bluuebunny/crossref_metadata_2025 huggingface dataset:
A New PvT Device for the Thermoplastics Characterization in Extreme Thermal Conditions
Authors: Tardif Xavier , Boyard Nicolas , Sobotka Vincent , Lefèvre Nicolas , Delaunay Didier
Published: June 2013

In this work, we present an apparatus associated to a methodology that is able to determine simultaneously and according to temperature (up to 400°C) the specific volume (up to 200MPa), the thermal conductivity and the temperature function of the crystallization kinetics. The PvT-XT is a home-built device that is able to impose and quantify 1D heat transfer through the radius of a sample. This apparatus controls the applied pressure on the sample while measuring its volume variations. The associated moving boundary model takes into account the temperature and crystallinity gradients. Specific volume is determined from direct measurement whereas inverse methods are used to estimate the thermal conductivity and the crystallization kinetics (with cooling rates up to 200K/min). Specific volume measurements are compared with literature results and exhibit a very good agreement. Thermal conductivity identified in the present paper is also very close to literatures values. Finally identification of kinetic function values is consistent with previous studies.
Structure Development of Biodegradable Polymers: Crystallization of PLA
Authors: Refaa Zakariaa , Lipinska Magdalena , Boutaous M'hamed , Fulchiron René , Rousset François , Zinet Matthieu , Xin Shi He , Bourgin Patrick
Published: June 2013

Poly-(lactic acid) or PLA is a biodegradable polymer produced from renewable resources. Recently new polymerization routes have been discovered which allows increasing the produced quantity. Hence, PLA becomes of great interest to lessen the dependence on petroleum-based plastics. Due to its good mechanical properties, PLA is a potential substitute to some usual polymers such as PET. Nevertheless the kinetics of crystallization is relatively slow which can be an inconvenient in polymer processing. Thermomechanical history experienced by the polymer during processing affects drastically its relative crystallinity. For example, the flow is known to enhance the crystallization kinetics. Nevertheless, only a few studies were found in the literature about the crystallization of PLA under flow conditions. In the present work we investigate the crystallization of PLA under quiescent and flow conditions. A combination of DSC, rheological and optical measurements is used to identify the crystallization kinetic parameters. Thermal and flow-induced crystallization are then simulated using two sets of Schneider’s differential equations [1] based on a previously developed model Zinet & al [2]. Experimental results are analyzed and compared to the numerical model. New features about the influence of thermal and flow conditions on the crystallization of PLA are discussed.
Thermo-Kinetic Analysis of Liquid Silicone Rubber
Authors: Harkous Ali , Colomines Gaël , Allanic Nadine , Mousseau Pierre , Deterre Rémi
Published: June 2013

Modeling and optimization of LSR parts require an accurate kinetic modeling of the material crosslinking. Calorimetric and mechanical measurements for different temperature ramps are used in order to calculate the crosslinking extent as a function of time and temperature. These measurements are numerically treated in order to determine the parameters of a representative model. The chosen model will be used to simulate a LSR molded parts and design a LSR controlled molding setup.
Evaluation Method for Stretch Blow Moulding Simulations with Process-Oriented Experiments
Authors: Zimmer Johannes , Detrois Christian , Stommel Markus
Published: June 2013

In the Stretch blow moulding (SBM) process, polyethylene terephthalate (PET)-preforms are biaxially deformed to produce thin walled bottles. Finite-Element (FE)-Simulations are an important tool to optimise this process in terms of material usage and product performance. Thereby, the implementation of the thermo-mechanical material behaviour of PET plays an important role to achieve realistic simulation results. A common approach for this purpose is to calibrate a material model with stress-strain curves from biaxial stretching experiments. Thin PET-sheets are stretched under defined temperatures and strain rates. However, these experiments include process simplifications concerning geometry, heating and deformation parameters. This paper presents a method for extracting temperature dependent stress-strain-curves from experiments close to the production process. PET-Preforms receive thermal treatment with Infrared (IR)-heaters from an SBM-machine and are subsequently inflated in free air (free blow trial). A high-speed-IR-camera is used to image the axial and radial temperature distribution on the preform immediately before blowing. The deformation process is recorded via 3d-high-speed-cameras with a frame rate of 2000/s. The cameras are synchronised with a pressure sensor to consequently calculate reliable stress-strain curves at any point on the preform. In addition FE-simulations of the free blow trials are conducted using a material model calibrated with the simplified stretching experiments of thin PET sheets. Resulting stress-strain-curves from simulations and free-blow-trials are finally compared to evaluate the quality of the material model as well as the underlying testing procedure.
Thermal Simulation of Polymer Crystallization during Post-Filling
Authors: Spina Roberto , Spekowius Marcel , Küsters Klauss , Hopmann Christian
Published: June 2013

Crystallization from polymer melt is one of the most fundamental phenomena of material phase transformations. The possibility of controlling crystallization kinetics is essential to achieve the proper polymer microstructure and consequently obtain desired material properties, reducing undesired effects such excessive anisotropy of shrinkage, warping and insufficient dimensional stability. Due to the high transformation rate, the simulation of crystallization is fundamental to mimic this important physical phenomenon under several testing and processing conditions by using commercial software. User subroutines were developed and implemented into finite element-based model to simulate crystal growth in semicrystalline polymers with various crystal morphologies. These subroutines allowed the commercial program Abaqus to be customized for solving the Kolmogoroff-Avrami-Evans equation with Hoffmann-Lauritzen model in order to simulate the variation of the polymer crystallization degree. The micro-structural evolution in non-isothermal conditions and with different cooling rates was considered. The study was performed on isotactic PP (SABIC PP 505) for its simplicity to the measure polymer crystals. A tensile test specimen, produced by injection molding, was chosen as case study to evaluate the crystallization evolution. The paper reports the numerical and experimental results.
Morphology-Crystallinity Relationship in PLA-PHBV Blends Prepared via Extrusion
Authors: Guinault Alain , Dutarte Gaelle , Boufarguine Majdi , Miquelard-Garnier Guillaume , Sollogoub Cyrille
Published: June 2013

Poly(lactic acid) (PLA) is a biodegradable thermoplastic polyester derived from renewable resources which may replace conventional polymers for some applications. To overcome some of its limitations such as poor gas barrier properties and low elongation at break, one method is to blend PLA with small amounts of other bio-based polymers. In this study, two processes, eg classical twin screw extrusion and a multilayer co-extrusion process have been used to combine PLA and poly(3-hydroxybutyrate-co-3-valerate) PHBV to obtain films with different blend morphologies. The effect of the morphology on the crystallinity has been studied and has hightlightned new behavior of PHBV. The addition of a nucleating agent in the PHBV to modify its crystallinity, has also been studied.
Physical Modelling and Identification of Polymer Viscoelastic Behaviour above Glass Transition Temperature and Application to the Numerical Simulation of the Hot Embossing Process
Authors: Cheng Gang , Gelin Jean Claude , Barrière Thierry
Published: June 2013

The experimental processing parameters, such as applied pressure and forming temperature have been analysed during polymer hot embossing of micro-cavities. The viscoelastic characteristics of polymer above the glass transition temperature have been investigated with the classical viscoelastic models. Generalized Maxwell Model has been used to describe polymer behaviours in the glass transition temperature range. The parameters include relaxation time, storage modulus and loss modulus of the Generalized Maxwell Model that have been introduced. The identification of polymer characteristics has been carried out through Dynamic Mechanical Analysis (DMA). The storage modulus, the loss modulus and the damping factor of the selected polymer have been obtained with different imposed frequencies. The master curve of complex modulus has been obtained by applying the time temperature superposition principle. The experimental data has been identified with optimized fitting parameters of Generalized Maxwell Model. A proper agreement between the experimental measurement and the identification of viscoelastic model is observed. The resulting constitutive equations have been implemented in finite element software in order to achieve the numerical simulation of the hot embossing process.
Spring Back of Curved Flanges of Rubber Formed Aluminum Parts
Authors: Sinke J.
Published: June 2013

Rubber forming is a common process for the fabrication of flanged metallic parts in the aerospace industry. The process enables cheap tooling, which is important since the product series are limited. In the process a rigid and a soft tool are combined to form a metal blank into the required shape. Most components made in this way are “flanged parts”, i.e. parts with a rather flat web plate and curved flanges at the periphery of the web plate. For flanged parts the determination of spring back of the flanges, straight or curved, is important, since the forming dies compensated with the spring back, will result in accurate products. Like all metal forming processes elastic and plastic deformations are combined in the same process cycle. The elastic deformations result in spring back and residual stresses, the ratio between these two depends on the shape of the product and the distribution of the plastic and elastic deformations. In this research aluminum alloys were used. The low Young’s modulus of these alloys results in rather high elastic responses upon deformation. Other aspects that have been evaluated are the effect of processing parameters like friction and distribution of strains. For stretch flanges the strain is distributed evenly along the flange, but not for shrink flanges, where buckling plays a role. Experimental research shows that the spring back of the flanges depend on a number of variables like the thickness, flange geometry, and material parameters. The spring back of a flange is also a mixture of different contributions: spring back due to the bending over the bend line, spring back due to the curvature of the flange, and spring back due to in-plane deformations. The research performed focused on the different components of the spring back and their interaction. Analysis of the data resulted in a new parameter by which a number of variables could be captured. This improves the understanding of the spring back phenomena and is a generalization of the results.
Numerical Simulation of Laser Bending of Aluminum Foams
Authors: Quadrini Fabrizio , Bellisario Denise , Ferrari Daniele , Santo Loredana , Santarsiero Anna
Published: June 2013

Laser forming of open-cell aluminum foams has been modeled by means of a 3D finite element model which is able to take into account the real foam geometry as well as the main process variables. A parametric procedure has been defined for the geometry construction and meshing, and the simulation run. In order to calibrate and validate numerical modeling, compression and flexure tests were performed on a closed-cell aluminum foam. The simulation of mechanical tests allowed a correct modeling of the aluminum alloy behavior under plastic deformation. The same material behavior was implemented in a complex thermo-mechanical model for laser bending simulation. The final model is able to predict the shape evolution during forming and the correlation between process variables and final bent angles.
Analysis of the Incremental Forming of Titanium F67 Grade 2 Sheet
Authors: Daleffe Anderson , Schaeffer Lirio , Fritzen Daniel , Castelan Jovani
Published: June 2013

Analysis of a formed metal sheet shows the data of the incremental forming process. Variation in sheet deformation results from the process and shows how forming occurred. Another important result is the surface roughness of the sheet, which reports the parameters of the process, machine and tool used. Incremental forming of the titanium CP-Ti grade 2 sheet was performed in the SPIF modality – forming without a point of support, in order to look at the thickness deformations. SPIF incremental forming is characterized as forming that does not use points of support, and therefore simple tooling is used in the process. The following resources were used to perform the practical tests: CAD/CAM software, CNC machining center, incremental die, incremental forming tool and a sheet press device. The results obtained were the finish of the formed surface, measured by the roughness parameter RZ, and the measurement of the true strains ( ) and thickness (s1). Practical tests showed that the limit wall angle ( ), for the CP Ti grade 2 sheet, 0.5 mm thick, is 47º.
Experimental Study of tool Wear Mechanisms in Conventional and High Pressure Coolant Assisted Machining of Titanium Alloy Ti17
Authors: Ayed Yessine , Germain Guenael , Ammar Amine , Furet Benoit
Published: June 2013

Titanium alloys are known for their excellent mechanical properties, especially at high temperature. But this specificity of titanium alloys can cause high cutting forces as well as a significant release of heat that may entail a rapid wear of the cutting tool. To cope with these problems, research has been taken in several directions. One of these is the development of assistances for machining. In this study, we investigate the high pressure coolant assisted machining of titanium alloy Ti17. High pressure coolant consists of projecting a jet of water between the rake face of the tool and the chip. The efficiency of the process depends on the choice of the operating parameters of machining and the parameters of the water jet such as its pressure and its diameter. The use of this type of assistance improves chip breaking and increases tool life. Indeed, the machining of titanium alloys is generally accompanied by rapid wear of cutting tools, especially in rough machining. The work done focuses on the wear of uncoated tungsten carbide tools during machining of Ti17. Rough and finish machining in conventional and in high pressure coolant assistance conditions were tested. Different techniques were used in order to explain the mechanisms of wear. These tests are accompanied by measurement of cutting forces, surface roughness and tool wear. The Energy-dispersive X-ray spectroscopy (EDS) analysis technique made it possible to draw the distribution maps of alloying elements on the tool rake face. An area of material deposition on the rake face, characterized by a high concentration of titanium, was noticed. The width of this area and the concentration of titanium decreases in proportion with the increasing pressure of the coolant. The study showed that the wear mechanisms with and without high pressure coolant assistance are different. In fact, in the condition of conventional machining, temperature in the cutting zone becomes very high and, with lack of lubrication, the cutting edge deforms plastically and eventually collapses quickly. By contrast, in high pressure coolant assisted machining, this problem disappears and flank wear (VB) is stabilized at high pressure. The sudden rupture of the cutting edge observed under these conditions is due to the propagation of a notch and to the crater wear that appears at high pressure. Moreover, in rough condition, high pressure assistance made it possible to increase tool life by up to 400%.
Investigation of the Impact of Orthogonal Cutting Processes on Nanocrystalline Surface Layer Generation
Authors: Schulze Volker , Zanger Frederik , Ambrosy Florian
Published: June 2013

The present work analyzes the influence of an orthogonal machining process on the generation of nanocrystalline surface layers. Thereby, AISI 4140 is used as work piece material. Metallic parts with a severe nanocrystalline grain refinement in the near-surface area show many beneficial properties. Such surface layers considerably influence the friction and wear characteristics of the work piece in a subsequent usage as design elements working under tribological loads. The focus of this paper is an experimental analysis of a finishing orthogonal cutting operation, carried out with a broaching machine, to generate nanocrystalline surface layers. The influence of process and geometry parameters on the generation of nanocrystalline surfaces is investigated with the aim to massively decrease the grain size in the work piece surface layer. Parameters that are studied and taken into account in the manufacturing process are cutting edge radius rβ, depth of cut h and cutting velocity vc. The cutting edge radius rβ is modified by a drag finishing process. The generation of nanocrystalline surface layers is especially influenced by the design of the uncoated carbide cutting tools. Additionally, cutting force Fc and passive force Fp are determined by a 3-component dynamometer to calculate the relationship between specific cutting force kc and specific passive force kp. The temperature beneath the clearance face is detected by a fiber optic pyrometer. These measurement methods and devices are applied to detect the impact of the most relevant measurement values occurring during machining and causing a drastic reduction of grain size in the surface layer. The evaluation of the manufacturing process is carried out by detailed analyses of the microstructural conditions in the surface layer after processing using a Focused Ion Beam (FIB) system. These material characterizations provide information about the surface engineering concerning the microstructural changes in the surface layer of the work piece due to finishing orthogonal cutting processes.
Thermo Mechanical Loads in Ti-6Al-4V Machining
Authors: Arrazola Pedro J. , Matsumura Takashi , Armentia Igor , Kortabarria Aitor
Published: June 2013

In recent years titanium alloys demand has increased considerably. Although many progresses have been made during the last years, machining titanium alloys still is considered as quite challenging. This paper shows the results of the fundamental research carried out to understand the thermochemical loads when machining Ti-6Al-4V. A comparative study of empirical and modelling results is carried out on cutting forces and temperatures in orthogonal conditions. Empirical cutting forces are obtained with a piezoelectric sensor while the temperature fields are obtained with an infrared camera. The commercial software AdvantEdge (finite element modelling) is employed to obtain temperature and forces. In 3D, analytical modelling based on energy approach is used to estimate cutting forces while finite difference method is employed to obtain temperature fields. Results show a good correlation among all the approaches.
3D Simulation of Laser Assisted Side Milling of Ti6Al4V Alloy Using Modified Johnson-Cook Material Model
Authors: Zamani Hassan , Hermani Jan Patrick , Sonderegger Bernhard , Sommitsch Christof
Published: June 2013

During machining of hard materials, one approach to reduce tool wear is using a laser beam to preheat the material in front of the cutting zone. In this study, a new concept of laser-assisted milling with spindle and tool integrated laser beam guiding has been tested. The laser beam is located at the cutting edge and moving synchronously with the cutter. In experiment, a reduction in the resulting process cutting forces and tool wear has been observed in comparison to milling without laser. A three-dimensional finite element model in DEFORM 3D was developed to predict the cutting forces in the milling process with and without an additional laser heat source, based on a Johnson-Cook-type material constitutive model adapted for high strains and strain rates. Both in experiment and simulation, the deformation behavior of a Ti-6Al-4V workpiece has been investigated. The comparison of the resulting cutting forces showed very good agreement. Thus the new model has great potential to further optimize laser assisted machining processes.
Potential of Modern Lubricoolant Strategies on Cutting Performance
Authors: Klocke Fritz , Lung Dieter , Krämer Alexander , Cayli Tolga , Sangermann Hubertus
Published: June 2013

Besides developments in the area of dry machining and minimum quantity lubrication, the use of coolant lubricants is still essential when machining high alloyed steels or heat resistant materials like titanium and nickel based alloys. Experts agree that this fact will not change in the next decade. For this reason it is necessary to use coolant lubricants as effectively as possible to maximise their positive effect on productivity and process stability. High-performance cooling strategies like high-pressure cooling and cooling with cold gases (cryogenic cooling) have received increased attention in the last years. Through the targeted supply of coolant lubricants to the cutting site it is possible to decrease tool wear, increase cutting speeds, guarantee defined chip breakage and chip transport and – in terms of cryogenic cooling – waive part cleaning. This paper shows current research results in the above mentioned field. Since the performance of a high-pressure coolant lubricant supply in turning difficult to cut materials has been shown in many previous papers, this paper focuses on the quantification of the potential in turning different steels, namely quenched and tempered but also stainless steel in comparison to the conventional flood cooling. Since energy efficiency is very crucial, pressure and flow rate have to be adjusted carefully and in accordance with the cutting parameters to guarantee best results with less energy. Moreover the effects of cryogenic cooling will be evaluated in comparison to high-pressure cooling and conventional flood cooling. In latter field, cutting tests were carried out under variation of the flow rate in order to find the minimum required value for a certain machining task with the overall aim to prevent waste of the media used. Especially in cryogenic cooling technologies, many fundamental research regarding the working mechanisms but also further developments in cutting tool and machine tool technology are still necessary to make this technology ready for industrial use.
Formability of Hybrid Aluminum-Magnesium Compounds
Authors: Feuerhack Andreas , Binotsch Carolin , Awiszus Birgit
Published: June 2013

In the SFB 692 HALS (High-strength aluminum based lightweight materials for safety components), subproject B-3, the production of an aluminum magnesium compound by a hydrostatic co-extrusion process was investigated. The quality of these semi-finished products, especially the stability and robustness of the interface between the aluminum (AlMgSi1) sleeve and magnesium (AZ31) core, was of particular interest. Previous papers have described the first process optimization steps as the improvement of the die design as well as the numerical methods for identification of important process parameters and the development of a quality model for the interface. This paper describes the formability of such semi-finished products with subsequent forging processes, especially die forging. Therefore, two different die forging strategies were investigated. In the first approach the strand-shaped work piece, with a circular cross-section, was formed along its longitudinal axis with die forging. In the second approach the same geometry was radially formed with die forging. Thereby, the compound was formed in longitudinal direction up to an analytical equivalent strain value of 1.61 and in radial direction up to 1.38. First results showed that the interface of the aluminum magnesium compound is very stable and ductile enough to be forged. Dye penetration tests were performed to prove the stability of the interface in a first step. Then, micro sections were made to investigate the interface metallographically. No cracks or damages were detected with both test methods in the interface of the forged aluminum magnesium compound. Furthermore, numerical simulations were performed to analyze the forging processes in detail. Therefore, a full 3D simulation model was set-up with Forge2011 and the calibration was performed with the press force as well as the geometry aspects. The correlations between experiments and simulations are very well. By means of the calibrated simulation detailed analyses of interface section are performed and the stability of the interface was investigated. This shows that the compound quality reached by the hydrostatic co-extrusion process is very suitable for subsequent forming steps as die forging. The investigations show the potential of such hybrid compounds and clarify their application, especially in the automotive sector.
On the Development and Identification of Phenomenological Damage Models - Application to Industrial Wire Drawing and Rolling Processes
Authors: Cao Trong Son , Bobadilla Christian , Montmitonnet Pierre , Bouchard Pierre-Olivier
Published: June 2013

The continuum thermodynamics-based Lemaitre damage model is nowadays widely used to deal with coupled damage analyses for various mechanical applications (e.g. forming process simulations). However, such a model, which only accounts for the stress triaxiality (the ratio between the first and the second invariants of stress tensor) has been found to give incorrect results under shear dominated loading (in terms of damage location as well as risk of crack). Several recent studies have demonstrated the importance of the third stress invariant in damage prediction; the Lode angle parameter is generally used to include it. The idea is to describe completely the stress state in damage model’s formulations, which is defined by the equivalent stress, the stress triaxiality ratio and the Lode angle parameter. This later parameter has proved to have an important influence on ductile damage under low stress triaxiality. Xue’s coupled damage model accounts for the third invariant of the deviatoric stress tensor, allowing a better balance between respective effects of shear and elongation on damage. Some extensions of more physically based damage models, such as the Gurson-Tvergaard-Needleman model, have also been presented to account for this influence of the third stress invariant. In the present work, the phenomenological damage models have been implemented in Forge® Finite Element (FE) software to investigate ductile damage occurring during industrial forming processes. This paper presents the comparative study of Xue’s model and Lemaitre’s model. A complete procedure is detailed to identify the material and damage parameters from experimental mechanical tests on high carbon steel. This identification process has been carried out both for Lemaitre’s coupled damage model and Xue’s coupled damage model. Application to wire drawing followed by flat rolling shows that in such shear-inducing processes, these models predict damage at different locations, due to their different emphasis on shear with respect to elongational strain damage.
Applying Nagata Patches in the Description of Smooth Tool Surfaces Used in Sheet Metal Forming Simulations
Authors: Neto Diogo M. , Oliveira Marta C. , Alves José Luis , Menezes Luis Filipe , Manach Pierre Yves
Published: June 2013

This study deals with the new strategy currently implemented in DD3IMP in-house code to describe the forming tools using Nagata patches. The strategy is based on the use of the Nagata patch interpolation to generate smooth contact surfaces over coarse faceted finite element meshes. The description of the adopted algorithm is briefly presented, highlighting the contact search algorithm employed. The reverse deep drawing of cylindrical cups, proposed as benchmark at the Numisheet’99 conference, is selected to examine the accuracy and robustness of the proposed approach. The effect of the gap between the blank-holder and the die is studied, adopting two distinct strategies: fixed gap and variable gap. The numerical results are compared with the experimental ones, previously presented and discussed in [1]. It is shown that the agreement is very good both in terms of punch force evolution and thickness distribution.
The Influence of Cold Forming Conception on the Springback Magnitude
Authors: Bałon Paweł , Świątoniowski Andrzej
Published: June 2013

Cold forming, especially for steels of increased mechanical properties, encounters problem with a springback. Most of the tools require compensation of that effect, however it is not always feasible in a conventional way. In some special cases such as twisting springback, compensation of a tool remains an ineffective method of solving the problem. This paper aims to investigate the behaviour of springback deviation which may be reduced using the change of forming conception such as: crash forming, holding and stamping or stamping with pad. The results lead to an in-depth understanding of the design process and parameters for advanced high strength components. It is immensely important for tool shops which usually have only few weeks to make a tool. The essence of designing and numerical simulations must be emphasized. Without them some problems with twisting springback may be encountered during trial test what would involve labour absorbing corrections and some extra costs. Therefore, it is crucial to pay attention to forming conception, as using it we can obtain entirely different
A Micro-Scale Model for Fiber Tow Characterization under Nondeterministic Assumption: Longitudinal and Transverse Permeability
Authors: Carlone Pierpaolo , Palazzo Gaetano S.
Published: June 2013

Liquid Composite Molding processes are characterized by the impregnation of a dry fibrous perform by means of injection or infusion of a catalyzed resin. In recent years computational flow and cure models allowed for a remarkable time and cost compression in process planning with respect to trial and error procedures. In this contest multi-scale simulative approaches are gaining considerable attention and intriguing results have been recently presented. Most of the proposed models, however, rely on deterministic hypothesis, assuming perfect fiber packing and neglecting dimensional variations between fibers, in strong contrast with experimental observations. In this paper the influence of the stochastic variability of the fiber packing on tow permeability has been investigated by means of a CFD micro scale model. The variability of the microstructure defining the Representative Volume Element has been considered introducing random perturbations of the fiber packing. The components of the permeability tensor, in each case, have then been derived applying the Darcy model to flow simulations through the representative cell.
Micromechanical Modeling of Damage and Failure in Dual Phase Steels
Authors: Lian Jun He , Vajragupta Napat , Münstermann Sebastian
Published: June 2013

Dual phase (DP) steels consisting of two phases, ferrite and dispersed martensite, offer an attractive combination of strength and stretchability, which is a result of the strong distinctions of these constituents in mechanical properties. However, the damage behavior in DP steels exhibits a rather complex scenario: voids are generated by the debonding of the hard phase from the matrix and the inner cracking of the hard phase in addition to by inclusions. The target of this study is to describe the initiation and evolution of damage in DP steel and develop a microstructure-based model which is capable of reflecting the underlying damage mechanisms. Both uniaxial and biaxial tensile tests are performed and the subsequent metallographic investigations are executed to reveal the mechanisms of damage initiation and evolution under different stress state condition and attention will be paid on the influence of various microstructural features on the initiation of damage. In finite element (FE) simulations, the microstructural features are taken into account by the representative volume elements (RVE). Different treatments of the constitutive behaviour of each constituent including isotropic hardening rule and crystallographically dependent configuration with crystal plasticity finite element method are investigated. Several numerical aspects are also discussed, such as RVE size, mesh size, element type, and boundary connections. In the end, the study is attempting to achieve a quantitative assessment of the cold formability of the investigated steel in a microscopic level based on microstructure information of material as well as to understand the damage mechanisms under different stress states condition which cause the macroscopic failure during plastic deformation.
Influence of the Number of Tensile/Compression Cycles on the Fitting of a Mixed Hardening Material Model: Roll Levelling Process Case Study
Authors: Silvestre Elena , Mendiguren Joseba , Galdos Lander , Sáenz de Argandoña Eneko
Published: June 2013

After roll forming processes, metallic coils show several flatness imperfections and residual stresses that must be minimized when high quality components are manufactured by means of sheet metal forming processes. The equipments typically used for this purpose are roll leveling facilities. In the present work, a uniaxial cyclic tension-compression test has been used to determine the mechanical response of steel sheet under the different loading modes. After this, the Chaboche and Lemaitre nonlinear mixed hardening model has been fitted to the material behavior. This hardening model is able to reproduce some phenomena which occur during low cyclic deformation such as Bauschinger effect and workhardening. During the fitting of the model, the number of tension-compression cycles performed in the material characterization and the number of backstresses used for the model definition have been analyzed. Finally the influence of the material model in the roll leveling process results has been numerically analyzed. Different simulations have been performed by introducing initial defects with the objective of predicting residual stresses, residual curvatures, leveling force and torque force at the end of the process.
Test Procedures and Simulation Model Calibration Strategies for Nonlinear Stiffness Behavior of Joints in Large-Scale Structures
Authors: Hensel Sebastian , Jesche Fred , Neugebauer Reimund , Mauermann Reinhard
Published: June 2013

State-of-art models for mechanical joints in large scale structures typically consider only the linear behavior of the joint zones with lower complex approaches, such as rigid or elastic beams or a merge of opposite sheet metal nodes. In the present study several feasible methods to model nonlinear joint behavior and the connection between sheets and joint are investigated and evaluated. A preferred combination based on nonlinear springs was chosen, which meets the requirements for application in large scale structure models: low computation time, mesh independence and availability in several FEM software packages. For the calibration of the joint zone models a 2-point-tension-specimen was used. Five different joint types and the two sheet material combinations aluminium/aluminium as well as steel/steel were investigated. With the calibrated models a more complex 5-point-tension-specimen was used to consider the local interoperation of the joints. Some deviations were determined especially for highly stressed joint zones. Hence an average function was defined to consider both, the local deformations in the joint zone and additionally the more global sheet deformations. Finally, the simplified joint models were used in a complex specimen model with 22 joints. The comparisons between experimentally and numerically determined results show a good accordance. The nonlinear joint behavior is captured very well. A method is presented, which uses 2-point-specimens to calibrate simplified joint models with nonlinear deformation characteristics. The efficient application in large scale structure models is possible due to simplicity, stability, low computation times and mesh independent implementation.
Numerical Implementation and Finite Element Analysis of Anisotropic Hyperelastic Biomaterials - Influence of Fibers Orientation
Authors: Djeridi Rachid , Ould Ouali Mohand
Published: June 2013

Modeling anisotropic behavior of fiber reinforced rubberlike materials is actually of a great interest in many industrials sectors. Indeed, accurately description of the mechanical response and damage of such materials allows the increase of the lifecycle of these materials which generally evolve under several environment conditions. In this paper theoretical study and finite element analysis of anisotropic biomaterials is presented. The mechanical model adopted to achieve this study has been implemented into the finite element code Abaqus using an implicit scheme. This constitutive law has been utilized to perform some numerical simulations. The material parameters of the model have been determined by numerical calibration. One fiber family is considered in this work. Effects of the fiber orientation on the mechanical response and stiffness change of biomaterial is studied. Both the compressible and incompressible states have been taken into account. The results show firstly the capability of the model to reproduce the known results and that optimal fiber orientation can be found.
Validation of the Computer Simulation Process Applied to the Incremental Forming Process for the Evaluation of Strain Paths
Authors: Lora Fabio Andre , Boff Uilian , Yurgel Charles Chemale , Folle Luis Fernando , Schaeffer Lirio
Published: June 2013

In recent decades,the forming area advanced both in terms of material used as well as in flexibilityand process cost reduction. New processes are been studied, including theIncremental Sheet Forming – ISF. The ISF is a process characterized by theproduction of small batches of parts, rapid prototyping, and manufacturingflexibility with reduced operational cost. This study aims to compare thecomputer simulation with real experiments from ISF. The results of strain pathsof the three main strains simulated were consistent with the experimentalmanufacture of a symmetrical sample.
Optimization of the Heat Treatment Layout and Blank Outline of THTB
Authors: Lechner Michael , Kuppert Andreas , Hagenah Hinnerk , Merklein Marion
Published: June 2013

Tailored heat treated blanks (THTB) is the generic term for an innovative approach to enhance the formability of blanks made out of high strength steel or aluminum alloys. Key idea of the technology is the adaption of the mechanical properties by a local heat treatment. Based on the new property distribution, the material flow during the forming operation can be improved and the forming limit can be enhanced. In comparison to conventional temperature assisted approaches the forming is performed at room temperature and therefore all advantages of a cold forming process can be used. Most challenging within the application is the definition of the heat treatment layout. Up to now the layout is dimensioned in a time-consuming trial and error procedure. In this paper a new approach for the automatic optimization of the heat treatment layout and the blank outline is presented.
Application of a Fast Calculation Model for the Process Monitoring of Open Die Forging Processes
Authors: Rosenstock Dirk , Recker Dominik , Hirt Gerhard , Steingießer Klaus J. , Rech Ralf , Gehrmann Bodo , Lamm Rolf
Published: June 2013

To provide a high quality of forged products, a homogeneous distribution of material properties has to be achieved inside the ingot. As the properties are not visible from the outside, an online monitoring during the forging process is required. By using modern measuring equipment and fast calculation models, the equivalent strain, temperature and average grain size in the core fibre of a forging ingot can be calculated parallel to the process. Software implementing the fast calculation models has been established and connected to the measuring system of two different open die forging presses. Two experimental forging processes with ten passes have been performed (20 ton steel ingot, 750 kg Ni-base alloy ingot). Parallel to the process, the current strain, temperature and average grain size in the centre of the ingot are visualised in the graphic user interface and recorded by the process monitor. It was shown that the calculation speed is high enough to allow online capability. After finishing the process, the developed software can further be used to analyse in detail the impact of every single stroke or pass on the whole process. Additionally, information like minimum or maximum grain size or recrystallized fraction is calculated and can be used to get insight into the process and optimize its design. Comparing the metallographically measured average grain size from experiment with the grain size estimated by the process monitor, the average deviation of three measured points is less than 13 %.
Metamodeling Based on the Fusion of FEM Simulations Results and Experimental Data
Authors: Colosimo Bianca Maria , Pagani Luca , Strano Matteo
Published: June 2013

In this Paper an Innovative Multistage Metamodeling Technique is Proposed for Linking Datacoming from Two Different Sources: Simulations and Experiments. the Model is Hierarchical, in Thesense that One Set of Data (the Experiments) is Considered to be more Reliable and it is Labeled as“high-Resolution” and the other Set (the Simulations) is Labeled as “low-Resolution”. the Results Ofexperiments is Obviously Fully Accurate, Except for the only Approximation due to the Measurementsystem and Given the Intrinsically Aleatory Nature of all Real Experiments. in the Proposed Approach,Gaussian Models are Used to Describe Results of Computer Experiments because they are Flexible Andthey can Easily Interpolate Data Coming from Deterministic Simulations. A Second Stage Model is Used,in Order to Link the Prediction of the First Model to the Real Experimental Data. for the Linkage Model,as in the First Stage, a Gaussian Process is Used. in this Second Stage a Random Parameter can be Addedto the Model, Known as Nugget, in Order to take into Account the Process Variability. this Kind Ofmetamodeling can have Different Purposes: Adjusting or Tuning the Simulations, Having a Better Tool Todrive the Design Process, Making an Optimization of a Parameter of Interest. in the Paper, its use Foroptimization of a Single Responsey with Two Design Variables x1 and x2 is Demonstrated. the Approachis Applied for Modeling the Crash Behavior in Three Point Bending of Metal Foam Filled Tubes.
Investigation on the Influence of Manufacturing Parameters on the Fatigue Strength of Components
Authors: Reiss Andrea , Engel Ulf , Merklein Marion
Published: June 2013

With cold forging processes it is possible to produce parts characterized by high strength, high dimensional accuracy and high surface quality. In order to optimize the forming process and to be able to use the advantages of cold forging specifically and combined, it is necessary to find correlations between the manufacturing parameters, the strength and the properties, like hardness distribution and surface quality, of the component. The research work covered in this paper focuses on the influence of the components properties influenced by its manufacturing history on their fatigue strength. The used component is a flange hub, produced by a four-stage cold forging process. To obtain different component properties the production process of the hub was varied for example by changing the heat treatment or by producing the parts by turning process. First of all, the components’ properties, for example hardness distribution, remaining residual stresses, orientation of fibers and surface quality, were determined. Moreover, a special experimental setup for the fatigue tests has been designed. The components’ fatigue behavior was determined using a high frequency pulsator and evaluated in terms of finite life fatigue strength and fatigue endurance limit. These examinations were used to produce Woehler curves for the differently manufactured components with a certain statistical data analysis method.
Experimental & Numerical Study of the Hot Upsetting of Weld Cladded Billets
Authors: Wang Jing Cai , Langlois Laurent , Rafiq Muhammad , Bigot Régis , Lu Hao
Published: June 2013

The presented work is dedicated to studying the forgeability of bimaterial cladded workpiece. Hot upsetting tests of cylindrical low carbon steel (C15) billets weld cladded (MIG) by stainless steel (SS316L) are experimentally and numerically studied. Upsetting tests with different upsetting ratios are performed in different tribology conditions at 1050°C which is within the better forgeability temperature range of both substrate and cladding materials[ ]. Slab model and finite-element simulation are conducted to parametrically study the potential forgeability of the bimaterial cladded workpiece. The viscoplastic law is adopted to model the friction at the die/billet interface. The friction condition at the die/billet interface has a great impact on the final material distribution, forging effort and cracking occurrence. With Latham and Cockcroft Criterion, the possibility and potential position of cracks could be predicted.
Potential of Duplex Plasma Deposition Processes for the Improvement of Wear Resistance of Hot Forging Dies
Authors: Behrens Bernd-Arno , Yilkiran Timur , Braeuer G. , Paschke H. , Weber M.
Published: June 2013

The efficiency offorging processes is significantly influenced by the tool and scrap costs whichin their turn depend on the life time of forging dies. The tools used for hotforging are subject to process-related high mechanical, tribological, chemicaland thermal-cyclic loads which usually interact with each other. In comparisonto other manufacturing methods, the resulting load spectrum leads to extensivewear and thus to the failure of forging dies after a short tool life. Toincrease the wear resistance of forging dies, duplex treatments consisting ofplasma nitriding and plasma deposition techniques were used to improve thesurface properties and hence to increase the die life time. By basicinvestigation of the wear mechanisms the potentials of newly developed vanadiumdoped chromium nitride and boron containing titanium nitride coating systemswere investigated. Within the presented work it is demonstrated that vanadium-dopedchromium nitride layers have a high wear reduction potential for hot forgingdies.