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Laser shock hole-clinching is one of mechanical joining processes in which two or more metal foils are connected together through plastic deformation under the effect of laser-induced shock wave. The experimental investigation encounters many limitations in the influence rules of process parameters on the forming quality of joints due to the ultrashort laser-material interaction time. The present study attempts to analyze the effect of various process parameters such as laser spot diameter, foil thickness, and spacer height on joint forming quality in terms of the evolution of interlock value, the distribution of equivalent plastic strain, and the thickness distribution of the joint. An axisymmetric finite element analysis model of laser shock hole-clinching is developed using ABAQUS software. The dimension parameters of joints obtained from numerical model closely agree with experimental results. Based on the validated finite element analysis model, it is revealed that the ratio of laser spot diameter to pre-pierced hole diameter is adaptive to assess the effect of spot diameter on joint forming quality. The thinnest position varies as the ratio increases due to the change in the directly affected area of laser beam under different ratios. The evolution of interlock values strongly relates to the thickness of the joining partner I, whereas it is little changed for the thickness of partner II. The ratio of spacer height to the thickness of partner I needs to be determined considering both the joint forming quality and the clinching efficiency. According to the numerical results, the following matching relationship of process parameters is preferred: The ratio of laser spot diameter to pre-pierced hole diameter equals to 1; The ratio of the thickness of joining partner I to that of partner II is bigger than 0.2; The ratio of spacer height to the thickness of partner I is in the range of 2.67 to 5. [ABSTRACT FROM AUTHOR]

Current poly‐l‐lactide acid (PLLA) scaffolds have issues of inadequate mechanical strength leading to thrombosis formation. Designing a novel bioabsorbable PLLA stent with a novel structure and improved mechanical property is urgently needed. In this study, stent structure modification and optimization based on bioresorbable vascular scaffold Version 1.1 (BVS 1.1, Abbott Laboratories) were conducted. The mechanical property of the redesigned stent was studied using both computerized finite element analysis and experimental mechanical deformation testing, including radial strength (RS), acute recoil (AR), foreshortening (FS), and bending stiffness (BS). The simulated and experimental results showed that the mechanical properties of the modified structure were significantly improved (modified stent vs. BVS 1.1: RS: 2.25 vs. 1.29 N/mm; AR: 3.03 vs. 4.41%; FS: 1.13 vs. 6.89%; BS: 1.49 vs. 0.72 N mm2). [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a promising manufacturing process in which flat metal sheets are gradually formed into 3D shapes using a generic forming tool. To further improve the forming accuracy and formability, an ultrasonic-assisted incremental forming process has been proposed. This study aims to explore how the superposition of ultrasonic vibration affects the contact behavior and material deformation mechanism during ISF process. First, finite element (FE) simulations were conducted using LS-DYNA to investigate the effects of ultrasonic vibration on a point-forming process. In particular, changes of vibration amplitude (5 µm, 10 µm and 20 µm), tool diameter (10 mm and 20 mm) and material type (AA1050 and AA5052) on forming forces and strain evolution have been presented. This leads to the discussion on the softening mechanism of the formed material. It was found that forming forces reduced considerably with increasing vibration amplitude, especially at later stage. However, the influences of tool size on forming force under ultrasonic (US) condition is two-sided. In terms of material type, softening effect is more profound for materials with larger yield strength. Besides, it was found that the effective plastic strain increases as the increase of the vibration amplitude. Larger tool diameter results in more uniform distribution of effective strain and higher formability. It was suggested that US vibration is a very promising strategy to promote ISF to satisfy industrial requirements. [ABSTRACT FROM AUTHOR]

This paper presents a detailed literature review on the current research of incremental sheet forming relating to deformation mechanism, modelling techniques, forming force prediction and process investigations. First, a review of the fundamental deformation mechanism and formability in incremental sheet forming (ISF) is provided. Subsequently, the modelling techniques for ISF are reviewed and categorised into two approaches: analytical modelling and finite element modelling. Special interest is given to a critical review regarding the forming forces analysis and prediction during the process. Then, previous publications related to geometric accuracy, surface finish and forming efficiency in ISF are reviewed. Finally, several potential hybrid incremental sheet-forming strategies are discussed. This leads to a statement of conclusion which may act as an inspiration and reference for the researcher. [ABSTRACT FROM AUTHOR]

The pyramid die extrusion for a hollow aluminum profile was analyzed to investigate the potential of such innovative dies. For this purpose, the pyramid and conventional porthole dies were respectively designed for a given hollow aluminum profile. And the extrusion process was comprehensively studied by performing different types of finite element simulation, such as the analysis of steady state, transient state and billet skin tracking. The effects of pyramid angle on the evaluation parameters of extrusion, such as extrusion load, material flow, exit temperature, length of transverse weld, quality of longitudinal weld, back end defect and die stress were overall analyzed and compared with the conventional porthole die. Through this study, the advantages and shortcomings of pyramid die were well concluded, which should be important information for die designers and makers. [ABSTRACT FROM AUTHOR]

In this paper, the 'trial-and-repair' process of the extrusion die is transferred from the workshop to the computer for a complex hollow aluminum profile used in high-speed trains. Firstly, a finite element (FE) model of the extrusion process is established with the arbitrary Lagrangian-Eulerian code HyperXtrude. To balance the material flow velocity in the die cavity, more than ten baffle plates are used and distributed in the welding chamber. Then, taking the exit velocity uniformity as the evaluating criterion, the initial extrusion die is modified by adjusting the shapes, the layout, and the heights of the baffle plates. Through a series of modifications, the velocity difference in the cross-section of the extrudate decreases significantly from 102.3 mm/s with the initial die to 26.6 mm/s with the final one. The local twisted or bent deformation of the extrudate is well controlled with the optimal die. Finally, a real extrusion die is manufactured and a practical profile is extruded. The difference in the rib thickness of the profile between the experimental measurements and desired dimensions is 0.12 mm, which satisfies the practical requirements. Moreover, the microstructures in the profile and its ribs are examined, and no heat defects are observed in the profile. Therefore, the virtual tryout of the extrusion die in this work are well verified, and the design rules of extrusion dies could provide theoretical guidance for practical repairs of complex extrusion dies in workshop. [ABSTRACT FROM AUTHOR]

Although the extruded profiles of 7005 aluminum alloy have been widely used in the components of high speed train, automobile and aircrafts, the plastic deformation behavior of homogenized 7005 aluminum alloy at evaluated temperature has not been fully clarified. In this study, the isothermal hot compression tests of homogenized 7005 aluminum alloy at the deformation temperatures ranging from 623 K to 823 K and with the strain rates ranging from 0.001 s −1 to 10 s −1 were conducted for constitutive analysis. It was found that the flow stress increased with decreasing deformation temperatures and increasing strain rates. Two Arrhenius-typed constitutive equations without and with the compensation of strain were developed based on the true stress–strain curves. Although both constitutive equations show their excellent predictability on the flow stress, the one considering the influence of strain has higher accuracy. Furthermore, the extrusion experiment and corresponding finite element simulation using the developed constitutive equation with strain compensation were carried out. The simulated results confirmed that the material flow behavior of the 7005 aluminum alloy during extrusion process was well predicted. [ABSTRACT FROM AUTHOR]

The continuous viscoelastic flow, swell and crystallization behaviors of polymer melts experienced within and through out of the die/mould can significantly influence the variation of internal structure, and hence determine the performance and dimension of final products in practical processing. However, traditionally theoretical and experimental methods are difficult to be afforded to this problem. In the study, the continuous viscoelastic flow, swell and crystallization behaviors of polymer melts within and through out of practically used die/mould are investigated by means of finite element-finite difference simulation. The mathematical model of three-dimensional viscoelastic flow of polymer melts is established with Phan-Thien and Tanner constitutive model. The streamface–streamline method is introduced to adjust the swelling free surface of the extrudate. The influence of the thermal and flow state on the crystallization phenomenon are discriminated using a modified Schneider’s approach. A decoupled solving algorithm for the governing equations is introduced and the corresponding penalty finite element-finite difference model is derived. The discrete elastic viscous split stress algorithm incorporating the streamline upwind scheme is adopted to improve calculation stability. The essential viscoelastic flow characteristics, extrudate swell phenomenon and flow induced crystallization of polymer melts in the hollow profile extrusion process are investigated based on the proposed mathematical model and numerical methods. Both the distribution of flow variables within the extrusion die and the variation of crystallization kinetic process within the shaped mould are successfully predicted by means of finite element-finite difference simulation of flow-swell-crystallization continuous behaviors of viscoelastic polymer melts. [ABSTRACT FROM AUTHOR]

SUMMARY The investigation of the extrusion swelling mechanism of viscoelastic fluids has both scientific and industrial interest. However, it has been traditionally difficult to afford theoretical and experimental researches to this problem. The numerical methodology based on the penalty finite element method with a decoupled algorithm is presented in the study to simulate three-dimensional extrusion swelling of viscoelastic fluids flowing through out of a circular die. The rheological responses of viscoelastic fluids are described by using three kinds of differential constitutive models including the Phan-Thien Tanner model, the Giesekus model, and the finite extensible nonlinear elastic dumbbell with a Peterlin closure approximation model. A streamface-streamline method is introduced to adjust the swelling free surface. The calculation stability is improved by using the discrete elastic-viscous split stress algorithm with the inconsistent streamline-upwind scheme. The essential flow characteristics of viscoelastic fluids are predicted by using the proposed numerical method, and the mechanism of swelling phenomenon is further discussed.Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A 3D thermomechanical finite element analysis model for laser tube bending is developed based on the software MSC/Marc. The processes of single- and multi-scan are analyzed numerically. The gradient and development of the temperature between the laser scanning side and the nonscanning side leads to the changing complexity of the stress and strain. Consequently, the length of the laser scanning side becomes shorter than that of nonscanning side after cooling. The length difference between both sides makes the tube produce the bending angle. The relationship between the number of scans and the bending angle is about in direct ratio. The bending angle induced by the first irradiated time is largest. Meanwhile, the finite element simulation is integrated with the genetic algorithm. Aiming at different process demands, corresponding objective functions are established. Laser power, beam diameter, scanning velocity, and scanning wrap angle are regarded as design variables. Process optimizations of maximum angle bending and fixed angle bending after single laser scan are realized. Groups of optimized process parameters can be obtained according to different optimization objectives. The bending angle can approach to the maximum when the laser power, spot diameter, scanning velocity, and scanning wrap angle are 381.24 W, 3.37 mm, 16.34 mm/s, and 123.1°, respectively. When the laser power, spot diameter and scanning velocity are 426.12 W, 4.9 mm, 14.31 mm/s respectively, a fixed angle bending can be achieved. [ABSTRACT FROM AUTHOR]

The forming limit diagrams (FLDs) of AZ31B magnesium alloy sheet at temperatures of 150,200, and 300°C were experimentally determined by conducting hemispherical punch stretching tests in combination with a grid measurement and analysis system. The effects of temperature on the forming properties of AZ31B magnesium alloy sheets were discussed. At temperatures below 150°C, brittle fracture occurs, while fracture occurs by ductile rupture at elevated temperatures above 200°C. The forming limit curves (FLCs) of AZ31B magnesium alloy sheet move upwards with the increase of temperature, but the shapes of FLCs under different temperatures are similar. The relationship between the major and minor principal strains can be described by using an equation, and all the equation parameters can be expressed as a function of temperature. Finally, the regression model of FLDs for AZ31B magnesium alloy sheet is established at different temperatures. The results calculated using the regression model are in good agreement with the experimental data. The regression model established in this article can be used as a fracture criterion in finite element simulation of AZ31B magnesium alloy sheet forming processes. [ABSTRACT FROM PUBLISHER]

Abstract: Boundary matching is an important problem in automatic generation of three-dimensional finite element meshes. In this paper, a combined algorithm for characteristic edge match of hexahedral meshes based on priority nodes and relative position relationships was proposed. The geometric and topologic conditions for characteristic edge (C-edge) match were firstly introduced. Seven types of free facet configurations and corresponding matching rules were established. A C-edge matching algorithm which combined priority nodes with relative position relationships was proposed by introducing priority nodes into the relative position relationship method. The identification method for each level of priority nodes was presented. The basic algorithms and implementation strategies of the combined method were introduced in detail. An effective method for characteristic point (C-point) match was also proposed on the basis of geometric topology and priority nodes. In addition, a method for treating the special sub-surface that intersected itself on a boundary line was proposed. A correction method was correspondingly proposed to deal with the nodes matched on unreasonable C-edges. Several examples of automatic meshing for hexahedral elements were provided to demonstrate the accuracy and effectiveness of the boundary matching algorithms proposed in this paper. The results show that the newly proposed algorithms not only can realize accurate match of mesh boundaries, but also establish reasonable geometric and topologic relationships of matched nodes. [Copyright &y& Elsevier]

Abstract: The thermally and flow induced crystallization behavior of semi-crystalline polymer in processing can significantly influence the quality of final products. The investigation of its mechanism has both scientific and industrial interest. A mathematical model in three dimensions for thermally and flow induced crystallization of polymer melts obeying differential Phan-Thien and Tanner (PTT) constitutive model has been developed and solved by using the finite element–finite difference method. A penalty method is introduced to solve the nonlinear governing equations with a decoupled algorithm. The corresponding finite element–finite difference model is derived by using the discrete elastic viscous split stress algorithm incorporating the streamline upwind scheme. A modified Schneider''s approach is employed to discriminate the relative roles of the thermal state and the flow state on the crystallization phenomenon. The thermally and flow induced crystallization characteristics of polypropylene is investigated based on the proposed mathematical model and numerical scheme. The half crystallization time of polypropylene in a cooled couette flow configuration obtained by simulation are compared with Koscher''s experimental results, which show that they agree well with each other. Two reasons to cause crystallization of polypropylene in pipe extrusion process including the thermal state and the flow state are investigated. Both the crystalline distribution and crystalline size of polypropylene are obtained by using the finite element–finite difference simulation of three-dimensional thermally and flow induced crystallization. The effects of processing conditions including the volume flow rate and the temperature boundary on the crystallization kinetics process are further discussed. [Copyright &y& Elsevier]

Abstract: The planar contraction flow is a representative benchmark problem that is often used as a stringent test for the robustness of the numerical method to predict real flow patterns of viscoelastic fluids. A numerical methodology based on the penalty finite element method with a decoupled algorithm is presented in the study to simulate three-dimensional flow of viscoelastic fluids through planar contraction. The viscoelastic rheological responses are described by using three kind differential constitutive models including the Phan-Thien–Tanner (PTT) model, the Giesekus model and the finite extensible nonlinear elastic dumbbell with a peterlin closure approximation (FENE-P) model. The discrete elastic viscous split stress (DEVSS) formulation in cooperating with the inconsistent streamline upwind (SU) scheme is employed to improve the computational stability. The simulation results of flow velocity and stress on different sections of the flow field are compared with Quinzani’s experimental results that detected by laser-doppler velocimetry and flow-induced birefringence technologies. It is found that the simulation results predicted with three kind differential constitutive models agree well with the experimental results. The numerical methodology proposed in the study can be used successfully to predict complex flow patterns of viscoelastic fluids. [Copyright &y& Elsevier]

Abstract: The mesh density has an important affect on finite element analysis of engineering problems. This paper studies the adaptive and local refinement techniques of hexahedral element meshes. A set of refinement templates and its converting rules of refinement fields are established. The refinement field propagation problem is solved using two corner templates and an isolated node template. A relative curvature criterion for constructing refinement source point fields is proposed by introducing the relative area of STL (stereo lithography) facets into the curvature criterion. The adaptive refinement of meshes can be easily realized using the constructed refinement source point fields. Examples show that the relative curvature criterion can more accurately capture the curvature features of solid models than the conventional curvature refinement criterion. To facilitate users and obtain the effective local refinement, this paper proposes a local refinement technique. The levels of local refinement can be self-controlled by users. The geometric features can be easily identified before each level of refinement. The effective refinement of nodes, elements, element-edges, element-surfaces, mesh-boundaries, mesh-faces and local regions can be realized. The accuracy and robustness of the adaptive and local refinement algorithms presented in this paper are demonstrated using several examples. The mesh refinement quality and flexibility are improved significantly. [Copyright &y& Elsevier]

A 3D finite element model of modal analysis has been established based on MSC.MARC software according to the practical structure of 195/60R14 radial tire. The rebar model is employed to simulate complex multilayer rubber-cord composites. The model considers the geometric non-linearity and the non-linear boundary conditions from tire-rim contact and tire-road contact. The modal test systems are developed for the free suspension tire and the grounding tire. The vibration characteristics of the radial tire are studied numerically and experimentally. Mode shapes (lobes) of the radial vibration are in a strong regularity with the change of the mode order. The first mode shape has two lobes, the second mode shape has three lobes, and so on. Changes of the inflation pressure do not affect the mode shape, but the natural frequency of higher mode shape is sensitive to the change of the inflation pressure. The mode shapes of the grounding tire become asymmetric due to the effect of the vertical load, and the frequency of each mode has a mutation when the vertical load is larger than 3000 N. It is in good agreement between the FEA and experimental results of the free suspension tire. [ABSTRACT FROM PUBLISHER]

In order to improve vehicle safety, the accurate determination of the tire's loading behaviour is necessary in the domain of vehicle dynamics. The interaction between the tire and the surface of the road must be understood thoroughly. A 3D finite element model of the tire-road has been built by using MARC software according to the actual construction of the 195/60R14 radial tire. The rebar model of the radial tire is employed to simulate the complex multilayer cord-rubber composites and directly define the cord directions varying with their positions. The geometric nonlinearity due to large deformation, material nonlinearity and the nonlinear boundary conditions from tire-rim contact and tire-road contact are also considered. The relationships between load and the tire deflection, the tire deformation, the contact stress distribution and the distribution of the contact friction force are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The layout of the heating/cooling channels is of great significance for rapid heat cycle molding (RHCM) mold with steam heating and coolant cooling because it not only affects heating/cooling efficiency, temperature uniformity of mold cavity surface, but also has a great influence on mold strength. Thermal, structural and fatigue analysis based on finite element method (FEM) is performed to investigate the effect of the heating/cooling channels layout on thermal response, structural strength and fatigue life of the RHCM mold. In order to obtain a reasonable layout of heating/cooling channels, this study focuses on the development of an effective methodology for the layout optimization of the heating/cooling channels by integrating response surface methodology (RSM) and multi-objective particle swarm optimization (MOPSO) algorithm. Three design variables describing the layout and scale of the heating channels are selected to do the design of Box-Behnken experiment with three factors and three levels. Thermal/structural analysis is carried out using ANSYS to obtain the corresponding values of three objective variables, including required heating time, maximum cavity surface temperature difference and maximum von-Mises stress due to thermal expansion, which are used to describe heating efficiency, temperature uniformity and mold strength, respectively, for different sets of design variables. RSM is utilized to analyze the effect of the design parameters and further construct mathematical models to quantitatively describe the relationship between design variables and objective variables via regression analysis. Analysis of variance (ANOVA) demonstrates that the developed quadratic models are highly effective and significant. Confirmation experiment is also conducted to verify the effectiveness and accuracy of the developed quadratic polynomial models. Based on these mathematical models, a MOPSO algorithm is then introduced to optimize the design variables by comprehensively considering thermal efficiency, temperature uniformity and structural strength of the RHCM mold. The optimum results show that thermal efficiency and temperature uniformity of the RHCM mold can be greatly improved with the optimum design variables for the layout of the heating/cooling channels. The following verification experiment demonstrates the validity of the optimum results. [Copyright &y& Elsevier]

The 3D finite element method modeling based on MSC.MARC software was studied and a non-linear FEM model was developed. The non-linear mechanical properties of elastomers were described by the Mooney—Rivlin model. The rebar model was employed to simulate complex multilayer rubber—cord composites and directly define the cord directions varying with their positions. The radial tire model was established based on consideration of the geometric non-linearity due to large deformation, the material’s non-linearities of cord—rubber composites, the non-linear boundary conditions from tire—rim contact and tire—road contact. The steady-rolling performance of 195/60R14 radial tire was analyzed numerically. Under free-rolling state, centrifugal force had a certain effect on the contact performance of the radial tire. Under load rating, the stiffness of tire increased with the increase of the rotary speed. Under braking state, high stress region moves to the direction contrary to the running direction. The high stress region moves to the running direction under driving state. Compared with braking condition, the level of normal stress and friction stress in the contact region was higher under the driving conditions. Cord equivalent stress of the tire belt was larger near the tire shoulder, and smaller in the center of contact zone. Cord equivalent stress increased sharply with the rotary speed. Meanwhile, the maximum cord equivalent stress was higher under the driving state. The gradient of strain energy density near the belt end was larger. The strain energy density of the tire shoulder was the largest. [ABSTRACT FROM AUTHOR]

Abstract: Quenching process is a thermo-elastic-plasticity problem with a high material non-linearity. The numerical oscillation is likely caused in the simulation of quenching process. In order to avoid the numerical oscillation and improve the calculation accuracy of temperature and phase-transformation fields in the quenching process, a new self-adaptive time-step size method is presented. The method can adjust the time-step size according to the maximum and minimum differences of temperature fields between the previous simulation step and the current simulation step. FEM software for evaluating the temperature, stress/strain and phase-transformation is also developed. A cooling example with numerical analytical results and a quenching example with experiment results are used to verify the calculation accuracy of this software. Five methods including the method in this paper, two constant time-step sizes and two geometric proportion time-step sizes are applied to simulate the quenching process of a 40Cr steel cylinder, respectively. A comparison of the simulation results shows that, the method presented in this paper can effectively avoid the numerical oscillation, ensure the calculation accuracy and cost less calculation time. [Copyright &y& Elsevier]

Abstract: In the paper, some hypotheses for the elastic–plastic metal material in quenching process are given. According to these hypotheses, Mises yield criteria and Prandtl–Reuss flow rule, the stress–strain relationships of elastic and plastic regions in quenched material are attained. Some key technologies for finite element method (FEM) based simulation of quenching process are presented, such as FEM equations of elastic–plastic problem, the method of computing right row vector, convergence regulation, elastic–plastic ratio and initial strains in quenched material. A finite element simulation software for evaluating the stress/strain fields in quenched material is developed. A thermal elastic–plastic problem with phase-transformation and a thermal elastic problem without phase-transformation are simulated using the software. The comparisons between the simulation results and experimental/analytical results show that the simulation results are consistent with the experimental results or the analytical results. [Copyright &y& Elsevier]

A three-dimensional non-linear FEA model of radial tire was established. The rebar model was employed to simulate complex multilayer cord-rubber composites and directly define the cord directions varying with their positions. Meanwhile, the geometric non-linearity due to large deformation, material non-linearity, and the non-linear boundary conditions from tire-pavement static camber contact were considered. The static camber performance of the radial tire was studied. Relationships among load and the tire deflection, the tire deformation, contact stress distribution, contact friction force distribution, side force, and deflection were discussed. A set of special testing equipment was designed to realize quasi-static loading with continuous loading and unloading. Then the static camber performance of the radial tire was tested. The contact pressure distribution and the shape of contact area in different camber states of the tire were measured by pre-scale films. The simulation result was in good agreement with the test result. [ABSTRACT FROM AUTHOR]

Abstract: Several technological parameters have an effect on residual stress, hardness, distortion and other quenching results in the process of high pressure gas quenching. In order to research the effect of technological parameters, finite element method (FEM) is used to simulating the high pressure gas quenching in the paper. The evaluation functions are built on the average surface hardness, the standard deviation of surface hardness, the average equivalent residual stress of surface, the standard deviation of surface equivalent residual stress and the distortion of quenched part. The heat transfer coefficient, the preheat temperature and the quenchant temperature are regarded as the objective variables to evaluating their effects to the quenching results in the paper. The research results show that, the heat transfer coefficient is the most important factor of affect the quenching result, the preheat temperature and the quenchant temperature have a slight effect on the quenching result. The heat transfer coefficient is a perfect objective variable for optimization. [Copyright &y& Elsevier]

Abstract: Equal channel angular pressing (ECAP) has the capability to process sub-structured or nano-structured bulk ultra-fine grained (UFG) materials. ECAP is largely influenced by process routes and process parameters changed which includes die geometries, friction conditions and so on. Those factors have effected homogeneous distribution of accumulated effective strain in the workpiece largely. In this paper, the distribution rules of accumulated effective strain in the main deformation zone of workpiece during ECAP with different die channel angles and corner angles are presented by a great deal simulations. Optimal processing route, uniformity of deformation distribution and load stroke curves of ECAP is observed with optimize processing parameters by node mapping method. The obtained count results and rules can offer valuable guidelines for ECAP die geometries optimization and uniformity effective strain distribution in the workpiece. [Copyright &y& Elsevier]

Abstract: Bulk ultra-fine grained (UFG) materials can be obtained by equal channel angular pressing (ECAP) process. Using our own commercial metal forming finite element code CASFORM/PC, ECAP process is analyzed numerically in this paper. The grain refinement mechanism is presented. The node mapping method is employed to realize the analysis of multi-pass ECAP process. Rules of acquiring the uniform deformation distribution of the final workpiece are put forward for pure aluminum material. The obtained results can offer valuable processing parameters and optimal processing routes of ECAP for producing UFG materials. Meanwhile, the microstructure evolutions of grain refinement mechanisms for different multi-pass ECAP processing routes are verified by using ECAP experiments and microstructure analysis. Through the numerical simulations and experimental studies, the uniformly deformed UFG materials with high angle grain boundary microstructure can be obtained by adjusting processing routes and parameters. The formation mechanism of nanostructure was given for the ECAP through studying the deformation behavior and dislocation''s evolution. The process of grain refinement can be described as continuous dynamic recovery and recrystallization. From the viewpoint of the microstructure analysis, the grain refinement process is to control the dynamic balance of the generation and annihilation of the dislocations. From the viewpoint of the macro deformation analysis, the grain refinement process is to seek optimal processing routes. [Copyright &y& Elsevier]

Abstract: Equal channel angular pressing (ECAP) is one of the important methods to produce bulk ultra-fine grain materials. This paper gives three kinds of processing routes for round billet, named as A, B and C, respectively. The processing routes A, B and C are analyzed in detail by using finite element method with node mapping method through rotating three-dimensional model in multi-pass pressing. The distribution of accumulated effective strain and the rules of deformation uniformity of three pressing routes for round workpiece are obtained. The better processing route is acquired through comparing the results of three pressing routes. Influences of different die channel angles on deformation uniformity are studied. The grain refinement mechanisms of equal channel angular multi-pressing for different processing routes are obtained. The obtained results can offer valuable guidelines for ECAP experiments and practical process planning. [Copyright &y& Elsevier]

In this paper, an optimization method for metal forming processes, especially for forging process designs using finite element based sensitivity analysis method is briefly introduced. On the basis of the authors’ previous studies, this paper gives further improvements concerning several critical techniques of the optimization method. An approach for improving the computational efficiency is introduced and demonstrated. After introducing the optimization method of multi-stage forming processes, the paper presents an optimization method for single stage forming processes. The initial billet dimension is optimized for achieving a net-shape final forging. Besides, the paper also gives a method for dealing with the velocity sensitivity boundary conditions for both moving upper dies and stationary lower dies. Using this boundary condition treatment method, not only can we optimize the upper die shape but also the lower die shape, even if both of the dies have different shapes. The paper also extends the optimization to the more complex forming processes with multiple cavities. [Copyright &y& Elsevier]

The kinetic model of liquid silicone rubber hydrosilation is determined with measuring apparatus for vulcanization extent. The definition of increment of vulcanization ratio is introduced, so the numerical computation expression of the full dose of vulcanization ratio is obtained. The foundational control equation of the vulcanization temperature field accompanied by reaction heat is derived. Then two types of thermal boundary conditions are analyzed. The implementation procedures of the finite element simulation are described in detail. Finally, the finite element simulation software of hot vulcanization process of moldable silicone rubber is designed, and the rationality of the simulation theory and algorithm is verified by one typical engineering example and its hardness test as well as its engineering application. [ABSTRACT FROM AUTHOR]

A finite element based sensitivity analysis method for preform die shape design in metal forging by controlling the deformation uniformity is developed in this paper. The optimization problem is to minimize the effective strain variation within the final forging through optimizing the preform die shape, so that a more uniform deformation within the final forging can be obtained. The preform die shapes are presented by cubic B-spline curves. The control points of the B-spline curves are used as the design variables. The objective function expressed by the effective strain variation is constructed. For two-dimensional forging problems, the sensitivity equations of the objective function, elemental volume, elemental effective strain-rate and the elemental strain-rate with respect to the design variables are developed. The optimization procedures of the method are given. The preform die shapes of two H-shaped forging processes in axisymmetric and plane-strain deformation are designed using the method. [Copyright &y& Elsevier]

Preform design in forging processes is an important aspect for improving the forging quality and decreasing the production cost. Forward and backward simulations of the forging process based on rigid visco-plastic finite element methods (FEMs) can directly provide a preform shape from the final forged shape at a given stage. The objective of this effort is to reduce the material lost as flash by the design of an improved busting operation for a track link forging. This paper uses the FEM-based inverse die contact tracking method to design the preform shapes for a representative plane-strain cross section of the track link blocker forging. This procedure establishes a record of the boundary condition time sequence via forward simulation, using a candidate preform, into the final forged shape. This recorded time sequence is then modified according to the material flow characteristics and the state of die fill to satisfy the requirement of material utilization and forging quality. The modified boundary condition sequence is then applied to control die/node separation during the backward deformation simulation. The backward simulation for the section analyzed provided the blocker preform shape from which the buster dies can be designed. The preform for the section is then evaluated by forward FEM simulation and compared with the results from the original busting operation. Performance measures for the comparison includes die fill, flash size, strain variance, frictional power and die load. Use of round billet stock was also investigated for producing the required preform shape. [Copyright &y& Elsevier]