Plastic flow and interfacial bonding behaviors of embedded linear friction welding process:Numerical simulation combined with thermophysical experiment

In this study,a new linear friction welding(LFW)process,embedded LFW process,was put forward,which was mainly applied to combination manufacturing of long or overlong loadcarrying titanium alloy structural components in aircraft.The interfacial plastic flow behavior and bonding mechanism of this process were investigated by a developed coupling EulerianLagrangian numerical model using software ABAQUS and a novel thermo-physical simulation method with designed embedded hot compression specimen.In addition,the formation mechanism and control method of welding defects caused by uneven plastic flow were discussed.The results reveal that the plastic flow along oscillating direction of this process is even and sufficient.In the direction perpendicular to oscillation,thermo-plastic metals mainly flow downward along welding interface under coupling of shear stress and interfacial pressure,resulting in the interfacial plastic zone shown as an inverted“V”shape.The upward plastic flow in this direction is relatively weak,and only a small amount of flash is extruded from top of joint.Moreover,the wedge block and welding components at top of joint are always in un-steady friction stage,leading to nonuniform temperature field distribution and un-welded defects.According to the results of numerical simulation,high oscillating frequency combined with low pressure and small amplitude is considered as appropriate parameter selection scheme to improve the upward interfacial plastic flow at top of joint and suppress the un-welded defects.The results of thermo-physical simulation illustrate that continuous dynamic recrystallization(CDRX)induces the bonding of interface,accompanying by intense dislocation movement and creation of many low-angle grain boundaries.In the interfacial bonding area,grain orientation is random with relatively low texture density(5.0 mud)owing to CDRX.

Generalizing J_2 flow theory: Fundamental issues in strain gradient plasticity

It has not been a simple matter to obtain a sound extension of the classical J2 flow theory of plasticity that incorporates a dependence on plastic strain gradients and that is capable of capturing size-dependent behaviour of metals at the micron scale. Two classes of basic extensions of classical J2 theory have been proposed： one with increments in higher order stresses related to increments of strain gradients and the other characterized by the higher order stresses themselves expressed in terms of increments of strain gradients. The theories proposed by Muhlhans and Aifantis in 1991 and Fleck and Hutchinson in 2001 are in the first class, and, as formulated, these do not always satisfy thermodynamic requirements on plastic dissipation. On the other hand, theories of the second class proposed by Gudmundson in 2004 and Gurtin and Anand in 2009 have the physical deficiency that the higher order stress quantities can change discontinuously for bodies subject to arbitrarily small load changes. The present paper lays out this background to the quest for a sound phenomenological extension of the rateindependent J2 flow theory of plasticity to include a de- pendence on gradients of plastic strain. A modification of the Fleck-Hutchinson formulation that ensures its thermo- dynamic integrity is presented and contrasted with a comparable formulation of the second class where in the higher or- der stresses are expressed in terms of the plastic strain rate. Both versions are constructed to reduce to the classical J2 flow theory of plasticity when the gradients can be neglected and to coincide with the simpler and more readily formulated J2 deformation theory of gradient plasticity for deformation histories characterized by proportional straining.

Multi-layer Tectonic Model for Intraplate Deformation and Plastic-Flow Network in the Asian Continental Lithosphere

In a large area of the east—central Asian continent there is a unified seismic network system composed of two families of large—seismic belts that intersect conjugately. Such a seismic network in the middle—upper crust is actually a response to the plastic flow network in the lower lithosphere including the lower crust and lithospheric mantle. The existence of the unified plastic flow system confirms that the driving force for intraplate tectonic deformation results mainly from the compression of the India plate, while the long-range transmission of the force is carried out chiefly by means of plastic flow. The plastic flow network has a control over the intraplate tectonic deformation.

Homogeneous Plastic Flow of Fully Amorphous and Partially Crystallized Zr_(41.2)Ti_(13.8)Cu_(12.5)Ni_(10)Be_(22.5) Bulk Metallic Glass

The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.

THE VOID-SIZE EFFECT ON PLASTIC FLOW LOCALIZATION IN THE GURSON MODEL

Recent studies have shown that the size of microvoids has a significant effect on the void growth rate.The purpose of this paper is to explore whether the void size effect can influence the plastic flow localization in ductile materials.We have used the extended Gurson's dilatational plasticity theory,which accounts for the void size effect,to study the plastic flow localization in porous solids with long cylindrical voids.The localization model of Rice is adopted,in which the material inside the band may display a different response from that outside the band at the incipient plastic flow localization.The present study shows that it has little effect on the shear band angle.

Quantitative Expression of Heat Flow versus Tectonic Deformation in the China Continent: The Effects of Plastic-Flow Network and Stable Block

Based on the heat flow data published in 1990 and 2001, a study of the factors influencing the terrestrial heat flow distribution in the China continent and its quantitative expression is carried out using the ＂Netlike Plastic-Flow＂ continental dynamics model and the methods of statistic analysis and optimum fitting. The result indicates that the factors influencing the heat flow distribution is classified into two groups, i.e. background and tectonic ones, in which the former mainly involves the non- uniform distribution of mantle heat flow, heat production of radioactive dements in the crust, heattransfer media and hydrothermal circulation, while the latter mainly involves plastic-flow networks and relatively-stable blocks. The plastic-flow network is a manifestation of shear localization in the netlike plastic-flow process in the lower lithosphere, which is composed of two sets of plastic-flow belts （PFBs） intersecting each other and, as one of the basic action regimes, controls the intraplate tectonic deformation. Relatively stable blocks （RSBs）, which are the tectonic units with relatively-high viscosities existing in the netlike plastic-flow field, as one of the principal origins, result in the development of large-seale compressional basins. PFB and RSB, as the active and quiet states of tectonic deformation, give rise to the higher and lower heat flow values, respectivdy. The provincial average heat flow in continent can be estimated using the expression qav = q0 ＋ a Pbt-c Pbk, where the three terms of the right side are background heat flow, PFB-positive contribution and RSB-negative contribution, Pbt and Pbk are the PFB- and RSB-coverage ratios, respectively, a is the coefficient of PFB- positive contribution depending mainly on the strain in the lower lithosphere, and c is the coefficient of RSB-negative contribution related mainly to the thickness of the lithosphere, the aseismic-area ratio and the tectonic age. For the major portion of the China continent excluding some of the southeastern region of China, the confidence interval of the provincial average background heat flow is qo=57.25±24.8 mW/m^2 and the PFB-positive- and RSB-negative-contribution coefficients are a=14.8-71.9 mW/m^2 and c=0-25.6 mW/m^2, respectively. The concepts of PFB and RSB effects and the heat flow expression suggested provide a new choice of the approach to the quantitative description of the characteristics of heat flow distribution in continent and their physical mechanisms.

A phenomenological model for plastic flow behavior of rotating band material with a large temperature range

The plastic flow behavior of the rotating band material is investigated in this paper. The rotating band material is processed from H96 brass alloy, which is hardened to a much higher yield strength compared to the annealed one. The dynamically uniaxial compression behavior of the material is tested using the split Hopkinson pressure bar(SHPB) with temperature and strain rate ranging from 297 to 1073 K and500 to 3000 s^(-1), respectively, and a phenomenological plastic flow stress model is developed to describe the mechanical behavior of the material. The material is found to present noticeable temperature sensitivity and weak strain-rate sensitivity. The construction of the plastic flow stress model has two steps. Firstly, three univariate stress functions, taking plastic strain, plastic strain rate and temperature as independent variable, respectively, are proposed by fixing the other two variables. Then, as the three univariate functions describe the special cases of flow stress behavior under various conditions, the principle of stress compatibility is adopted to obtain the complete flow stress function. The numerical results show that the proposed plastic flow stress model is more suitable for the rotating band material than the existing well-known models.

Plastic-Flow/Seismic" Network Systems and Tectonic Units in Central-Eastern Asia

The study of the netlike earthquake distribution indicates that in the central-eastern part of Asia continent there are two network systems: the central-eastern Asia system and the southeastern China system.As interpreted by the multilayer tectonic model,they might be a manifestation of the plastic-flow network systems in the lower lithosphere,including the lower crust and the mantle lid.Each network system is enclosed by different types of boundaries,including one driving boundary and some constraining and releasing boundaries.The two plastic-flow network systems with the Himalayan and Taiwan arcs as their driving boundaries play the role of controlling the intraplate tectonic deformation,stress field,seismicity,and subdivision of tectonic units.

Investigation of semi-solid aluminum alloy filling-plastic flowing in thixoforging

The semi-solid filling-plastic flowing integrated forging process of semi-solid 6061 Al alloy was simulated by commercial finite element software DEFORM-3D.Temperature,fluid and stress-strain fields were considered in numerical simulation.The simulation results show that the plastic deformation of billet of the ends is higher than that of billet in the straight cylinder.The value of plastic deformation varies with loading mode and plastic deformation fields at the stage of increasing pressure to constant value.When the thixoforging experiments were performed at 590 ℃,15 mm/s of punch velocity and 46 MPa of pressure side urn,it gets the filling wholly and dense internal organization of semi-solid thixoforging parts is gotten.Finite element analysis results are compatible with experimental ones.

Photoplastic Experimental Research on Material Plastic Flow Law of Connecting Rods during Finish Process

Photoplastic experiment were conducted with connecting rods of AX100 motorcycle engine during finish forging to investigate material plastic flow law of long -axis forgings with comples geometrie’s by observing

Flow stress model considering the transformation-induced plasticity effect and the inelastic strain recovery behavior

On the basis of continuum mechanics and the Mori-Tanaka mean field theory, a micro-mechanical flow stress model that considered both the transformation-induced plasticity （TRIP） effect and the inelastic strain recovery behavior of TRIP multiphase steels was presented. The relation between the volume fraction of constituent phases and plastic strain was introduced to characterize the transformation-induced plasticity effect of TRIP steels. Loading-unloading-reloading uniaxial tension tests of TRIP600 steel were carried out and the strain recovery behavior after unloading was analyzed. From the experimental data, an empirical elastic modulus expression is extracted to characterize the inelastic strain recovery. A comparison of the predicted flow stress with the experimental data shows a good agreement. The mechanism of the transformation-induced plasticity effect and the inelastic recovery effect acting on the flow stress is also discussed in detail.

STUDY ON FLOW STRESS OF 7022 ALUMINUM ALLOY SHEET UNDER DIFFERENT TEMPERATURES AND STRAIN RATES

Warm tensile tests for aluminum alloy 7022 sheet are held at different temperatures and strain rates. The range of temperature is 293-773 K and that of the strain rate is 0. 001-0.1 s^-1. The warm tensile properties,relations among temperature,strain rate,and the flow stress are discussed. Constitutive equations under the warm tension are obtained based on revised Hooke law and Grosman equation. It is concluded that flow stress declines with the increase of the temperature and the decrease of the strain rates. The elongation percentage increases with the increase of the temperature and the decrease of strain rate.

基于Flow Simulation的气力脱膜装置流场分析

为解决目前残膜回收机脱膜难题,设计了一种气力脱膜装置。采用SolidWorks软件对该装置进行了几何建模,利用其附带的CFD插件Flow Simulation对模型进行流场特性模拟,得出了在不同结构参数下吹气口压强和风速的分布特性。结果表明:圆室圆口风箱吹气口的压强和风速均比方室方口风箱大,在风箱入口风压为101 826 Pa、流量为2 006 m3/h时,吹气口最小风压为101 462.83 Pa,最小风速为11.729 m/s,能够很好地满足脱膜条件。此研究结果可以为气力脱膜机械的研发提供参考。

Moldflow在塑料注射模CAE中的应用

阐述了注塑模具CAE技术的概念,并通过三个应用案例说明注塑模分析软件Molflow在塑料注射成型中浇口位置分析、熔体流动分析及冷却分析中的应用。最后对未来注塑模CAE技术的发展趋势进行了展望。

基于MoldFlow的塑料流动分析及应用

详细介绍了MPI/Flow的塑料流动分析功能以及分析步骤,并运用MPI/Flow软件进行了实例分析,显示了CAE技术在模具开发过程中对于最佳浇口位置与浇口数量的确定、流道系统的布置等方面起到了突出的作用。

基于Moldflow的薄板塑件翘曲成因与改善措施

采用Moldflow软件的MPI模块分析薄板类塑件在注射成型过程中是否会出现翘曲,产生翘曲的主要原因以及改善翘曲的方法。分析认为,产生翘曲的主要原因是塑件在成型冷却过程中存在不同方向的收缩,可以通过改进模具结构,改善成型工艺条件来减小塑件在不同方向的收缩,从而减小翘曲变形。

基于Moldflow的双色注射模设计

基于Moldflow MPI软件,对双色塑件的成型过程进行模拟分析,设计了一副连体式热流道双色注射模,分析了双色注射模设计的关键,阐述了模具的工作过程。模具已应用于生产,成型的塑件质量良好。

基于Plastic Advisor 7.0的注塑模具模流分析的研究与应用

分析了传统注塑模具设计方法中存在的不足,介绍了利用Pro/E Wildfire 4.0内建的Plastic Advisor 7.0软件进行模流分析的方法和技巧,并对风机盖塑件实例进行了详细的模流分析,指出了借助计算机辅助工程分析软件可大幅度提高注塑模具的设计效率、产品的合格率,缩短了产品的开发周期。

基于Creo-Plastic Advisor的注塑模具模流分析与模具设计

Creo作为美国参数技术公司(PTC)推出的设计软件,在机械CAD/CAE/CAM领域应用广泛,Creo针对塑料产品设计和注塑模具而开发的模流分析系统可对塑料产品进行填充分析。以遥控器前盖为例,详细介绍了应用Creo中的Plastic Advisor功能对塑件进行最佳浇口位置、塑料填充、冷却质量、缩痕分析的方法和过程。根据分析结果进行浇注系统设计和注塑参数优化,根据产品结构特点进行侧向分型滑块机构和模架设计,最终完成遥控器前盖模具的结构设计。研究表明,使用Creo的Plastic Advisor对塑件进行模流分析,方法易于掌握,分析结果可靠有效,能够帮助设计者提高模具设计效率,缩短设计周期,降低设计成本。

基于Moldflow的塑料伞柄注射模设计

以塑料伞柄注射模设计为例,通过分析软件Moldflow对塑料熔体充模时间、注射压力、体积收缩率以及塑件熔接痕和翘曲变形等进行模拟分析,并根据模拟结果优化模具设计方案,从而提高塑件质量,节约模具开发时间和成本。