bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Behavior of 980MPa NANOHITENTM at Elevated Temperatures and its Effect on Springback in Warm Forming
Authors: Minote Toru , Funakawa Yoshimasa , Saito Naoko , Fukahori Mitsugi , Hamasaki H. , Yoshida Fusahito
Published: May 2014

High tensile strength steel sheets have large springback after being formend at room temperature. Warm forming can be a solution to reduce springback of high tensile strength steel parts. NANOHITENTM is a high strength ferritic steel precipitation-strengthened by nanometer-sized carbides developed by JFE Steel Corporation. Tensile strength of the steel at room temperature does not change before and after deformation at elevated temperatures up to 873K since the carbides in the steel are stable at high temperatures less than 973K. Therefore, the steel is suitable for warm forming. Springback of 980MPa NANOHITENTM parts warm formed at 873K is the same level of that of cold formed conventional 590MPa steel parts. In this study, two kinds of material testing at room temperature and at elevated temperatures between 573K and 937K were performed to understand the mechanical behavior of 980MPa NANOHITENTM: uniaxial tensile tests and bending tests. The steels flow stress depends on not only material temperature but also strain rate in uniaxial tensile tests. After a bending test, the specimen shows springback measured by the change of an angle between the two sides. Stress relaxation happens while a test specimen is held at the bottom dead point after bending. And the stress relaxation could be used to reduce springback of warm formed parts.
Influence of Cooling Rate on Free Interstitial Concentration in Type 430 Ferritic Stainless Steel
Authors: Juuti Timo J. , Manninen Timo , Porter David A.
Published: May 2014

In ferritic steels, the amount of free C and N should be as low as possible to avoid the formation of Cottrell atmospheres and their associated discontinuous yielding and Lüders bands during forming. During the post-annealing cooling of ferritic stainless steel, carbides and nitrides of the type MX and M23C6 precipitate. The volume fraction of the precipitates is determined by chemical composition, microstructure and the cooling path. In some cases, precipitation might not be sufficient to remove all free interstitials from the matrix, in which case, the process parameters or composition of the steel should be reconsidered. Here, thermodynamic and kinetic calculations using Thermo-calc and TC Prisma software have been made to investigate the precipitation of C and N as a function of total interstitial content and cooling rate. According to the calculations, decreasing the cooling rate would result in a more efficient precipitation and hence, less free C and N in the matrix, but the amount is not sufficient to remove the upper yield point. Furthermore, changing the C and N content of the steel was found to have insignificant influence. However, the free C and N could possible be bound through a more complex cooling.
An Experimental Investigation of Parameters Influencing Dimensional Accuracy in Rotary Stretch Bending
Authors: Welo Togeir , Bolstad Mads
Published: May 2014

The rapid application of alternative materials is vital to the environmental and sustainable development of the European manufacturing industry. In many cases, companies seek using ‘old’ materials, such as aluminum alloys, magnesium, titanium, composites and plastics, for new applications in order to improve customer value; i.e., the perceived product benefits subtracted its price. For a subset of manufacturing companies, one of the most viable strategies is to offer weight savings at an affordable price by replacing steel with aluminum alloys, typically providing added value in the 0.25 - 0.5 kg/€ range, depending on application. Hence, weight savings shave to come with minimum cost penalty, which calls for a balanced optimization of manufacturing process and material consumption. For formed products, the latter optimization is driven by the performance characteristics of the final product as well as its quality capabilities relating to dimensional accuracy. The former is closely related to the attributes of the particular forming method. In this study, an industry-like rotary stretch bending set-up has been equipped with two different modular die inserts to determine how process characteristics impact dimensional accuracy of the product, as represented by local cross-sectional distortions and global elastic springback in industrial practice. A number of cross-sectional profile geometries with different wall thickness, depth, width and number of internal chambers have been simultaneously stretched and bent into the shapes provided by two die different configurations. The extruded profiles were made in different heat treatable alloys within the AA6xxx and AA7xxx series and formed according to industrial practices, which for the latter included solution heat-treatment immediately before forming. The results show that the slenderness of the external flange of the cross section is the main parameter with regard to the magnitude of local cross-sectional distortions. In practice, therefore, wall-thickness is the critical quality control parameter. The material’s yield characteristic proved to have limited impact on local distortions, although this is usually a major concern with regard to springback variations. The results from the experimental series have been structured into a design relationship for assessment of local distortions where the problem is reduced to the use of a proposed dimensionless bendability parameter as input.
Development of Hole Making Technology of Bi-Layer Composite Materials Consisting of CFRP Laminates and Titanium Alloys
Authors: Yagishita H.
Published: May 2014

Recently, to construct an airframe 2-layer composite materials consisting of carbon fiber reinforced plastic (CFRP) laminates an TiAl6V4 still need to be machined, whereby drill holes are frequently machined. Special attention has to be paid to the machining quality, which implies hole dimensional accuracy, defect free peripheral zone, edge quality at inlet and outlet of hole and so on. In this research, first by using a high performance CNC machine tool equipped with potent control unit, drilling and circular milling are compared for hole making in CFRP laminates and it is ascertained that circular milling is superior to drilling in defect free peripheral zone and also tool life [. Second, from comparing drilling and circular milling in hole making of 2-layer composite materials consisting of CFRP laminates and TiAl6V4, the superiority of circular milling caused by lower thrust force and lower thermal load than those of drilling has been made clear [. Third, the author has devised a new spindle designed based on double eccentric mechanism so that circular milling can be executed at an airframe assembly site. By using a new handy type apparatus having the spindle driven by air motors, hole making tests were executed to 2-layer composite materials consisting of CFRP laminates and TiAl6V4 with cemented carbide endmill [.
Heat Treatments Analysis of Steel Using Coupled Phase Field and Finite Element Methods
Authors: Vasconcelos Patricia , Giessmann Adam , Dias-de-Oliveira João , Andrade-Campos António
Published: May 2014

Steels are known for their remarkable mechanical properties being extensively used in industry. Furthermore, phase transformations in metals and alloys, particularly in steels, are widely studied due to their importance. The understanding of the microstructure evolution in this type of materials is vital to reproduce the thermomechanical behaviour and to create new materials. To analyse the thermomechanical behaviour of steel during phase transition of steels, a phase field model was coupled with a finite element model in order to simulate the heat treatment and microstructure evolution of austenite to pearlite/ferrite. The thermoelastoplastic constitutive equations for each phase were implemented through a user routine in commercial FE software. This procedure presents a more quantitative understanding of the phase transformation in steels and a deeper comprehension of the mechanical behaviour of these materials when subject to heat treatments.
Experimental Comparison between Traditional and Cryogenic Cooling Conditions in Rough Turning of Ti-6Al-4V
Authors: Tirelli Stefano , Chiappini Elio , Strano Matteo , Monno Michele , Semeraro Quirico
Published: May 2014

Titanium alloys, mainly because of their poor thermal conductivity, need to be cut at relatively low cutting speeds to avoid a severe diffusion wear, with obvious negative consequences on the profitability of machining. An important amount of research activities has been done in order to increase productivity in titanium machining operations and one of the most promising solutions is represented by the use of liquid nitrogen as a coolant during the machining operation.
The aim of this paper is to compare traditional and cryogenic turning of Ti6Al4V in a region of cutting parameters particularly relevant to the aerospace industry where no previous data are available. The cutting parameters are those typical of titanium alloys rough machining which is considered, cost-wise, the most important operation because, for aerospace components, the so-called Buy-To-Fly ratio can reach values up to 20:1.
The experiments have been performed using a full factorial design in order to statistically evaluate, using ANOVA and regression analyses, the significance of the input factors on the process most interesting outputs. The considered input factors are: type of cooling method, cutting speed and feed rate. The main analysed responses are: tool wear, surface roughness, cutting forces, coefficient of friction and chip morphology.
The results show the significance of the cooling method on the tool life and that cryogenic machining is able to increase the tool life with respect to wet cutting. On the other hand, the beneficial effect of the liquid nitrogen cooling is reduced at high cutting speed and feed rate. Besides, the results showed that a small but significant reduction can be achieved for both the repulsion force and the coefficient of friction at the tool-workpiece interface.
Identification of Friction Law to Model Orthogonal Cutting
Authors: Senecaut Yannick , Watremez Michel , Brocail Julien , Dubar Laurent
Published: May 2014

A first approach of tool-chip interface behaviour for high-speed machining modelling has been carried out by Al Brocail and 2010 and an empirical friction law has been first determined. This law has been established for high temperatures (initial sample temperature equal to 750 K) and low sliding velocities (less than 0.5 m.s-1) and an extrapolation has been considered for higher velocities. This article intends to determine an empirical friction law for low temperatures (ambient) combined with high sliding velocities (up to 1.5m.s-1) by means of a tribometer developed by Meresse and Al. A new experimental device is designed to carry out several tests and simulate the friction behaviour at the tool-chip interface. The experimental results are compared with a numerical model and an iterative method is used to minimize the error between experimental and numerical simulations on normal and tangential forces. This method allows to recover a Coulomb friction coefficient which is associated to local pressure, temperature and sliding velocity. The completion of several tests provides an empirical friction law for high sliding velocities and low temperatures.
Fitting of Constitutive Material Parameters for FE-Based Machining Simulations for Functionally Graded Steel Components
Authors: Tiffe Marcel , Biermann Dirk , Zabel Andreas
Published: May 2014

The composition of different materials and their specific properties like tensile strength and toughness is one way to achieve workpiece characteristics which are tailored to the later application. Another approach is the subsequent local heat treatment of workpieces made of homogeneous materials. However, both ways are costly and go along with several subsequent process steps. Therefore, mono-material workpieces which were manufactured by thermo-mechanical forming processes may provide such tailored properties in the form of functional gradations. Furthermore, the process chain is shortened by the combination of forming and heat treatment, but nevertheless machining processes are still needed for proper workpiece finish. This puts the challenge of varying process conditions due to hardness alterations within a single process step, e.g. turning. In addition to experimental investigations simulative analysis techniques are desired to evaluate mechanical as well as thermal loads on tool and workpiece. In the case of FE-based microscopic chip formation simulations proper material behaviour needs to be determined with respect to material hardness. This paper describes the approach of fitting Johnson-Cook material parameters as a function of workpiece material hardness. In order to achieve realistic stress states within the process zone, this approach considers the yield strength as a linear function of the hardness. It is shown how the hardness influences the cutting conditions and how the Johnson-Cook parameters are identified. Then these parameters are validated in three-dimensional simulations of exterior dry turning by comparison of simulated process forces and chip formation to experimentally achieved ones.
Influence of Cutting Parameters and Tool Geometry on Cutting Forces and Damage on 2D and 3D Carbon/Epoxy Composites in Drilling
Authors: Turki Yosra , Habak Malek , Velasco Raphael , Vantomme Pascal , Khellil Kamel
Published: May 2014

The evolution of carbon/epoxy composites use in aeronautics requires a better comprehension of the machining conditions influence on these materials. This study aim is to establish, based on the experimentation, the relationship between machining conditions and the behavior of drilled 2D and 3D carbon/epoxy composites. Two drill geometries, seam introducing and a range of cutting speed and feed have been tested. The effect of each parameter has been assessed in terms of thrust force, moment (recorded during machining) and defects (performed by macroscopic analyses and quantified using delamination factor Fd). Experimental results have shown significant influences of feed and drill geometry on delamination reduction. The use of a spur drill and a low feed generates minor defects and produces the best results. Furthermore, stitching helps reduce damage inside the hole.
Residual Stresses in Machining of AISI 52100 Steel under Dry and Cryogenic Conditions: A Brief Summary
Authors: Caruso Serafino , Outeiro J.C. , Umbrello Domenico , Batista António Castanhola
Published: May 2014

Residual stress is one of the most important surface integrity parameter that can significantly affect the service performance of a mechanical component, such as: contact fatigue, corrosion resistance and part distortion. For this reason the mechanical state of both the machined surface and subsurface needs to be investigated. Residual stress induced by dry and cryogenic machining of hardened AISI 52100 steel was determined by using the X-ray diffraction technique. The objective was to evaluate the influence of the tool cutting edge geometry, workpiece hardness, cutting speed, microstructural changes and cooling conditions on the distribution of the residual stresses in the machined surface layers. The results are analysed in function of the thermal and mechanical phenomena generated during machining and their consequences on the white layer formation.
The Effects of Cutting Conditions on Surface Integrity in Machining Waspaloy
Authors: Umbrello Domenico
Published: May 2014

Machining of advanced aerospace materials have grown in the recent years although the difficult-to-machine characteristics of alloys like titanium or nickel based alloys cause higher cutting forces, rapid tool wear, and more heat generation. Therefore, machining with the use of cooling lubricants is usually carried out. To reduce the production costs and to make the processes environmentally safe, the goal is to move toward dry cutting by eliminating cutting fluids. This objective can be achieved by using coated tool, by increasing cutting speed and by improving the product performance in term of surface integrity and product quality.
The paper addresses the effects of cutting speed and feed on the surface integrity during dry machining of Waspaloy using coated tools. In particular, the influence of the cutting conditions on mechanical power consumption, the tool wear and some important indicator of the surface integrity (surface roughness, affected layer, microhardness, grain size and microstructural alteration) were investigated. Results show that cutting conditions have a significant effect on the parameters related to the surface integrity of the product affecting its overall performance.
Experimental Research of Micro-Textured Tool for Reduction in Cutting Force
Authors: Kiyota Hiroki , Itoigawa Fumihiro , Nakamura Takashi
Published: May 2014

An effect of micro-textured tool on a reduction in cutting force has reported in recent years. Some researchers have discussed that the microstructures contribute to the reduction in friction force at tool-chip interface by acting as cutting fluid reservoirs. In this study, on the other hand, a reduction in cutting force achieved by using the textured tools was confirmed even under dry condition. The results of orthogonal cutting tests employing AISI 1045 steel with non-textured and textured tools indicated that the cutting force and calculated friction coefficient at the tool-chip interface definitely reduce at relatively high cutting speed. For this friction reduction effect, effective texture patterns and optimal area ratio of concave portion to total surface were empirically suggested. Moreover, from results of the tests using tools with sectionally textured surface, it was revealed that the texture only around the position in which the chip flow separates from the tool rake face is effective to reduce the cutting force. Close observation of both tool edges and formed chips under various cutting tests indicated that changes in geometry and dimensions of dead metal formed around the cutting edge is essential for the reduction in cutting force. Finally, a mechanical cutting model having an agreement with the experimental results was discussed by employing the slip-line field method.
Experimental Analysis of Milling Operations in Ti-6Al-4V and Co-28Cr-6Mo Alloys for Medical Devices
Authors: Ferreira Pedro , Simões Fernando , Relvas Carlos
Published: May 2014

In order to understand the problems that arising during machining and contribute to find the best way to produce medical prosthesis, an experimental milling analysis was conducted in Ti-6Al-4V and Co-28Cr-6Mo alloys. The thermal gradient and the cutting forces created on the surface during the machining were evaluated for different cutting speeds. Moreover, the roughness and Vickers hardness were evaluated. Based on the results obtained, it is possible to conclude that the difficult to cut of Co-28Cr-6Mo alloy is higher than Ti-6Al-4V alloy.
Methods to Decrease Cut Edge Sensitivity of High Strength Steels
Authors: Gläsner Thorsten , Sunderkötter Christina , Plath Armin , Volk Wolfram , Hoffmann Hartmut , Golle Roland
Published: May 2014

The edge cracking sensitivity of AHSS and UHSS is quite challenging in the cold forming process. Expanding cut holes during flanging operations is rather common in automotive components. During these flanging operations the pierced hole is stretched that its diameter is increased. These flanging operations stretch material that has already been subjected to large amounts of plastic deformation, therefore forming problems may occur. An innovative cutting process decreases micro cracks in the cutting surface and facilitates the subsequent cold forming process. That cutting process consists of two stages, which produces close dimensional tolerance and smooth edges. As a result the hole expanding ratio was increased by nearly 100% when using thick high strength steels for suspension components
Weak Formulations with Upwind Shift for Calculation of Free Surface Corrections and Simulation of Steady-State Forming Problems
Authors: Fourment Lionel , Ripert Ugo
Published: May 2014

For many material forming processes steady-state formulations allows reducing numerical simulation time by an order of magnitude with respect to more conventional approaches. In the presented approach, the steady regime is iteratively computed by a free surface algorithm that alternates computations of the metal forming flow over a known geometry and known contact surfaces, with computations of domain corrections to satisfy free and contact surface conditions. Several weak formulations of the second problem equations are investigated to get a robust algorithm suitable for parallel computations with unstructured meshes. Analytical problems show the necessity to introduce an upwind shift within these weak formulations. Contact inequations enforces this necessity by requiring a more dramatic shift. A robust and accurate algorithm is so obtained, which is successfully applied to 3D complex metal forming processes like rolling. In the wire drawing application, computational time is reduced by more than fifteen with respect to the incremental calculation of the steady-state.
Online Prediction of Machining Distortion of Aeronautical Parts Caused by Re-Equilibration of Residual Stresses
Authors: Poulhaon Fabien , Rauch Matthieu , Leygue Adrien , Hascoet Jean Yves , Chinesta Francisco
Published: May 2014

This paper is concerned with the prediction of part distortion induced by residual stress relief during machining. Aeronautical manufacturing requires nowadays the production of large monolithic parts from workpieces obtained by forging or rolling operations. Residual stresses induced during these forming steps are often consequent and represent a significant obstacle for manufacturers. Re-equilibration of initial residual stresses induced by material removal causes the part to deform.The method presented in this paper provides a tool for predicting changes in the geometry of the part occurring during machining and after unclamping. This prediction is based on an on-line data acquisition. From the predicted shape, the manufacturer is able to anticipate extra conforming steps eventually required afterwards and an updated toolpath accounting for geometrical changes happening during the on-going operation can be derived.The impact of the unknown initial residual stresses on the part deformation during machining is predicted on-line by comparing measured deformations to a reduced basis of mechanically admissible evolutions for the part geometry induced by material removal. This reduced basis is extracted from a larger database constructed off-line thanks to machining simulations and observations of previously machined similar parts.An auxiliary database for post-machining distortion is constructed similarly and makes possible a quick and reliable on-line prediction of the final shape of the part (i.e. after unclamping).
Modelling of Inertia Friction Welding Using Finite Element Analysis and Computational Fluid Dynamics
Authors: Muhammad Ossama , Bennett Christopher J. , Morvan Hervé P.
Published: May 2014

Inertia Friction Welding (IFW) is a solid-state joining process where one rotating (connected to an inertia) and one stationary part are brought together under an axial load, causing frictional heat generation and plastic deformation at the interface; upon cooling a weld is formed between the components. There is evidence in welds between dissimilar materials which show a flow regime that may keep impurities at the weld interface and may have implications for weld strength and fatigue life. Numerical modelling of IFW using Finite Element Analysis (FEA) has allowed the successful prediction of temperature profile, upset (length loss) and flash shape and process parameters such as flywheel slowdown. However, due to the lack of knowledge of the behaviour of the severely plasticised zone (shear zone) and the fluid-like nature of the material near the interface, the use of Computational Fluid Dynamics (CFD) has been considered. This paper presents a method to utilise both FEA and CFD modelling techniques to provide a better modelling strategy for the IFW processes. By using the results of an FEA model as the boundary/initial conditions for the CFD, simple models have allowed comparison between the two numerical approaches and have validated the implementation and consistency of material properties and modelling methodology for both. A model of the interface has been produced with CFD with this method which illustrates the possible material behaviour and material flow in that zone.
Data Exploration Approach Versus Sensitivity Analysis for Optimization of Metal Forming Processes
Authors: Regulski Krzysztof , Szeliga Danuta , Kusiak Jan
Published: May 2014

Product properties for innovative materials, e.g. dual phase steels, require precise control of production processes. Difficulties in optimization of process parameters correspond with large number of control variables, which should be considered in the technology design. Sensitivity analysis allows evaluating the importance of all process inputs on the final properties of material. Information on the most important inputs is crucial for further design of the process. Application of sensitivity analysis requires detailed knowledge of the process phenomena as well as the definition of the mathematical model of the thermomechanical process. Furthermore, some sensitivity analysis algorithms are of the high computational cost. Presented work concerns possibility of the application of data exploration approach in evaluation of the importance of process inputs as the alternative for sensitivity analysis. Use of data mining algorithms eliminates necessity of mathematical model development, it also does not require any apriori knowledge about the process. Authors presents the comparison of sensitivity analysis and data exploration approach in evaluating relationships between inputs and outputs of the hot rolling for dual phase steel strips. The presented approach and the perspectives of the practical application could lead to significant decrease of time necessary for the computations of process design. The theoretical considerations are supplemented with the results of both types of analysis.
Basic Investigations of Non-Pre-Punched Joining by Forming of Aluminium Alloy and High Strength Steel with Shear-Clinching Technology
Authors: Merklein Marion , Meschut Gerson , Müller Martin , Hörhold Réjane
Published: May 2014

Facing a decreasing amount of resources on the one hand and an increasing demand for comfort on the other, more and more attention is being paid to sustainability and care for the environment. Particularly in the automotive sector, lightweight design principles continue to prosper rapidly. As a result, adjusted materials for different applications were developed. Due to the formation of intermetallic phases, most multi-material mixes cannot be welded and require adapted joining technologies. Mechanical joining technologies such as self-piercing riveting and mechanical clinching have proven effective methods of joining lightweight materials like aluminium and ductile steels. New high-strength steels are increasingly used in crash-sections, where limited deformation under impact load is required. These hot stamped steels have a very low elongation at break and therefore a low formability. Currently there is no joining by forming technology without pre-punching available using these grades of steels on die-side. The newly developed shear-clinching process is one possible method of joining this kind of material without additional elements. The fundamental idea of shear-clinching is a single-stage process in which pre-punching of the die-side material is performed by indirect shear-cutting and subsequent forming of the upper layer into this hole. This would immensely enlarge the application segment of mechanical clinching even if hot stamped steels are positioned on die-side. Fundamental studies are required to ensure process reliability and it is necessary to break down the joining process into fragments, like pre-punching and clinching with pre-punched sheet, and superpose them to form the combined procedure shear-clinching. This paper presents a detailed investigation of the sub-process clinching with pre-hole.
Friction Stir Lap Welding of Aluminium Alloys
Authors: Bruni Carlo , Quercetti Giovanni , Pieralisi Massimiliano
Published: May 2014

The friction stir welding of lap sheets can be performed considering different variables in terms of process parameters, tool configuration, welding typology and so on. The proposed investigation deals with the friction stir welding of blanks, with the same thickness, performed under lap configuration with the sheets welded, in one-side and in both sides as well, with different tool geometries and tool rotation-wise. The double side allows to extend the weld through the whole thickness leading to better mechanical welding properties at the blank to blank interface. The weld morphology has been investigated through microstructure observations performed on the transverse area, with respect to the welding velocity, of each joint. The tensile shear strength of the joint in one-side weld is generally lower than that detected in two side weld.
Ti 6Al-4V FSW Weldability: Mechanical Characterization and Fatigue Life Analysis
Authors: Lertora Enrico , Mandolfino Chiara , Gambaro Carla
Published: May 2014

Friction stir welding (FSW) is an innovative solid-state process, patented in 1991 by The Welding Institute, which avoids solidification problems associated with conventional fusion welding, providing joints having excellent mechanical and metallurgical properties. Due to its many advantages, FSW is successfully applied to weld various aluminium, magnesium and copper alloys. In recent years, FSW of high melting temperature materials such as steels and titanium alloys has become a key research topic. However, the high softening temperature of high melting temperature materials result in extreme stress of the pin tool during FSW, which adds to the difficulty in creating defect-free joints, especially for titanium alloys. This work is a preliminary investigation of FSW application on titanium alloy Ti6Al4V. The research focused on optimization of tool material and geometry, as well as process parameters. Complete microstructural and microhardness evaluations were conducted in addition to surface examinations. In order to evaluate the service behaviour of the joints realized with the optimized parameters, an in-depth investigation was also conducted on the fatigue properties of FSW joints.
Effect of Cold Plasma Treatment on Surface Roughness and Bonding Strength of Polymeric Substrates
Authors: Mandolfino Chiara , Lertora Enrico , Gambaro Carla
Published: May 2014

For an effective application of polymers, it is essential to have good adhesion behaviour to ensure good mechanical properties and durable components. Unfortunately, in general terms, polymers are characterized by high chemical inertness, which leads to very low surface energy values and, consequently, poor adhesive properties; this is particularly true for polyolefins. In this study, the effects of low pressure plasma treatment on surface roughness of polyethylene and polypropylene samples and on shear properties of adhesive bonded joints based on these substrates have been investigated. In particular, the optimization of three plasma process parameters, exposure time, voltage and working gas, were studied performing roughness measurement, contact angle evaluation and lap-shear tests. The experimental results show that the optimized plasma process may remarkably change the surface morphology, increasing wettability properties of the surfaces and shear strength of the bonded joints. These good properties remain almost unchanged even after some days of storage in the laboratory.
Numerical Investigation of Temperature and Phase Development of (Deformation-) Dilatometer Specimens
Authors: Lutz Stefan , Weninger Johannes , Helldörfer Bastian , Merklein Marion
Published: May 2014

The Gleeble 3500 thermo-mechanical testing machine with ISO-Q dilatometer set-up allows the creation of time temperature transformation diagrams at high cooling rates, after deformation and under constant load with a simple experimental set-up. An isothermal plane with temperature gradients perpendicular to this plane arises in the sample which is used for dilatometrical evaluation. The homogeneity and size of this isothermal region has a decisive influence on the measurement results, but cannot be measured with sufficient accuracy. To gain an accurate understanding of the processes in the sample, a coupled thermo-electrical, thermo-metallurgical, thermo-mechanical finite element model of the experiments is set up. To map the temperature control circuit of the machine, a PID controller is implemented, which controls the voltage of the conductive sample heating between the simulation steps. By comparing the temperature and hardness distribution with the experiments, it is shown that in this way the temperature distribution and phase transformation can be mapped. By the findings, the experimental setup was adjusted. This led to an improvement of the measurement results.
CFD Simulation of Heating a Cu Pipe with a Safe H2/O2 Flame
Authors: Kjäldman Lars , Syrjänen Jouni
Published: May 2014

As part of the EU/SME project SafeFlame (www.safeflameproject.eu ) the heating of a Cu pipe by a H2/O2 flame has been modeled and the results are compared to experiments. CFD (Computational Fluid Dynamics) modeling has been utilized to study the flow and combustion in the flame and the heat transfer from the flame to the pipe. The simulation results are compared with the measured temperature history of the pipe at different locations and with the visual flame. The influence of distance between the burner and the pipe and of using two opposite H2/O2 flames on the heating rate of the pipe has been investigated. Reasonable agreement between modeling and experiments has been obtained. The reasons for differences between modeling and experimental results are discussed.
Thermal Modeling in Composite Transmission Laser Welding Process: Light Scattering and Absorption Phenomena Coupling
Authors: Akue Asseko André Chateau , Cosson Benoît , Schmidt Fabrice , Gilblas Rémi , Le Maoult Yannick , Lafranche Eric
Published: May 2014

In previous studies [1, , we have presented a detailed formulation of a macroscopic analytical model of the optical propagation of laser beams in the case of unidirectional thermoplastic composites materials. This analytical model presented a first step which concerns the estimation of the laser beam intensity at the welding interface. It describes the laser light path in scattering transparent composites (first component) by introducing light scattering ratio and scattering standard deviation. The absorption was assumed to be negligible in regard to the scattering effect. In this current paper, in order to describe completely the laser welding process in composite materials, we introduce the absorption phenomenon in the model, in the absorbing material (second component), in order to determine the radiative heat source generated at the welding interface. Finally, we will be able to perform a three dimensional temperature field calculation using a commercial FEM software. In laser welding process, the temperature distribution inside the irradiated materials is essential in order to optimize the process. Experimental measurements will be performed in order to valid the analytical model.
Thermomechanical Effects in PVTα Measurements
Authors: Peron Mael , Sobotka Vincent , Boyard Nicolas , Le Corre Steven
Published: May 2014

Knowledge of the different properties of thermoset composite materials is of great importance for the manufacturing of high quality composite parts. The resin bulk modulus is one of them and is essential to define the composite parts compressive behaviour under uniform compression. The evolution of this property with temperature and conversion degree of reaction is a challenging task and has been tentatively measured with a home-made apparatus, named PVTα, on which temperature, volume change and degree of cure are simultaneously recorded. But as the sample is contained in a non-reactive and deformable capsule, which mechanical behaviour may interfere with the measurement, a validation is required. The aim of this work is to develop a finite element model of the problem in order to simulate the thermal mechanical behaviour of the sample and the capsule, and so to validate the measurement process. The multiphysical numerical model accounts for phase change kinetics and non-linear thermal properties as well as thermo-dependent elastic properties, all problems being solved through a strong iterative coupling scheme. Mechanical contact problems between the capsule and the resin sample are handled through a penalization method contact algorithm which enables to capture the effects of chemical and thermal shrinkage in the sample and the capsule. The heterogeneous stress state generated by the material transformation is assumed to induce heterogeneous strain states which may lead to misinterpretations of macroscopic measurements. This model is a first approach and will be improved using a more sophisticated rheological model. Nevertheless, results show that the usual experimental analysis method can be used as long as the gel point is not reached. After a certain conversion degree, the measured bulk modulus is different from the effective one so corrections have to be brought.
Numerical and Experimental Investigation of Deep Drawing of Sandwich Panels
Authors: Tipalin Sergey A. , Petrov Michael A. , Saprikin Boris , Kosatchyov Nikolay , Shpunkin Nikolay , Petrov Pavel A.
Published: May 2014

Commonly investigated problem on composite fabrication and forming for weight reduction in transportation and aerospace area is not completely cleared. The main difficulties on composites forming without building any defects caused new ways on process characterization due to the key parameters. In the paper two main problems were investigated, i.e. material fracture and material thinning during deep drawing. Through mechanical tests and numerical simulation the authors tried to couple the fracture with the technological boundary conditions of the deep drawing process and form a housing test part from a three-layer material.
Modelling of Thermoset Matrix Composite Curing Process
Authors: Carlone Pierpaolo , Aleksendrić Dragan , Ćirović Velimir , Palazzo Gaetano S.
Published: May 2014

Autoclave curing is a common practice to manufacture high temperature thermoset matrix composites in order to improve the mechanical properties of the final product. The cycle design i.e. the definition and optimization of the temperature-time curve is a key issue for a competitive production. In this paper a very fast and effective procedure, based on the coupling of a finite element thermochemical model of the process and an artificial neural network, is proposed to predict the evolution of temperature in predefined control points inside the processing material. The model has been tested against the imposed thermal cycle used as an input. The procedure is tested simulating the curing process of a three-dimensional double-curved shape. Obtained outcomes highlighted the remarkable capabilities of the implemented procedure in terms of reliability of temperature predictions and of drastic reduction of the computational time with respect to classic computational models.
Numerical Modeling of AA2024-T3 Friction Stir Welding Process for Residual Stress Evaluation, Including Softening Effects
Authors: Sonne Mads Rostgaard , Carlone Pierpaolo , Palazzo Gaetano S. , Hattel Jesper Henri
Published: May 2014

In the present paper, a numerical finite element model of the precipitation hardenable AA2024-T3 aluminum alloy, consisting of a heat transfer analysis based on the Thermal Pseudo Mechanical model for heat generation, and a sequentially coupled quasi-static stress analysis is proposed. Metallurgical softening of the material is properly considered and included in the calculations by means of the Myhr and Grong model, implemented as a user subroutine in ABAQUS. Numerical outcomes are compared with experimental results, highlighting the intriguing predictive capabilities of the model for both temperatures and residual stresses. The contour method is employed to map the longitudinal residual stress distribution on a transverse cross section of the joint. The influence of the applied boundary conditions and of the release of the clamping system on residual stresses is also assessed.
Development of a Tool Design Method in Cross Wedge Rolling: Description and Applications
Authors: Gutierrez Catalina , Mangin Philippe , Langlois Laurent , Bigot Régis
Published: May 2014

Till now, the definition of cross wedge rolling dies requires know-how and important expertise from the designers. A decision-making methodology is being developed to provide sequential and logical steps to draw easier and faster the tool geometry. This methodology is based on designing rules found in literature that link the geometrical parameters of the desired rolled part and the geometrical parameters of the tool. Nevertheless, in the literature, the rules are not always consistent because the admissible domain for a parameter can differ from one author to another. In order to take into account this variability, a stability index is associated to each rule and to the designed tool. The methodology allows updating of the existing rules and the implementation of new rules. The set of parameters defining the geometry of the tool can be exported in the CAD/CAM software and FEM software. A case-study is presented to illustrate and validate the methodology.
Identification of Anisotropic Yield Criterion Parameters from a Single Biaxial Tensile Test
Authors: Zhang Shun Ying , Leotoing Lionel , Guines Dominique , Thuillier Sandrine
Published: May 2014

The present work deals with the calibration strategy of yield functions used to describe the plastic anisotropic behavior of metallic sheets. In this paper, Bron and Besson yield criterion is used to model the plastic anisotropic behavior of AA5086 sheets. This yield model is flexible enough since the anisotropy is represented by 12 parameters (4 isotropic parameters and 8 anisotropic parameters in plane stress condition) in the form of two linear fourth order transformation tensors. The parameters of this anisotropic yield model have been identified from a single dedicated cross biaxial tensile test. It is shown, from finite element simulations, that the strain distribution in the center of the cruciform specimen is significantly dependent on the yield criterion. Moreover, this cross biaxial test involves a large range of strain paths in the center of the specimen. The calibration stage is performed by means of an optimization procedure minimizing the gap between experimental and numerical values of the principal strains along a specified path in the gauge area of the cruciform specimen. It is shown that the material parameters of Bron and Besson anisotropic yield model can be determined accurately by a unique biaxial tensile test.
Influence of Friction Stir Welding Effects on the Compressive Strength of Aluminium Alloy Thin-Walled Structures
Authors: Paulo Rui Miguel Ferreira , Carlone Pierpaolo , Valente Robertt , Teixeira-Dias Filipe , Palazzo Gaetano S.
Published: May 2014

The main objective of the present work is to investigate the effect of the residual stresses originated by the friction stir welding (FSW) process in the compressive strength of aluminium alloy plates. The finite element method (FEM) is used to simulate the welding process and calculate the distribution of the residual stresses. The model is validated using a residual stress map obtained by means of the contour method from a friction stir welded AA2024-24 plate. The results from the welding simulation were then used to numerically assess the influence of the residual stresses on the collapse load of the plate.
Effect of the Kinematic Hardening in the Simulations of the Straightening of Long Rolled Profiles
Authors: Bouffioux Chantal , Boman Romain , Caillet Nicolas , Rich Nicolas , Ponthot Jean Philippe , Habraken Anne Marie
Published: May 2014

Residual stresses and lack of straightness appear during the cooling of sheet piles where the initial temperature field is not homogeneous. To meet the standards, the long hot rolled pieces are straightened using a series of rollers placed alternately above and below the pieces with shifts which create a succession of bendings.
The process is modeled to study the impact of the industrial parameters (the duration of the cooling and the rollers positions), to improve the final geometry and to reduce the residual stresses. Tests are carried out on this structural steel to observe the material behavior, then material laws are chosen and the parameters of these laws are defined using an inverse method. Two sets of material data are obtained: for the first one, the hardening is supposed to be isotropic, and for the second one, additional tests are performed to describe isotropic and kinematic hardenings. The cooling followed by the straightening is then simulated by the finite element method with these two sets of data.
The comparison of the rollers forces, the deformation and the residual stresses show the impact of the kinematic hardening on such a process where the material undergoes a succession of tensions and compressions.
The real forces applied by the rollers, the real curvature of the interlocks at the end of the straightening process and the distribution of the residual longitudinal stresses measured on the web using the ring core method are used to validate the numerical model.
Numerical Investigation for Evaluation and Prevention of Casting Defects in TiAl Alloys
Authors: Peter Ildiko , Rosso Mario , Forno Ilaria
Published: May 2014

Simulation tools have been effectively employed in many applications for numerically investigate on the development of efficient production processes aiming to materials quality enhancement. Such studies allow drastically reduction of the number of experimental tests and consequently of the development costs and further of the time-to-market. In this framework, the present paper focuses on the study of filling rate and of the solidification times of Titanium alloys. Starting from some acquired experimental data, considering appropriate boundary conditions and properly setting of the external parameters (flow-rate, liquid temperature, etc.), the study targets optimizing the processing cycle and reducing the presence of defects in casting. The cast tree used for the research is a symmetric one, including two samples used for Charpy impact tests and two samples for tensile tests. The considered commercial software provides a complete finite element solution and has been employed facilitating to prevent casting defects. During the simulations, the process parameters and the alloy properties have been explicitly taken into account. Information about how the parameters should be modified to achieve the optimal conditions close to a defects-free castings was achieved. A good correlation, in terms of microstructural analysis, between the simulation data and the experimentally obtained results was obtained, confirming the reliability of the model.