bluuebunny/crossref_metadata_2025 huggingface dataset:
Historical Riddles in Cheyenne: A Re-examination of Goddard’s So!taa!e Evidence
Authors: Alford Danny K. H.
Published: July 2015

Proceedings of the Fifth Annual Meeting of the Berkeley Linguistics Society (1979), pp. 438-452
How Not to Tell a Passive: The Case of Old Persian mana krtam Reconsidered
Authors: Statha-Halikas Hariklia
Published: July 2015

Proceedings of the Fifth Annual Meeting of the Berkeley Linguistics Society (1979), pp. 350-361
Peak Vary, Endpoints Don’t: Implications for Intonation Theory
Authors: Boyce Suzanne , Menn Lise
Published: July 2015

Proceedings of the Fifth Annual Meeting of the Berkeley Linguistics Society (1979), pp. 373-384
Spokes in a Wheel: A Linguistic and Rhetorical Analysis of Native American Public Discourse
Authors: Cooley Ralph
Published: July 2015

Proceedings of the Fifth Annual Meeting of the Berkeley Linguistics Society (1979), pp. 552-557
The Acquisition of Word Meaning: A Reexamination
Authors: Silva Marilyn N.
Published: July 2015

Proceedings of the Fifth Annual Meeting of the Berkeley Linguistics Society (1979), pp. 500-509
Trickster and the Village Women: A Psychosymbolic Discourse Analysis of a Lahu Picaresque Story
Authors: Matisoff James A.
Published: July 2015

Proceedings of the Fifth Annual Meeting of the Berkeley Linguistics Society (1979), pp. 593-636
The Evolution of Certain Cochimí Aspectuals and the Cochimí-Yuman Hypothesis
Authors: Mixco Mauricio J.
Published: July 2015

Proceedings of the Fifth Annual Meeting of the Berkeley Linguistics Society (1979), pp. 484-488
WATER VAPOR TRANSMISSION AND WATERPROOFING PERFORMANCE OF CONCRETE SEALER AND COATING SYSTEMS
Authors: Safiuddin Md. , Soudki Khaled A.
Published: July 2015

This paper reports the water vapor transmission and waterproofing performance of a silane-based penetrating sealer (PS), two cementitious coatings (CC1 and CC2), and a polymeric coating (PC). The sealer and coating products were applied on 100-mm concrete cubes. In total, fifteen concrete cubes including the control specimens were prepared. The treated concrete cubes were tested to determine the ability of the selected products to improve waterproofing and to transmit water vapor. The correlation between water vapor transmission and waterproofing performance was also examined. Experimental results revealed that the cementitious coating CC2 had the lowest degree of water vapor transmission but the highest degree of waterproofing performance. In contrast, the highest degree of water vapor transmission but the lowest degree of waterproofing performance were observed for the cementitious coating CC1. The penetrating sealer PS provided greater water vapor transmission but lower waterproofing ability than the polymeric coating PC and the cementitious coating CC2. The best-performing coating with regard to water vapor transmission and waterproofing was the polymeric coating PC. Furthermore, the water vapor transmission and waterproofing performance of the sealer and coating systems were strongly correlated; this suggests that one of these two properties can be predicted by testing the other.
Prediction of Crashworthiness for Extruded Magnesium Materials
Authors: Steglich Dirk , Tian X.
Published: July 2015

To assess the crashworthiness of simple wrought magnesium structures, the axial deformation behaviour of different square tubes produced from magnesium alloys AZ31 and ZE10 were numerically investigated under quasi-static compressive loading conditions. Finite-element simulations were conducted to predict and assess the plastic buckling and crush behaviour. The necessary data to determine parameters for the plastic potential were taken from compression tests conducted along different orientations. The yield function Hill48 was selected, despite its inability to capture the strength differential effect. The modelling approach pursued is justified by considering the mechanical loading conditions, the fabrication process of the profiles and its implication on strain anisotropy, balancing achievable accuracy and computational efforts. The simulation results revealed that the material work hardening rates evidenced in uniaxial compression tests influenced the buckling modes as well as the energy dissipation.
Non-Linear Numerical Simulation of Coiling by Elastic Finite Strain Model
Authors: Weisz-Patrault Daniel , Ehrlacher Alain , Legrand Nicolas , Mathey Eliette
Published: July 2015

The coiling process under traction is considered, with an incoming residual stress profile (that can be sufficiently compressive to make the strip buckle): a flatness defect. This paper details a 3D non-linear numerical simulation taking into account the contact of the strip on itself, with a perfect contact law. The model relies on elastic behavior at finite strain because of large rotations. Even though the behavior is elastic, the yield Von Mises criterion is computed and gives information about flatness defects (plastic zones are approximated by zones where the yield stress is exceeded). Furthermore, the paper aims at very short computation times. The modeling strategy relies (for each time step) on two analytical sub-steps. Numerical minimization procedure is used in order apply weak boundary conditions. Results are discussed with respect to a comprehensive Finite Element simulation and good agreement is observed.
Multiobjective Optimization Problem of Dieless Incremental Forming
Authors: Arfa Henia , Bahloul Riadh , Belhadj Salah Hedi
Published: July 2015

Single Point Incremental Forming (SPIF) technology has been announced in the recentpast to manufacture sheet metal products by using Computer Numerical Control machines (CNC). Ithas been frequently used in different fields like the aeronautics. In incremental forming, materialsare submitted to permanent deformation by cold forming to produce a variety of three complicateddimensional shapes. The final form of the parts in sheet metal forming is highly affected by thespring-back and the pillow effect, occurring when the material is set free of the forming constraints.In this sense, the best solution is to adopt a process of multiobjective optimization in which a set ofnumerical simulations can be achieved on the basis of the box-Behnken experimental design. In thisway, the design variables are wall angle, initial thickness, tool diameter and incremental size. Tostudy the geometric characteristics, a cone-shaped part with circular base is considered. This paperaims to identify an overview of multiobjective design optimization of incremental metal formingparameters in order to minimize objective functions of pillow effect, springback and thinning ratesimultaneously. In an attempt to solve fitness functions, the method of Multiobjective GeneticAlgorithm (MOGA) is developed in this investigation. In this case, we should consider severalpoints of the appropriate process parameters which correspond to the best compromises with respectto several antagonistic objectives. As well as, a generation of the approximate Pareto optimalsolutions is presented in this study.
Robot Controlled Rotary Peen Forming by Laser-Assisted Distance Control
Authors: Gottschalk Markus , Bambach Markus , Hirt Gerhard
Published: July 2015

Surface curvature radii required for aircraft fuselage as well as structural components can be produced by peen forming processes. The innovative process idea of Rotary Peen Forming is a modification of the well-known Shot Peen Forming. Here, the impactors are flexibly connected to a rotating hub and thus moving on circular trajectories. As a consequence, there is no need to pressurize and recirculate the shots, as it is essential in Shot Peen Forming. Using a six axes robot, the rotating hub can be guided flexibly. The resulting machine design is more compact compared to traditional Shot Peen Forming.However, in Rotary Peen Forming not only principal stresses but also shear stresses are caused in the deformation zone which has a fundamental influence on the curvature. In order to generate defined curvatures on the workpiece, the capability to precisely adjust the intrusion depth of the impactors is essential.In this paper, a laser-assisted distance control for the Robot Controlled Rotary Peen Forming is introduced. By means of a point laser, the set-up allows for a distance control to adjust and keep a determined intrusion depth. This way, the machine design provides a mechanism to readjust the intrusion depth of the impactors while the desired curvature is formed during the process by the introduced plastic strains at the specimen’s surface. Using the distance control, the resulting curvature is two to four times bigger compared to experiments without a readjustment of the intrusion depth.
Influence of a Single Bend in the Bumping Process of Large Radius Air Bending
Authors: Vorkov Vitalii , Aerens Richard , Vandepitte Dirk , Duflou Joost R.
Published: July 2015

Bump bending or step bending is a forming technique that allows making large radius bends in a sheet metal part by means of a series of bends performed close to each other. The bump bending process has been studied by means of both an experimental campaign and finite element analysis. High-strength steel Weldox 1300 and a punch of radius 30 mm have been used. The finite element calculations have been performed with Abaqus using the solid formulation and Implicit/Explicit solvers. The results of the finite element analysis have been validated experimentally by monitoring the bending process using a camera system aligned with the bending line. Experiments were performed on a press-brake with a capacity of 50 metric tons. Deflections of a sheet during and after bending have been measured using the images recorded by the camera. In order to investigate the influence of a new bend on a previously formed bend, experiments have been performed with different distances between two consecutive bends. Based on the experiments, the size of the affected zone for the bend has been measured. The dependence of the distance between two consecutive bends on the resulting global bending angle has been studied. Moreover the influence of the bump distance on the springback has been investigated.
Friction-Spinning - Influence of Tool and Machine Parameters on the Surface Texture
Authors: Lossen Benjamin , Homberg Werner
Published: July 2015

The incremental forming process of “friction-spinning” is suited to the manufacture of functionally graded workpieces made from tubes and sheets with the defined adjustment of material properties. The innovative feature of this new process is the use of process elements from both metal spinning and friction welding. As the workpieces are being processed, friction sub-processes are employed to achieve self-induced heat generation. Compared with conventional spinning processes, this in-process heat treatment permits the extension of existing forming limits and allows more complex geometries to be achieved, together with defined, favorable part properties. These properties, like strength, grain size or surface conditions, can be influenced by the set of specific temperature profiles that prevail during the manufacturing process in combination with the degree of deformation. The temperature profiles can be adjusted by selecting appropriate process and tool parameters in a defined manner. This paper presents the influence of the aforementioned parameters on the surface texture. The results presented start with the analysis of the surface texture development. Following this, the effects of the significant process parameters and tool geometries that give rise to the typical structure and hardness are explained.
Challenges and Process Strategies Concerning Multi-Pass Double Sided Incremental Forming
Authors: Moser Newell , Ndip-Agbor Ebot , Ren Hua Qing , Zhang Zi Xuan , Ehmann Kornel , Cao Jian
Published: July 2015

The design domain of Double Sided Incremental Forming (DSIF) can be enhanced through the use of multipass strategies. The chosen tool gap in multipass DSIF, or multi-DSIF, is dependent on the estimated thickness of the sheet being formed, which is traditionally done through the Sine Law. In this work, a simple modification to the Sine Law is performed so as to prevent the tool gap from approaching zero at regions where the part contains a near vertical wall. Additionally, various multipass strategies regarding the design of the intermediate stages were trialed in an effort to increase geometric accuracy. Increasing the depth between subsequent stages of DSIF was found to provide the best results due to the accommodation of rigid body motion.
Multi-Objective Optimization of Metal Forming Processes Based on the Kalai and Smorodinsky Solution
Authors: Iorio Lorenzo , Fourment Lionel , Marie Stephane , Strano Matteo
Published: July 2015

The Game Theory is a good method for finding a compromise between two players in a bargaining problem. The Kalai and Smorodinsky (K-S) method is a solution the bargaining problem where players make decisions in order to maximize their own utility, with a cooperative approach. Interesting applications of the K-S method can be found in engineering multi-objective optimization problems, where two or more functions must be minimized. The aim of this paper is to develop an optimization algorithm aimed at rapidly finding the Kalai and Smorodinsky solution, where the objective functions are considered as players in a bargaining problem, avoiding the search for the Pareto front. The approach uses geometrical consideration in the space of the objective functions, starting from the knowledge of the so-called Utopia and Nadir points. An analytical solution is proposed and initially tested with a simple minimization problem based on a known mathematical function. Then, the algorithm is tested (thanks to a user friendly routine built-in the finite element code Forge®) for FEM optimization problem of a wire drawing operation, with the objective of minimizing the pulling force and the material damage. The results of the simulations are compared to previous works done with others methodologies.
Numerical Simulation of Spin-Blind-Riveting of Magnesium and Fibre-Reinforced Plastic Composite
Authors: Kaboli R. , Podlesak F. , Mayr Peter
Published: July 2015

Spin-blind-riveting
(SBR)
is
a
newly
developed
joining
process,
which
combines
the
advantages
of
conventional
blind
riveting
and
flow
drilling
screws.
With
this
technology,
it
is
possible
to
join
two
different
materials
by
one-sided
accessibility
without
the
need
of
pre-drilling
holes.
This
complex
process
cannot
be
simulated
by
2D
finite
element
method.
Therefore,
a
more
realistic
3D
finite
element
model
for
the
SBR
process
is
developed
using
the
commercial
software
package
ABAQUS.
The
applicability
of
this
work
is
demonstrated
for
joining
magnesium
alloy
AZ31B
and
carbon-fibre
reinforced
plastics.
Dynamic
effects,
thermomechanical
coupling,
material
damage
laws,
and
contact
criterion
were
taken
into
account
in
the
model.
The
Johnson–Cook
material
constitutive
equation
was
used,
considering
the
effects
of
strain,
strain
rate,
and
temperature
on
material
properties.
Finally,
through
simulation,
the
joint
formation,
stress
distribution
and
riveting
temperature
were
obtained.
Furthermore,
a
series
of
experiments
were
carried
out
to
validate
the
simulation
results.
The
numerical
results
are
in
a
good
agreement
with
the
experimental
results
and
confirm
the
promising
properties
of
SBR
joints
between
metal
and
fibre-reinforced
plastics.
A Comparative Study on the Formability Prediction of Steel Sheets by Anisotropic Models Based on Associated Flow Rule and Non-Associated Flow Rule
Authors: Lian Jun He , Ahn Deok Chan , Chae Dong Chul , Münstermann Sebastian , Bleck Wolfgang
Published: July 2015

A comparative study on the formability prediction of a ferritic steel sheet by anisotropic models based on associated flow rule and non-associated rule is carried out. The uniaxial tensile tests along seven directions of the sheet from rolling direction to transverse direction with an interval of 15° are performed for the anisotropic yield stress and r-value. For the biaxial stress state, both bulge test and punch test are performed. The BBC2003 based on the associated flow rule is employed and its anisotropic parameters are calibrated to the yield stresses and r-values from the tensile tests along rolling direction, transverse direction and diagonal direction and the biaxial test. The non-associated quadratic Hill48 model is also calibrated to the same set of experimental data. Similar level of the predicative capability on the yield and plastic deformation directionality by the associated and non-associated based models is observed. With the common basis on the anisotropic plasticity characteristics, they are combined with the Marciniak–Kuczynski (MK) model to predict the formability of the steel sheet and distinct difference in the prediction is observed between the two models.
Modelling of Laser Welding Process on Thermoplastic Composites
Authors: Cosson Benoit
Published: July 2015

Thermoplastics composites for structural applications are under growing development from the aerospace (carbon fibers with PEI, PPS or PEEK matrices mainly) to the automotive industry (glass and carbon fibers with PP, PA). The plastic deformation they can provide and the assembly facilities through welding techniques are well appreciated. Among the available welding technics, laser offers the possibility to assemble materials in a precise and localized manner and can be easily automated. However, due to the presence of continuous fibers at a high fiber volume fraction, propagation of the laser energy through the composite that present local variation of fiber volume fraction is not as straight forward as in a homogeneous material. Modelling of the laser welding of a thermoplastic/continuous glass fiber is considered here. The study takes into account the microstructure of the composite in order to evaluate changes in local energy absorption and diffusion directly linked with the thickness. Modelling of the welding process is developed from the representation of the moving laser beam. The beam propagation through the composite thickness is considered thanks to the ray tracing method. The proposed method is able to optimise the welding process in function of the microstructure and the material properties of the welded parts.
Numerical Heat Treatment Modelling of Fine Blanked Sheet Metal and Experimental Validation
Authors: Peterli Maurice , Manopulo Niko , Hora Pavel
Published: July 2015

Heat treatment is one of the major sources of dimensional inaccuracy in the manufacturing of fine blanked parts. Tools and equipment often need to be iteratively corrected in order to achieve the desired quality. Numerical simulation of the heat treatment process can substantially reduce these efforts. The simulation accuracy on the other hand is strongly dependent on the accurate characterization of the thermo-mechanical boundary conditions as well as material properties. The present contribution aims to propose a novel approach in the calibration of numerical models by using a modified Jominy test as well as heat treatment experiments with parts having residual stresses from a bending process. The results are validated by comparing numerical phase content and hardness values with the corresponding experiments.
Research of Dynamic Recrystallization Processes in Heat-Resistant Ni-Based Alloy
Authors: Zotov Oleg G. , Shamshurin Aleksey I. , Kononov Aleksander A. , Naumov Anton A.
Published: July 2015

Dynamic recrystallization processes in heat-resistant Ni-based alloy was investigated depending on temperature, strain rate and deformation ratio. Recrystallization intensity is determined by the temperature and deformation conditions. The factors that increase the degree of dynamic recrystallization include temperature and amount of strain increasing, as well as decreasing of strain rate. Increasing the volume fraction of recrystallized structure causes a uniform fine-grained structure.
Experimental and Numerical Analysis of Residual Stress in Cast Aluminum Alloy after FSP Process
Authors: Weglowski Marek S. , Sedek Piotr , Hamilton Carter
Published: July 2015

The effect of FSP modification of cast aluminum alloy AlSi9Mg on residual stress are presented. The numerical results are compared with the residual stresses experimentally measured by the trepanation method. Experimental results show that the residual tensile stresses are higher on the advancing side than on the retreating side. The simulation successfully captures the asymmetric behavior of the residual stress profile, and the predicted maximum residual stress values show relatively good agreement with the experimental values. The simulated profile, however, is more narrow than the experimental profile, yielding a smaller region of residual tensile stresses around the process zone than experimentally observed
The Impact of Torsion on the Bending Curve during 3D Bending of Thin-Walled Tubes - A Case Study on Forming Helices
Authors: Staupendahl Daniel , Becker Christoph , Tekkaya A. Erman
Published: July 2015

Chassis or cabin designs in the transportation sector are currently manufactured out of several single structural elements. To save handling steps and energy intensive joining processes and furthermore support lightweight design, bending processes can be used that offer the direct production of structural parts that incorporate the functionality of several single elements. In recent years, several processes for the kinematic bending of three-dimensional tubes and profiles have been developed. Additionally, three-roll push bending has gained in importance in manufacturing three-dimensional tubes. In this kinematic process, three-dimensional bending is achieved by continuously changing the bending plane relative to the workpiece during the forming process. Several studies exist that investigate the mechanisms that lead to three-dimensional bending contours. These were, however, based on the generation of empirical models, e.g. characteristic maps. Up until now, no analytical model exists, which describes the process of bending three-dimensional tubes in a comprehensive manner, especially taking into account tube torsion. In the following case study, the tube rotation needed to produce helices is measured and compared to helix radii and helix height. The results were subsequently used to set up an analytical model, which, first of all, describes the tube rotation needed to produce the torsion of the investigated helices and, more importantly, can be generalized to describe the tube rotation needed for the torsion of arbitrary bending curves.
Influencing the Forming Limits in Air Bending Using Incremental Stress Superposition
Authors: Chatti Sami , Weinrich Andres , El Budamusi Mohamed , Becker Christoph , Maevus Frauke , Tekkaya A. Erman
Published: July 2015

High springback and limited forming limits of modern high strength steels are a big challenge in manufacturing engineering. Both aspects are crucial in sheet metal bending processes. Different modifications of the air bending process have already been developed in order to reduce springback and also to increase the forming limits of materials. The innovative process of incremental stress superposition on air bending, developed at the IUL, is an alternative to conventional processes. Studies of this new process alternative show a positive effect on the considerable reduction of the sheet metal springback and extension of forming limits. Using the principle of incremental stress superposition leads to several advantages compared to conventional bending processes like die bending, bending with an elastomer tool, or three point bending. The bending force and, therefore, the consumed energy during air bending with incremental stress superposition are much lower. This paper presents the new process alternative and shows the latest investigation results.
Lode Parameter Dependence and Quasi-Unilateral Effects in Continuum Damage Mechanics: Models and Applications in Metal Forming
Authors: Soyarslan Celal , Richter Helmut , Bargmann Swantje
Published: July 2015

This work concerns with two successive modifications of the Lemaitre's damage model tomeet the requirements of formability prediction for today's modern steels. The first one is the quasiunilateraldamage evolution which modifies the damage driving force by scaling the elastic energyrelease rate due to compressive principal stress components. The second one is the shear modificationby which the damage rate is multiplied by a normalized maximum shear stress dependent factor.With the assumption of non-rotating principal axes of deformation, proportional strain paths and rigidplasticity, closed form expressions for the isochronous fracture surfaces are derived for each modelvariant and resulting surface plots at various spaces are compared. The findings show that the formermodification not only remedies the pathological reflective symmetry of the fracture surface acrossthe plane with vanishing stress triaxiality ratio, but also allows hindering fracture under uniaxialcompression. The latter modification by adding a direct Lode parameter dependence to the damageevolution function allows prediction of premature fracture at generalized shear stress states, a conditionobserved for certain advanced high strength metallic sheets. Parameter calibration is realized foreach model variant using the experimental data from the literature. It is shown that the fracture modelwith both the shear modification and the quasi-unilateral enhancement shows the best fitting quality.Finally, the models are implemented as user subroutines for ABAQUS/EXPLICIT and used in predictionof initiation and propagation of cracks for a series of deep-drawing punch tests. A good agreementwith the outputs reported in the literature is observed in terms of the shear damage occurrence zonesas well as corresponding punch force-displacement diagrams.
Sheet Metal Rolling of Molybdenum: Thermo-Mechanical FEM Simulations
Authors: Schäfer Jonathan , Schober Michael , Plankensteiner Arno
Published: July 2015

Metal forming simulations based on the finite element method are a frequently used tool for the prediction of the deformed shape, material state and reaction forces. The most critical prerequisite for any reliable result is a reasonable description of the constitutive behavior of the underlying material. The presented work focusses on the latter for the case of molybdenum via advanced formulations for the temperature and strain rate dependence. The quality of the results is compared for several approaches. Sheet metal rolling serves as an example application. Verification is based on comparison with data from industrial processes.
Technological Investigation of Clad Sheet Bonding by Hot Rolling
Authors: Szabó Gábor , Mertinger Valéria , Zupkó István , Mikó Tamás
Published: July 2015

In this study the bonding properties of three layer-plated aluminum sheets are investigated. The alloys applied in specific layers were as follows: AlMn1Si0.8 (core alloy) and AlSi10 (liner). The bonding was performed on a Von Roll experimental roll mill using hot rolling. The experimental temperatures were 460, 480 and 500 °C, respectively. To qualify bond development, T-peel test was used. The test was performed using an Instron universal material testing machine. T-peel test can be well used for the qualification of bond strength as the peel-off force and bond value developed on contacting surfaces are proportional. In addition to T-peel test, optical micrographs and SEM micrographs were also captured, in which typical bond faults were sought. The study aims at modelling the technology used in industry and exploring some typical bond faults as well as suggesting the causes generating these and their remedy. The impact of surface roughening before heating was studied as well. Also, the study aimed at confirming the suitability of T-peel test to qualify bond strength.
First Experimental and Numerical Study on the Use of Sheet Metal Die Covers for Wear Protection in Closed-Die Forging
Authors: Rosenstock Dirk , Segebade Eric Thore , Hirt Gerhard
Published: July 2015

To reduce the failure of dies by abrasive wear, mechanical fatigue and thermal fatigue in closed-die forging usually measures like nitriding, deposition of ceramic layers by Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD) or deposition welding are used. However, after some time wear appears and the dies have to be replaced. A new concept implements sheet metal die covers, which are placed on the die engraving during forging and will absorb abrasive wear, thermal and mechanical load. The inexpensive cover will be replaced quickly by a new one after it is worn-out. This concept is regarded in a first numerical and experimental study by comparing a covered die (C) and an uncovered die (U) for the production of the same part. A one-time use of the die cover showed a reduction of the peak temperature by 140 K and of the temperature amplitude by 37 %. The temperature reduction and the increase of inner radii of the engraving to fit the 1mm thick die cover doubled the expected die life time. The experiment showed that the soft deep drawing steel DC04 is not suitable in the current case for a die cover and a higher strength sheet metal should be applied.
Measurement of Radial-Axial Rolled Rings by Using Image Processing and Thermography
Authors: Husmann Tobias , Kreimeier Dieter
Published: July 2015

Radial-axial ring rolling is a hot forming technology to produce seamless rings, which are used in several industrial sectors, such as gear manufacturing, aviation and aerospace as well as transportation and energy. The use of allowances in the industrial production of these rings via radial-axial ring rolling is still very common to ensure that the rings’ final dimensions are reliably inside the given tolerances. Rolling a ring with allowances causes a lot of additional costs, for example purchasing and processing of the extra material.To enable ring manufacturers to reduce allowances for periodical ring errands, a rating of rings directly after the rolling process is benefical. In this paper the approach using image processing and thermography to detect the outer diameter and the surface temperature of the rolled ring to allow for a rating will be presented.
Mechanical Properties in Hot Forged Steel Parts in Relation to Properties in Corresponding Parts Made by Casting Solely
Authors: Valberg Henry , Langøy Morten , Nedreberg Mette
Published: July 2015

It is a common understanding that hot forging will improve the properties of a steel part in relation to when the same part is made by casting solely. A study has been performed where two crank pin disks of a particular steel alloy, one hot forged and the other cast, both in quenched and annealed condition, have been tested using a new innovative “eye”-specimen bending test. The used test procedure is described, and it is shown that the forged and the cast material will collapse and beak down in very different way in this test.
Simulation and Modeling of Sintering Process for 316L Stainless Steel Metal Injection Molding Parts
Authors: Sahli Mohamed , Gelin Jean Claude , Barrière Thierry
Published: July 2015

The metal injection molding (MIM) process allows the manufacturing of small and very complex metallic components. The metal injection molding processing combines the shaping capability of polymer injection molding with the large material variety of metals and ceramics. This paper discusses in detail the development of a numerical model capable of simulating micro-structural evolution and macroscopic deformation during sintering of complex powder compacts. A sintering model based on elastic–viscoplastic constitutive equations was proposed and the corresponding parameters such as bulk viscosity, shearing viscosity and sintering stress were identified from dilatometer experimental data. The constitutive model was then implemented into finite element software in order to perform the simulation of the sintering process. The numerical simulation methods being compared against results of the sintering experiments. The experimental data were obtained from sintering of 316L stainless steel powders.
The Bending Behaviour Characterisation of Thermoplastic Prepregs and its Influence on the Wrinkling
Authors: Liang Biao , Hamila Nahiene , Boisse Philippe
Published: July 2015

The bending deformation of thermoplastic prepregs is one of the key deformation modes in the thermoforming due to its crucial role in the wrinkling occurrence. The influence of temperature is of main importance because the viscous effect of resin is temperature dependent and prepregs thermoforming is usually performed closed to resin’s melting point. The currently available bending test devices are not adapted for thermoplastic prepregs since these devices can only be operated at room temperature. To solve this problem, a new cantilever test with an optical measuring performed in an environmental chamber is proposed. The bending properties of PPS-carbon satin prepregs are measured at a series of high temperatures. It’s shown that the bending stiffness of the fore-mentioned pepregs is strongly affected by the temperature and shows a non-linear bending behaviour. The measured bending properties are used to simulate a thermoforming process. The influence of bending properties on the simulation results, especially to the wrinkling is presented as well.
Comparison of 15Cr-15Ni Austenitic Steel Cladding Tubes Obtained by HPTR Cold Pilgering or by Cold Drawing
Authors: Courtin L. , Urvoy Stephane , Bossu Didier , Bosonnet Sophie , Tabarant Michel , Kedjar Bouzid , Olier Patrick , Thilly Ludovic
Published: July 2015

Due to their high void swelling resistance, work-hardened titanium stabilized austenitic steels have been chosen as cladding material for sodium cooled fast reactor. In this study, HPTR cold pilgering process is compared to cold drawing at the last shaping step of the tube processing. The effects of the cold work accumulation and heat treatments are studied in connection with the microstructure (grain size), the hardness and the texture. The following results were found:- As larger amount of cold work can be applied by HPTR cold pilgering, a lower number of intermediate heat treatments are required. In addition, the bending of the tube is significantly reduced after each pass for this process allowing for a limitation of the straightening operations.- For both processes, optical micrographs show micrometric titanium carbide precipitates and the presence of deformation twins on a few grains on the final tube. A significant grain size refinement from ≈45 μm to ≈17 μm can be obtained by reducing annealing temperature from 1403K down to 1353K. For the latter, the precipitated mass fraction measured by selective dissolution of the alloy matrix is the largest, revealing a possible negative impact on swelling under irradiation.- Through-wall Vickers hardness profiles show an increase of the hardness at the outer diameter for HPTR cold pilgering whereas the hardness profile remains continuous for cold drawing. It is found that the Q-factor has an influence on these wall-thickness hardness profiles.- For each process, neutron diffraction measurements on finished tubes reveal two main fiber texture components 〈111〉 and 〈100〉 parallel to the tube axis with differences in their relative intensities.
Thermoforming Modelling and Simulation of Multilayer Composites with Continuous Fibre and Thermoplastic Matrix
Authors: Maldonado Eduardo Guzmán , Hamila Nahiène , Boisse Philippe , Wang Peng , Chaudet Philippe
Published: July 2015

CFRTP prepreg laminates thermoforming (Continuous Fibre Reinforcements and Thermoplastic Resin) is a fast composite manufacturing process. Furthermore the thermoplastic matrix is favourable to recycling. The development of a thermoforming process is complex and expensive to achieve by trial/error. A simulation approach for thermoforming prepregs thermoplastic is presented. This model is based on a continuous approach. A hyperelastic behaviour is associated with dry reinforcements. The hyperelastic potential is built from the contribution of three principal deformation modes that are supposed to be independent. A nonlinear viscoelastic model based on the generalization of simple rheological models is associated with the in-plane shear mode. The finite element simulation of a thermoforming example using this model is presented.
Development of a New Ecological Lubrication System for Sheet Metal Forming Based on CO2 in Liquid
Authors: Singer Markus , Liewald Mathias , Feuer Anne
Published: July 2015

Ecological aims and political requirements today are increasing demands on lubricants in sheet metal forming and their impact on environment. For that reason, metal forming industry wants to reduce the amount of lubricants containing polluting additives with a long-term goal of avoiding lubrication entirely. Additionally, dry metal forming will reduce the cleaning steps after the forming operation. This paper shows a new tribological system in which lubrication is replaced by CO2 in a liquid state. Here, CO2 is expanding directly into contact area between workpiece and tool surface and changes its state from gas to solid. The combination of this particular dry ice as well as the pressure of approximately 57 atm affects resulting friction coefficient significantly. After forming operation, CO2 medium vaporizes and a dry component can be used immediately for the next process steps. In this case, the lubricant is applied directly into the contact area. Therefore, laser drilled micro holes are located in the contact area of the tool. Very first gained experimental results disclose such feasibility, the effects and the potential of this new lubrication system at that moment is based on strip draw tests. Different numbers of micro holes are examined to support blank holder pressure ranging between 5 MPa and 6 MPa. In this investigation a mild strength steel DC04 is used as sheet material. This knowledge is aimed to be used for further investigation and later transfer into real deep and stretch forming processes.
Complementary Approaches for the Numerical Simulation of the Micro-Plasto-Hydrodynamic Lubrication Regime
Authors: Hubert Cédric , Dubois André , Dubar Laurent , Laugier Maxime , Legrand Nicolas , Boman Romain , Ponthot Jean Philippe , Carretta Yves
Published: July 2015

This paper presents recent investigations in the field of lubricant escapes from asperities. This phenomenon, named Micro Plasto Hydrodynamic Lubrication (MPHL), induces friction variation during metal forming processes. A better understanding of MPH lubrication would lead to a better management of friction, which is a central element in most sheet metal forming processes. To fulfil that goal, experiments were conducted in plane strip drawing using a transparent upper tool in order to observe lubricant flow around macroscopic pyramidal cavities. These experiments were then numerically reproduced with two complementary Finite Element models. The numerical results are discussed in this paper and show good agreement with experimental measurements.
Analysis of Steel Phase Transformations Using a Multiscale Transient Model
Authors: Barroqueiro B. , Dias-de-Oliveira João , Andrade-Campos António
Published: July 2015

Multiphase steels offer impressive mechanical properties. However, their characterization still represents a challenge. In a quenching processes, phenomena such as undesirable strains or residual stress are inevitable and can be the cause for non-admissible final parts. Microstructural phase transformations generally magnify the problem. This fact leads to the need of numerical tools capable of quantifying these residual stresses, due to the non-existence of efficient non-destructive experimental procedure capable of measuring them. In this work, a numerical multiscale transient model, that uses the Asymptotic Expansion Homogenisation (AEH) method combined with finite element method (FEM), is proposed. The implementation of the AEH method is carried out using the commercial program Abaqus, considering an uncoupled and quasi-static transient problem with implicit time integration. Within the homogenisation method, the existence of two distinct scales is assumed, defining a micro and a macroscale. Within the smaller scale, the evolution of a steel periodic microstructure is analysed in detail and an equivalent homogeneous material model is established for macroscopic use. However, the microstructural evolution leads to the need of new equivalent homogeneous models in order to predict the macro response. Consequently, several mechanical, thermomechanical and transient thermal homogenization procedures are carried in order to establish different equivalent homogeneous models.
Comparison of the Johnson-Cook and VPSC Models to Describe the Constitutive Behaviour of Ti-6Al-4V in an Implicit Finite Element Scheme
Authors: López Jesús Galán , Verleysen Patricia , Naghdy Soroosh , Kestens Leo A.I.
Published: July 2015

The use of finite element simulations has become one of the main tools of the mechanical engineer. The method is applied to the analysis and design of engineering structures, the study of manufacturing processes and even to perform virtual experiments. Traditionally, the constitutive laws chosen for finite element analysis have been as simple as possible, mainly due to the limitation imposed by the available computing power. However, the development of more powerful computers and more efficient methods is opening the possibility of using more elaborated (and, most often, more accurate) material models. In particular, polycrystal models capable of predicting not only the mechanical behaviour of the material, but also of the evolution of properties with increasing strain, are particularly well suited for the simulation of forming processes, for which a precise knowledge of the properties of the resulting product is of paramount importance.The present work studies how the Visco Plastic Self-Consistent model (VPSC) can be used in combination with the implicit finite element package Abaqus/Standard to simulate the behaviour of Ti-6Al-4V sheet, and compares it with the more common (and much simpler) Johnson-Cook model. More specifically, the goal of this study is to determine whether or not, with using similar experimental calibration data, the use of the much more complex polycrystal model, justifies the increased complexity and execution time. Using standard tensile experiments at different strain rates, the parameters of the VPSC and Johnson-Cook models are fitted using a minimization method. Then, both models are used in finite element simulations and the results given by both models are compared.
Modelling Microstructure Evolution in Polycrystalline Aluminium – Comparison between One- and Multi-Parameter Models with Experiment
Authors: Kreyca Johannes , Falahati Ahmad , Kozeschnik Ernst
Published: July 2015

The plastic response of an aluminium alloy type A6061 is modelled using different state parameter‐based approaches. Several of these models (one‐ and two‐parameter models) have recently been implemented into the thermo‐kinetic software package MatCalc. In the present work, a model based on the Kocks-Mecking-law is used to investigate the capabilities of one and two parameter approaches in order to model experimental data. The experimental work presented here is performed on a Gleeble 1500 thermo‐mechanical simulator for different natural ageing times. We demonstrate that one‐parameter models offer a ready‐to‐use and easy‐to‐calibrate solution for a rough correlation between flow‐curve data and microstructure. Such models describe the evolution of the average dislocation density in time. In many practical cases, a single state parameter is insufficient and multi‐parameter models must be utilized, for instance, with consideration of separate populations of dislocations in walls and subgrain interior. These approaches can consistently represent the deformation behaviour of alloys in a variety of conditions with respect to temperature and strain rates.
Tailored Sheared Blanks Produced by Incremental ECAP
Authors: Rosochowski Andrzej , Olejnik Lech , Rosochowska Malgorzata
Published: July 2015

Incremental equal channel angular pressing (I-ECAP) is a process used for production of continuous ultrafine grained bars, plates and sheets. Normally the thickness of the processed billet is kept unchanged in consecutive passes to enable repetitive insertion into the same die. This is achieved by controlling the bottom dead centre of the reciprocating punch. However, if a final product requires being thinner and therefore longer, the bottom position of the punch can be lowered before the last pass. Going further, the bottom position of the punch can be changed during the process, which opens up a possibility to vary billet thickness along its length. Such a product, especially sheet, can serve as a preform for further metal forming operations and is known as tailored blank. This paper will show examples of varying thickness sheets produced by different configurations of I-ECAP. Experimental and finite element results will be presented.
Some Issues Regarding Finite Element Modelling of Micro-Electrical Discharge Machining Aided by Ultrasonics
Authors: Ghiculescu Daniel , Marinescu Niculae , Alupei Ovidiu , Carutasu Nicoleta
Published: July 2015

The paper deals with finite element modelling (FEM) of the process of micro-electrical discharge machining of micro-holes aided by ultrasonic longitudinal oscillations of workpiece (μEDM+US). FEM of the process comprises two components: the thermal one due to μEDM removal mechanism, and the ultrasonic one caused by cavitation effect generated inside the lateral working gap. The FEM results obtained are validated by experimental data in terms of craters dimensions produced by single discharges, leading to optimization strategy of process parameters.
Development and Characterization of Polymer Mixture (Binder) Based on Polyethylene Glycol (PEG) for a Superalloy A-286 to Powder Injection Moulding (MIM) Process
Authors: Royer Alexandre , Gelin Jean Claude , Barrière Thierry
Published: July 2015

Metal injection moulding (MIM) has over the past decade established itself as a competitive manufacturing process to produce in large quantities small precision components with complex shape which would be costly to produce by alternative methods. In this process, during the injection phase, segregation appears in the feedstock and defects will be appears in the component during the sintering. To limit this effect, during decades a vast variety of binder systems have been developed. Binder systems are formulated as a mixture of different organic or inorganic substances with several functions. Binder system has the main commitments of giving the necessary rheological behavior to the feedstocks for injection moulding to transport the powder particles into the mould cavity and the cohesion of the green part.In this paper a study of the behavior of binders based on polyethylene glycol (PEG) and feedstocks based on superalloy A-286 powder were investigated by Fourier Transform InfraRed spectroscopy (FTIR) coupling with rheology. This methodology permits to compare the rheological behavior of the materials with the thermal behavior of the binder at a temperature close to the temperature of injection. Analyzes was made for the mixing and injection process. It is shows relationship between interactions and miscibility of polymer and influences on the rheological and mechanical behavior. All methodologies revealed no chemical interactions between the powder and the binder. This result shows the formulation of binder for the superalloy A-286 is not homogenous and the PEG is degraded under mixing and injection process conditions of this kind of formulation of feedstock.