高温应变栅丝蠕变对应变测量精度影响与补偿

接触式应变测量是材料和构件高温力学行为研究的必要手段,其测量精度是高温应变测量领域关注的热点,而应变栅丝的高温蠕变性能是测量精度的主要影响因素.本文首先根据材料蠕变机理分析应变片的蠕变特性,搭建高温应变栅丝蠕变电测的系统,基于诺顿蠕变规律与试验的测量结果,建立应变栅丝的高温蠕变模型.论文基于应变栅丝蠕变输出有限元模型,对栅丝蠕变输出的影响因素进行研究;最后建立了高温应变蠕变补偿模型,以提高高温应变测量精度,并取得了试验验证.      

高温应变片的热输出耦合特性

系统运用材料物理学、弹性力学、热力学、工程测试技术的理论知识以及有限元数值仿真、实验分析等方法,研究高温应变片热输出误差的影响因素并得出补偿修正模型.首先根据材料电阻温度效应理论及热膨胀理论研究了高温应变片热输出的耦合特性,建立耦合作用下高温应变片的热输出模型,得到了构件、胶层和应变片三者耦合作用下应变片热输出的理论表达式;然后根据材料的电阻温度效应推导出不同栅丝材料的电导率参数,利用有限元仿真得到不同材料栅丝的热输出特性,选择其中的两种栅丝材料作为本文的研究对象得到其在耦合作用下的热输出并与实验数据对比,相对误差小于7%.最后基于理论模型和实验结果,建立了高温应变片热输出补偿模型,补偿修正后结果与理论值误差在9%以内,补偿效果良好.      

铁-铬-铝高温应变合金丝材的研究

本文报道了Fe-Cr-Al-V系高温应变合金的研制工作。用该合金制成的单丝粘贴式温度自补偿应变片,贴在镍基合金GH-30和GH-39试件上,其室温至700℃以上温度区间的热输出数值小于2000βε,能够满足700℃静态强度分析之用,现已广泛应用于喷气发动机涡轮盘及涡轮叶片等高温部件上。文中还分析了合金组元及工艺参数对电阻温度系数的影响,并对电阻稳定性、试件膨胀系数等进行了讨论。     

重油含水率自动检测系统研究

叙述了重油含水率自动检测系统的测量原理及该检测系统中传感器探头的设计,介绍了建立三维补偿校正标定表实现温度自动补偿与多参数的非线性校正方法,并对检测系统误差进行了分析,结果表明该检测系统的最大误差为±０．５％     

700℃Fe-Cr-Al应变电阻合金丝

在航空、宇航、原子能、动力、大型发电设备、重型机械等现代工程技术领域,常需在高温环境中进行材料结构试验。高温应变计应用电测量技术就能有效地获得各种结构材料在高温下的应力分布规律及高温强度。我所已成功地研制成用于700℃自补偿应变片的Fe-Cr-Al合     

基于立体靶标的摄像机标定方法

为获取视觉测量系统中二维图像到三维空间位置的变换关系,提出一种基于立体靶标的摄像机标定方法.针对无畸变小孔成像模型,使用最小二乘法求解初始投影矩阵后通过LM准则对其优化;根据多张图像对应的投影矩阵,求解摄像机内参数及各相应外参数;引入二阶径向畸变模型,建立理想图像坐标和实际图像坐标间的方程求解初始畸变系数;使用LM准则全局优化,得到更精确的摄像机内外参数及畸变因子.实验结果表明:仿真图像数据中高斯噪声小于0.5像素时,摄像机等效焦距误差小于0.1%,图像主点误差小于0.5像素;在相同噪声等级下,标定使用图像数越多获得的参数标准差越小;该方法标定参数对应的位置残差小于其他立体靶标标定方法.该标定方法具有较高的标定精度,且增加标定图像数有助于抑制噪声获取稳定的摄像机参数.     

涡轮转子叶片热障涂层损伤失效的实时检测与分析

在地面台或核心机上开展热障涂层试车需耗费巨大的人力物力,且无法捕捉涂层损伤演化的关键信息.通过研制高速旋转涡轮叶片热障涂层动态服役环境模拟与测试装置,并在转子叶片热障涂层表面敷设高温电阻应变计与热电偶可实现服役过程中的应变损伤与温度场的实时检测.敷设方法选择陶瓷棒火焰喷涂,应变计的温度补偿通过高温升降炉来实现,同时也开...     

55SiMnMo贝氏体钢高温流变应力本构方程

 采用Gleeble-3500热模拟试验机对55SiMnMo贝氏体钢进行了热压缩试验,得到了其在变形温度为950~1150℃和应变速率为0.01~10s-1条件下的高温流变应力行为。试验结果表明,峰值应力随变形温度的降低和应变率的提高而增大;当应变速率为0.01和0.1s-1,变形温度t ≥1000℃时,发生动态再结晶。基于试验结果,充分考虑了热变形工艺参数（应变、应变速率和变形温度）对流变应力的影响,建立了一种考虑应变速率补偿的高温流变应力本构方程。通过对该本构方程预测得到的流变应力值和试验值对比,验证了模型的准确性。     

WCF钢动态断裂韧性J_(1d)(K_(1d))的测试研究

利用 WCF 钢制试样,对动态断裂韧性测试方法进行了系统的研究.提出全范围小角度启裂标定方法。结果表明这一方法有效可行,同时试验考察了裂纹几何,侧槽形貌,温度等对测试结果的影响,并证实断裂参数选择的合理性取决于实际断裂的类型。     

H13钢制分流模低周疲劳寿命的预测方法及应用

 利用Gleeble1500热模拟试验机对H13模具钢在650-800℃温度范围,0.1-20s-1应变速率下的热压缩变形行为进行了研究,并得到了该材料在20-650℃范围内的弹性模量,建立了H13钢的有限元模型;通过高温拉伸实验和通用斜率法建立了H13钢的应变-低周疲劳寿命关系;结合有限元方法提出了一种预测H13钢制铝型材挤压模具低周疲劳寿命的方法,并在此基础上得到了工艺和结构参数对模具疲劳行为的影响规律。结果表明：疲劳应变损伤值随着挤压速度的增加以及模桥根部圆角半径的减小而增大,其中结构参数为关键影响因素。最后通过生产实际验证了该方法的可靠性。     

A Coupled Electrical–Thermal–Mechanical Modeling of Gleeble Tensile Tests for Ultra-High-Strength (UHS) Steel at a High Temperature

A coupled electrical–thermal–mechanical model is proposed aimed at the numerical modeling of Gleeble tension tests at a high temperature. A multidomain, multifield coupling resolution strategy is used for the solution of electrical, energy, and momentum conservation equations by means of the finite element method. Its application to ultra-high-strength steel is considered. After calibration with instrumented experiments, numerical results reveal that significant thermal gradients prevail in Gleeble tensile steel specimen in both axial and radial directions. Such gradients lead to the heterogeneous deformation of the specimen, which is a major difficulty for simple identification techniques of constitutive parameters, based on direct estimations of strain, strain rate, and stress. The proposed direct finite element coupled model can be viewed as an important achievement for subsequent inverse identification methods, which should be used to identify constitutive parameters for steel at a high temperature in the solid state and in the mushy state.     

In-situ nuclear magnetic resonance investigation of strain, temperature, and strain-rate variations of deformation-induced vacancy concentration in aluminum

Critical strain to serrated flow in solid solution alloys exhibiting dynamic strain aging (DSA) or Portevin-LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance (NMR) techniques can be used to monitor in situ the dynamical behavior of point and line defects in materials during deformation, and these techniques are nondestructive and noninvasive. The new CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and, thus, the excess vacancy concentration during deformation as a function of strain, strain rate, and temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (vs thermal jogs), while in situ annealing of excess vacancies is noted at high temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain rate, and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformation-induced vacancies in situ in a noninvasive fashion.     

电感耦合等离子体原子发射光谱法测定镍基单晶高温合金中钨钽铪铼

镍基单晶高温合金中高含量的钨、钽、铪、铼等难熔元素,不仅对样品前处理造成阻碍,而且其元素间的光谱干扰会对测定结果造成严重影响。实验采用18mL盐酸-2mL硝酸-2mL氢氟酸溶解样品,再加入酒石酸可使样品溶液长期稳定存在。通过研究单晶高温合金中钨、钽、铪、铼的谱线干扰情况,选择W 207.911nm、Ta 240.063nm、Hf 282.022nm、Re 197.312nm作为分析谱线,采用基体匹配法配制标准溶液系列绘制校准曲线,使用电感耦合等离子体原子发射光谱法(ICP-AES)测定镍基单晶高温合金中钨、钽、铪、铼。各元素在线性范围内校准曲线线性关系良好,相关系数均不小于0.9997;方法检出限为0.0001%~0.0008%。按照实验方法测定DD6单晶高温合金样品中钨、钽、铪、铼,结果的相对标准偏差(RSD,n=11)为1.0%~2.5%;加标回收率为96%~102%。     

On minimizing the bauschinger effect in steels by dynamic strain aging

The Bauschinger effect was measured in the conventional tension-compression mode in five steels, AISI 1020, 1522, and 1035, ASTM A374 (Cor-Ten) and an HSLA Mn-Mo-Cb steel. The results were compared with those obtained by performing the forward strain at a temperature near the peak of dynamic strain aging for each of the steels and the subsequent reverse strain at room temperature. The dynamic strain aging process sharply reduced the extent of the Bauschinger effect and was particularly effective in re-storing the elastic portion of the flow curve during the reverse strain. We conclude that the straightening of steel parts after heat treatment should be done warm, in the dynamic strain aging range, whenever feasible. Formerly students at the University of Michigan.     

惰气熔融-脉冲加热法同时测定人造金刚石中氧和氮

在称样量为0.067～0.12 g, 镍助熔剂为0.37 g, 分析功率为5.5 kW的条件下, 建立了用惰气熔融-脉冲加热法同时测定人造金刚石中氧和氮含量的方法, 并对氧和氮校准曲线的制作问题进行了讨论。对人造金刚石样品中氧和氮进行了9次测定, 其测定结果的相对标准偏差分别小于3.0%和3.5%。按照方法, 使用不同氧氮标样建立的两条校准曲线对人造金刚石样品中氧和氮进行测定, 所得氧和氮的测定值一致, 并且与惰气高温萃取-脉冲加热法所得氧和氮的测定值一致。     

The determination of the relationship between strain and microhardness by means of visioplasticity

The determination of strain values by means of microhardness measurements is a useful technique in that it can be used to measure plastic strains either on the surface or within the body of a specimen or structural component. A method is described whereby a calibration curve between strain and microhardness can be obtained by use of the visioplasticity technique. The curve thus obtained is valid for complex stress and strain states and for high strains. The microhardness was found to be a single valued function of the true effective strain independent of how this strain was produced. Agreement was found between the microhardness and values calculated from the flow stress.     

电感耦合等离子体质谱法测定高纯镍板中砷锡锑铅铋

采用10 mL硝酸(1+1)低温加热至沸溶解0.100 0 g试样,在优化仪器参数的基础上,通过选择合适的同位素以避免质谱干扰和采用标准加入法绘制校准曲线以消除基体效应,建立了电感耦合等离子体质谱法(ICP-MS)测定高纯镍板中砷、锡、锑、铅、铋的方法。各元素校准曲线的相关系数为0.999 2～0.999 9,方法检出限为0.009～0.047 μg/g。方法应用于高纯镍板实际样品分析,测得结果的相对标准偏差(RSD, n=9)为2.4%～5.4%,加标回收率为95%～106%。方法测定高纯镍板实际样品的结果与原子吸收光谱法(AAS)相吻合。     

惰气熔融-热导法测定氮化铬铁中氮

研究了用氧氮分析仪测定氮化铬铁中氮的最佳工作条件,并重点对方法的准确性进行了讨论。利用氮化硅粉和氮化锰铁两种高氮标样分别建立了两条校正曲线,结果表明两条校正曲线间存在较大的系统误差。用测定硝酸盐基准试剂中氮量对两条校正曲线的准确性进行了验证,结果表明氮化硅粉校正曲线的准确度较高,硝酸银和硝酸钾中氮的回收率分别达到99%、98%,而用氮化锰铁校正曲线计算得到的回收率仅为94%。采用惰气熔融-热导法测定样品,方法的相对标准偏差为0.17%~0.45%,分析结果与蒸馏滴定法测定结果一致。     

Constitutive Model of Warm Deformation Behavior of Medium Carbon Steel

The compressive behaviors of medium carbon steel specimens were investigated over a wide range of tem-peratures and strain rates using a Gleeble-3500 thermo-simulation machine.The results show that the flow stress in-creased with strain at first,and then gradually decreased after reaching a peak value.The flow stress softening rate at a high strain rate was larger than that at a low strain rate.The effects of deformation heating and friction on flow stress were analyzed.A new friction correction method,wherein the effect of strain on frictional coefficient was con-sidered,was established here.The stresses revised by the new method deviated from the measured stresses with in-creasing strain.Meanwhile,the apparent frictional coefficient variation law with strain was obtained.The frictional coefficient increased as the strain increased and then slightly decreased after maintaining a constant value.The stress was corrected by considering deformation heating.The accuracy of the temperature correction method was verified using a special experiment.The results of the verification experiment show that the temperature correction method exhibited a good accuracy in calculating the variation of stress caused by deformation heating.A constitutive model considering strain was proposed here to describe the deformation behaviors.Compared with experimental data,the modified constitutive model exhibited a good accuracy as to constitutive correlation.