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Any physical modelling of a circuit-breaker arc therefore requires an understanding of the radiated energy which is taken into account in the form of a net coefficient. The evaluation of the net emission coefficient is performed by the knowledge of the chemical plasma composition and the resolution of the radiative transfer equation. In this paper, the total radiation which escapes from a CH4-N2 plasma is calculated in the temperature range between 5000 and 30000K on the assumption of a local thermodynamic equilibrium and we have studied the nitrogen effect in the hydrocarbon plasmas. [ABSTRACT FROM AUTHOR]

This paper contains our last results concerning the understanding of fundamental processes occurring inside metallic melt pool produced during deep penetration CW Nd-Yag laser welding. When the welding speed varies from a few m/min to a few tens of m/min, one can observe that melt pool behavior has very different and complex hydrodynamics. At low welding speed, the keyhole appears to be quite vertical, embedded inside a large pool that fluctuates due to friction effects induced by the quite vertical ejected plume. At high welding speeds, laser interaction is only localized on the keyhole front whose inclination increases with the welding speed. Induced melt flow then dominates and can generate the humping regime, with severe undercuts. For intermediate welding speeds, it is the interaction of the vapor plume with the melt pool that controls its stability and the final quality of the weld seam. The vapor plume behavior that is ejected from the keyhole, such as its fluctuations or its dynamic pressure, has been also studied as a function of these different operating parameters. Also the behavior of the keyhole and more precisely its front wall is analyzed by using a simple modeling approach that allows us to reproduce its main characteristics such as the penetration depth or the keyhole front wall inclination dependences with operating parameters. The interpretation of these different experiments allows us to confirm that the dynamic pressure of the vapor plume, which is emitted with a variable intensity and direction perpendicularly from the inclined keyhole front, has an essential role for the melt pool stability and its dynamics in deep penetration laser welding. [ABSTRACT FROM AUTHOR]

The power supply of flash lamp-pumped solid-state lasers (such as ND: YAG Laser) basically consists of a trigger circuit, a simmer circuit and the main discharge circuit. All of which are synchronized by a command circuit. To reduce both size and weight of this power supply, we have modelled and designed it by using the concept of the switch mode power supplies. In this paper we will present the modelling of the main discharge transformer and the experimental characterization of the THT used in the trigger circuit. The results of modelling have been validated by an experimental development. [ABSTRACT FROM AUTHOR]

In this paper, we define plasma etch process and we describe two etch equipments used in our clean room: Lam 4500 and Lam 4400. [ABSTRACT FROM AUTHOR]

We use in this paper the semi-implicit finite difference operator splitting Padé (OSPD) method for solving the coupled higher-order nonlinear Schrödinger equation which describes the propagation of vector solitons in optical fibers. This method having a fourth order accuracy in space shows good stability and efficiency for the coupled HNLS equations describing vector solitons. We have tested this method for analyzing the behavior of optical pulses in birefringent fibers verifying that the third order dispersion TOD has different effects on the two polarizations and the asymmetric oscillation is significant only in one polarization. [ABSTRACT FROM AUTHOR]

The aim of this paper is to determine electric and physical properties by 2D modelling of glow discharge low pressure in continuous regime maintained by term constant source. This electric discharge is confined in reactor plan-parallel geometry. This reactor is filled by Argon monatomic gas. Our continuum model the order two is composed the first three moments the Boltzmann’s equations coupled with Poisson’s equation by self consistent method. These transport equations are discretized by the finite volumes method. The equations system is resolved by a new technique, it is about the N-BEE explicit scheme using the time splitting method. [ABSTRACT FROM AUTHOR]

In this paper a new method using the combination of Neural Networks and the Newton-Raphson algorithm is developped. The technique consists of the use of the solution obtained by Newton-Raphson algorithm between 0.5 and 2.1eV for pure manganese (Mn) and for the amorphous metallic alloy Al88Mn12, to construct two parts of datasets; the first one is used for training the neural network and the second one for the validation tests. The validated neural network model is applied to the determination of optical constants of the two materials Mn and Al88Mn12 in the range of 0.5 and 6.2eV (IR-VIS-UV). The results obtained over all the studied energy range are used to trace back to dielectric function, optical absorption and electronic structure of the same material. By using the partial solution obtained by Newton-Raphson as a database of the neural network prediction model, it is shown that the obtained results are in accordance with those of the literature which consolidate the efficiency of the suggested approach. [ABSTRACT FROM AUTHOR]

There are a number of key technologies involved in the successful design and construction of high power, Carbon Dioxide TEA lasers (Transverse Excitation Atmospheric). These include uniform field electrodes, excitation circuit design including high voltage switching, discharge preionisation and for high repetition, high power applications fast transverse gas flow and the management of acoustic waves. This paper provides a summary of the design aspects of high repetition rate, high average power CO2 TEA lasers. Experimental data measured on high power CO2 TEA laser systems delivering average outputs of several kW and kHz repetition rates will be reported showing the detrimental effect of acoustic waves on laser performance and the improvement that can be achieved through effective acoustic damping measures. [ABSTRACT FROM AUTHOR]

This paper studies nonlinear wave propagation in a slender elastic cylinder due to impacts. One purpose is to examine what kinds of wave patterns can arise when both the material nonlinearity caused by a non-convex energy function and the dispersion caused by the lateral movement are present. A high-order weighted essentially non-oscillatory (WENO) scheme is used to obtain the numerical solutions of a model equation which takes into account the dispersion and the above-mentioned nonlinearity. It turns out that a variety of wave patterns can appear, including the co-existence of a transformation front and solitons. We also find that pre-strains and the geometrical size can have some important influences. The interactions of transformation fronts and rarefaction waves (which have not been considered in literature before) are investigated and some interesting phenomena are found. [ABSTRACT FROM AUTHOR]

Centrifugation of organic liquids and metals has been widely used in biochemistry field and metallurgy field, respectively. The high-gravity field was recently used for the preprocessing for sintering of composite materials. The sedimentation of atoms was recently realized in alloys and semiconductors under ultra-high gravitational field in 1 million G level. The possibility in use of high gravity has, day by day, increased. In this mini-symposium, the conventional and recent methods for materials processing for functionally graded materials, metastable composite materials, thin film, etc. using high-gravity in gas, liquids, solids and also in vacuum will be treated. In this paper, the history of ultracentrifuges is reviewed, and the applications to materials science is discussed. [ABSTRACT FROM AUTHOR]

The paper describes the experimental procedures carried out in order to investigate the rheological properties of carbon fiber reinforced polyetheretherketone (PEEK) and the mechanical properties of injection-molded parts from this material. Four test nozzles have been designed for the investigation of the rheological properties of PEEK. The nozzles containing two pressure sensors and a temperature sensor have been mounted on a 22 Tons injection molding machine. As a result, pressure-time and temperature-time curves have been obtained and then used to calculate the PEEK viscosity as a function of shear rate. Several test specimens have been molded to study the properties of injection-molded parts. First, tension tests have been performed to obtain stress-strain curve and the strength value for PEEK. Then the Young modulus has been experimentally determined using a vibrational method. Flexion tests have allowed to estimate the flexural modulus value. The experimental results obtained in this study can be used to improve the accuracy of injection molding simulation and structural FEM analysis. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A parallel computational environment for modeling the resin transfer molding manufacturing process has been developed at the U.S. Army Research Laboratory. This environment utilizes an implicit numerical method for modeling resin flow, a thermal model for analyzing convection and conduction, and a resin kinetics model to compute the heat generated and degree of resin cure during the curing process. The computing environment also includes a multiscale thermal residual stress model for computing the distortions and residual stresses in the composite component caused by the manufacturing process. All of these models have been tied together within a parallel object-oriented programming framework. This paper will discuss the computing environment in detail and its utility to real world applications. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Glass fiber reinforced polymer is widely used in the products made using injection molding processing. The distribution of fiber orientation inside plastic parts has direct effects on quality of molded parts. Using computer simulation to predict fiber orientation distribution is one of most efficient ways to assist engineers to do warpage analysis and to find a good design solution to produce high quality plastic parts. Fiber orientation simulation software based on 2-1/2D (midplane /Dual domain mesh) techniques has been used in industry for a decade. However, the 2-1/2D technique is based on the planar Hele-Shaw approximation and it is not suitable when the geometry has complex three-dimensional features which cannot be well approximated by 2D shells. Recently, a full 3D simulation software for fiber orientation has been developed and integrated into Moldflow Plastics Insight 3D simulation software. The theory for this new 3D fiber orientation calculation module is described in this paper. Several examples are also presented to show the benefit in using 3D fiber orientation simulation. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The machining of FRP composites has posed a serious challenge to industry and academia alike as far as the sub-surface damage is concerned caused by fiber-matrix debonding. Proper prediction of sub-surface damage is thus essential for different fiber orientations and fiber-matrix bonding. A Cohesive Zone Modeling (CZM) of the fiber-matrix debonding leading to interfacial separation is presented in this paper. The cohesive bonding strength existing between the fiber and matrix increases with increased separation, reaches a maximum value before causing permanent debonding when the cohesive strength between the interfaces vanishes. An effort is made to implement the Cohesive Zone Model (CZM) and to ascertain the extent of debonding below the trim plane at fiber failure. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, statistical continuum mechanics modeling is applied to predict the elastic mechanical properties of an anisotropic Al-SiC composite. Two-point statistics are measured on vertical metallographic planes in three-dimensional microstructures. As a result of anisotropy the correlation functions are orientation dependent. Longitudinal and transverse elastic moduli are calculated for two samples with different PSR and clustering, and the results are compared with upper and lower bound and experimental data. It’s observed that the theoretical results are in good agreement with experimental data and two-point statistics significantly contribute to the estimation of the elastic modulus. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Usually, in the finite element analysis of metal forming processes tools are assumed to be rigid. However, processes like flat rolling clearly show the necessity of taking into account elastic effects. The distribution of strip tension influences the shape of the rolling gap and vice versa. Considering all elastic effects in one finite element model of the rolling process leads to a very large model that is difficult to manage and suffers from severe numerical problems due to the multiple contact situations. Therefore, a concept is being developed that very efficiently meets the above demands. Elastic effects are computed separately and coupled with the simulation of the actual rolling process via data interchange. In this paper, experience with this iterative concept is shown concentrating on run-time, reliability of the results, and the convergence of the coupled elastic models and the conventional rolling process model. All algorithms have been implemented in the commercial nonlinear finite element code LARSTRAN/SHAPE. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents an approach of direct die shape compensation implemented in a forging optimization system in order to achieve net-shape forging production for aeroengine blade components. This approach is based on the modification of die shape in relation to the dimensional errors of forged aerofoil shape due to the die and press deflections during forging and the thermal distortion upon cooling. In hot forging of a Ni-based alloy, the forging errors due to die elastic deformation, thermal distortion and press elasticity were quantified and further minimized by up to 95% of the original errors prior to the die shape compensation. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Numerical models are used extensively in the aerospace sector to identify appropriate manufacturing parameters, and to minimize the risk associated with new product introduction and manufacturing change. This usage is equally prevalent in original equipment manufacturers (OEMs), and in their supply chains. The wide range of manufacturing processes and production environments involved, coupled with the varying degrees of technology maturity associated with numerical models of different processes leads to a situation of significant complexity from the OEM perspective. In addition, the intended use of simulation technology can vary considerably between applications, from simple geometric assessment of die shape at one extreme, to full process design or development at the other. Consequently there is an increasing trend towards multi-scale modelling, i.e. the use of several different model types, with differing attributes in terms of accuracy and speed to support a range of different new product introduction decisions. This makes the allocation of appropriate levels of activity to the research and implementation of new capabilities a difficult problem. This paper uses a number of industrial cases studies to illustrate a framework for making such allocation decisions such that value to the OEM is maximized, and investigates how such a framework is likely to shift over the next few years based on technological developments. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Over the past two decades, various finite element formulations and solution techniques for metal forming analysis have been developed. Most finite element codes for bulk metal forming used in the industry today are based on static implicit solution schemes wherein a non-linear system of equations is solved iteratively for each time increment. For simple 2D problems, static implicit analysis models are generally known to be more accurate and efficient than dynamic explicit analysis models. However, for complex 3D forming problems, the static implicit procedures encounter a number of inherent difficulties especially in incremental forming processes such as ring rolling in which several surface nodes repeatedly make contact with and separate from the dies. Static implicit finite element formulations require a very long computational time for the analysis of ring rolling. Several solution techniques have been developed to reduce the computational time of static implicit finite element analysis, namely the dual mesh technique, Arbitrary Lagrangian Eulerian (ALE) technique, etc. The dynamic explicit method on the other hand appears to be very effective in analyzing complex incremental forming problems. In this paper, a comparison of the analysis results obtained using dynamic explicit finite element method and static implicit method using a dual mesh approach is presented. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The hot rolling of thin strip can result in several problems in hot rolling, for instance, the control of strip steering, strip shape and flatness and surface roughness etc. Therefore, the hot rolling of thin strip brings out a requirement of innovative technologies such as the extended control of shape and flatness, steering control and reduction of load by roll gap lubrication. In this paper, the authors focus on the analysis of thin strip snaking movement, as well as solve the related problems such as the shape and flatness due to a larger reduction applied when the strip is thinner. A finite element method was used to simulate this nonsymmetricity rolling considering the non-uniform reduction along the strip width. The calculated spread is compared with the measured values obtained from the rolling mill in laboratory and the friction effect is also discussed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A helical skew rolling process is a continuous hot forming process that produces near net-shape parts from tubing for hard turning or machining to the finished parts. The process can challenge forging processes in a number of applications by its high production rate and ability of forming intricate geometry. Because of its technical complexity, a number of tests have to be performed to improve and validate the design before a part can be put into production. To reduce the design lead-time and cost as well as improving the production quality, developing and implementing the finite element analysis procedures in design is an inevitable step. In literature, it has not been seen that the numerical simulation is applied to the skew rolling process so far. Simulation of the skew rolling is in a complicated three-dimensional metal large-deformation category, characterized by its severe mesh distortion and consistent contact and separation between the workpiece and dies. This paper describes the new development in finite element modeling of the skew rolling process and demonstrates the application of finite element modeling to aid the design of tooling and process parameters. By the use of the DEFORM-3D finite element program, the simulations can predict the geometry and some defects in parts reasonably well agreed with the actual products. However, one of the key issues is simulation time due to the nature of the nonlinear finite element method and the Lagrangian formulation adopted in the DEFORM-3D program. Solving nonlinear algebraic equations in each time step combined with iterative procedures is very computationally demanding and time consuming. Repeatedly reduction in time step size to satisfy the contact criterion prolongs the simulation significantly. Therefore, the improvement in the finite element theories and solving methods is necessary before the simulation can achieve reasonable timing. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

It is widely recognized that subgrain size has significant influence on the strength and ductility of metals. Modelling of subgrain size evolution is essential for the detailed understanding and control of mechanical properties. In the present paper, the evolutions of subgrain size during hot extrusion of various aluminum alloys are first predicted. A nearly constant distribution of subgrain size is pursued by iso-subgrain extrusion processes. Substructural strengthening coupled with microstructural evolution is also studied in addition to the normal thermal-mechanical coupled analysis. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

For many years, metal cutting simulations have been performed using two dimensional approximations of the actual process. Factors such as chip morphology, cutting force, temperature, and tool wear can all be predicted on the computer. However, two dimensional simulation is limited to processes which are orthogonal, or which can be closely approximated as orthogonal. Advances in finite element technology, coupled with continuing improvement in the availability of low cost, high performance computer hardware, have made the three dimensional simulation of a large variety of metal cutting processes practical. Specific improvements include efficient FEM solvers, and robust adaptive remeshing. As researchers continue to gain an improved understanding of wear, material representation, tool coatings, fracture, and other such phenomena, the machining simulation system also must adapt to incorporate these evolving models. To demonstrate the capabilities of the 3D simulation system, a variety of drilling, milling, and turning processes have been simulated and will be presented in this paper. Issues related to computation time and simulation accuracy will also be addressed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper investigates the effects of edge radius of a round-edge PVD coated tool upon chip formation, cutting forces, and tool stresses in orthogonal cutting of an alloy steel 42CrMo4 (AISI 4142H). A comprehensive experimental approach based on end turning of thin-walled tubes is conducted using advanced coated tools with well-defined cutting edge radii ranging from 9 to 28 microns. In parallel, 2-D finite element cutting simulations based on Lagrangian thermo-viscoplastic formulation are used to analyze cutting temperature and tool stress distributions within the coating layer and tool substrate. The results obtained from this study provide a fundamental understanding of the cutting mechanics for the coated tool used and can assist in the optimization of tool edge design for more complex geometries such as chamfered edge. Particularly, the results obtained from the experiments and simulations of this study have underlined that there exists an optimum cutting edge radius that minimizes tool stresses, especially within the coating layer, and prolongs the tool life. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Numerical cutting modeling provides understanding and prediction of chip formation process variables such as stress, temperature, cutting forces... . Thus, it could help to improve several areas related to the cutting process as cutting tool development, machining parameter set up, material development and so on. However, several aspects as numerical model definition, validation of numerical results and identification of entry parameters should be improved prior to offering it as a robust and reliable tool to the industry. This paper deals with workpiece material flow stress identification. Several aspects are pointed out : the difficulty to validate numerical results, the influence of the material flow stress, the need to establish tolerances during parameter identification and the difficulty to properly identify by inverse simulation material flow stress coefficients. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Recently, weight reduction of vehicles has been of great interest, and consequently, the use of low-density materials in the automotive industry is increasing every year. Materials should not be substituted such a way that material of component parts is simply changed because there is a problem in achieving stiffness and strength. To achieve these requirements, the automobile should be redesigned totally. Aluminum spaceframe is rapidly being adopted as a body structure for accommodating lightness, stiffness and strength requirement. In aluminum spaceframe manufacturing, it is often required to join aluminum tube. But there are few suitable methods for joining aluminum tube, so that much interest has been focused on testing suitable joining methods. Joining by electromagnetic forming(EMF) can be useful method in joining aluminum tube, which offers some advantages compared with the conventional joining method. In this paper, joining by EMF was investigated as a pre-study for applying an automotive spaceframe. Finite element simulations and strength tests were performed to analyze the influence of geometric parameters on joint strength. Based on these results, configurations of axial joint and torque joint were suggested and guidelines for designing EMF joint were established. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Although deformation features of ECAP have been widely studied and investigated through numerical approaches, experimental observations are very scarce in the literature. Therefore, in this paper, quasi-3D strains in multi-sectioned samples during one pass of ECAP are analyzed, for different friction conditions and material properties. From this study, it can be concluded that ECAP is a plane-strain process and friction and material properties affect the strain distribution, strain homogeneity and also the work-piece geometry. Furthermore, ECAP can be interpreted as a combination of shear and stretch. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

One of the most practical methods for simulation of steady state thermal processing is the Arbitrary Lagrangian-Eulerian method. Each calculation step is split into two phases. In the first phase, the Lagrangian phase, the element mesh remains attached to the material. The evolution of the state variables is monitored and the state at the end of the phase is calculated. In the second phase, the Eulerian phase, the mesh is, broadly speaking, restored to its original position with respect to a window attached to the moving heat source. The mesh is not restored to its exact original position, but some allowance is made perpendicular to the flow direction in order to capture movement of the free surfaces. In this paper a finite element model for Lagrangian simulation of thermo-mechanical processes with phase transformations is combined with a second order discontinuous Galerkin method for modeling of Eulerian advection. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The equipment and technology of small bar tandem rolling line of Shijiazhuang Iron & Steel Co. in China has reached the 90’s international advanced level in the 20th century, but products on the line are mostly of common carbon steel. Currently there are few steel plants in China to produce 45 steel bars for cold drawing, which is a kind of shortage product. Development of 45 steel for cold drawing has a wide market outlook in China. In this paper, continuous cooling transformation (CCT) curve of 45 steel for cold drawing used for rolling was set out first. According to the CCT curve, we determined some key temperature points such as Ac3 temperature and Ac1 temperature during the cooling procedure and discussed the precipitation microstructure at different cooling rate. Then by studying thermal treatment process of 45 steel bars for cold drawing, the influence of cooling time on microstructure was analyzed and the optimum cooling speed has been found. All results concluded from the above studies are the basis of regulating controlled cooling process of 45 steel bars for cold drawing. Finally, the feasible production process of 45 steel bars for cold drawing on common carbon steel production line combined with the field condition was recommended. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The aluminum can industry in the United States and Canada manufactures over 100 billion cans per year. Two-piece aluminum cans are commonly used to seal and deliver foodstuffs such as soft drinks, beer, pet food, and other perishable items. In order to ensure product safety and performance, the double seam between the can body and lid is a critical component of the package. Double-seaming is a method by which the flange of the can body and the curl of the end are folded over together such that the final joint is composed of five metal thicknesses. There are a number of design challenges involved with the art of double seaming, especially with the push to lightweight. Although the requirements vary by product, the typical beer package must be able to hold pressures in excess of 90psi. In addition, in production, double seaming is a high-speed operation with speeds as high as 3000 cans/minute on an 18-spindle seamer. For this high volume, low cost industry, understanding and optimizing the seaming process can advance the industry as well as help prevent various manufacturing problems that produce a poor seal between the two pieces of the can. To aid in understanding the mechanics of the can parts during double-seaming, a simulation procedure was developed and carried out on a 202 diameter beverage can and lid. Simulations were run with the explicit dynamics solver ABAQUS/Explicit using the continuum shell element technology available in the ABAQUS general purpose FEA program. The continuum shell is a shear-deformable shell element with the topology of an eight node brick. The element’s formulation allows continuously varying, solution-dependent shell thickness and through-thickness pinching stress. One important advantage of using the continuum shell as opposed to a traditional shell element is that true contact interactions at the top and bottom surfaces of the can body and lid can be accurately modeled. With a conventional shell element, contact is performed at the shell mid-surface or at an offset point representing where the top or bottom surface is expected to be. This paper discusses this new simulation technique and provides an example of its use. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Spatial and temporal limitations of atomistic simulations necessitate the development of multiscale methodologies that link atomic and continuum scales. In this paper, a hierarchical multiscale model is presented to study the thermomechanical behavior of carbon nanotube (CNT) based composites. The method explicitly accounts for the behavior of nanoscale interfaces existing between the matrix and CNT. Molecular dynamics simulations based on Tersoff-Brenner potential are employed to study the interfaces in CNT based composites, while finite element method simulates macro behavior with the link provided by cohesive zone model parameters. The multiscale model is used to study the effect of interface strength on stiffness of the composite. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Homogenization theory has been well accepted by the applied mechanics modeling community for its ability to integrate small-scale microstructure phenomena into bulk continuum equations using convergent features of asymptotics. This paper describes an extension of the method to handle asymptotically small atomic scale systems at zero temperature embedded within a deforming continuum. A so-called inner displacement naturally arises in the formulation that enables the consideration of distributed anharmonic crystalline effects that would otherwise be unapproachable with bulk continuum methods alone. The result is a simple computational mechanics method that, first, maps instantaneous continuum deformation gradients to deforming defected crystalline arrangements then, second, provides convergent effective material properties to be used for consistent continuum calculations. The intended applications are those involving patterned defects, either in bulk or on surfaces, which allude to possible manufacturing scenarios. Simple 2-D examples are shown for in-plane deformation of graphene possessing various types of point defects. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Crystallographic homogenization procedure is implemented in the piezoelectric and elastic-crystalline plastic finite element (FE) code to assess its macro-continuum properties of piezoelectric ceramics and BCC and FCC sheet metals. Triple scale hierarchical structure consists of an atom cluster, a crystal aggregation and a macro- continuum. In this paper, we focus to discuss a triple scale numerical analysis for piezoelectric material, and apply to assess a macro-continuum material property. At first, we calculate material properties of Perovskite crystal of piezoelectric material, XYO3 (such as BaTiO3 and PbTiO3) by employing ab-initio molecular analysis code CASTEP. Next, measured results of SEM and EBSD observations of crystal orientation distributions, shapes and boundaries of a real material (BaTiO3) are employed to define an inhomogeneity of crystal aggregation, which corresponds to a unit cell of micro-structure, and satisfies the periodicity condition. This procedure is featured as a first scaling up from the molecular to the crystal aggregation. Finally, the conventional homogenization procedure is implemented in FE code to evaluate a macro-continuum property. This final procedure is featured as a second scaling up from the crystal aggregation (unit cell) to macro-continuum. This triple scale analysis is applied to design piezoelectric ceramic and finds an optimum crystal orientation distribution, in which a macroscopic piezoelectric constant d33 has a maximum value. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Numerical codes based on the ideal flow theory have been mainly developed for nonsteady sheet (membrane) metal forming processes. To account for thickness effects in sheet metal forming processes, two- and three- dimensional theories should be adopted. The simplest theory of this class is the theory of plane strain deformation. In particular, it can be applied to design sheet bending. It is known that pure bending under the plane strain condition produces redundant work in a layer near the center of the material. To exclude such redundant work, appropriate loading conditions should be chosen. One way to determine such loading conditions is to apply the ideal flow theory. In general, the ideal flow theory is restricted to perfectly plastic materials. However, in the case under consideration, viscoplastic hardening materials can be treated as well. In the present paper, a semi-analytical solution for such materials is found. An optimal initial shape is determined by adopting the criterion that the work required to transform the initial shape into the final shape attains a minimum among a class of initial shapes. The solution also gives tractions for obtaining the final shape of given geometry with no redundant work. Comparison with pure bending is made. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

With advances in computer capabilities, cost of sheet metal forming has being reducing mainly due to the reduction of trial and error approaches. At the moment, a complete process can be simulated on computer and appropriate forming conditions optimized before actual industrial forming process is carried out. While formability predictions have improved, the problem of springback exhibited by most metal, including aluminum alloy AA6111-T4, after forming persist and often leads to significant part fit-up problems during assembly. There are a number of factors that affect springback and perhaps the most significant one is constitutive equation. In this paper springback predicted by six advanced kinematic models are evaluated. In addition an improved constitutive kinematic model is presented. It is shown that by adding stress correction term (SCT) to Armstrong-Frederick model a relatively simple and yet accurate stress prediction could be obtained. The SCT was developed with the assumption that the yield surface remains convex, yield center depends on translation, size and shape variations of the yield surface. The model is implemented in a commercial finite element code (ABAQUS/Standard) via its user material interface (UMAT). Numerical simulations of U-bending were performed using automotive aluminum sheet material (AA6111-T4). It was noted that springback has inverse relationship with residual stress. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A study on parameter identification of thermal visco-plastic model considering dynamic recrystallization is presented in this paper. A hybrid global optimization method is constructed and applied in the parameter identification. The hybrid global optimization method is a combination of the Real-coded genetic algorithm (RGA) and some classical local search methods (such as Levenberg-Marquardt method, augmented Gauss-Newton algorithm and the flexible tolerance method) in order to accommodate the characters of the objective function used for parameter identification of the thermal visco-plastic model considering dynamic recrystallization. A special numerical procedure of the parameter identification is also made through cooperation of the hybrid global optimization and a thermal rigid-plastic FEM for simulation of hot forging process. Finally, as numerical example, a set of satisfactory material parameters for 26Cr2Ni4MoV steel is presented by the numerical procedure. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper discusses the forging process of a wayshaft with sector gear through computer simulation, including the forming technology and technology parameters. Combined with the microstructure of structure steel 20CrMnTi, the computing method for the evolution of microstructure is studied. The process is analyzed and simulated by thermo-mechanically-coupled method and the microstructure was predicted by using 3D rigid-plastic FE software. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The paper describes a model and an inverse identification procedure for the material behaviour of new austenitic stainless steels used for car body panels, exhibiting transformation induced plasticity effects. The modelling is based on a phenomenological macroscopic approach and describes well the evolution of martensitic phase during deformation. The identification is based on a combination of experiment simulations by FEM and optimization. The resulting model and parameters are then used to illustrate in typical sheet metal forming cases the main effects associated to these new materials exhibiting martensitic transformation. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

To better predict the polycrystalline behavior at large deformations, a robust time integration algorithm at the single crystal level is of vital importance. The present paper analyzes often-used integration approaches for rate-dependent single crystal plasticity in the area and classifies them into three representative approaches. Three different formulations are grouped into the first approach, which is based up the deformation gradient. The second approach is defined in terms of the slip rates. A modification is proposed to alleviate the numerical stabilities to the second approach upon analyzing the Jacobian. Comparisons between these two approaches show that they demonstrate very similar phenomenology in terms of kinematics and kinetics. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper a Voronoi Cell Finite Element (VCFEM) scheme is presented to model ductile damage in metal matrix composites (MMCs). Particle fracture and matrix cracking are used to model failure of the composite. Numerical examples for simple microstructures are used to validate the model. An example of an actual morphological description of a MMC is used illustrate the potential of the method. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

New production technologies have been developed in these last few years as answers to new market needs such as high production flexibility, low volume batches, more complex shapes of the final pieces and new materials. In particular, for sheet forming the new developed technologies are flexible forming, sheet die-less forming and sheet fluid forming. In previous works the authors have already described the results obtained studying a new sheet forming process based on general purpose CNC machine (called sheet incremental forming on CNC machines) equipped with special tool. This kind of process can be used to produce prototypes of industrial components and also for low volume batches. The present paper reports the results of the analysis conducted on the produced pieces in terms of metallographic structure, hardness distribution and breaking conditions. These results are very interesting in order to understand the physical limits of the material when subjected to this peculiar deformation process. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Fibre reinforced composites are replacing conventional materials due to its compatible and superior properties at low temperatures. Transverse thermal conductivity of plain fabric E-glass/Epoxy composites with the fibre concentrations of 32.5%, 35.2%, 39.2% and 48.9% has been studied in a GM-refrigerator based experimental setup using guarded hotplate technique. Experiments are carried out with the sets of stability criteria. This paper presents the investigation of the influence of the fibre concentration and temperature on the thermal conductivity of fabric composites from 30 K to 300K. It is observed from the experimental results that thermal conductivity increases with the increase of temperature and also with fibre concentration with different rate in different temperature range. The series model has been used to predict the thermal conductivity and compared with the experimental results. It is observed that below the crossover temperature of the composites, which varies from 150–225K depending upon their fibre concentration, the experimental results are within 10% with that of predicted values. The possible causes of variation are analyzed. The physical phenomenon behind the temperature dependence of thermal conductivity is discussed in detail. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Thermal expansion is a crucial parameter for the selection of material to be used along with any other materials in cryogenic system. This paper presents the analysis of such data obtained by a very precisely controlled experimental setup using 3-terminal capacitance method. The measurements are carried out for the E-glass fabric-epoxy samples of 32.5%, 35.2%, 39.2% and 48.9% fibre concentration at perpendicular to the fabric direction. The results show that coefficient of thermal expansion (α) decreases with the increase of fibre concentration but increases with temperature. At 30K, α decreases about 32% when the fibre concentration increases from 32.5% to 48.9% and at 300K, it decreases to about 50%. Quantitative comparison of thermal expansion of composites is done with the stainless steel and epoxy. It is observed that at 32.5% and 48.9% of fibre concentration, thermal expansion decreases from 6% to 50% and 45.6% to 72.6% at 30K and 250K respectively. An attempt is made to prepare composite samples with different concentrations in order to make the thermal expansion very near to conventional metal. The best-fit curves are developed on the basis of the experimental data, which will predict the thermal expansion values at any desired temperature and fibre concentration. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper summarizes the results of an experimental and analytical study conducted to investigate the effect of mixed-mode ratio on the cryogenic interlaminar fracture toughness of woven fabric glass/epoxy laminates. Interlaminar fracture tests were performed and a three-dimensional finite element analysis was carried out to obtain critical strain energy release rates. The cryogenic interlaminar fracture toughness increased upon the introduction of the mode II component. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Pipe freezing is increasingly used in a range of industries to solve otherwise intractable pipe line maintenance and servicing problems. This paper presents the interim results from an experimental study on deliberate freezing of polymeric pipelines. Previous and contemporary works are reviewed. The object of the current research is to confirm the feasibility of ice plug formation within a polymeric pipe as a method of isolation. Tests have been conducted on a range of polymeric pipes of various sizes. The results reported here all relate to freezing of horizontal pipelines. In each case the process of plug formation was photographed, the frozen plug pressure tested and the pipe inspected for signs of damage resulting from the freeze procedure. The time to freeze was recorded and various temperatures logged. These tests have demonstrated that despite the poor thermal and mechanical properties of the polymers, freezing offers a viable alternative method of isolation in polymeric pipelines. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

First principles or ab initio calculations are now routinely applied to problems in physics, chemistry and minerals science. These calculations are now even being applied to biological systems. However, the number of applications of such calculations in materials science remains relatively low. This is somewhat surprising given the system sizes and complexities that are amenable to modern first principles calculations. In this paper I shall discuss some of the challenges of materials science in order to explain why first principles calculations alone will have very little impact on materials modelling. I shall also highlight some successful applications of first principles calculations to materials problems and outline possible developments that would significantly extend the range of successful applications in the future. [ABSTRACT FROM AUTHOR]

Several factors influence the accuracy of results when using the Split Hopkinson bar. These include longitudinal wave dispersion, and impedance mismatch of the bars with the specimens. In this paper, we discuss our approach to choosing specimen dimensions based on their impedance, thereby improving the transmitted stress signal-to-noise ratio. We also show that, by implementing numerical procedures, precise alignment of the strain-pulses is facilitated that is essential for proper dispersion correction. [ABSTRACT FROM AUTHOR]

Analytical models of the penetration process focus on estimating depth of penetration based on target density, target strength (sometimes associated with the unconfined compressive strength of the target for geological targets), the areal density of the penetrator (W/A), and the impact velocity. In this paper, an expression for work is used in conjunction with thermodynamic considerations to devise a simple estimate for mass lost by a high velocity projectile during the penetration process. The result shows that the mass loss is directly proportional to the tunnel length and the target shear strength. The constant of proportionality is not easy to deduce, however, in that it contains an unusual factor from the work analysis. A method for estimating target shear under high pressure from penetration experiments is introduced. [ABSTRACT FROM AUTHOR]