Maxwell strata in the Euler elastic problem

The classical Euler problem on stationary configurations of elastic rod in the plane is studied in detail by geometric control techniques as a left-invariant optimal control problem on the group of motions of a two-dimensional plane E(2). The attainable set is described, the existence and boundedness of optimal controls are proved. Extremals are parametrized by the Jacobi elliptic functions of natural coordinates induced by the flow of the mathematical pendulum on fibers of the cotangent bundle of E(2). The group of discrete symmetries of the Euler problem generated by reflections in the phase space of the pendulum is studied. The corresponding Maxwell points are completely described via the study of fixed points of this group. As a consequence, an upper bound on cut points in the Euler problem is obtained. This work was partially supported by the Russian Foundation for Basic Research, project No. 05-01-00703-a.     

07MnNiMoVDR连续冷却过程相变行为研究

利用MMS-200热模拟试验机测定了07MnNiMoVDR钢的动态CCT曲线,研究了07MnNiMoVDR钢奥氏体连续冷却时的相变行为规律和显微组织。结果表明：随着冷却速度的增大,其组织由铁素体＋珠光体逐渐向贝氏体转变;随冷却速度不同,在CCT图中存在两个相变区,即低冷速的先共析铁素体＋珠光体相变区、中冷速的贝氏体相变区。     

07MnNiCrMoVDR钢焊接粗晶热影响区的韧化机理

选用垂直于07MnNiCrMoVDR钢板轧制方向的模拟试样,在Gleeble-3500热模拟试验机上对该钢焊接粗晶热影响区的组织转变和韧性进行了研究.结果表明,粗晶区的组织类型主要是贝氏体和低碳板条马氏体的混合组织,粗晶区的低温韧性最差,随着冷却速度的减小,贝氏体由下贝氏体向上贝氏体和粒状贝氏体转变.在高温回火热处理后,粗晶区有再热脆化的倾向,易产生再热脆化,存在再热裂纹的可能性较大.再热脆化的主要原因是晶界析出粗大的碳化物,冷却速度越大,再热脆化现象越严重.     

Hamiltonian structures in optimal control theory

The concept of a piecewise smooth Hamiltonian system, motivated by optimal control theory, is introduced and developed. It is proved that the Poisson bracket of two integrals of such a system is globally continuous. Integrable piecewise smooth systems are proved to be equivalent to smooth integrable systems.This research was partially supported by the Russian Foundation for Fundamental Research, grant No. 93-012-470     

热处理工艺对100mm特厚07MnCrMoVR水电钢板组织性能的影响

对07MnCrMoR水电钢板的淬透性曲线进行了测定,利用淬火机和热处理炉对100 mm厚试验钢板进行了淬火和回火试验,并对试验钢进行了组织观察和力学性能测定。结果表明,随着试验钢距水冷端的距离增大,淬火组织由马氏体转变为粒状贝氏体,距离端部50 mm处转变为铁素体和粒状贝氏体的混合组织。试验钢板利用淬火机淬火后得到板条贝氏体+粒状贝氏体+先共析铁素体,回火后转变为铁素体+粒状贝氏体,同时大量的碳化物在铁素体基体和晶界处析出。试验钢最合理的热处理工艺为930℃ 30min水冷淬火,660℃ 60min空冷回火。     

某水电站07MnCrMoVR钢岔管焊缝裂纹成因分析

07MnCrMoVR是一种常用在大型构件上的低合金高强度钢,具有优良的焊接性能和低温韧性.但某水电站在现场安装此种钢材的压力钢岔管时却在制造焊缝上发现了大量裂纹.通过分析,确定裂纹是由于焊接工艺不当产生的延迟裂纹,并提出了避免此类焊接裂纹的建议及处理方法.     

Zr-rich layers electrodeposited onto stainless steel cladding during the electrorefining of EBR-II fuel

Argonne National Laboratory is developing an electrometallurgical treatment for spent nuclear fuels. The initial demonstration of this process is being conducted on U–Zr alloy fuel elements irradiated in the Experimental Breeder Reactor II (EBR-II). We report the first metallographic characterization of cladding hull remains for the electrometallurgical treatment of spent metallic fuel. During the electrorefining process, Zr-rich layers, with some U, deposit on all exposed surfaces of irradiated cladding segments (hulls) that originally contained the fuel alloy that was being treated. In some cases, not only was residual Zr (and U) found inside the cladding hulls, but a Zr-rind was also observed near the interior cladding hull surface. The Zr-rind was originally formed during the fuel casting process on the fuel slug. The observation of Zr deposits on all exposed cladding surfaces is explained with thermodynamic principles, when two conditions are met. These conditions are partial oxidation of Zr and the presence of residual uranium in the hulls when the electrorefining experiment is terminated. Comparisons are made between the structure of the initial irradiated fuel before electrorefining and the morphology of the material remaining in the cladding hulls after electrorefining.     

Geometric modeling of spatial constraints: objectives, methods and solid-modeling requirements

Robust Product Lifecycle Management (PLM) technology requires availability of informationally- complete models for all parts of a design-project including spatial constraints. This is the subject of the present investigation, leading to a new model for spatial constraints, the ``virtual solid', which generalizes a similar concept used by Sapidis and Theodosiou to model ``required free-spaces' in plants [14]. The present research focuses on the solid-modeling aspects of the virtual-solid methodology, and derives new solid-modeling problems (related to object definition and to object processing), whose robust treatment is a prerequisite for developing efficient models for complex spatial constraints.