Dynamic recrystallization behavior and microstructural evolution in SPHC steel

The dynamic recrystallization(DRX) behaviors in SPHC steel were investigated with hot compression tests at deformation temperatures of 950-1 150,strain rates of 0.1-15 s-1,and initial austenite grain sizes of 86-232 μm.The effects of deformation temperature,strain,strain rate and the initial austenite grain size on the microstructural evolution during DRX were studied in detail.The results show that DRX is observed under the condition of the Zener-Hollomon parameter being less than 1.07×10 13 s-1.The deformation activation energy for SPHC steel is calculated to be 299.4 kJ/mol by regression analysis.Austenite grain size of DRX is refined with decreasing temperature and increasing strain rate under steady state conditions,but it is not influenced by the initial grain size.The mathematical equation of DRX grain size of SPHC steel is obtained.     

Research on voids deformation welding condition for manufacturing of heavy forgings

Crushing and diffusion welding are two critical healing stages of interior void defects in heavy forgings. The healing result depends on many factors during the forging process, such as stress, temperature, deformation and type of material, while the void diffusion welding condition is still not well known at the present. This paper is concerned with the deformation welding condition of the closed void interface in heavy ingot during the hot forging process. A void crushing experiment is carried out to recognize the microstructure of the closed void interface. According to the healing mechanism at high temperature, a new physical simulation model is setup to study the deformation welding process of the closed void interface based on the theory of atom diffusion and the interface contact mechanics prototype. Compared with the experimental results, the influence of deformation degree, forming temperature and holding time on the welding quality is discussed, and then the deformation welding condition of closed void interface is presented. The proposed condition helps to improve forging technology and product quality.     

Computer Aided Simulation on Precision Cold Forging of Universal Joint Cross

IntroductionThefiwtee1emenmethod(FEM)playsanextrmelyimPortantroleintheanalysesofengineeringproblems.ForalongtimethismethodhasmainlybeenaPPliedinthelinearfieldandshownitsgreatpower.HoweveealOtofnonlinearengineeringPrOblemsWhichcanneitherbesimPlyreducedtolinearonesnorrCPresentedbylinearlyanalogywhichshallchnsethePfacticalconditionsrelativelymuch,havechallengedfiniteelementmethod(FEM).RecentymuchProgresshasbeenmadebothinthemathematicalandmechanicaltheoryandthecomPulertechnologysothatevent…     

Microstructure Evolution of Different Forging Processes for 12％Cr Steel During Hot Deformation

Five forging experiments were designed and conducted to investigate the effect of process parameters on microstructure evolution during hot deformation for X12CrMoWVNbN10-1-1 steel.The experimental results indicated that average grain size became finer with the increasing number of upsetting and stretching.Especially,the size of stretching three times with upsetting twice had the most remarkable effect on refinement,and the size was only 27.36%of the original one.Moreover,the stress model was integrated into the software and finite element models were established.Simulation results demonstrated that the strain at center point of workpiece was far larger than critical strain value in each process,so that dynamic recrystallization(DRX) occurred in each workpiece,which implied DRX could occur for several times with the increasing number of upsetting and stretching,and uniform finer microstructure would be obtained.However,the results also showed that higher temperature was an unfavorable factor for grain refinement,so the times of heating should be limited for workpiece,and as many forging processes as possible should be finished in once heating.     

Coupled Thermo-Mechanical Modeling of Long Cone-Shaped Forging Based on Rigid Visco-Plastic FEM

Based on synthetically considering the coupled thermo-mechanical relations between temperature and deforming,a numerical simulation of the forging process for the special long cone-shaped workpiece of Al-5.44M-2.15L-0.12Zr alloy at high temperature was conducted by using the rigid visco-plastic finite element method.The relations between the total load and the displacement druing the forging ,and the distributions of stress,strain,temperature and strain rate,which can provide useful information for the process design,are obtained.     

基于FBG的沥青混合料横向流动变形评价

为了分析沥青混合料横向流动变形, 进行了沥青混合料的车辙试验, 利用布设于沥青混合料板表面的光纤布拉格光栅传感器, 研究了沥青混合料表面的横向应变规律; 以最大应变和蠕变稳定阶段横向应变速率绝对值为评价指标, 分析了沥青混合料横向流动变形。分析结果表明: 横向流动变形随沥青混合料的最大应变和横向应变速率绝对值的减小而降低; 横向流动变形在循环轮载作用下不断发展, 测试点距离轮载愈近其流动变形愈剧烈; 当胶粉掺量分别为0、15%、18%时, 距离轮载63 mm的测试点横向应变速率分别为6.8×10-6、4.0×10-7、6.4×10-6 min-1, 因此, 掺15%胶粉的沥青混合料具有较大的抵抗高温横向流动变形的能力; 对于15%胶粉掺量的沥青混合料, 当其集料级配分别为AC-13粗级配和AC-13细级配时, 距离轮载28 mm的测试点横向应变速率分别为6.0×10-7、7.7×10-6 min-1, 因此, AC-13粗级配沥青混合料高温抗横向流动变形能力优于AC-13细级配; 胶粉改性沥青混合料最大应变为1.96×10-4, 而胶粉和抗车辙剂复合改性沥青混合料最大应变只有1.22×10-4, 说明在高温情况下, 胶粉和抗车辙剂复合改性沥青混合料整体结构强度较大, 能够承受来自轮载的直接作用而不向轮迹两边产生横向推移致使发生较大的横向流动变形。基于光纤布拉格光栅横向应变的沥青混合料横向流动变形评价能较好地说明不同材料和级配对沥青路面产生侧向流动变形规律的影响。      

Forging penetration efficiency of steel H13 stepped shaft radial forging with GFM forging machine

The numerical thermal mechanical simulation of radial forging process of steel H13 stepped shaft with GFM (Gesellschaft fur Fertigungstechnik und Maschinenbau) forging machine was carried out by three-dimensional finite element code DEFORM 3D. According to the effective plastic strain, the mean stress and the mean plastic strain distribution of the radial forging, the forging penetration efficiency (FPE) was studied throughout each operation. The results show that the effective plastic strain in the center of the forging is always greater than zero for the desirable larger axial drawing velocity. The mean stress in the center of the workpiece is proposed to describe hydrostatic pressure in this paper. There is compressive strain layer beneath the surface of the workpiece to be found, while there is tensile strain core in the center of the workpiece. These results could be a valuable reference for designing the similar forging operations.     

Simulation and analysis of microstructure evolution of IN718 in rotary forgings by FEM

A numerical analysis was performed to study the in?uence of process parameters on the microstruc-ture evolution of IN718 alloy in rotary forging using the finite element method(FEM).For this purpose, a constitutive equation considering the effects of strain hardening and dynamic softening of IN718 alloy was built.The constitutive equation and microstructure models were implemented into the finite element code to investigate the microstructure evolution during rotary forging subject to large deformations.The simulations were carried out in the ratio of initial height to diameter range 0.2-0.8, the angle of the rocker 3°-7° and the relative feed per revolution range 0.01-0.1 r-1.The research results revealed the deformation mechanism and the correlation of process parameters with the grain size evolution of IN718 alloy during rotary forging.These provide evidence for the selection of rotary forging parameters.     

Numerical analysis of unconventional forging process of hollowed shaft from Ti-6Al-4V alloy

This paper presents theoretical analysis of unconventional forging process of hollowed shaft from Ti-6Al-4V alloy in a three-slide forging press. This method in comparison with other metal forming methods allows for obtaining of hollowed products. The designed process is verified theoretically by means of numerical simulations based on finite element method with assumption of 3D state of strain. The following factors are considered in the analysis: material flow kinematics, strain distribution, temperature distribution and force of process. On the basis of results, it is stated that the application of designed technology allows for obtaining of a product of assumed quality. A comparison is made between material consumption in analyzed process and material consumption in typical metal forming methods, also in used at present technology of shaft manufacturing by machining only. It is stated that the application of forging in the three-slide forging press allows for a considerable decrease of manufacturing costs due to material savings and decrease of labor consumption of operations at finishing.     

Study on Damage of High Temperature Plastic Deformation for Al-Li Alloy

The security of use for Al-Li alloy will be greatly influenced by the damage degree of plastic deformation within it at high temperature . Based on continuum damage mechanics theory, the damage evolution of Al-5.44Mg-2.15Li-0.12Zr alloy during plastic deforming at high temperature is simulated by using the damage evolution model of high temperature plastic deformation. The changing rule of its inner damage with deformation temperature, strain rate and strain is gained in this paper. The equation of damage evolution for high temperature plastic deformation is developed, providing an academic basis for the technology of plastic process of Al-Li alloys.     

三轴重复荷载作用下AC-13沥青混合料永久变形试验分析

采用半正弦波间歇荷载,使用MTS(Material Test Systerm)材料试验机对AC-13沥青混合料进行三轴重复荷载蠕变试验,研究试验温度和应力水平对沥青混合料永久变形特性的影响,得到了AC-13沥青混合料在不同温度和不同应力水平下的永久变形规律,对永久应变与荷载作用次数、应力水平和温度的关系进行非线性回归分析,提出来能够全面反映沥青混合料永久变形特性的模型,并绘制了不同温度下的三维图形,直观全面地反映沥青混合料变形的特性。     

基于HyperXtrude的薄壁铝型材挤压成形仿真模拟

基于HyperXtrude软件分析薄壁六边形结构挤压成形稳态过程,研究不同状态下金属材料的应力应变、挤压力变化、流速变化和温度等物理参数量的变化趋势,以这些物理参数变化趋势来量化预测该型材挤压成形性。通过仿真模拟清楚反应薄壁六边形结构铝型材在挤压过程的变化特性,预测薄壁结构挤压成形过程中的变形、翘曲、开裂和流速不均等缺陷,为及时对挤压成形工艺方案调整或模具结构改进设计提供指导。     

应力梯度作用下非均质岩体材料变形参数的研究

针对节理岩体非均质性特征,利用概化模型、变形等效及当量化处理等方法,研究了梯度应力作用下节理岩体的变形参数变化规律.研究表明:构成岩体的成分不均匀性越显著时,等效弹性模量变化越大,计算得到的最大等效弹性模量当量变化达136%;而当岩体均匀性较好时,等效弹模当量变化小于110%.     

Two step forging process of spur gear based on rigid parallel motion

To improve the forging process of spur gear,the metal flow rule is investigated in detail,and a hypothesis of radial rigid-parallel-motive (RPM) flow mode is given. Based on the RPM mode a novel specific gear forging technology is put forward by introduced upend forging process and constrained divided-flow technique. Firstly,finite element method is used to simulate the upend forging pre-forming and RPM finish forging,and equivalent stress field and load-stroke curve are investigated. Secondly,a correspondi...     

Computer Simulation of Thermal-Mechanical Processing

AlterationIntroductionThereisastrongini6ractionamongtemPetalrefield,strCssfield,andmicrosttuctutulaltOrationinm8terialsduringtheirhotworking[l'2].Especiallyduringthecoolingprocess,inwhichtemPeratorechangnsgreatly,intendionsbecomemorecomplexbecauseoftransformationoccurmnce.Duringthehotdeformation,thingswillaPpearsuchas:a.hotdeformation,relatedtostressfieId,changesessentiallytheshaPeofmaterialsandcausesthevariationofthecontactstatebetWeenthedieandsample,resultinginchangeofthethermalboundnyco…     

Static softening characteristics and static recrystallization kinetics of aluminum alloy A6082 after hot deformation

The static softening behavior of aluminum alloy A6082 was investigated by interrupted hot tests conducted on Gleeble-1500 simulator at deformation temperatures from 573 to 773 K and strain rates from 0.1 to 10 s⁻¹, with a pre-strain from 0.3 to 0.7 and variable inter-pass delay times. The offset method was applied to convert the changes in flow stress between two passes to static softening fraction. The microstructural changes were characterized by the quantitative metallography of quenched specimens. The results showed both static softening and static recrystallization curves exhibited a simple sigmoidal shape; the static softening is related to the static recrystallization in a nonlinear manner with 50% static recrystallized volume fraction corresponding to 80% static softening fraction; an increase in temperature, strain rate or pre-strain yields a decrease in the time for 50% static recrysallized volume fraction, on which the temperature has the most remarkable influence; Si and Mn additions accelerate the process of static recrystallization. Finally, the equations of static recrystallization kinetics of this alloy were developed with a good agreement between the predicted and experimental results.     

模具间隙对液态模锻溢料的影响

通过液态模锻成型压力和温度参数对模具间隙影响的研究,以及模具结构分析,找出了由于模具间隙变化造成溢料的原因,提出了解决方案,对液态模锻模具设计具有一定的参考价值。     

铝合金货车侧墙多道焊变形预测

基于热弹塑性有限元法,对铝合金货车侧墙多道焊焊接变形进行仿真预测,仿真中充分考虑了材料热物理属性的影响．基于实体一壳单元混合模型,建立了侧墙有限元网格模型,应用3D高斯双椭球热源模型实现了焊接过程温度场分析．从工程实际出发设计了四种焊接顺序,通过对四种焊序下仿真结果的对比分析,讨论了不同焊接顺序对铝合金货车侧墙焊接成形的影响,为研究大型铝合金薄板焊接过程中的应力应变和减少焊接应力与变形提供了参考依据．     

高地应力隧道施工对围岩应力与变形的影响研究

依据围岩稳定性理论,通过数值模拟方法,针对参数变化较大的几类围岩及参数在小范围变化的同一类围岩在高地应力圆形隧道施工过程中围岩应力与变形的表现形式,建立大量数值模型进行分析。结果表明：围岩较好的隧道主要应解决高地应力集中问题,围岩较软弱的隧道主要应解决变形问题;围岩参数小范围变化时,对围岩应力影响由大到小的参数依次为内摩擦角、粘聚力、泊松比、弹性模量,对围岩变形影响由大到小的参数依次为弹性模量、粘聚力、内摩擦角、泊松比。     

Determining Loading Field based on Required Deformation for Isotropic Hardening Material

Eringen's and Trusedell's polar decomposition are formulated by explicit formulation of displacement field, based on Chen's additive decomposition of deformation gradient. Then the strain introduced by the multiplicative decomposition and the strain introduced by the additive decomposition are formulated explicitly with displacement gradient. This formulation clears the intrinsic contents of strains defined by taking the Eringen's and Trusedell's polar decomposition. After that, Chen's strain definition was introduced to show that the plastic deformation can be understood as the irreversible local average rotation. For initial isotropic simple elastic material, the research shows that path-dependent feature of classical plasticity theory is naturally expressed in Chen's strain definition. For rate-independent plasticity, the related deformation stress was discussed. The research shows that for isotropic hardening material the relation equation between the required geometric configuration and the corresponding loading field is explicitly formulated. Hence, for metal forming, this paper explicitly formulates the related fields by displacement field and invariant elastic constants.