典型零件形体的热变形模型及其有限元仿真

随着精密技术的精度不断提高,温度变化引起零件形变带来的影响不容忽视,为了解决此问题,根据弹性力学和热力学理论,建立了典型零件形体的热变形模型,利用ANSYS有限元分析软件对典型零件形体的热变形误差及其分布进行了仿真,并进行了模型实验验证,给出了实例应用的分析,说明了热变形模型在公差与配合中的应用。结果表明,所建立的模型考虑了热应力的影响,相对于传统计算方法更加合理可靠,为合理进行零件的公差与配合设计提供了理论依据和参考。

绝对检验参考镜误差分析与热变形模型建立

绝对检验是提高菲佐(Fizeau)型干涉仪参考面面形精度的重要方法。研究了过程中温度、重力和夹持力对绝对检验精度的影响。采用Gram-Schmidt拟合方法对参考面面形的变形量进行了拟合,分析了K9、融石英和微晶材料的参考镜均匀温度变化下的热变形及由于热变形导致的相应泽尼克(Zernike)系数的变化。最后,分析了变形量对应的面形误差,建立了每种材料的热变形模型。结果表明,经过重力、夹持力和温度三者的叠加耦合,温度变化产生的变形量与温度变化量仍呈近似的线性关系。在相同的外界条件下,融石英材料产生的整体变形量最小;而微晶材料产生的热变形量最小。微晶参考面由于热变形产生的面形变化量均方根为0.37 nm/℃。

各向异性弹性孔隙介质中的热-流-变形耦合模型

研究微小孔隙介质中应变导致渗透率各向异性的问题.采用有限单元法综合分析处理储层变形-渗流-热传导耦合模型与应变导致渗透率变化模型,并用该方法分析弹性多孔介质的二维非等温变化单相渗流的耦合问题.对比结果表明,应变导致的渗透率变化模型能有效反映蒸汽注入引起的岩层各向膨胀,与热采过程中油藏的实际情况更吻合.

基于COMSOL的热—流—变形耦合模型在稠油热采中的研究

针对稠油热采开发过程中高温蒸汽注入引起的岩层骨架应力、储层压力、温度耦合变化问题,应用连续介质力学和能量守恒理论,建立了稠油注蒸汽热采开发的热—流—变形耦合分析模型。在此基础上,应用COMSOL软件进行数值模拟计算和分析。计算结果表明:温度波及范围和传播速度与岩石的物性参数孔隙度和渗透率有关,并且在开发过程中热—流—变形耦合效应显著,由于地层流体高温膨胀引起的高压力,会导致位移、变形,甚至地层结构破裂。这个模型可以用于蒸汽注入温度优化和油藏、地质、热-流动力反应、地应力水平等综合作用效应研究。

精密技术中热变形误差影响的基本问题

在精密测量和精密机械等精密工程技术领域,影响精度的众多因素中,温度变化引起的热变形误差已成为主要的甚至决定因素.由于精度不断提高,传统热变形误差的某些概念与方法已失去实用价值,该文分析了热变形误差的研究与应用现状,研究了适应高精度技术的热变形误差新概念、新方法,提出了几种实用性不同的热膨胀系数概念以及精确热膨胀系数和科学热膨胀系数定义.在全面分析热变形误差的多种因素基础上,研究了物体形状结构对其参数热变形影响的新认识并举例说明,同时提出相应的热变形系数,最后简介了考虑形状影响的热变形误差建模方法.

页岩结构完整性评价的热-流体-变形耦合理论与方法

该文应用连续介质力学理论建立了与蒸汽注入过程相关的热-流-变形耦合问题的基本数学模型;应用全隐式顺序Galerkin有限元数值解方案,对注蒸汽井的热-流体-变形耦合过程进行了数值模拟。结果表明,由于低渗透页岩地层流体高温膨胀导致的超高孔隙压力,有可能产生拉张应力,严重时会导致地层破裂。

1700MPa级热成形钢的流变行为研究

本文以1 700 MPa级热成形钢为研究对象,进行了热变形模拟实验,研究了不同变形条件下的流变应力-应变曲线,分析了热变形过程中各参数对流变应力的影响,并在已有流变应力模型的基础上提出了本试验钢的流变应力数学模型.结果表明,流变应力均随变形温度的降低呈整体升高趋势;应变速率对流变应力的影响具有双重性;试验钢在热变形过程中的稳态流变应力数学模型和热变形方程分别为σ=22.117 98ln Z-1423.592 3和σ_p=22.117 98lnε＋751.588×10~3/T-423.592 3.流变应力的峰值主要与应变速率和温度有关.

钢化真空玻璃在温差作用下的变形特征

钢化真空玻璃两侧存在温差是导致其弯曲失效的重要原因之一。通过钢化真空玻璃温差变形试验和数值模拟,得到不同尺寸的钢化真空玻璃(5+0.5V+5)在不同温差下的变形特征。结果表明:钢化真空玻璃受两侧温差形成的球面弯曲曲率半径与钢化玻璃基片的厚度成正比,与钢化玻璃基片的线膨胀系数及两侧温差成反比;钢化真空玻璃的变形量与钢化玻璃基片尺寸、温差大小及曲率半径呈正相关;同一温差下钢化真空玻璃变形量随长边尺寸增大而增大;数值模拟结果与试验结果吻合,相对误差在5%以内,能够为不同尺寸钢化真空玻璃在温差下的变形预测提供参考。

热采过程中井眼热应力定量评价方法

应用连续介质力学理论,建立了与蒸汽注入过程相关的热-流-变形耦合问题的基本数学模型;应用全隐式顺序有限元数值解方法,对该数学模型进行了求解,获得了井眼热应力与超孔隙地层压力的部分数值结果。结果表明,在300℃注入蒸汽温度情况下,由温度变化引起的井眼区域超孔隙压力可以达到15MPa的水平。由于低渗透页岩地层流体高温膨胀导致的超孔隙压力,有可能产生有效拉张应力,严重时会导致地层破裂。

热采过程中地层超孔隙压力与井眼应力的定量评价

基于连续介质力学理论,建立了热采蒸汽注入过程中地层超孔隙压力和有效应力定量评价的热流变形耦合数学模型,应用Galerkin有限元全隐式顺序迭代方案,建立了求解该类复杂耦合模型的有效数值解法。数值结果表明,当井筒加热速率为46.82℃/d时,低渗透页岩地层的最高超孔隙压力达13.8 MPa,相应的页岩层径向有效应力和周向有效应力分别达到了14 MPa和9 MPa。因此,设计注入蒸汽加热速率的最佳方案应综合考虑页岩的热流动力反应、地应力水平和套管强度等因素。

Modeling constitutive relationship of 6013 aluminum alloy during hot plane strain compression based on Kriging method

Hot plane strain compression tests of 6013 aluminum alloy were conducted within the temperature range of 613?773 K and the strain rate range of 0.001?10 s?1. Based on the corrected experimental data with temperature compensation, Kriging method is selected to model the constitutive relationship among flow stress, temperature, strain rate and strain. The predictability and reliability of the constructed Kriging model are evaluated by statistical measures, comparative analysis and leave-one-out cross-validation (LOO-CV). The accuracy of Kriging model is validated by the R-value of 0.999 and the AARE of 0.478%. Meanwhile, its superiority has been demonstrated while comparing with the improved Arrhenius-type model. Furthermore, the generalization capability of Kriging model is identified by LOO-CV with 25 times of testing. It is indicated that Kriging method is competent to develop accurate model for describing the hot deformation behavior and predicting the flow stress even beyond the experimental conditions in hot compression tests.

Effects of initial δ phase(Ni_3Nb) on hot tensile deformation behaviors and material constants of Ni-based superalloy

Effects of initial δ phase（Ni_3Nb） on the hot tensile deformation behaviors and material constants of a Ni-based superalloy were investigated over wide ranges of strain rate and deformation temperature. It is found that the true stress-true strain curves exhibit peak stress at a small strain, and the peak stress increases with the increase of initial δ phase. After the peak stress, initial δ phase promotes the dynamic softening behaviors, resulting in the decreased flow stress. An improved Arrhenius constitutive model is proposed to consider the synthetical effects of initial δ phase, deformation temperature, strain rate, and strain on hot deformation behaviors. In the improved model, material constants are expressed as the functions of the content of initial δ phase and strain. A good agreement between the predicted and measured results indicates that the improved Arrhenius constitutive model can well describe hot deformation behaviors of the studied Ni-based superalloy.

Constitutive modeling of hot deformation behavior of X20Cr13 martensitic stainless steel with strain effect

Hot deformation behavior ofX20Cr13 martensitic stainless steel was investigated by conducting hot compression tests on Gleeble-1500D thermo-mechanical simulator at the temperature ranging from 1173 to 1423 K and the strain rate ranging from 0.001 to 10 s^-1. The material constants of a and n, activation energy Q and A were calculated as a function of strain by a fifth-order polynomial fit. Constitutive models incorporating deformation temperature, strain rate and strain were developed to model the hot deformation behavior of X20Cr13 martensitic stainless steel based on the Arrhenius equation. The predictable efficiency of the developed constitutive models of X20Cr13 martensitic stainless steel was analyzed by correlation coefficient and average absolute relative error which are 0.996 and 3.22%, respectively.

基于视觉的超窄间隙焊接坡口宽度测量方法

针对超窄间隙焊接因坡口窄且深的结构特点而导致当前焊道坡口宽度难以直接测量的问题,提出一种基于视觉和焊接热变形模型的当前焊道坡口宽度软测量方法。为克服激光线投射于焊件表面所造成的亮度分布不均,二值化阈值难以确定的问题,提出使用顶帽变换与Otsu共同作用的方法,将激光线灰度均衡化的同时从背景中有效分离,骨架法和最小二乘法相结合可准确提取单像素的激光条纹中心线并对特征点识别,完成上坡口宽度的测量。依据坡口角变形量与焊缝厚度关系,建立当前焊道坡口宽度计算模型。实验结果表明:此方法可以实现超窄间隙厚板焊接上下坡口宽度的准确测量,且最大误差不超过0.2 mm,能满足超窄焊接工艺参数设定对坡口宽度测量精度的要求。

Characterization of hot deformation behavior of AA2014 forging aluminum alloy using processing map

The hot deformation behavior of AA2014forging aluminum alloy was investigated by isothermal compression tests attemperatures of350-480°C and strain rates of0.001-1s-1on a Gleeble-3180simulator.The corresponding microstructures of thealloys under different deformation conditions were studied using optical microscopy(OM),electron back scattered diffraction(EBSD)and transmission electron microscopy(TEM).The processing maps were constructed with strains of0.1,0.3,0.5and0.7.The results showed that the instability domain was more inclined to occur at strain rates higher than0.1s-1and manifested in theform of local non-uniform deformation.At the strain of0.7,the processing map showed two stability domains:domain I(350-430°C,0.005-0.1s-1)and domain II(450-480°C,0.001-0.05s-1).The predominant softening mechanisms in both of the twodomains were dynamic recovery.Uniform microstructures were obtained in domain I,and an extended recovery occurred in domainII,which would lead to the potential sub-grain boundaries progressively transforming into new high-angle grain boundaries.Theoptimum hot working parameters for the AA2014forging aluminum alloy were determined to be370-420°C and0.008-0.08s-1.

Effects of solution treatment on high temperature deformation behavior of extruded Mg-0.35Y-2.17Nd-0.36Zr biomedical alloy

The high temperature deformation behavior of an extruded Mg-0.35 Y-2.17 Nd-0.36 Zr(wt.%) alloy was investigated for biomedical application by employing compression tests in temperature range of 225-525 ℃ and strain rate range of 0.0003-0.03 s-1. To study the significance of solute elements, the material was solution-treated before deformation. The low temperature yield strength of the as-extruded material significantly decreased after solutionizing process. A drastic change in the strength of solutionized alloy was recorded as the temperature was raised to 450 ℃, which was attributed to the promotion of grain boundary sliding(GBS). It was evidently shown that the slip-to-twinning transition temperature did not necessarily coincide with the strength-drop temperature. Based on constitutive equations, deformation parameters and related activation energy for the experimental alloy have been determined, incorporating the strain-dependent material constants. The verification of predictability of the developed models indicates a good agreement between experimental and predicted data.

A new mathematical model for predicting flow stress of X70HD under hot deformation

To realize numerical simulation of rolling and obtain the hot forming process parameters for X70 HD steel, the flow stress behaviors of X70 HD steel were investigated under different temperatures（820-1100 ℃ and strain rates（0.01-10 s-1） on a Gleeble-3500 thermo-simulation machine. A new flow stress model was established. The linear and exponential relationship methods were applied to the parameters with respect to temperature and deformation rates. The rise of curve ends under certain conditions was analyzed. The flow stress of X70 HD steel predicted by the proposed model agrees well with the experimental results. So, it greatly improves the precision of the metal thermoplastic processing through finite element method and practical application of engineering.

Flow behavior and constitutive description of 20CrMnTi steel at high temperature

In order to research the flow behavior of 20CrMnTi and obtain its constitutive equation, the isothermal compression tests of 20CrMnTi were carried out using the Gleeble-3500 thermo-simulation machine, up to a 60% height reduction of the sample at strain rate range from 0.01 s 1 to 10 s 1 and deformation temperature range from 1123 K to 1273 K. According to the experimental results, the constitutive equation of 20CrMnTi was established based on Arrhenius model. In addition, the compensation of strain was taken into account and a new method of modifying the constitutive equation was proposed by introducing a coefficient K related to the deformation temperature and stain rate, which effectively improved the prediction accuracy of the developed constitutive equation. The results show that the flow stress decreases with increasing deformation temperature and decreasing strain rate, and the proposed constitutive equation well predicts the flow stress of 20CrMnTi during the high temperature deformation.

Hot deformation behaviors and flow stress model of GCr15 bearing steel

The hot deformation behaviors of GCr15 bearing steel were investigated by isothermal compression tests, performed on a Gleeble-3800 thermal-mechanical simulator at temperatures between 950 ℃ and 1 150 ℃ and strain rates between 0.1 and 10 s-1. The peak stress and peak strain as functions of processing parameters were obtained. The dependence of peak stress on strain rate and temperature obeys a hyperbolic sine equation with a Zener-Hollomon parameter. By regression analysis, in the temperature range of 950-1 150 ℃ and strain rate range of 0.1?10 s?1, the mean activation energy and the stress exponent were determined to be 351kJ/mol and 4.728, respectively. Meanwhile, models of flow stress and dynamic recrystallization (DRX) grain size were also established. The model predictions show good agreement with experimental results.

Prediction on hot deformation behavior of spray-formed 7055 aluminum alloy via phenomenological models

Hot compression tests in the temperature range of 340-450 ℃ and strain rate range of 0.001-1 s^-1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological models including Johnson-Cook, modified Fields-Backofen and Arrhenius-type were introduced to predict the flow stresses during the compression process. And then, a comparative predictability of the phenomenological models was estimated in terms of the relative errors, correlation coefficient（R）, and average absolute relative error（AARE）. The results indicate that Johnson-Cook model and modified Fields-Backofen model cannot well predict the hot deformation behavior due to the large deviation in the process of line regression fitting. Arrhenius-type model obtains the best fit through combining the effect of strain rate and temperature.