Cu-15Ni-8Sn(Zr)合金的高温压缩变形流动应力研究

在温度765～915℃、应变速率0．0011～0．33s^-1的试验条件下，测定了两种热处理状态的Cu-15Ni-8Sn(Zr)合金的高温压缩变形流动应力，并进行了分析。结果表明，应变速率和变形温度影响合金流动应力，流动应力随变形温度升高而降低，随应变速率提高而增大。在相同变形条件和变形程度下，固溶处理的试样要比未固溶处理试样的流动应力小。其它条件不变时，变形温度越高，或者应变速率越低，材料越容易发生动态回复和动态再结晶。     

口模压缩段对塑料挤出流动影响的有限元分析

在塑料挤出成形过程中，压缩段是调节模头流道各部分流量(流速)的主要区段，对熔体的流动具有重要影响。本文采用有限元数值分析方法，计算了熔体在口模内流动的速度场和压力场，定量分析了压缩比和压缩角等压缩段模具结构参数对挤出速度分布、挤出流量和挤出流动均匀性等的影响规律，为优化流道结构参数，提高挤出流动均匀性的研究提供了基础。     

助推可调鼓风机的研究

从改善罗茨鼓风机内压缩流动入手,提出了一种具有新结构的助推可调鼓风机,即容积射流式新机型。经实验证明,机内压缩流动理想,涡流极小,本体噪声下降15dB,电耗减少4%以上。     

非回转对称拉深中材料流动变形规律的研究

作为非回转对称拉深系统研究的一部分,根据矩形盒件拉深中网格变形的测量结果,分析了压料面和盒底面材料的流动变位及其规律。指出了凸缘周向压缩变形与径向拉伸变形不成比例,曲边部流动变形不连续,盒底面短轴上产生与拉深力作用方向相反的塑性流动等变形现象是与圆筒拉深变形的最大区别,同时也是非对称成形有限元计算试验所必须认识和掌握的基本关键点。试验表明,如果根据材料流动规律合理地实施规范化局部润滑,可使大型覆盖件拉深成形极限进一步提高。     

涡旋压缩机压缩腔内气体非稳态流动研究

为了研究涡旋压缩机工作过程中腔内气体非稳态流动过程,建立了涡旋压缩机压缩腔的模型,依据动静涡旋齿啮合间隙调节压缩腔内流体区域的动网格分布,采用RNG k-ε湍流数学模型,实现了压缩腔内气体流动的数值模拟,研究气体速度场、压力场和温度场分布规律,分析了流场分布不均匀性的形成原因,探索了压缩腔间气体泄漏引起的传热、传质过程对非稳态流动的影响。     

大块非晶合金Zr55Al10Ni5Cu30在过冷液相区中的性能

通过DSC实验确定了大块非晶合金Zr55A110Ni5Cu30的过冷液相区，并由等温DSC曲线得到此合金在过冷液相区中各个温度下可用于塑性加工的时间的估算公式。在前人研究的基础上，提出一种得到此合金在过冷液相区中的流动应力的新的测试方法：变应变速率压缩实验。这种方法可以由较少的试样得到较多的应力数据。这些试验为将来塑性加工中应变速率、加工温度、加工时间的选择提供了依据。     

超声振动对轻合金塑性压缩变形过程的影响

将超声振动叠加到AZ31镁合金、6061和7075铝合金的镦粗压缩变形过程,以研究高频振动对轻合金塑性压缩变形时的流动特性、断裂失效方式以及压缩表面状态的影响。实验发现,叠加振动后,"体积"和"表面"两种效应对3种材料的压缩变形过程都存在不同程度的作用。具体表现为材料的屈服强度、流动应力出现降低,且降低幅度与材料特性相关,其中6061对振动效应更为敏感;随着振幅的增加,AZ31材料体积效应中的硬化机制逐渐占据主导;此外,振动有助于提高压缩表面的质量。     

流体压缩系统管道内部速度与压力的动态测量

通过将动态静压测试系统与TSI热线风速仪测试系统结合,实现压力与速度的同时测量,实时测试管道内流体速度压力瞬时响应情况,并观测到一些非定常流动现象。     

GH4169合金塑性变形行为及加工图

通过GH4169合金的热模拟压缩实验,研究了变形工艺参数对GH4169合金高温变形时流动应力的影响规律,建立了GH4169合金高温变形时的加工图,结果表明：变形温度升高和应变速率减小使GH4169合金高温变形时峰值流动应力和稳态流动应力显著降低;GH4169合金高温变形时存在三个非稳定区域,第一个区域的变形温度在970～1030℃之间,应变速率在10．0～50．0s^-1之间;第二个区域的变形温度在930～940℃之间,应变速率在0．15～7．Os^-1之间;第三个区域的变形温度在930～960℃之间,应变速率在7．0～50．0s^-1之间的区域。     

基于热模拟试验的大尺寸6061铝合金轮毂旋压工艺

随着电池、轻量化技术的成熟，新能源汽车朝向大型化发展，带动大尺寸汽车轮毂的应用。开展大尺寸6061变形铝轮毂旋压工艺的研发，首先对6061铝合金进行等温热压缩实验，得到在不同温度和应变速率下的真实应力应变曲线，拟合出本构方程。将所得数据导入有限元仿真软件对某款大尺寸铝合金轮毂的轮辋进行旋压模拟，通过分析旋压过程中轮辋材料的流动，总结对比了轮辋上下分开旋压方案和轮辋上下同时旋压方案的优缺点；对轮辋旋压过程中的应力应变场、温度场的分布规律进行总结，验证该成形方案的可行性，为大尺寸铝合金轮毂的旋压成形提供理论支持和工艺参考。     

GH4169合金不同热变形条件下的流变应力研究

在Gleeble－3500型热加工模拟试验机上进行了GH4169镍基合金的高温压缩试验,变形温度为980℃～1100℃、应变速率为0,01s^-1、0,1s^-1、1s^-1、10s^-1,变形程度为50％。通过绘制真应力一真应变曲线,研究了GH4169镍基高温合金高温下的流变应力行为。结果表明：GH4169是应变速率和变形温度敏感型材料,变形温度升高和应变速率减小使流变应力显著减小;在变形的初始阶段,流变应力迅速增加,在到达峰值后,随着应变的增加,流变应力逐渐下降,并趋于一稳定值。采用简化后的双曲正弦模型Arrhenius方程,建立了GH4169高温条件下的本构方程,运用该方程计算出的峰值应力与试验测量值相比,拟合度达到了95.95％。     

一种铁素体钢热变形流变应力行为

利用Gleeble热力模拟试验机在温度为1 123～1 473 K和应变速率为0.001～0.1 s-1的条件下对试验钢进行了热压缩变形试验,测定了其真应力-应变曲线,试验结果表明:试验钢在热压缩变形过程中发生了明显的动态再结晶,流变应力随变形温度的降低和应变速率的提高而增大。通过线性回归分析确定了试验钢的流变应力本构方程。     

Deformation analysis of plastic strain rate hardening material using stress function under plane strain condition

The two-dimensional plane strain equation of plastic flow in accordance with the Levy-Mises constitutive relation is expressed in terms of stress functions of complex variables. Expressions for the stress, strain rate and velocity are derived for plastic flow in a non linear viscous medium assuming the stress function in the form of both the summation and product of conjugate stress functions. The plastic states are derived, also using a mixed mode solution expressed in terms of non-seperable, independent conjugate complex variables.The analysis of the block indentation associated with a nonlinear viscous (strain rate hardening) material under plane strain condition using the product form solution is performed. The effect of the variation in the strain-rate hardening exponent on the contact stress is investigated. The predicted behavior of the vertical component of the contact stress suggests the possibility of the development of a specially instrumented plane strain block indentation tests, for the rapid determination of the strain-rate sensitivity of the real material. The vertical contact stress and strain-rate obtained from the product of the complex conjugate stress function are compared with those obtained from the summation form of the complex conjugate stream function.     

A modified micromechanical approach to determine flow stress of work materials experiencing complex deformation histories in manufacturing processes

Work materials experience a broad range of strains, strain rates, and temperatures in many manufacturing processes such as machining, forming, etc. Strain rate has an important effect on the yield and flow stress of work materials, especially metals, since at higher strain rates there is less time for thermally activated events; consequently, it is equivalent to a lowering of the temperature of the materials. On the other hand, it is also true that, for high strain rate deformations such as metal cutting, adiabatic plastic flow may produce significant temperature changes in the materials. Flow stress is significantly affected by the strain rate history; hence, mechanical behavior may not be fully described in terms of a mechanical equation of state relating the instantaneous stress, strain, strain rate, and temperature.Based on the concept of dislocation mechanics, a micromechanical approach with the new concept of temperature coefficient has been explored to overcome the model issues such as negative or constant flow stress above the critical temperatures. The flow stresses of aluminum 6061-T6 and titanium Ti-6Al-4V have been predicted, for the first time, using the modified micromechanical model based on the available baseline high strain rates test data. The constitutive model was further modified and extended to predict flow stress below as well as above the critical temperature. The corresponding model predictions were compared with the experimental data, attaining good agreement.     

Plastic deformation analysis of strain-rate sensitive materials under plane strain conditions

The two-dimensional plane strain equation of plastic flow in accordance with the Levy-Mises constitutive relation is expressed in terms of stream functions of complex variables. Expressions for the stress, strain-rate and velocity are derived, assuming the stream function in the forms of both the summation and product of conjugate flow functions, for plastic flow in a nonlinear viscous (strain-rate sensitive) medium. The plastic states are also derived using a mixed mode solution expressed in terms of non-separable, independent conjugate complex variables. Application of the summation form solution is illustrated through the block indentation problem. Calculations are made on the effect of variation of the strain-rate sensitivity exponent on the contact stress. The predicted behavior of the contact stress suggests the possibility of the development of a specially instrumented plane strain block indentation test for the rapid determination of the strain-rate sensitivity of real materials. By reducing the results of the indentation of a perfectly plastic material it is found that the contact stress is uniform and the external load is constant. The stress on the contact surface obtained using the present analysis is identical to that available from a slip line solution to the problem.     

整体式立铣刀三维建模及切削力预测研究

针对立铣刀三维建模困难及铣削时切削力难以预测等问题,根据微分几何原理建立立铣刀数学模型。基于数学模型将铣刀切削刃离散成斜角切削单元,根据剪切区应力、应变和温度控制方程,由材料本构方程计算流动应力,通过坐标变换关系建立铣削力预测模型。得到的铣削力与已有铣削试验数据一致,验证了铣削力模型的有效性。     

高应变速率下铸态AM80镁合金的变形行为及数值模拟

采用INSTRON准静态压缩实验机和分离式霍普金森压杆装置对铸造固溶态AM80镁合金不同应变速率下的压缩变形行为进行了研究,应变速率分别为0.0001s-1、800s-1、1050s-1、1600s-1、1850s-1和2100s-1。结果表明：当应变速率ε˙≤1850s-1时,实验用AM80镁合金的流变应力随应变速率的增大而增大,表现出明显的正应变速率敏感性;当应变速率增至2100s-1时,由于局部温升效应,合金产生了明显的动态软化,导致流变应力反而略有减小。采用Johnson-Cook材料模型对实验用AM80镁合金在不同应变速率下的变形行为进行描述,并取材料应变速率强化参数为应变速率的函数。对比结果表明,所建立的本构方程与实验结果基本吻合。此外,由于力学本构忽略了由形变引起的温升软化,基于ABAQUS的仿真结果在较低应变速率（800s-1）和高应变速率（1850s-1）的中低应变下与实验结果吻合得较好;而在高应变速率（1850s-1）的较高应变条件下,仿真结果与实验结果差异较大。     

惯性摩擦焊接钢管焊合区热塑性变形参量场的数值分析

根据金属塑性成形过程的大变形热弹塑性理论和虚功原理 ,建立了惯性摩擦焊接过程温度场、应力场及应变场的有限元热力耦合分析计算模型和有限元列式 ,并在给定边界条件下 ,解算了 34 Cr Mo4钢惯性摩擦焊接头动态温度场、应力场及应变场     

Plane strain tension of thermo-elasto-viscoplastic blocks

The thermocoupled flow localization of plane strain tension blocks has been investigated. These blocks have a relatively low strain rate sensitivity and comply with an elasto-viscoplastic constitutive equation which has a viscoplastic strain rate noncoaxial with the stress tensor. Attention has been paid to deformations with a strain rate in the range of 0.02–2000/s under isothermal, conductive and adiabatic conditions. A full plane strain finite element analysis of the velocity and temperature fields has partially clarified the effects of the deformation rate, material strain rate sensitivity, thermal conductivity and size of the blocks on flow localization, including the shear band type of flow localization.     

A new approach for the quasi-plane strain-softening problem of cylindrical cavity expansion based on Cam-Clay model

This paper focuses on the quasi-plane strain-softening problem of cylindrical cavity expanding in Cam-Clay soil mass. The quasi-plane strain-softening problem is defined based on the assumptions that the initial axial total strain is a non-zero constant and the axial plastic strain is not zero. A new approach for the major, intermediate, and minor principal strains are proposed based on the associated flow rule, 3-D plastic potential function, Hooke’s law, stress equilibrium equation and Cam-Clay model. The correctness of the proposed approach is validated by the results in Cao and Teh. Parametric studies were performed to investigate the influences of the intermediate principal stress on the radial and circumferential stresses and the radial displacement, respectively.