6209轴承内套滚道剥落原因分析

通过常规金相检验方法分析了6209轴承内套滚道剥落的原因。结果表明：由于材料原始带状组织较为严重,引起带上与带间的碳、铬浓度的偏析,造成淬火组织和残余应力的分布不均匀并增加了基体脆性,导致了剥落。     

扩散工艺对渗铝钢循环氧化和剥落性能的影响机理研究

通过不同扩散工艺实验,研究了热浸渗铝钢的抗氧化和剥落性能及其机理.结果表明,随扩散温度升高和时间延长,扩散层的空洞不断增加,次外层和过渡层之间空洞逐步聚集连接成波浪线状空洞带.在高温氧化期间,空洞带又连接成平行于表面的线状裂纹,其内部产生了内氧化.因此,渗铝钢的抗循环氧化和剥落性能不仅与扩散层组织和表面的氧化速度有关,而且与扩散层的空洞和内氧化有关.最佳的扩散工艺参数是900℃×2h.     

Spalling of concrete cover of fiber-reinforced polymer reinforced concrete under thermal loads

A finite element method using a proposed mesoscopic thermoelastic damage model (MTED) is verified for simulating the cracking process of a concrete section reinforced with fibre-reinforced polymer (FRP) bars. The cracking was due to the significant difference in thermal expansion properties between the concrete and the FRP materials at elevated temperatures. The numerical study reveals that although a conventional elastic analytical method can provide good estimates of the critical temperature increment of concrete cover failure of a cylindrical concrete section that is reinforced with a single bar, it gives too conservative predictions for typical rectangular sections with multiple bars. The study also shows that the concrete cover and the horizontal bar spacing have more influence than the vertical bar spacing on the determination of the critical temperature increments. Horizontal lapping of bars significantly lowers the critical temperature increment.     

Prediction of the Brittle Fracture Toughness of Neutron-Irradiated Reactor Pressure-Vessel Steels. Part 1

The irradiation effect on the temperature dependence of the brittle fracture toughness of reactor pressure-vessel steels is simulated using the probabilistic model for the fracture-toughness prediction, which was proposed by the authors earlier. The paper analyzes the irradiation effect on the parameters controlling the plastic deformation and brittle fracture of reactor pressure-vessel steels. We consider the mechanisms of microcrack nucleation in nonirradiated, irradiated, and post-irradiation-annealed reactor pressure-vessel steels.     

Optimization of hydraulic cylinder housing

This paper concerns the optimization of the fatigue-critical part of a hydraulic cylinder. The investigation includes optimization, fatigue testing, residual stress measurements, life predictions and, finally, reliability computations. The optimization reduced the critical parameter, the stress intensity factor in the end weld root, by 40%. The fatigue tests verified this reduction. Life predictions based on available da/dN data, combined with computed and tabulated stress intensity factor solutions, were in good agreement with the fatigue test data. Fractography of the fatigue sites revealed the existence of initial cracks of size 0.02 to 0.06 mm in all the welded joints examined. Reliability computations based on the test results and long-term load data demonstrate the type of results that are of major interest for designers.     

窄带随机激励下的结构动力学拓扑优化设计

基于模态截断法和一些近似处理,导出了一套窄带随机均方动响应及其灵敏度公式,再根据工程实际要求,研究了静载荷和窄带随机载荷作用下结构的动力学拓扑优化设计方法和算法,提供的算例显示了本方法的合理性和有效性。     

Prediction of the Brittle Fracture Toughness of Neutron-Irradiated Reactor Pressure Vessel Steels. Part 2

We apply the proposed model to study the effect of irradiation on the temperature dependence of brittle fracture toughness of 15Kh2MFA steel. We analyze also the influence of irradiation and the content of phosphorus and copper on the brittle fracture toughness. It is demonstrated that the probabilistic model, which is based on a new formulation of the brittle fracture criterion, allows an adequate prediction of the irradiation effect on the fracture toughness of reactor pressure vessel steels. Alternative models of prediction of fracture toughness are discussed.     

Structural macromechanics approach in dynamics of fracture

Discrete features of the dynamics of fracture of solids are analyzed. The problem of modeling of some of the specific effects of brittle fracture in the high loading rate conditions is discussed. An approach based on the system of fixed material constants describing macro‐strength properties of the material is considered. New principles of material testing are analyzed. The corresponding incubation time criterion allows one to manage without the a priori given rate dependences of dynamic strength and fracture toughness. An application of the incubation time criterion to the problem of erosion is considered.     

纳米孪晶镍镀层制备工艺的正交设计优化

过去对采用脉冲电镀法制备纳米孪晶镍镀层研究较少.以镍镀层的耐腐蚀性能作为镀层性能的检测指标,应用正交试验设计优化了脉冲电镀工艺,制备出纳米孪晶镍镀层.结果表明:以主盐NiSO4·2H2O浓度为400 g/L,脉冲平均电流密度为1.5 A/dm2,占空比为20%制备的纳米孪晶镍镀层的耐腐蚀性能最好,维钝电流密度达到0.67 μA/cm2;镀层为纳米孪晶结构晶粒,尺寸为50～150 nm.     

几何与动力约束结合的凸轮机构基本尺寸优化

考虑凸轮与转子间最大压力角及凸轮轮廓最小曲率半径等几何约束条件的同时,结合最大接触压应力、最大剪应力等动力约束条件,对凸轮机构基本尺寸优化问题进行了研究,提出了优化方法。最后辅之实例,结果表明低速上述最小尺寸由几何约束条件控制,中速时主要受动力约束条件限制,高速时则完全由动力约束条件所主宰。     

基于瞬态动力学分析的波纹管结构优化

目的 优化波纹管结构尺寸,最大程度地减小波纹管的应力集中,提高波纹管的疲劳寿命。方法 利用ANSYS Workbench对真空灭弧室用波纹管进行参数化建模,对其耦合速度压力复杂工况进行瞬态动力学分析,借助DOE(DesignofExperiment)技术对波纹管关键几何参数进行单目标优化设计,对优化结果进行强度校核和疲劳寿命计算。结果 优化结果符合设计要求,波纹管在耦合速度压力复杂工况下满足强度的同时,最大等效应力减小了28.8%,疲劳寿命由3 064次提高到32 260次。结论 优化后的结构有效减小了波纹管危险部位的应力集中,疲劳寿命得到提高。     

桁架动力学形状优化的统一设计变量方法

研究了具有多种约束 ,特别是动力学约束 (频率约束 )作用下的平面桁架形状优化问题。提出一种将两类不同性质的设计变量 (尺寸变量、节点几何坐标变量 )变换为统一形式的无量纲设计变量的方法 ,解决了不同性质变量耦合引起的收敛困难问题 ,并拓展了设计空间。联合运用内点罚函数法、DFP法 (即变尺度法 )和一维搜索技术 (二次插值法 ) ,将约束优化问题转化为无约束序列优化问题 ,得到了满意的优化结果。算例表明本文方法对桁架形状优化的有效性 ,并显示了算法的简洁性和工程设计实用性     

机枪结构动态特性的优化研究

利用Ansys有限元分析软件对建立的有限元模型进行了模态分析,通过对设计变量、状态变量和目标函数的合理选择建立了优化模型,对机枪的机构参数进行了优化.建立了某机枪的有限元实体模型,在模态分析的基础上优化武器的机构动态特性.求解了机枪的自由模态参数,与试验模态分析所得到的模态参数进行了对比验证,通过结构优化得到了结构修改方案.机枪的有限元模型通过优化结构参数提高了机枪的结构动态特性,武器的射击频率与机枪整体结构的固有频率匹配更加合理,提高了武器的射击精度.     

Dynamic Simulation and Optimization Design of the Pendulum Ring Mechanism Based on ADAMS

For pendulum ring mechanism, the working principle is analyzed by using the ADAMS software. Confirming the simulation to accord with the actual motion law, the main bars＇ length is taken as the design variables in order to optimize the cutting speed. The optimization results show that the length of the pendulum rod increases by 3.22%, the cutting speed increases by 30. 8%. It shows that the length of pendulum rod determines the cutting speed at a given pendulum angle. Designers can adjust the length of pendulum rod so as to select the appropriate cutting speed. The virtual prototype technology could the performance of the product is not only improved, and the design efficiency is also done.     

激光法合成纳米金刚石的高分辨电镜研究

在常温常压下,采用脉冲激光作用循环的石墨悬浮液,收集并烘干得到样品B,另一部分用高氯酸进行酸煮提纯提到样品A.对样品A、B分别进行高分辨电子显微镜（HRTEM）和显微拉曼光谱（Micro-Raman）分析.结果表明,部分石墨经激光作用后转变成了具有多重孪晶结构特征的、尺寸为5 nm的金刚石颗粒,同时还得到了非晶碳.高分辨电子显微镜照片证明,石墨转变成纳米金刚石的机理为快速成核长大过程.     

Role of strain and nanoscale defects in modifying the multiferroicity in nanostructured BiFeO3 films

BiFeO₃ (BFO) multifunctional oxide exhibits fascinating multiferroic properties suitable for potential application in nanoscale electronic devices such as non-volatile random accesses memory (FeRAM), field effect transistors, capacitors, logic circuits, etc. In this communication, we report the results of studies on 200 MeV Ag⁺¹⁵ ion irradiation-induced modifications in the structural, microstructural, electrical (I–V, C–V and P–E) and magnetic properties of pulsed laser deposited nanostructured BFO films grown on conducting SrTi_0.998O_0.002TiO₃ (SNTO) substrates. Role of nanoscale structural defects and oxygen vacancies in modifying the physical properties of BFO/SNTO has been discussed in this work.     

非平稳随机激励下基于动力可靠性的结构优化设计

基于Priesfley的演变谱密度理论，对于工程中常用到的衰减指数函数调制的演变过程激励，通过对结构响应的合理简化，得到响应特征的解析形式。结合首次超越破坏的二状态马尔可夫假设和结构系统可靠性理论计算系统的动力可靠性，并在此基础上进行了优化设计。和常用算法相比，减少了计算量。     

Ultra‐High‐Speed Full‐Field Deformation Measurements on Concrete Spalling Specimens and Stiffness Identification with the Virtual Fields Method

Abstract: For one decade, spalling techniques based on the use of a metallic Hopkinson bar in contact with a concrete sample have been widely employed to characterise the dynamic tensile strength of concrete at strain rates ranging from a few tens to hundreds of s^?1. However, the processing method based on the use of the velocity profile measured on the rear free surface of the sample (Novikov formula) remains quite basic. In particular, the identification of the whole softening behaviour of the concrete material is currently out of reach. In the present paper, a new processing technique is proposed based on the use of the virtual fields method (VFM). First, a digital ultra‐high‐speed camera is used to record the pictures of a grid bonded onto the specimen. Then, images of the grid recorded by the camera are processed to obtain full‐field axial displacement maps at the surface of the specimen. Finally, a specific virtual field has been defined in the VFM equation to use the acceleration map as an alternative ‘load cell’. This method applied to three spalling tests with different impact parameters allowed the identification of Young's modulus during the test. It was shown that this modulus is constant during the initial compressive part of the test and decreases in the tensile part when microdamage exists. It was also shown that in such a simple inertial test, it was possible to reconstruct average axial stress profiles using only the acceleration data. It was then possible to construct local stress–strain curves and derive a tensile strength value.     

基于ADAMS的十六开折页机构优化设计

通过赋予相应的设计参数,得到真实十六开折页机构系统的三维仿真模型.通过模拟动态仿真和分析,以及对模型结构的不断完善、优化和细化,从而达到对该机构进行优化设计的目的.     

动力响应约束下的桁架结构拓扑优化

采用自适应遗传算法求解了以脉冲激励下的动力响应作为约束条件、以结构重量最小化为目标函数的桁架结构拓扑优化问题。其中遗传算子分别采用轮盘赌选择算子以及自适应的交叉和变异算子。定义了一些启发式准则来引导优化过程中杆件和节点的删除，另外引入了刚度矩阵的奇异性判断以防止桁架在杆件删除过程中变为机构。算例表明，用此方法可以得到桁架结构在脉冲激励下的最优拓扑形式，且能在满足动力响应约束要求的前提下极大地减轻结构重量，达到优化的目的。