考虑材料参数的刚粘塑性有限元初始速度场自动生成方法

本文采用一种包含材料硬化指数ｎ和速率敏感性指数ｍ的刚粘塑性有限元模型，阶段硬化处理考虑到等效应力公与应变率有关，依据线粘性材料假设，提出了考虑材料参数ｎ、ｍ影响的刚粘塑性有限元初始速度场自动生成方法，改进了文献［３］方法。数值模拟结果与有关文献的计算和实验结果进行了比较，表明本文方法是有效的。     

Modelling of the thermomechanical coupling during hot forming of viscoplastic materials

In the present paper, a strategy for solving transient thermoviscoplastic problems is described. The general thermal and mechanical coupling phenomena are discussed by assuming material properties to be temperature-dependent and accounting for the mechanical terms in the non-stationary heat conduction equation. Time integration is carried out with an implicit scheme. An interesting version of the three-field approach is presented to obtain an accurate solution for the stress field. Finally, a global product coupling algorithm, in which the unknown nodal velocities and temperatures are solved with a two-step solution procedure is suggested. The proposed fractional step method partitions the initial coupled problem into an isothermal viscoplastic problem followed by a purely heat conduction problem at fixed configuration. Applications in metal forming analyses involving full thermomechanical coupling conclude the paper.     

A Lubrication Deviation From the Classical EHL Theory by the Lubricant Viscoplasticity: Part II — Boundary of Lubrication Regimes

This paper distinguishes elastahydrodynamic lubrication (EHL) regimes in isothermal pure rolling case as three kinds according to lubricant rheology. In these regimes, the lubricants are respectively viscoelastic, viscoplastic, and non-continuum. Mathematical expressions are introduced ta describe the boundaries among these three regimes. H_c - r_it and U - W charts respectively plot the operational scopes of these lubrication regimes. The present study holds significance to understanding EHL film formation and more clearly embodies elastohydrodynamic film failure stage transitions.     

Rapid implementation of material models within finite element analysis

This paper presents a simple procedure for obtaining a numerical approximation to the consistent tangent matrix, together with a straightforward implicit (Euler backward) integration algorithm. The combined algorithm is used to incorporate four models into the commercial finite element package ABAQUS/Standard; illustrating how it can be used to rapidly implement material models within finite element analysis. The models have been chosen, not only because they help to illuminate the structure of the algorithm, but also because they illustrate its wide ranging applicability and permit the procedure to be tested against analytical results and an existing, well established, model.     

DESCRIPTION OF A THERMO-INELASTIC BODY WITH A MOVING SOLID/LIQUID INTERFACE AND SIMULATION OF THE WELDING PROCESS

Conservation laws of mass, momentum, and energy for the thermo-inelastic body in the region involving the moving interface between the solid and liquid are introduced to derive jump conditions of velocity, stress, and energy on the interface as the sequence of local form for the generalized Reynolds transport theorem. The jump condition of energy is revealed to be the generalized Stefan condition for moving interface problems. The finite element formulation is used to analyze the modes of flow, deformation, and stresses in a melting or solidifying process by employing a viscoplastic constitutive equation that describes the mechanical behavior of both the solid and liquid phases. The mathematical formalism is applied to simulate bead-on plate welding.     

Numerical and experimental analysis of superplastic-like uniaxial tensile necking of coarse-grained LY-12

In this work, numerical and experimental studies of superplastic-like uniaxial tensile behavior of coarse-grained LY-12 have been performed. Larger tensile elongation to fracture is observed and several necks are exhibited at 10⁻¹ and 10⁻⁴ s⁻¹ respectively although not very clearly. Chaboche viscoplastic constitutive equations are used and implemented in a finite element code to simulate the process of necks formation and development before fracture during uniaxial tension. The simulated characteristics of more than one necks along the specimens help to obtain large elongation, which is in agreement with experimental observations. Local strain rate distribution as the function of strain can explain how and when microscopic necks take place.     

粘塑性挤压成形变形规律研究

为了寻求一种能全面揭示象等温和超塑性这类粘塑性复合挤压成形变形规律的方法，采用刚一粘塑性有限元对常温具有粘塑性行为的工业纯铅复合挤压进行了数值模拟。计算结果揭示了变形规律，如分流层的变化、速度场的分布、折叠缺陷的形成及原因等。计算表明，粘塑性复合挤压成形的最大变形区集中在凸模拐角处，变形分布梯度随着变形程度的增大而变小。增大变形速度、改善润滑条件有助于提高变形均匀性。对新旧网格的场变量传递、翻边现象的处理及初始速度场生成，采用有效的处理方法     

Electrorheological responses of particulate suspensions and emulsions in a small-strain dynamic shear flow: Viscoelasticity and yielding phenomena

The dynamic rheological behavior of multiphase electrorheological (ER) fluids was considered, as continuation of a previous paper [Chin and Park, 2000]. Oil-in-oil emulsions, which differ in electrical conductivity and dielectric constant, were employed for an ER-active emulsion and also for a multiphase ER fluid with enhanced performance. The polyaniline particle suspension in an electric field showed viscoelastic behavior within a very limited range of strain amplitude, indicating the transition from viscoelasticity to viscoplasticity. Within the region of visco-elasticity, the linear region was restricted below the amplitude of 0.1%, whereas the ER-active emulsions showed a rather wide linear regime. Frequency dependence of the storage shear modulus in the linear viscoelastic region revealed the typical features of an elastic solid. When the fraction of emulsion drops (Ф) in multiphase ER fluids increased, the limiting strain for viscoelasticity showed a higher value.     

Finite element analysis for the semi-solid state forming of aluminium alloy considering induction heating

The major objective of this study is to establish an analytical technique in order to investigate the behavior of semi-solid material considering induction heating of the workpiece. The induction heating process is analyzed using the commercial finite element software, . The finite element program, , for the simulation of deformation in the semi-solid state is developed in the present study. The behavior of semi-solid material is described by a viscoplastic model for the solid phase and by Darcy’s law for the liquid flow. Simple compression and closed-die compression processes considering induction heating are analyzed. To validate the effectiveness of the proposed analytical technique, the results of simulation are compared with those of experiment.     

Simulation of deformation and lifetime behavior of a fcc single crystal superalloy at high temperature under low-cycle fatigue loading

This work deals with the formulation of a three-dimensional crystallographic time-incremental lifetime rule for face-centered cubic (fcc) single crystals used for gas-turbine blade applications. The damage contribution rate of each slip system to the total damage is governed by the current values of the resolved shear stress and the slip rate on the corresponding slip system. The damage rule is combined with a crystallographic viscoplastic deformation model. For the nickel-base single-crystal superalloy CMSX4 at 950 °C, various strain- and stress-controlled uniaxial cyclic tests with and without hold-times can be described for different crystal orientations by one set of material parameters. For verification, simulation results for a single-crystal specimen with a notch have been compared with corresponding experimental results. The predicted lifetime is within the factor of two of the measured one.