RUDIMENTAL EQUATIONS FOR THERMO－ELASTO－PLASTIC STRESS ANALYSIS DURING CONTINUOUS CASTING WITH PHASE CHANGE

Coupled relations among temperature, phase transformation and stress have beendiscussed here in the present paper. Thermo-elasto-plastic constitutive equationsincluding creep and iterative finite element formulation during continuous casting withphase change have also been presented.

A spatiotemporal signal processing technique for wafer-scale IC thermomechanical stress monitoring by an infrared camera

In this paper, we describe a new silicon-die thermal monitoring approach using spatiotemporal signal processing technique for Wafer-Scale IC thermome- chanical stress monitoring. It is proposed in the context of a wafer-scale-based (WaferICTM) rapid prototyping platform for electronic systems. This technique will be embedded into the structure of the WaferIC, and will be used as a preventive measure to protect the wafer from possible damages that can be caused by excessive thermomechanical stress. The paper also presents spatial and spatiotemporal algorithms and the experimental results from an IR images collection campaign conducted using an IR camera.

冷却速度对Thermo-Span合金组织和持久性能的影响

采用扫描电镜(SEM)、透射电镜(TEM)研究了固溶冷却速度对改型低膨胀Thermo-Span合金组织和持久性能的影响。结果表明:固溶冷却速度由空冷变为水冷,其它热处理条件不变,含0.05%B合金晶内析出γ′相的数量未见明显增多,而颗粒的尺寸变小,形态没有改变,晶界析出增多。合金650℃,600MPa的光滑持久性能保持较高水平,合金的缺口敏感性消失。

高温长期时效对改型低膨胀Thermo-Span合金热稳定性和性能的影响

研究了高温时效对标准和改型Thermo-Span合金组织和持久性能的影响,在650℃时效1000 h,标准合金的晶内与晶界Laves析出相均发生了粗化,而改型合金的析出相形貌没有改变,当时效温度增高到680℃时,标准合金在时效500 h时,合金的析出相已经发生了严重的粗化,Laves相的形态由圆粒状变成条状,而改型合金的析出相没有变化,当时效到1000 h后,标准合金析出相已经完全粗化,析出相几乎布满了整个晶内,而改型合金晶界只有少量析出相开始发生粗化,经650℃时效1000 h后,改型合金具有较好的组织热稳定性,合金650℃/600 MPa的持久性能比标准合金高109 h。

STRESS ANALYSIS OF INJECTION MOLDED PARTS IN POST-FILLING STAGE

The linear isothermo-viscoelastic constitutive equation is established according to the principle of viscoelastic mechanics. Given the boundary conditions of the temperature field, the linear thermo-viscoelastic constitutive equation is established acording to the analysis of the thermorheologically simple. The stress analysis model is constructed on the base of some reasonable hypotheses which consider the restraint conditions of mold and the characteristics of injection molding in the post-filling stage. The mathematical model is calculated by the finite difference method. The results can help to predict the warpage of plastic products.

Temperature and Thermal Stress Distribution for Metal Mold in Squeeze Casting Process

In the squeeze casting process, loaded high pressure （over approximately 200 MPa） and high temperature influence the thermo-mechanical behavior and performance of the used metal mold. Therefore, to safely maintain the metal molds, the thermo-mechanical characteristics （temperature and thermal stress） of metal mold in the squeeze casting must be investigated. In this paper, temperature and thermal stress distribution of steel mold in squeeze casting process were investigated by using a three-dimensional non-steady heat conduction analysis and a three-dimensional thermal elastic-plastic analysis considering temperature-dependent thermophysical and mechanical properties of the steel mold.

Stress Dependence of Transformation Plastic Behavior

Transformation plasticity is known to play an important role in the course of heat treatment processes, and so affect the results of heat treatment simulations, which means that the transformation plasticity coefficient is necessary to be identifies. The authors developed a new method by use of four-point bending system of a beam to identify transformation plasticity coefficient taking advantage of its easiness and high accuracy compared with other conventional methods like tension test, etc., and identified the coefficient for four kinds of steels; plane carbon steel, Cr-steel, Cr-Mo steel and bearing steel. In this paper, further experimental data are presented for the steels if the coefficient Kp during pearlite transformation depend on the applied stress. Obtained results reveals that the stress dependence of Kp is rather trivial except for uncertain tendency detected in plane carbon steel. The relation between the Kp and carbon content included is discussed in comparison with other data referred from references.

IMPROVING THE MECHANICAL PROPERTIES OF COPPER ALLOYS BY THERMO-MECHANICAL PROCESSING

Systematic physical simulation of thermo-mechanical processing routes has been ap-plied on a Gleeble 1500 simulator to four copper alloys (mass %) Cu-0.57Co-0.32Si,Cu-0.55Cr-0.065P, Cu-0.22Zr-0.035Si and Cu-1.01Ni-0.43Si aimed at clarifying theinfluences of processing conditions on their final properties, strength and electricalconductivity. Flow curves were determined over wide temperature and strain rateranges. Hardness was used as a measure of the strength level achieved. High hard-ness was obtained as using equal amounts (strains 0.5) of cold deformation beforeand after the precipitation annealing stage. The maximum values achieved for theCu-Co-Si, Cu-Cr-P, Cu-Zr-Si and Cu-Ni-Si alloys were 190, 165, 178 and 193 HV5,respectively. A thermo-mechanical schedule involving the hot deformation-ageing-colddeformation stages showed even better results for the Cu-Zr-Si alloy. Consequently,the processing routes were designed based on simulation test results and wires of 5 and2mm in diameters have been successfully processed in the industrial scale.

Molecular dynamics study of thermal stress and heat propagation in tungsten under thermal shock

Using molecular dynamics （MD） simulation, we study the thermal shock behavior of tungsten （W）, which has been used for the plasma facing material （PFM） of tokamaks. The thermo-elastic stress wave, corresponding to the collective displacement of atoms, is analyzed with the Lagrangian atomic stress method, of which the reliability is also analyzed. The stress wave velocity corresponds to the speed of sound in the material, which is not dependent on the thermal shock energy. The peak pressure of a normal stress wave increases with the increase of thermal shock energy. We analyze the temperature evolution of the thermal shock region according to the Fourier transformation. It can be seen that the “obvious” velocity of heat propagation is less than the velocity of the stress wave; further, that the thermo-elastic stress wave may contribute little to the transport of kinetic energy. The heat propagation can be described properly by the heat conduction equation. These results may be useful for understanding the process of the thermal shock of tungsten.

Effect of thermo-mechanical properties of PIM feedstock on compacts shape retention during debinding process

The removal of the binder from the powder compacts (debinding) can be a slow step and a source of problems. To improve the debinding process of powder injection molding operation, it’s necessary to understand the thermal and mechanical properties of powder injection molding feedstocks and to find the major causes responsible for molding difficulties and compacts shape retention during debinding process. The effects of thermo mechanical properties of the PIM feedstock on the compacts shape retention during debinding process were discussed and explained from practical point of view. The results indicate that the heat of fusion affects the cooling time. The binder component with high heat of fusion and high decomposed temperature is more effective as the second binder component for the compact to retain its shape during debinding.

Influence of thermo hydrogen treatment on hot deformation behavior of Ti600 alloy

Hot compressive deformation of Ti600 alloy after thermo hydrogen treatment (THT) was carried out within hydrogen content range of 0-0.5%, temperature range of 760-920 ℃ and strain rate range of 0.01-10 s-1. The flow stress of Ti600 alloy after THT was obtained under hot deformation condition, and the influence of hydrogen on work-hardening rate (S*), strain energy density (U*), and deformation activation energy (Q) was analysed. The results show that the flow stress of Ti600 alloy decreases remarkably with the increase of hydrogen when the hydrogen content is less than 0.3%. Both S* and U* decrease with the increase of hydrogen when the hydrogen content is less than 0.3%, and when the hydrogen content is more than 0.3%, S* and U* increase with hydrogen addition. The value of Q decreases with the increase of strain at the same hydrogen content. The addition of small quantity of hydrogen leads to an increase of Q at small strain values, and when the strain reaches 0.6, the value of Q decreases gradually with the increase of hydrogen. When the hydrogen content is within the range of 0.1%-0.3%, the flow stress of Ti600 alloy is decreased when being deformed at the temperature range of 760-920 ℃.

Numerical Simulation and Technological Parameter Optimization for Quenching Process of a Gas Turbine Compressor Disk Based on Metallo-Thermo-Mechanics

Thermal, mechanical and microstructural phenomena are involved in the process of steel quenching. Based on the coupled metallo-thermo-mechanics theory, a calculation model has been developed in this study to simulate the quenching process of a gas turbine compressor disk by finite element method. The thermal physical and mechanical properties were treated as a functions of temperature. Moreover, a series of subroutines were developed on the MARC software platform. Consequently, simulated results on temperature, internal stress and distortion during the quenching were illustrated. With the aid of the simulated results, an optimum quenching scheme was proposed. The quenching process simulated in this study appears to be a promising tool in design of heat-treatment processing parameters for gas turbine compressor disks.

Transient thermo-mechanical coupling simulation of wet brake friction disk on tracked vehicle

The transient finite element technique is applied, and a transient heat conduction model of wet brake friction disk is established. For obtaining the accurate heat flow density mathematic model and avoiding possibly instable thermoelastic stress produced by the non uniform contact pressure of friction pair, a test method is applied to collect accurate contact pressure between the dual sheet steel and friction disk in the combining process. And then the heat-flow density and transient ther mo mechanical coupling simulation are analyzed. At the same time all possible boundary conditions are considered, such as the heat generation, heat conduction problem, relation between friction and contact, variation in load and heat change problem etc. The simulation results show that the me chanical model of thermo mechanical coupling can express well the dynamic characteristics of fric tion disk, and gives perfect reference for more study on thermoelastic distortion of brake friction pairs.

Physiological Mechanism of Thermotolerance in Wheat (<i>Triticum aestivum</i>Lin.) Seedlings

A research work was performed under sub-tropical condition (24&deg;8'N, 90&deg;0'E) at Bangabandhu Sheikh Mujibur Rahman Agricultural University with three wheat genotypes (BARI Gom 25, BARI Gom 26 and Pavon 76) to observe the mobilization of seed reserve and seedling growth under normal (15&deg;C/25&deg;C) and elevated (25&deg;C/35&deg;C) temperature in growth chamber. The effect of high temperature on wheat seedling was observed in terms of mobilized seed reserve, respiration and transpiration efficiency and seedling growth. At 35&deg;C temperature, maximum mobilization of seed reserve was observed in BARI Gom varieties (BARI Gom 25 and 26) but the respiration efficiency was higher in Pavon 76 in comparison to other genotypes. Maximum loss of respiration and transpiration at 35&deg;C temperature was found to produce low seedling growth in Pavon 76. It appeared from the result that at high temperature the maximum mobilized seed reserve and subsequently minimum loss of respiration and transpiration collectively contributed a positive role for better seedling growth in BARI Gom 25 and BARI Gom 26. Therefore the better mobilized seed reserve and subsequently minimum loss of respiration and transpiration during seedling development are indicators of the thermo tolerance in growing wheat seedling.

A new thermo-elasto-plasticity constitutive theory for polycrystalline metals

In this study, the behavior of polycrystalline metals at different temperatures is investigated by a new thermo-elasto-plasticity constitutive theory. Based on solid mechanical and interatomic potential, the constitutive equa- tion is established using a new decomposition of the deformation gradient. For polycrystalline copper and magnesium, the stress-strain curves from 77 to 764 K （copper）, and 77 to 870 K （magnesium） under quasi-static uniaxial loading are calculated, and then the calculated results are compared with the experiment results. Also, it is determined that the present model has the capacity to describe the decrease of the elastic modulus and yield stress with the increasing temperature, as well as the change of hardening behaviors of the polycrystalline metals. The calculation process is simple and explicit, which makes it easy to implement into the applications.

一种采用柔性缓冲垫块的双面散热SiC MOSFET双向开关模块研究

随着功率模块朝着高温、高功率、高密度方向发展,这对模块的封装结构提出了新的要求。较传统的引线键合结构,双面散热结构由于具有高散热能力和低寄生电感等特点受到广泛关注。但是双面散热结构材料间热膨胀系数的差异使之承受较大的热-机械应力,降低了功率模块的可靠性。因此,为设计具有低热-机械应力双面散热双向开关,本研究首先使用仿真分析了芯片布局对模块散热性能以及寄生电感的影响,在此基础上提出了一种具有低杨氏模量的柔性缓冲垫块,综合仿真及试验初步证明其降低热-机械应力、提高模块可靠性的可行性。

计及硅橡胶应力松弛的电缆接头界面压力演变仿真研究

高压电缆中间接头的电气性能与其硅橡胶-交联聚乙烯界面压力的大小密切相关。为探究实际电缆接头界面压力的演变规律,开展了考虑老化过程中硅橡胶应力松弛现象的220 kV电缆中间接头界面压力仿真研究。首先综合电缆接头处物理场特点建立有限元模型,确定了电缆中间接头硅橡胶-交联聚乙烯界面的初始压力分布情况;其次通过力学理论计算的解析解以及预置压力传感器的实测结果对有限元分析结果进行验证;之后结合硅橡胶的热机械老化实验结果,提出一种将老化过程中硅橡胶应力松弛转化为过盈量变化的方法,得到了考虑老化过程中应力松弛与弹性模量变化的多参量有限元分析方法,并成功应用于电缆中间接头绝缘硅橡胶-交联聚乙烯界面压力的分析。分析认为,硅橡胶的老化同时导致应力松弛和弹性模量增大。综合考虑弹性模量和应力松弛的仿真结果表明:对中间接头硅橡胶在100℃、125℃、150℃下分别经过2040 h、1680 h、1200 h热机械老化后,界面压力从0.156 MPa分别下降到0.129 MPa、0.125 MPa、0.107 MPa。这说明应力松弛对于界面压力的影响更显著,界面压力随着老化时间的增加而下降,同时温度升高会显著加快中间接头界面压力的衰减过程。该文研究结果可为提升电缆中间接头设计与运行可靠性提供理论依据。

PQF连轧过程轧件三向应力有限元分析

为提高无缝钢管产品质量,依据实际连轧生产工艺,基于Abaqus软件建立5机架PQF连轧三维热力耦合有限元模型,结合连轧过程的特点对模拟结果进行了分析。结果表明,受各道次轧辊位置、变形量、轧制速度等工艺参数的影响,连轧时孔型顶部和辊缝处的径向、周向、轴向应力分布状态并不相同,管内、外表面的轴向应力状态也有差异。进一步对相应规律进行了总结,并讨论了各向应力产生变化的原因及其影响。荒管尺寸参数和轧制力的模拟结果与实测结果相吻合,验证了模型的可靠性。研究结果对连轧过程相关工艺的设计与优化具有参考价值。

基于不同Ta10W渗镀层厚度的火炮身管热力耦合数值分析

采用双辉等离子渗金属技术于火炮身管内膛渗镀抗烧蚀涂层,是延长身管武器寿命的重要手段之一。为探究Ta10W渗镀层对火炮发射传热过程以及应力分布的影响规律,该文以某125 mm口径火炮为研究对象,通过热力耦合数值分析法,根据内弹道时期火药高温高压燃气的动态变化过程定义热力载荷以及边界,从而获得在高速热流工况下,Ta10W渗镀层厚度为0.04~0.10 mm时,火炮身管的传热变化过程以及应力分布特点。结果表明:随着渗镀层厚度的增加,弹后炮尾的最高温度呈下降趋势,不同厚度产生的应力差值在身管中段会大于身管尾部,同时在炮尾的涂层与基体结合处产生应力集中,0.04 mm、0.07 mm和0.10 mm厚度Ta10W层的应力最大值分别为891.4 MPa、884.3 MPa和879.1 MPa。

裂隙岩体渗透率与应力耦合对EGS采热性能的影响

在增强型地热系统(enhanced geothermal system,EGS)热开采过程中,储层渗透率受应力的影响而动态变化。为揭示裂隙岩体渗透特性和应力之间的耦合作用对系统采热性能的影响,建立双重介质热流固(thermo-hydro-mechanical,THM)耦合模型,分析基质和裂隙渗透率随应力动态变化时储层THM三场变化规律。结果表明:在热应力与水压力共同作用下,基质渗透率逐渐减小,裂隙渗透率呈指数式增加,采热速率主要由裂隙渗透率的动态变化决定,但如果忽略基质渗透率的动态变化,预测的裂隙渗透率比实际提高41.8%,热突破时间提前,会低估近2年的系统运行寿命。因此,同时考虑裂隙和基质渗透率与应力的耦合作用对合理评价EGS系统使用寿命有重要意义。