A Numerical Model for Multiple Phase Transformations in Steels during Thermal Processes

IntroductionltiswellknownthatmetallmpicalstrUcforeofsteelsandheattransferarefullycouPled.PhasechangesdependontemPertheeevoluton,whereastemPertheeisinfluencedbycontrastsofmaterialcharacteristicsbetWeenphasesandlatenheateffects.AlotofworkhasbeenpefformedonthssubeCt,andclassicalmodelsarenowwidelyimPlementedintofiniteelementcomPutercodes[l][2][31[4][5][61.Thesemodelsaregenerallybasedonf.AVramityPekinetics[7][8]l9]Whnthephasechangeisgovernedbydiffusion,.TheKoistinen-Marburgerlaw[l0]fOrmfornsi…     

Prediction of Welding Residual Stress in 2. 25Cr-1Mo Steel Pipe

Introduction2.25Cr-1Mo-steel is widely used in thepetroleum industry and in steam power generatingof both nuclear and conventional power plants be-cause of its excellent high-temperature strength,corrosion resistibility,and resistance to high-tem-perature hydrogen attack.Because several alloy el-ements are added into2.25Cr-1Mo-steel,marten-site is prone to form after welding.It has been rec-ognized that phase transformation can radically af-fect the development of residual stresses[1-2].Inor…     

X65管线厚板控制冷却时的相变效应

为明确相变效应对X65管线厚板控制冷却的影响,通过开发线性混合热膨胀模型、拓展Avrami相变动力学模型和应用Leblond模型建立了热力耦合有限元模型.用该模型研究了X65管线厚板在上下层流冷却系数分别为3和1 kW/(m2.K)的非对称控制冷却时,相变效应对温度、残余应力和应变的影响.结果表明:相变期间,潜热减缓心部和下表面的冷却速度达50%、25%;潜热和TRIP效应分别产生峰值为89、-89 MPa,并且130、-170 MPa的应力可减小整体残余应力;相变膨胀产生峰值为723、-479 MPa的组织应力决定了整体残余应力大小及分布.     

Calculation on the incubation period of proeutectoid ferrite transformation for Si-Mn TRIP steel

The incubation period of proeutectoid ferrite transformation for Si-Mn transformation induced plasticity (TRIP) steel has been calculated by the Aaronson’s incubation period model for transformation. The influences of chemical compositions and hot deformation of austenite on the incubation period have been taken into consideration in the calculation, and some parameters have been proposed and validated with the measured time temperature transformation (TTT) curves from dilation tests. The calculation results show that it is essential to take into account of the effect of solute atoms on the interfacial energy in the austenite grain boundaries. For hypoeutectoid steel, the incubation period of ferrite transformation increases with the increase of C and Mn contents, and C has a greater impact than that of Mn, while the incubation period of ferrite transformation decreases with the increase of Si content. Hot deformation shortens the incubation time and promotes austenite to ferrite transformation.     

机车轮对过盈配合温差法装配的有限元模拟

与经典的力学方法相比，用有限元方法可以有效地分析复杂形状轴毂过盈配合的各种问题，从而提高轴毂过盈配合设计的可靠性．对机车轮对过盈配合温差法装配过程的有限元模拟说明，虽然在过盈量较小时，弹性和弹塑性有限元模拟都能够比较真实的模拟车轮与车轴中的应力分布，确切地反映轮毂配合间的接触边缘应力集中等，但是，当过盈量较大而发生塑性变形时，弹塑性模拟分析，能够比较准确地计算出轮对的塑性变形，因而，比弹性有限元模拟更加真实，因此，弹塑性有限元分析对安全性要求很高的机车轮对过盈配合的设计就更有指导意义．     

二次方程的标准方程分析

本文讨论了如何利用正交仿射变换将二次方程化为标准方程,这为处理直角坐标系下的曲线或曲面奠定了基础,并对二次曲线进行了分类,从而可以直接从二次方程的系数判定该方程的类型。     

桥梁结构钢裂纹塑性区的研究及应用

为了研究裂纹塑性对裂纹扩展的影响,利用工程简化算法、应力函数法、扩展有限元法对桥梁钢裂尖塑性区的尺寸和形状分别进行了计算;由于平面应力和平面应变情况下尾迹场循环塑性的特性不同,利用不连续扩展有限元对两种情况下尾迹场的循环塑性和塑性累积进行了模拟分析,探讨了裂尖塑性区、循环塑性区的形成和尾迹场产生压应力的机理.研究结果表明:裂尖塑性区尺寸与应力水平（名义应力与屈服极限的比值）的平方成正比,当应力水平大于0.4时,裂尖塑性区尺寸需要考虑应力水平的影响;裂尖塑性区的形状以蝶形向前伸展,使裂纹尾迹场免受裂尖高应力场的拉伸作用,有利于裂纹闭合;裂尖塑性区存在材料的逆向流动,在循环塑性区裂纹表面的塑性累积产生压应力效应有利于裂纹提前闭合,这种塑性诱发的裂纹提前闭合对研究变幅加载、过载引起的裂纹扩展滞后有重要意义.      

公路升级技术改造及应用

公路升级改造的目的在于消除原有公路存在的病害并使路面拓宽。通过采取拓宽公路、加强路基基础建设与边坡保护等一系列措施,通过公路升级改造的理论性分析与施工检验,最终得出公路升级技术改造的合理措施。经实际工程检验,确认改造方案是正确的。     

软土结构性影响系数的研究

以营口地区深灰色粉质粘土为研究对象,采用重塑的方法改变了天然原状软土的原始结构.将重塑土和原状土分别进行直剪蠕变实验并对实验结果进行对比分析,归纳出软土结构变化对宏观流变力学特性的影响.     

TMIS应用数据转换工具的设计

根据ＴＭＩＳ的需求，给出了应用数据转换工具系统的总体结构，并在应用环境中实现了该系统。本数据转换系统具有较好的通用性，实时性，可用性，完全可满足ＴＭＩＳ应用的要求。     

低碳双相钢的形变强化研究

通过亚温淬火热处理获得双相组织，在此基础上，对试样进行冷拉形变复合强化处理。结果表明，15SiMnTi钢经热处理后，强度明显提高，塑性也好；在复合强化后，强度进一步提高，而塑性仍保持较好。     

平面单轴柔性关节的力传递关系

采用变形叠加方法分析了柔性微动关节的受力（矩）变形位移过程,推导了柔性关节两端广义力传递的矩阵变换.以对称半圆弧曲线柔性关节为例进行分析,并与以往采用伪刚体方法进行运动学建模的分析结果相比较,其结果与有限元分析结果更接近,从而大大提高了模型精度.     

考虑结构性的土体本构模型的建模方法

土体的结构性模型是土力学的核心问题.本文根据不同的模型理论和方法,把土体的结构性模型分为复合体本构模型、微观力学本构模型和土体的塑性理论模型,并对各个模型的研究现状、建模的思路与实质进行研究.     

考虑结构性的土体本构模型的建模方法

土体的结构性模型是土力学的核心问题.本文根据不同的模型理论和方法,把土体的结构性模型分为复合体本构模型、微观力学本构模型和土体的塑性理论模型,并对各个模型的研究现状、建模的思路与实质进行研究.     

Two-dimensional Continuum Modeling Approach to Transportation Problems

The continuum modeling approach to transportation models is now gaining much attention because of its advantages in dealing with dense-network models, macroscopic problems, and initial phase planning. This paper aims to provide a comprehensive review of the development and applications of the two-dimensional continuum modeling approach. The theoretical development and models with specific or arbitrary region configurations are first discussed, and then the applications of the continuum modeling approach to the determination of facility location, route choice, pedestrian flow, and policy and socio-economical analysis are reviewed. Finally, some prospective directions for future research are proposed.     

某加固楼板的原位荷载试验

某商住楼为框架剪力墙结构,现浇钢筋混凝土楼盖,其中501房的客厅楼板由于混凝土出现质量问题,进行了加固处理。为检验该混凝土楼板是否满足承载能力要求,对其进行了原位荷载试验。通过荷载试验实测数据与理论计算数据进行比较,评价该构件安全状态及加固效果。文章可为现浇钢筋混凝土楼板原位荷载试验分析方法,以及评价楼板加固效果提供参考。     

既有高架桥盖梁改造技术

文章以某立交匝道桥改造工程为例,通过对墩柱接高和盖梁改造设计、施工的重难点分析、结构体系转换的理论计算,提出了合理的设计方案。施工实践及监控量测表明,该设计方案及施工工艺安全、可靠。     

Determining Loading Field based on Required Deformation for Isotropic Hardening Material

Eringen's and Trusedell's polar decomposition are formulated by explicit formulation of displacement field, based on Chen's additive decomposition of deformation gradient. Then the strain introduced by the multiplicative decomposition and the strain introduced by the additive decomposition are formulated explicitly with displacement gradient. This formulation clears the intrinsic contents of strains defined by taking the Eringen's and Trusedell's polar decomposition. After that, Chen's strain definition was introduced to show that the plastic deformation can be understood as the irreversible local average rotation. For initial isotropic simple elastic material, the research shows that path-dependent feature of classical plasticity theory is naturally expressed in Chen's strain definition. For rate-independent plasticity, the related deformation stress was discussed. The research shows that for isotropic hardening material the relation equation between the required geometric configuration and the corresponding loading field is explicitly formulated. Hence, for metal forming, this paper explicitly formulates the related fields by displacement field and invariant elastic constants.     

转型发展时期我国城市交通的发展战略——以宁波市为例

城市交通发展战略作为影响城市未来发展的重要公共政策,应在城市转型发展过程中发挥引导和带动作用.依据转型期城市在外部环境、空间格局、发展模式等方面发生的变化,提出转型发展时期我国城市在区域交通、城乡关系、绿色交通等方面的应对策略.以宁波市为例,系统探讨如何通过制定转型发展时期的城市交通发展战略,以适应并促进城市社会经济的转型发展进程.