6061铝合金触变压缩数值模拟

基于连续多孔介质的材料模型方法,将半固态材料假设为连续可压缩多孔介质骨架,利用DEFORM有限元软件进行单轴压缩模拟,分析触变成形过程中应变速率对6061铝合金成形性能的影响,得出初始固相体积分数为0.82的半固态6061铝合金的固相率分布及应变应力场分布。模拟结果表明,随着变形程度的增大,材料中心区域固相率分布较边缘均匀,随着变形速度的增加,材料的等效应变场分布与固相率分布呈现出相同的变化趋势。模拟曲线与实验曲线吻合,证明了数值模拟的可行性。     

镁合金汽车轮毂半固态触变成形的刚-粘塑性有限元分析

镁及镁合金由于具有比重低、较高的比强度和比刚度、优良的电磁屏蔽性和阻尼性能等优点,日益受到人们的关注,作为结构和功能元件已越来越多的应用于汽车、电子等行业。采用半固态方法生产的镁及镁合金零部件,可以大大降低或消除通常压铸方法产生的气孔或疏松。采用Gleeble-1500热模拟机,对半固态AZ91D镁合金进行大量、系统的单向压缩试验,以此研究AZ91D镁合金在半固态温度区间的变形力学行为,建立AZ91D合金不同温度、应变和应变速率下的粘塑性本构关系,在此基础上采用DEFORM-3D商用软件模拟镁合金轮毂触变成形过程,得到触变成形过程流动和应力-应变场以及他们之间的关系。上述工作为镁合金半固态触变成形过程的实际应用和零件质量的提高打下基础。     

镁合金半固态坯料重熔过程数值模拟

选取了有限元软件ANSYS对镁合金半固态坯料重熔过程进行了数值模拟,并采用电磁感应加热方法。该方法不仅可以提高加热速度,还能使温度均匀化。通过改变电流密度、加热时间、初始温度及频率等参数,找出加热参数与坯料重熔参数之间的关系,以取得通过控制加热工艺参数来获取理想的镁合金半固态坯料组织的理论依据,从而指导生产过程。将所模拟的几组数据比较,选择电流密度为15e6Mm^2,对生产比较有利。考虑到实际的条件。提出了较低电流密度与多极加热结合的想法指导生产。     

厚壁筒形工件连续感应热处理有限元模拟

对麦克斯威方程组和导热微分方程进行分解化简 ,得到计算无限长轴对称工件的电磁场、感生涡流和温度场分布的基本方程。基于这些方程在ANSYS软件上实现了对厚壁筒形工件连续感应热处理的计算机模拟计算。计算了加热、淬火和回火等热处理过程中 ,工件温度变化和加热功率变化 ,预测工件淬火冷却时的组织转变 ,计算中考虑了工件材料物理参数随温度变化对加热过程的影响。通过模拟计算 ,实现了对连续感应热处理工艺的优化分析 ,而且找到了一种对连续感应热处理设备结构设计和工艺参数配置优化的方法     

半固态镁合金AZ91D变形行为研究

对应变诱发法制得的半固态镁合金AZ91D坯料进行了单向压缩实验,研究了不同工艺参数对半固态镁合金的压缩流变应力的影响。流变应力不仅是变形量和变形温度的函数,而且是应变速率的函数,由此采用回归分析法建立了能综合反映热力参数对流变应力影响的半固态AZ91D合金的粘塑性本构方程,为半固态触变成形的数值模拟奠定了理论基础。     

MB15镁合金半固态压缩力学行为研究

通过MB15镁合金半固态等温压缩试验，研究了半固态材料的力学行为，提出了触变强度是半固态金属在稳态变形过程中触变点的应力，即半固态金属固体骨架所能承受的最大正应力，并分析了加热温度、应变速率、保温时间、固相晶粒大小、晶粒圆整度及材料本身的强度等因素对半固态触变强度的影响，提出了触变强度的存在条件。结果表明，半固态触变强度随着加热温度的升高、应变速率的降低及保温时间的延长而降低，随着固相晶粒的减小、晶粒圆整度的增加及材料本身强度的增加而增加；当半固态材料内部的固相颗粒相互连结形成固体骨架时，存在触变强度。     

Finite element analysis of the wrinkling initiation and growth in modified yoshida buckling test

Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation and growth of wrinkles are influenced by many factors such as stress ratios, mechanical properties of the sheet material, geometry of the workpiece, contact condition, etc. In the study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element method. The wrinkling initiation is found by checking the determinent of the stiffness matrix at each iteration and the wrinkling behavior is analyzed by successive iteration with the perturbed guess along the eigenvector. The effept of magnitude of perturbation on the wrinkling behavior can be avoided by the Newton-type iteration method. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. The finite element analysis is carried out using the continuum-based resultant shell elements considering the planar anisotropy of the sheet metal. In order to investigate the effects of geometry and stress state on the wrinkling initiation and growth, a modified Yoshida buckling test is proposed as an effective buckling test. The finite element analysis are carried out for the modified Yoshida buckling test. The buckling behavior of the sheet is analyzed for various modified dimensions.     

ZL112Y半固态连续触变成形料坯的温度场数值模拟

根据半固态连续触变成形的原理,自行设计了一套水平式二次重熔连续感应加热装置。采用商业软件ANSYS对该装置的3台感应加热设备不同加热功率匹配下料坯的温度场进行了计算机模拟,可得到与ZL112Y铝合金所需半固态触变温度为570-572℃相吻合的结果。而且通过模拟,获得了坯料连续式二次重熔时合理的加热参数,即大、中、小3种加热功率设备的电流分别为1350、800、600A,依次加热3min,得到的坯料温度接近于理想的半固态温度。     

感应透热有限元模拟分析

采用有限元分析法和ANSYS软件，引入复矢量磁位，推导了感应加热有限元模拟的数学模型。讨论了感应加热有限元分析中温度场与电磁场耦合、工件材料物理参数温度依赖性等关键技术问题的处理方法。分析了圆柱工件的感应透热过程，得到了坯料内的温度分布状况以及温度随时问的变化规律。结果表明，数值模拟结果与工程实际应用工况基本一致。     

一种制动杠杆螺栓用不锈钢热变形行为及锻造工艺

为研究一种制动杠杆螺栓用不锈钢材料的热变形行为及锻造工艺,利用热模拟试验机对材料进行了高温压缩试验,得到了该材料的真应力-真应变曲线和显微组织。将高温压缩试验得到的数据导入有限元模拟软件Deform-3D中,对制动杠杆螺栓的成形过程进行了数值模拟,分析了成形过程中的载荷-行程曲线、等效应力场分布等,最后根据优化得到的工艺参数设计了相应模具,并做了工艺试验,工艺试验得到的制动杠杆螺栓锻件充填饱满、尺寸符合要求、锻造流线分布合理,且锻件经过机加工后,没有发现锻造缺陷,符合使用要求。该研究对此类零件的生产具有一定的指导意义。     

Evaluation of residual stress distribution in Ni base alloy clad welds by numerical simulation and X-ray stress measurement

Abstract

Dissimilar material components such as clad welds are important to achieve both performance, and economic and ecological efficiency. The evaluation of the residual stress distribution in such components is needed to assess and assure the integrity of structures components. In this study, the residual stress distribution in clad welds of Ni base alloy over low alloy steel was investigated. A clad welded mock-up was fabricated, and the residual stress distribution was evaluated by X-ray stress measurement method and finite element simulation. The residual stress was measured with high accuracy even in coarsened Ni base alloy clad weld metal by X-ray stress measurement method utilising a two-dimensional detector and multiaxial rocking technique. The residual stress distribution was well reproduced by the finite element simulation considering the redistribution due to cutting off of the specimen from the fabricated mock-up.     

Temperature field analysis of main steam pipe under local post weld heat treatment

In local post weld heat treatment, the temperature difference is the criterion of the process. The temperature field in the main stream pipe under heal post weld heat treatment is simulated by finite element method. A close-loop control program-is designed to simulate the temperature field of two different pipes. Both the skin effect of induction heating and electro-thermal coupled effect are considered in the heating model. The local heat treatment temperature difference at the inner and outer side of the pipe is analyzed and the different convection conditions are also considered. The simulation results show that in appropriate induction heating process, the temperature difference in the pipe can be controlled within 30 ℃.     

Temperature dependent flow softening of titanium alloy Ti6Al4V: An investigation using finite element simulation of machining

Titanium alloy Ti6Al4V is the most commonly used titanium alloy in the aerospace and medical device industries due to its superior properties. There has been a considerable amount of research to better understand the serrated chip formation mechanism of titanium alloy Ti6Al4V by using finite element simulation of machining. An accurate representation of the behavior of the material is important in order to obtain reliable results from the finite element simulation. Flow softening behavior has been integrated into the material constitutive models to simulate adiabatic shear bands and serrated chips. Flow softening is usually related to the dynamic recrystallization phenomenon which initiates after a critical temperature. The aim of this study is to investigate the influence of various flow softening conditions on the finite element simulation outputs for machining titanium alloy Ti6Al4V. For this purpose, a new flow softening expression, which allows defining temperature-dependent flow softening behavior, is proposed and integrated into the material constitutive model. The influence of flow softening below the critical temperature, as adopted in recent studies, is also investigated. Various temperature-dependent flow softening scenarios are tested using finite element simulations, and the results are compared with experimental data from the literature. The results showed that the flow softening initiating around 350-500 °C combined with appropriate softening parameters yields simulation outputs that agree well with the experimental measurements.     

大口径挤压三通差温制坯新技术研究

为解决目前大口径热挤压三通生产过程中初始管坯加热时间长、能源浪费严重等问题,根据超音频感应加热设备的特点,提出了利用“梨”形铜线圈对管坯局部进行感应加热的方法.实验结果表明,该方法可有效快速地为压包工序提供具有特殊温度场要求的管坯,同时实现了管坯局部感应加热过程在模拟软件中的模拟仿真,为后续的大型三通热挤压工艺有限元研究奠定了基础.     

半固态触变成形二次加热数值模拟及参数优化

半固态触变成形技术以其节省能源、成形力小和近终成形等优点受到广泛关注。通过对ZL101铝合金试样在各种不同工艺参数下的感应加热温度及温度均匀性进行的研究，运用CAE技术模拟加热频率、加热时间、线圈电流强度、线圈尺寸、加热后停留时间等参数对坯料温度场的影响，提出二次加热中获得均匀温度场的工艺条件、参数与措施。模拟结果与感应加热的实测数据具有很好的吻合性。     

Numerical and experimental investigations of semi-solid AZ91D magnesium alloy in thixoforming process

Many complicated factors affect thixoforming fluidity in thixoforming process of semi-solid metal (SSM). So, it is important to forecast the flow property of SSM. Rigid visco-plastic constitutive model of semi-solid AZ91D Mg alloy was established at different strain rate. The thixoforming process of semi-solid AZ91D Mg alloy was simulated using commercial finite element software DEFORM-3D™. The fluid and effective stress–strain fields in the thixoforming process were obtained and the relationships among stress, strain rate and temperature also were analyzed. The thixoforming experiments were performed at 570 °C with different holding time. Finite element analysis results were compared with experimental ones, and experimental data has good agreements with the simulation results.     

平板件电磁成形技术的研究进展

在简述了平板件电磁成形原理的基础上,从以下4个方面综述了此技术的国内外研究进展:成形线圈设计方面,列举了平板线圈,匀压力线圈,并列线圈以及工艺校形线圈的使用;磁场力计算方面,讲述了解析法和有限元法的应用;试验研究方面,阐述了电磁成形板材成形性能研究、电磁辅助成形研究的进展;数值模拟方面,叙述了各种数值模拟方法以及有限元软件的应用。最后,指出了平板件电磁成形技术推广过程中所需攻克的技术难题。     

Deformation Behavior and Constitutive Equation Coupled the Grain Size of Semi-Solid Aluminum Alloy

Isothermal compression tests on Al-4Cu-Mg alloy were carried out in semi-solid state. Deformation behavior and microstructural evolution are discussed in this paper. Meanwhile, a new constitutive equation, which couples the grain size and liquid volume fraction, has been established for the semi-solid deformation behavior. The results show that the maximum difference between the calculated with the experimental data is less than 15%. The present equation is satisfactory for describing the correlation between the flow stress and microstructure of semi-solid Al-4Cu-Mg alloy. The coupled simulation of the deformation behavior and microstructural evolution during the semi-solid forming would be conducted easily through writing the present equation in a FE code.     

Theoretical and Experimental Investigation on SMA Superelastic Springs

The mechanical behavior of superelastic springs is investigated in this study. The goal is to evaluate the device response and to exploit the material superelastic behavior, main concerns being material and geometrical response nonlinearity. The investigation is made of two parts, i.e., an experimental campaign and a numerical model proposal. Experimental tests have been performed on superelastic SMA coil springs considering load history in tension and compression for three different spring geometrical configurations. Tested specimens experience a maximum elongation larger than the original spring axis length. The response is not symmetric and under compression it is affected by buckling instability. Nevertheless, experimental results show a very good superelastic behavior with no damage and with negligible residual displacements. Numerical analyses have been performed to reproduce the experimental campaign results. A simple finite element model is proposed. Experimental and numerical result agreement is very good. The numerical model turns out to be a powerful design tool even for the very complex geometrical and material nonlinear conditions under investigation. Hence, it is proposed as a useful tool for spring design validation and response prediction.     

Finite-element simulation of induction heat treatment

An efficient finite-element procedure has been developed for the analysis of induction heat treatment problems involving nonisothermal phase changes. The finite-element procedure first simulates the magnetic field developed when currents flow through an induction coil by solving Maxwell’s electromagnetic field equations; at the following step, it calculates the temperature distribution in the workpiece due to eddy currents induced by the magnetic field. The final stage of the simulation involves the determination of the distributions of residual stress, hardness, and microstructure in the workpiece. The finite-element analysis includes temperature-dependent material properties, changes in permeability of the workpiece at the Curie temperature, a mixed hardening rule to describe the material constitutive model, and the incorporation of time-temperature-transformation (TTT) diagram. The procedure was applied to the simulation of the induction hardening of 1080 steel bar. Firstly, the magnetic field and temperatures developed in the workpiece during (a) the induction heating of an infinitely long 1080 steel cylinder by a single encircling coil and (b) the induction heating of a semi-infinite half-space by a single coil suspended above it were calculated using the finite-element procedures. These were validated by comparing them with analytical solutions derived for these configurations using a Green’s function method. Finally, to demonstrate the predictive capability and practical applicability of the current finite-element procedure, two examples pertaining to the induction heat treatment of an infinite 1080 steel bar of square cross section and a notched finite 1080 steel cylinder of circular cross section were analyzed to predict the magnetic field, temperature, and residual stress distributions. The current finite-element procedure could be used as a powerful design tool for linking induction heat treating parameters with the mechanical property attributes of the heat treated component.