Forming Processes

Recently non-proportional deformation has received increased attention from researchers working in the area of experimental and computational modeling of metal deformation. However, most of them are numerical in nature with limited experimental data available, making it further difficult to model non-proportional deformation. In the present work, two-stage uniaxial tests, along with uniaxial cyclic and biaxial tests for different stress ratios, have been performed to evaluate deformation behavior of ultra-low carbon high strength automotive steel. Behaviors like cross-effect and hardening stagnation, which are attributed to the evolution of complex dislocation structures, were observed in this steel. It was also noticed that this steel exhibits tension-compression asymmetry. As for constitutive modeling, a modified asymmetric yield function is proposed to be used with a combined isotropic-kinematic hardening model. Also methods to account for the hardening stagnation during reverse loading and the cross-effect during two-stage deformation are proposed. The resulting constitutive model showed reasonably good agreement with experimental results.

L'évolution de la microstructure du poly(ethylene terephathalate) durant l'opération de soufflage a une influence importante sur les modifications de propriétés mécaniques . Pour mener à bien la simulation du procédé de soufflage par biorientation, il est nécessaire de prendre en compte ces évolutions. Dans une première partie, nous présentons le modèle de comportement (Poitou, 2001) dans le cas simple de viscosité en loi-puissance. Le modèle est identifié sur la base d'essais de traction uniaxiale et biaxiale régulés thermiquement. Dans la seconde partie, le problème axisymétrique de soufflage de membrane est résolu par éléments finis. Les simulations sont comparées aux préformes soufflées avec un succès encourageant compte tenu de la simplicité de la modélisation.

Abstrakt Tato bakalářská práce je rozdělena do dvou zpřízněných okruhů. Jeden se věnuje fotografii 19. století z širšího hlediska, sleduje především její snahy o prosazení uměleckého statutu pomocí přisvojování tradičních uměleckých pravidel i kritérií hodnocení. Tento základ následně posloužil ke zhodnocení tzv. ušlechtilých tisků v hlavní části práce. Na techniky ušlechtilých tisků není nahlíženo jen z hlediska technologie, ale také skrze problematiku amatérské fotografie a její institucionální zázemí či dobovou teorii umělecké fotografie. Práce představuje nejdůležitější zástupce tohoto oboru v českém prostředí a na konkrétních ukázkách demonstruje rozsah výrazových možností tvárných procesů i poloh jejich obrazového působení. Klíčová slova dějiny fotografie, dějiny umění, umělecká fotografie, piktorialismus, fotoamatéři, kluby fotografů amatérů, fotografové profesionálové, ušlechtilé tisky, tvárné procesy, uhlotisk, gumotisk, olejotisk, bromolejotisk Abstract This thesis is devided in two related fields. First of them observe photography in the 19th century in a broader context. Is focused on photography which borrow traditional art rules and aspects in aim to get an equal status between fine arts. This first part helped valuate technics of so-called photographic processes in the second part of the thesis. This domain of photography is concentrated not only on technology but also on problems of amateurism or a theory of artistic photography of the time. The last chapter presents the most important Bohemian representatives of this profession and demonstrates a broad scale of artistic posibilites on concrete samples.

Fineblanking combined with various metal-forming processes has been an important sheet metal forming process nowadays in industry. However, there are tremendous difficulties in process planning especially strip layout design. It still depends on the engineer's experience and know-how. This paper presents a knowledge-based system for strip layout design in fineblanking. The system speeds up the design process by automating the strip layout design. An example is included to show the system is effective for industry application.

Experimental results and numerical calculations show that multi-pass equal-channel angular drawing (ECAD) will be of little technical use because of the important cross-sectional reduction accompanying the shear deformation imparted by the process. Continuous equal-channel deformation without section reduction can only be performed by techniques based on rolling impulsion or hydrostatic ECA pressing. Ó

Recently non-proportional deformation has received increased attention from researchers working in the area of experimental and computational modeling of metal deformation. However, most of them are numerical in nature with limited experimental data available, making it further difficult to model non-proportional deformation. In the present work, two-stage uniaxial tests, along with uniaxial cyclic and biaxial tests for different stress ratios, have been performed to evaluate deformation behavior of ultra-low carbon high strength automotive steel. Behaviors like cross-effect and hardening stagnation, which are attributed to the evolution of complex dislocation structures, were observed in this steel. It was also noticed that this steel exhibits tension–compression asymmetry. As for constitutive modeling, a modified asymmetric yield function is proposed to be used with a combined isotropic–kinematic hardening model. Also methods to account for the hardening stagnation during reverse loading and the cross-effect during two-stage deformation are proposed. The resulting constitutive model showed reasonably good agreement with experimental results.

The influence of deformation temperature on the hot rolling textures of aluminium alloys has been investigated by channel die compression tests on All %Mg-l%Mn polycrystals and oriented single crystals in the temperature range 20&4OO"C. Quantitative texture measurements on the polycrystalline samples demonstrate a substantial increase in the { 1 lO}(172) "Brass" component at higher temperatures together with a small but significant amount of "near-cube" orientations. These texture variations with temperature occur in the absence of recrystallization. The single crystal experiments show that these textures can be related to the onset of non-octahedral slip in Al and Al-l%Mn under hot working conditions of high strains and medium strain rates. The "near-cube" orientations tend to be stabilized by slip on {I lo} planes while the "brass" orientation undergoes a substantially reduced LIZ (in-plane) shear. This behaviour is uredicted bv a rate sensitive crvstal nlasticitv model assuming f 111 j and f 1121 slin in accordance with the experimental results at 400°C

This paper focuses on numerical simulation of single point incremental forming (SPIF) process. Via a user-defined material (VUMAT) subroutine is employed to implement a non-associated mixed isotropic-kinematic hardening material model. The accuracy of the proposed non-associated flow rule model to predict the material behavior and the anisotropy in sheet metal forming simulations is examined by comparing numerical results with experimental measurements. The suggested model shows good agreement with experimental results compared to the associated Hill_R and Hill_S models. The proposed non-associated flow rule demonstrates a good efficiency to simulate the springback after sheet metal forming and to predict the thickness variation during incremental sheet metal forming process. The present non-associated model can improve the prediction of both anisotropic and hardening behaviors of material used in numerically controlled sheet metal forming technology. Keywords Single point incremental forming. Non-associated model. Mixed hardening material model. Anisotropy

During the cooling process in injection molding, heat fluxes in the mold are generally lower in inner regious of corners. This asymmetric cooling generates a corner deformation: the part angle is smaller than the mold one. This phenomenon is known to be the main cause of corner warpage in injection molding of thermoplastics. The second phenomenon leading to a corner warpage has firstly been described for thin compression molded SMC parts and is called "spring forward effect". Due to the large fiberlength / part-thickness ratio, most fibers in SMC parts are oriented in the planar direction leading to higher thermal expansion coefficients in the thickness direction as compared to those in the surface direction. When the part cools after polymer curing, a decrease of the enclosed angle in a corner occurs after mold extraction. Because of mold restraints for injection molded thermoplastic parts, the shrinkage in the thickness direction is much larger than the in-plane shrinkage and so the spring forward effect can appear. An experimental study and a two dimensional thermo-viscoelastic calculation of a polymer corner deformation in a mold performed on Abaqus code were carried out. We show that the spring forward effect is generally the major source of corner deformation for injected thermoplastic parts.

During the cooling process in injection molding, heat fluxes in the mold are generally lower in inner regious of corners. This asymmetric cooling generates a corner deformation: the part angle is smaller than the mold one. This phenomenon is known to be the main cause of corner warpage in injection molding of thermoplastics. The second phenomenon leading to a corner warpage has firstly been described for thin compression molded SMC parts and is called "spring forward effect". Due to the large fiberlength / part-thickness ratio, most fibers in SMC parts are oriented in the planar direction leading to higher thermal expansion coefficients in the thickness direction as compared to those in the surface direction. When the part cools after polymer curing, a decrease of the enclosed angle in a corner occurs after mold extraction. Because of mold restraints for injection molded thermoplastic parts, the shrinkage in the thickness direction is much larger than the in-plane shrinkage and so the spring forward effect can appear. An experimental study and a two dimensional thermo-viscoelastic calculation of a polymer corner deformation in a mold performed on Abaqus code were carried out. We show that the spring forward effect is generally the major source of corner deformation for injected thermoplastic parts.

The deep drawing of a very unbalanced fabric on a hemispherical shape is performed both experimentally and by a numerical simulation. The shape obtained depends mainly on the mechanical behaviour of the fabric and is highly non-symmetric. The simulation of the forming process is performed using finite elements based on the tensile energy of each yarn. This approach leads to very simple expression of the interior load vectors used in the explicit dynamic approach. The result of the simulation correctly describes the shape after forming and its non-symmetry. Such a result could not have been obtained by a fishnet method classically used for fabric draping.

The effect of oxygen on the work function of tungsten electrodes has been studied. As expected, it was found that the presence of the metastable A15 (β) phase is correlated with oxygen concentration. Tungsten films with minimal oxygen content contain only the stable bcc (α) phase. However, after a forming gas anneal was performed on MOS capacitors made from these films, it was found that the β phase converts completely to a strained α phase. Despite this uniform transformation, it was found that the work function of the tungsten gate electrodes varies from 4.54-4.91 eV, depending on the partial pressure of oxygen that the tungsten films were grown in. This is a novel work function tuning technique, and it is hypothesized that the observed variation is due solely to the incorporation of oxygen from the growth environment into the W layer at the SiO 2 /W interface.

Three-dimensional (3D) bulk forming simulation by reproducing kernel particle method is presented in this paper. For increasing computational efficiency a lower order integration scheme is proposed and a general benchmark test for explicit non-linear program is developed, to verify the correctness and the accuracy of the present scheme. A particle to segment contact algorithm for treatment of the contact between deformable and rigid bodies is also presented. The algorithm is found to be very effective and suitable for 3D bulk forming analysis.

The development of hot rolling textures in f.c.c. metals has been simulated numerically using a viscoplastic crystal plasticity model assuming different combinations of octahedral and non-octahedral slip systems for several grain-matrix interaction schemes. A combination of quasi-pencil glide and the Lebensohn and Tom6 self-consistent model [Acta Metall. Mater., 1993, 41, 261 l] gives a satisfactory simulation of typical hot rolling f.c.c. texture components, i.e. well balanced P-fibre components and a small amount of "Cube". 8 1997 Acta Metallurgica Inc.

Samples obtained from hot-rolled, low-carbon steel strips were subjected to a series of microstructural analyses to study the mechanisms responsible for their differences in mechanical behavior. The strips used in this study had the same composition and thickness but were produced in two different hot-rolling mills. The first one is a conventional second-generation mill, where the steel is cast in ingots and reheated in soaking pits before being hot rolled. The second one is a compact mill, where the steel is continuously cast into thin slabs and reheated in a continuous tunnel furnace before being rolled. Tensile specimens were machined at three different directions with respect to the rolling direction. Samples of both types of strips were prepared for metallographic inspection. Textural information was obtained by back-scattered electron diffraction using a scanning electron microscope (SEM). It was found that the differences in mechanical behavior were due not only from dissimilarities in their grain size but also due to variation in their textural components. D

The mechanical response of as-processed equal channel angular extrusion materials is anisotropic, depending on both direction and sense of straining. The stress-strain curves exhibit hardening characteristics different from the usual work hardening responses, e.g., Stages I-IV, expected in annealed fcc metals under monotonic loading. In this work, the anisotropic flow responses of two pure fcc metals, Al and Cu, processed by route Bc are evaluated and compared based on pre-strain level (number of passes), direction of reloading, sense of straining (i.e., compression versus tension), and their propensity to generate subgrain microstructures and to rearrange, should the slip activity change. In most cases, either macroscopic work softening or strain intervals with little to no work hardening are observed. Application of a crystallographically based single-crystal hardening law for strain-path changes [Beyerlein and Tomé , Int. J. Plasticity (2007)] incorporated into a visco-plastic self-consistent (VPSC) model supports the hypothesis that suppression of work hardening is due to reversal or cross effects operating at the grain level.

Sheet metal forming software is commonly used in the automotive and sheet metal sectors to support the design stage. However, the ability of the currently available software to accurately predict springback is limited. A sensitivity analysis of the springback behavior of a simple product is performed to gain more knowledge into the various factors contributing to the predictability of springback. The sensitivity analysis comprises both numerical and physical aspects and results are reported in this article.

Three-dimensional (3D) bulk forming simulation by reproducing kernel particle method is presented in this paper. For increasing computational efficiency a lower order integration scheme is proposed and a general benchmark test for explicit non-linear program is developed, to verify the correctness and the accuracy of the present scheme. A particle to segment contact algorithm for treatment of the contact between deformable and rigid bodies is also presented. The algorithm is found to be very effective and suitable for 3D bulk forming analysis.

Texture analysis of cold-rolled maraging 350 steel (40%, 60%, 80%, and 90%) and the influence of an intermediate austenitization at 820 jC have been studied. Results show that the crystallographic texture increases with cold rolling. The austenitization process partially destroys the rolling texture and aging after austenitization develops crystallographic texture similar to rolling texture. D

To study the emission properties of an AlGaAs–GaAs phonon laser we develop a formalism similar to that used to describe a laser. The device studied here consist of a double-barrier resonant tunneling diode tailored to generate an intense rate of primary LO1 phonons. These phonons are confined in the well and they decay into a pair of secondary LO2 and TA phonons. The TA phonons are generated by stimulated emission and they are partially reflected in the well walls. A combination of these two processes leads, for injection rates greater than the threshold, to the selection of a single phonon mode. Finally, the TA phonons escape through the barriers forming an intense coherent phonon beam. We start with a Hamiltonian that takes into account the electrons, the three phonon branches, the electron–phonon interaction and the phonon–phonon interaction. The last one is responsible for the TA phonon generation. From this Hamiltonian we get a set of five coupled Heisenberg–Langevin equations that are solved making an expansion in coherent states and doing the usual adiabatic approximation. The threshold for phonon lasing is calculated. The results show that it is not necessary to have a big pumping to get a single mode operation. This confirm our previous results obtained using rougher approximations. The phonon laser studied here has a very short wavelength. The mean free path of TA phonons is of the order of 2 mm. Therefore, it could be useful to perform acoustic nanoscopy and other applications.

Non-equilibrium redox chemical reactions of high orders are ubiquitous in fluid-saturated porous rocks within the crust of the Earth. The numerical modelling of such high-order chemical reactions becomes a challenging problem because these chemical reactions are not only produced strong non-linear source/sink terms for reactive transport equations, but also often coupled with the fluids mixing, heat transfer and reactive mass transport processes. In order to solve this problem effectively and efficiently, it is desirable to reduce the total number of reactive transport equations with strong non-linear source/sink terms to a minimum in a computational model. For this purpose, the concept of the chemical reaction rate invariant is used to develop a numerical procedure for dealing with fluids mixing, heat transfer and non-equilibrium redox chemical reactions in fluid-saturated porous rocks. Using the proposed concept and numerical procedure, only one reactive transport equation, which is used to describe the distribution of the chemical product and has a strong non-linear source/sink term, needs to be solved for each of the non-equilibrium redox chemical reactions. The original reactive transport equations of the chemical reactants with strong non-linear source/sink terms are turned into the conventional mass transport equations of the chemical reaction rate invariants without any non-linear source/sink terms. A testing example, for some aspects of which the analytical solutions are available, is used to validate the proposed numerical procedure. The related numerical solutions have demonstrated that (1) the proposed numerical procedure is useful and applicable for dealing with the coupled problem between fluids mixing, heat transfer and non-equilibrium redox chemical reactions of high orders in fluid-saturated porous rocks; (2) the interaction between the solute diffusion, solute advection and chemical kinetics is an important mechanism to control distribution patterns of chemical products in an ore-forming process; and (3) if the pore-fluid pressure gradient is lithostatic, it is difficult for the chemical equilibrium to be attained within permeable cracks and geological faults within the crust of the Earth. Copyright © 2005 John Wiley & Sons, Ltd.

The forming or draping of a textile composite preform may result in large changes in the ®brous microstructure of the preform. This change in the local ®ber orientation leads to signi®cant changes in the fabric permeability as well as the mechanical properties of the ensuing composite structure. Therefore, this change in orientation of the tows of the preform needs to be known accurately to calculate the various eective properties of the composite. A new ®nite element approach for stamping analysis of a plain-weave textile composite preform has been developed. This model is simple, ecient and can be used in the existing ®nite element codes. The model represents the preform as a mesh of 3-D truss elements and 3-D shell elements. The truss elements model the tows, which are allowed to both scissor and slide relative to one another. The shell elements represent a ®ctitious material that accounts for inter-tow friction and ®ber angle jamming. The model takes into account large strains and large deformations. In-plane uniaxial tension tests have been performed on plain-weave specimens for determining the constitutive law of the transforming medium and to show the inter-tow sliding. Application of the model is demonstrated by simulating the stamping of a preform by a spherical punch. The results from the simulation show good correlation with results from the experiments. Ó

The forming or draping of a textile composite preform may result in large changes in the ®brous microstructure of the preform. This change in the local ®ber orientation leads to signi®cant changes in the fabric permeability as well as the mechanical properties of the ensuing composite structure. Therefore, this change in orientation of the tows of the preform needs to be known accurately to calculate the various eective properties of the composite. A new ®nite element approach for stamping analysis of a plain-weave textile composite preform has been developed. This model is simple, ecient and can be used in the existing ®nite element codes. The model represents the preform as a mesh of 3-D truss elements and 3-D shell elements. The truss elements model the tows, which are allowed to both scissor and slide relative to one another. The shell elements represent a ®ctitious material that accounts for inter-tow friction and ®ber angle jamming. The model takes into account large strains and large deformations. In-plane uniaxial tension tests have been performed on plain-weave specimens for determining the constitutive law of the transforming medium and to show the inter-tow sliding. Application of the model is demonstrated by simulating the stamping of a preform by a spherical punch. The results from the simulation show good correlation with results from the experiments.

The implicit finite element (FE) simulation of incremental metal cold forming processes is still a challenging task. We introduce a dynamic, overlapping domain decomposition method to reduce the computational cost and to circumvent the need for sophisticated remeshing procedures. The two FE domains interchange information using the elastoplastic operator split and the mortar method.

In many forming processes -like backward extrusion -the material is subjected to very high local strains that can lead to microcracks and subsequently to in-service failure of the final piece. In order to model the defects nucleation and growth, a ductile damage model proposed by Lemaitre is introduced. The parameters of the constitutive equations are identified from micro-hardness measurements performed on a tensile test specimen after rupture. Numerical simulations of upsetting tests and their comparisons with experimental results are used to validate the introduction of a unilateral effect in the damage evolution law to take into account the case of high compressive stress states. KEY WORDS: ductile damage, unilateral effect, micro-hardness, identification, upsetting test, backward extrusion.

This paper encompasses the main conclusions obtained in the mini-symposium New and Advanced Numerical Strategies in Forming Processes Simulation, held during the 6th International ESAFORM Conference on Material Forming (Salerno 2003), particularly those aspects dealing with meshless and partition of unity methods applied to the simulation of forming processes.

A possibility to make near-net-shape functionally graded material (FGM) products has been examined. The FGM billets having a graded volume fraction of Al 3 Ni in thickness direction were machined from an Al-Al 3 Ni FGM thick-walled tube manufactured by a vacuum centrifugal method. Billets, which were set in the container for the backward extruding, were heated to 650 ЊC to 680 ЊC, at which temperature the FGM becomes a mixture of molten aluminum eutectic and solid intermetallics. Then, billets were extruded successfully to FGM cups by a semisolid forming, except at 650 ЊC. Residual bulky Al 3 Ni particles are found at higher temperature. Thus, an optimum operation temperature is found to be around 660 ЊC, because bulky Al 3 Ni particles transform to fine spheroidal or fibrous shape after the forming. The volume fraction of intermetallics at the bottom region of the cup was condensed more than 60 vol pct in a proper billet setting. YASUYOSHI FUKUI, Professor, HIROSHI OKADA, Associate Profesthe ability of the Al-Al 3 Ni FGM as a structural and composor, and NORIYOSHI KUMAZAWA, Assistant, are with the Department of Mechanical Engineering, Faculty of Engineering, Kagoshima University, nent material would be enhanced if near-net-shape products Kagoshima 890-0065, Japan. YASHIMI WATANABE, Associate Professor, were produced easily. The aim of the present study is reafis with the Faculty of Textile Science & Technology, Shinshu University, firmed to overcome the inherent brittleness of Al 3 Ni interme-Ueda 386-8567, Japan.

Superior mechanical properties with high ductility at room and higher temperatures have been achieved by extruding Mg 95 Zn 4:2 Y 0:8 and Mg 92:5 Zn 6:4 Y alloys at 523 K. The strengthening phases are the icosahedral quasicrystal, finely distributed nano-sized precipitates of a ternary phase s 1 and thin b 0 1 phase rods several hundreds of nanometers long.

The spray forming process is a novel method of rapidly manufacturing tools and dies for stamping and injection operations. The process sprays molten tool steel from a set of arc spray guns onto a ceramic former to build up a thick steel shell. The volumetric contraction that occurs as the steel cools is offset by a volumetric expansion taking place within the sprayed steel, which allows the dimensional accurate tools to be produced. To ensure that the required phase transformation takes place, the temperature of the steel is regulated during spraying. The sprayed metal acts both as a source of mass and a source of heat and by adjusting the rate at which metal is sprayed; the surface temperature profile over the surface of the steel can be controlled. The temperature profile is measured using a thermal imaging camera and regulated by adjusting the rate at which the guns spray the steel. Because the temperature is regulated by adjusting the feed rate to an actuator that is moving over the surface, this is an example of mobile control, which is a class of distributed parameter control. The dynamic system has been controlled using a PI controller before. The paper describes the application of H/sub /spl infin// tracking type controller as the desire was for the average temperature to follow a desired profile. A study on the controllability of the underlying system was aimed at.

A new sheet-bulk metal forming process for the production of bulk components out of a flat sheet has been developed. Superimposed oscillation has been applied to the new process. By this means, process limits regarding better mould filling were expanded, and forming forces could be reduced. In order to investigate the effects of superimposed oscillation on material behaviour, plane strain and ring compression tests were carried out. The superimposed oscillated plane strain compression test showed a reduction in biaxial flow stress and thus in plastic work. Furthermore, reduced friction and roughness were verified in ring compression tests using superimposed oscillation.

Due to the ongoing technological development, the demand for geometrically complicated high performance parts with great functional density is increasing. Often, the use of sheet metal is a beneficial approach in manufacturing technology to meet the requirements on components regarding material strength and lightweight construction goals. The forming of therefore required complex sheet metal part geometries with integrated functional elements cause the need for a three dimensional material flow. Sheet-bulk metal forming, characterized by the application of bulk forming operations on sheet metals, is a suitable approach to produce such components. A challenge is the material flow control, resulting in an insufficient die filling of the functional elements. The use of tailored blanks with a defined sheet thickness distribution is an auspicious approach to face this challenge in subsequent forming processes. In the presented work, semi-finished products with a continuous thickness prof...

The analysis of Markenscoff and Clifton (J Mech Phys Solids 29:253-262, 1981) for a generally nonuniformly moving Volterra edge dislocation, valid both for subsonic and intersonic/supersonic motion, is focused on the instant in which the dislocation accelerates through the shear-wave speed barrier. Mathematically, the roots (of the argument of the step function f x ð Þ ¼ t À h x ð Þ À rb that defines the intervals of the path of the motion that contribute to the field point) change from a pair of complex conjugate to a double real, splitting into two real ones, and, at the instant of the transition to intersonic motion, the stress analysis is performed at this double root maximum of f x ð Þ. The stress at the forming Mach front contains a log ξÀξ* j j ξÀξ* j j 1 2 singularity in the coefficient of the delta function, which can be removed by a ramp-core (delta sequence rather than delta function) model of the core displacement.

During the cooling process in injection molding, heat fluxes in the mold are generally lower in inner regious of corners. This asymmetric cooling generates a corner deformation: the part angle is smaller than the mold one. This phenomenon is known to be the main cause of corner warpage in injection molding of thermoplastics. The second phenomenon leading to a corner warpage has firstly been described for thin compression molded SMC parts and is called "spring forward effect". Due to the large fiberlength / part-thickness ratio, most fibers in SMC parts are oriented in the planar direction leading to higher thermal expansion coefficients in the thickness direction as compared to those in the surface direction. When the part cools after polymer curing, a decrease of the enclosed angle in a corner occurs after mold extraction. Because of mold restraints for injection molded thermoplastic parts, the shrinkage in the thickness direction is much larger than the in-plane shrinkage and so the spring forward effect can appear. An experimental study and a two dimensional thermo-viscoelastic calculation of a polymer corner deformation in a mold performed on Abaqus code were carried out. We show that the spring forward effect is generally the major source of corner deformation for injected thermoplastic parts.

Multi-level modeling adaptive to theoretical treatise of superplastic deformation is proposed not only to make process simulation for superplastic forming but also to describe the microstructural change taking place in materials processing. Use of the unit cell modeling enables us to make theoretical linkage between the macroscopic and the mesoscopic models. The fundamental theory is introduced with some comments on the unit cell model for macro-micro mechanics linkage and the advanced granular modeling for mesoscopic representation of superplasticicty. The sinter-forging process is employed for practical demonstration of the present multi-level modeling.

The development of hot rolling textures in f.c.c. metals has been simulated numerically using a viscoplastic crystal plasticity model assuming different combinations of octahedral and non-octahedral slip systems for several grain-matrix interaction schemes. A combination of quasi-pencil glide and the Lebensohn and Tom6 self-consistent model [Acta Metall. Mater., 1993, 41, 261 l] gives a satisfactory simulation of typical hot rolling f.c.c. texture components, i.e. well balanced P-fibre components and a small amount of "Cube". 8 1997 Acta Metallurgica Inc.

Both single-and multi-layer thin films of sol-gel-derived undoped and Al-doped zinc oxide material systems were fabricated for potential use in transparent conducting oxide modules. Functional properties of the resultant films were characterised comparatively. High degree of reproducibility was demonstrated for the characterised properties, with the exception of the electrical conductivity. Influences of Al doping on the characterised properties were also investigated. Al doping reduced the average crystallite size, and led to a denser and less porous morphology, and also caused an increase in transparency in the UV region. Moreover, it was shown that the electrical conductivity of this thin film system could be improved upon either the application of a forming gas process, or Al doping. ß

Laser dynamic forming ͑LDF͒ is a three-dimensional ͑3D͒ forming technique, which utilizes laser to induce shock wave and shape the target thin films onto micro/nanoscale 3D surfaces. This technique has been used to form metals on 3D surfaces. This letter extends LDF to functional and brittle materials sandwiched by elastomeric polymers on patterned 3D surface. The elastomeric polymers absorb the shock energy and minimize the degradation of the functional materials. The patterned 3D surfaces control the plasticity in the structure and therefore retain the function of the structure. The performance was evaluated and mechanisms were studied.

Superior mechanical properties with high ductility at room and higher temperatures have been achieved by extruding Mg 95 Zn 4:2 Y 0:8 and Mg 92:5 Zn 6:4 Y alloys at 523 K. The strengthening phases are the icosahedral quasicrystal, finely distributed nano-sized precipitates of a ternary phase s 1 and thin b 0 1 phase rods several hundreds of nanometers long.

Superior mechanical properties with high ductility at room and higher temperatures have been achieved by extruding Mg 95 Zn 4:2 Y 0:8 and Mg 92:5 Zn 6:4 Y alloys at 523 K. The strengthening phases are the icosahedral quasicrystal, finely distributed nano-sized precipitates of a ternary phase s 1 and thin b 0 1 phase rods several hundreds of nanometers long.

Size effects make most know-how of traditional macro forming inappropriate for the micro forming process. Material behavior greatly varies in micro forming process with the decreasing of the scale. The purposes of this paper are to analyze the influence of material size effects and establish a martial model in micro/meso-scale. By combining surface model with theories of single crystal and polycrystal, a mixed material model, which contains a size dependent term and a size independent term, is proposed in this paper. It finds that the flow stress of material in micro/meso-scale is between that of single crystal model (lower bound) and polycrystal model (upper bound). Based on a mixed material model, the influence of size effects is discussed in both micro bulk forming process and micro sheet forming process. At the end, the validity of the mixed model is approved by comparing the simulations with the experimental results.

For sheet metal applications, it is most desirable to simulate the plastic anisotropy accurately. This is reasonable because flow localisation, leading to shear bands and even to fracture, can be an immediate consequence of the plastic anisotropy. The anisotropic ...

We report extensive x-ray diffractometric measurements as well as conventional metallurgical and mechanical tests on thin steel sheets of FeP04 for deep drawability in order to identify key microscopic parameters that govern both texture evolution and mechanical response as function of the type of loading path. While Microhardness measurements, as expected show an evolution as function of material work hardening, the distribution of grain size seems to be unaffected by the different type of loading path. Quantitative texture measurements demonstrates a development of different texture components depending on the type of loading path used to achieve the plastic deformation. Indeed, when compared to as received samples significant variation was found on Poles density and orientation distribution unction versus the type of applied stress states. f