no change in the material properties of the work piece material due to the machining. As different studies showed it is possible to manufacture structures in the µm-range and also in the sub µm-range. The resulting geometry and feature size depend on the electrolyte, the working gap, the electric field, the flow conditions within the working gap and the material structure. The working gap is the most important parameter regarding the critical dimensions of ECM. Actual high resolution processes are limited by the process time due low current densities, while faster processes are limited by the resolution due to the dimensions of the double layer and the need for purging.\\Regarding these limits an enhanced understanding of the electrochemical processes within the working gap is mandatory for the optimization of the ECM. Therefore a measurement device is realised utilising electrochemical impedance spectroscopy (EIS), which is one technique to obtain a wide set of thermodynamic and kinetic parameters related to the electrochemical processes like reactions, adsorption, desorption and diffusion in the gap. There the impedance, which is the complex ratio between the voltage and the current in an AC circuit, is measured as a function of the frequency and it is compared to an equivalent circuit, composed out of basic elements representing the chemical sub processes. The spectrometer is realized by combining a commercial potentiostat with computer based signal processing realized in MATLAB\copyright. The spectrometer implements time-domain measurement techniques (Fourier transformation) for a strong reduction of measurement time. This time reduction allows in situ measurements.\\The presented spectrometer enables characterization of standard material systems like cooper, as well as the identification of the time-critical chemical processes and steps in more complex systems.
Fundamental Analysis of the Process Conditions during Electro Discharge Machining of Biodegradable Magnesium
Authors: Klocke Fritz , Schwade Max , Klink Andreas
Published: May 2014

Magnesium is one of the most promising materials for the application as degradable biomaterial for load bearing implants due to the initial stability and extraordinary biocompatibility. But up until now magnesium degrades too fast before the ingrowing bone can support itself. One possible approach is the application of an interconnecting channel structure. This design increases the surface area to promote bone regeneration and gives the bone the possibility to build a supporting structure throughout the implant. In combination with a surface modification which increases the corrosion resistance the bone can regain enough stability to support itself before the implant has dissolved noticeably. Due to the low process forces EDM is very suited for the machining of the necessary filigree structures. But up until now there are no standard technologies for the machining of this material available. Therefore a fundamental analysis of the material specific influence of magnesium on the EDM process is necessary. In this paper the machining of three different magnesium alloys are compared to the machining of a tool steel. Due to the numerous influencing factors and their interdependencies it is normally not possible to analyze the impact of each input parameter of a typical EDM technology on the continuous process separately making the correlation of input and output parameters very difficult. Therefore the electrical signals are recorded during the machining process to identify and monitor the resulting discharge conditions and frequency. These results are compared to the fundamental influence of the material derived from single discharge experiments in which the boundary conditions are constant to a large extent. By this method the material removal rate as well as the resulting surface roughness of the continuous process can be linked to the material dependent process conditions. As a result technologies for the machining of new materials can be developed and optimized based on fundamental knowledge.