铬铜热变形流动应力的实验研究

采用恒变形率凸轮压缩试验机对铬铜的流动应力进行了实验研究，分析了变形温度、变形速率、变形程度对流动应力的影响，同时对不同的数学模型结构进行了非线性回归，通过分析比较，提出了拟合精度高的流动应力数学模型。     

铝合金高温流动应力的研究

采用GIeeble-1500热模拟试验机，测定了3种铝合金材料在高温下的流动应力，分析了应变速率、变形程度和变形温度对流动应力的影响。通过分析，提出了拟合精度较高的流动应力的数学模型。     

高温高速下合金结构钢流动应力研究

采用恒应变速率凸轮式压缩试验机对8种合金结构钢的流动应力进行了实验研究。其变形温度(T)、应变速率((?))及变形程度(ε%)分别为850—1150℃,5—80s~(-1)及5—69%。分析了变形温度、变形程度及应变速率对流动应力(σ)的影响。通过对变形温度影响项具有两种表达式的流动应力数学模型的非线性回归分析及比较,提出了拟合精度较高的8个合金结构钢流动应力的数学模型,并给出了数学模型的回归系数值。     

THE FLOW STRESS OF ALLOY STRUCTURAL STEELS AT HIGH TEMPERATURE AND HIGH STRAIN RATE

采用恒应变速率凸轮式压缩试验机对8种合金结构钢的流动应力进行了实验研究。其变形温度(T)、应变速率((?))及变形程度(ε％)分别为850—1150℃,5—80s~(-1)及5—69％。分析了变形温度、变形程度及应变速率对流动应力(σ)的影响。通过对变形温度影响项具有两种表达式的流动应力数学模型的非线性回归分析及比较,提出了拟合精度较高的8个合金结构钢流动应力的数学模型,并给出了数学模型的回归系数值。     

粉末冶金钼热变形流动应力的研究

在Gleeble3800热模拟机上对粉末冶金钼进行高温热压缩试验，变形温度1100℃～1250℃，应变速率11．5s^-1～23s^-1，变形程度0．7。分析了变形温度、应变速率对流动应力的影响，用多元线性回归的方法建立纯钼的流动应力数学模型。     

U75V钢流动应力的试验研究

针对U75V钢,利用Gleeble-1500热模拟试验机对其在不同温度和应变速率下的流动应力进行试验研究.通过实测数据,分析变形温度、变形速率和变形程度与流动应力之间的关系,确定了U75V钢流动应力的数学模型.对其数学模型进行回归,将理论计算与试验数据进行对比,证明此模型具有良好的曲线拟合特性,可以做为工艺计算和数值模拟的依据.     

20CrMnTiH钢的温变形行为及其数学建模

利用热模拟试验研究了20CrMnTiH钢在1023～1173 K,变形速率为0.01～1 s-1条件下的温变形行为,并对其变化规律进行分析.以流动应力为目标函数,研究了主要工艺参数对目标函数的影响.基于统计分析建立了适用于20CrMnTiH钢温锻成形的流动应力数学模型,为该材料产品温成形工艺的合理制定和数值模拟提供依据.     

含Ti超低碳钢流动应力的研究

用Thermecmastor-Z热加工模拟试验机研究了含碳量为0.006%的超低碳钢在两相区变形的形变特征和规律;通过测定钢的流动应力和相变行为,得到了铁素体相变区间。在此基础上,研究了不同的变形工艺对流动应力的影响,建立了流动应力数学模型,从而为预测和控制铁素体区轧制负荷提供了依据。     

轴承套硬车加工的径向热变形研究

热变形的大小受零件的形状、材料以及表层残余应力等因素的影响。针对风电机组主轴轴承的内圈,基于工程弹性力学和热力学原理分析了精车加工中轴承套圈产生的表层残余应力对几何形体热变形的影响,并对加工过程中由残余应力产生的径向变形进行了定量分析,建立了套筒类零件的基于残余应力的热变形数学模型,并通过理论计算和实验测试,对套筒类零件的热变形数学模型进行了验证,实验数据与数学模型大致吻合。     

Ti——17合金的本构关系研究

在ＴＨＥＲＭＥＣＭＡＳＴＯＲ—Ｚ型热模拟试验机上对Ｔｉ—１７合金在温度８０５～９４５℃、应变速率１０－３～８０ｓ－１、最大变形程度５０％条件下的高温流动应力变化规律进行了研究，分析其变形温度、变形程度和应变速率对流动应力的影响规律后，对流动应力软化现象明显的Ｔｉ—１７合金提出了一种本构关系回归模型，拟合精度较高。     

7B04-T6铝合金板材温拉伸流变应力行为研究

在温度为473～623 K、应变速率为0.1 s-1～0.001 s-1的条件下对7B04-T6铝合金板材进行温拉伸实验,研究该材料在所选定温度和应变速率下的流变应力变化数据.分别对Fields and Backofen方程和加入软化因子"s"的流变应力数学方程进行修正,建立该材料的两个流变应力数学模型.两模型中,Fi...     

变形态Ti40合金的高温流变应力模型研究

利用变形态Ti40合金在变形温度范围为1223～1323K和应变速率范围为0.001～1.0s-1的不同应变下的热压缩实验数据研究了该材料的高温流变应力模型。利用实验数据分析了Arrhenius型方程对变形态Ti40合金的适用性,结果表明,采用双曲正弦型Arrhenius方程建立该材料的高温流变应力模型是适宜的,并通过对双曲正弦方程进行温度补偿及引入路径变量因子改进了模型。通过计算复相关系数和平均相对误差绝对值对该模型进行误差分析,经过改进的变形态Ti40合金的高温流变应力模型具有良好的精度。     

The flow stress anomaly in Fe–43at%Al single crystals

Fe–43at%Al single crystals were deformed in compression between room temperature and 700 °C. The strain rate sensitivity of the flow stress was measured by stress relaxation tests. The dislocation structure of the deformed samples was studied in a high-voltage transmission electron microscope. In addition, micro-tensile specimens were deformed in situ in this microscope to directly observe the dynamic behaviour of the dislocations. The specimens show a flow stress anomaly accompanied with an ‘inverse’ dependence of the strain rate sensitivity on the strain rate. Both the in situ experiments and the transmission electron micrographs of macroscopically deformed samples indicate the occurrence of climb at temperatures in and above the anomaly range. In the in situ experiments, viscously moving dislocations are straight and crystallographically oriented. The phenomena related to the flow stress anomaly are interpreted by the decomposition of the cores of dislocations with 〈111〉 Burgers vectors.     

扭杆弹簧硬化强扭理论的研究

提出了扭杆弹簧在塑性硬化扭转时断面应力分布假设、硬化强扭的概念和硬化强扭扭矩、断面残余应力、残余变形角的计算方法.计算结果表明:扭杆弹簧强扭变形量较大时断面存在3种变形区,即弹性变形区、屈服变形区和硬化变形区;按硬化强扭理论可以使扭杆弹簧的承载能力提高80%以上,突破了屈服强扭认为承载能力最大只能提高33%的界限;强扭的应变角可以突破γ≈0.022的界限而达到γ≈0.034以上,计算结果与实际情况接近.     

外缘外曲翻边时的应力应变分析

本文通过对外缘外曲翻边应力应变状态的分析 ,考虑应变硬化和材料各向异性 ,对于满足P Ludwik应力应变硬化关系式的刚塑性硬化材料 ,推出了变形区外边缘的周向应力应变计算公式 ,以及翻边过程中变形区外边缘长的计算公式。通过和数值模拟结果比较发现 ,数值模拟的结果和按本文公式计算得到的结果较接近。     

AZ31B镁合金中厚板轧制热力耦合场数学模型

采用Gleeble-1500D热力模拟试验机对铸态AZ31B镁合金圆柱试样进行了宽范围变形条件下的热压缩试验,拟合热压缩试验数据,针对镁合金应变软化特性建立了一种新的热力本构模型;依托于Deform-3D对镁板的实际热轧过程进行了热力仿真分析,依据轧制理论假设、宏观连续介质力学以及热力学原理,采用数学解析的方法建立了镁板热轧制区域中的应变、应变速率值分布模型以及三维温度场、应力场数学模型。研究结果表明:新建的热力本构模型预测精度较高,平均相对误差为5.1%;建立的轧制变形区域中的应变、应变速率值分布模型,温度场数学模型以及热力耦合场数学模型不仅形式简单易于为生产利用,更能精确表征中厚规格镁板热轧制过程中的热-力耦合变形机制。     

SCC initiation for X65 pipeline steel in the “high” pH carbonate/bicarbonate solution

The initiation of stress corrosion cracking (SCC) was studied using scanning electron microscope observations of linearly increasing stress test specimens. SCC initiation from the following surfaces was studied: (i) initiation from the commercial pipe surface covered by the Zn coating, (ii) initiation from a mechanically polished surface with a deformed layer, and (iii) initiation from an electro-polished surface. SCC initiation involved different features for these surfaces as follows. (i) For the Zn coated commercial pipe surface, a crack in the Zn coating led to the dissolution of the deformed layer and when the deformed layer was penetrated, intergranular SCC initiation became possible. (ii) For a mechanically polished surface with a deformed layer, cracks in the surface oxide concentrated the anodic dissolution to such an extent that there was transgranular SCC in the deformed layer. SCC was intergranular when the deformed layer had been penetrated. Transgranular stress corrosion cracks were stopped at ferrite grain boundaries (GBs) oriented perpendicular to the SCC propagation direction. (iii) For an electro-polished surface, the surface oxide film was cracked at many locations, but intergranular SCC only propagated into the steel when the oxide crack corresponded to a GB. An oxide crack away from a GB is expected to be healed. The observed SCC initiation mechanism was not associated with simple preferential chemical attack of the ferrite GBs.     

Effect of equal-channel angular pressing routes on high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy

The effect of equal-channel angular pressing (ECAP) route on the high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy was investigated. The 8-pass ECAPed specimens deformed via three different routes consisted of ultra-fine grains 0.5 μm in size, and contained a considerable amount of second-phase particles, which were fragmented and distributed in the matrix. In the torsion tests, the maximum shear stress significantly increased with increasing number of ECAP passes, while the maximum shear stress and fracture shear strain were lowest in the specimen deformed via route A among the three 8-pass ECAPed specimens. Observation of the deformed area beneath the fractured surface revealed the adiabatic shear bands of 100 μm in width in the specimen deformed via route A, which minimized the maximum shear stress and fracture shear strain, whereas they were hardly formed in the specimens deformed via route B or C. The formation of adiabatic shear bands was explained in terms of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.     

继电器触点冷镦成形过程的有限元分析

研究了Ag Sn O2类材料单体触点在镦制过程中的开裂问题,并将银丝材料拉伸试验曲线转化成真应力、应变数据,拟合得到银丝材料流变应力数学模型。应用有限元方法,模拟了银单体触点的冷镦成形过程,得到了冷镦成形过程中的等效应变、应力分布情况。研究结果表明,拉应力越靠近外层越大,而径向压应力则越靠近外层越小,变形物体的单位压力从外向内逐渐增大,因此,触点最大直径处为易开裂位置。此外,准确预测了成形过程中材料产生裂纹缺陷的位置及裂纹程度,当变形达到材料Damage值时,裂纹开始形成,Damage值随变形程度的增加而上升。通过试验,对开裂模拟结果进行了验证,模拟结果与试验吻合较好。