一种高强度钢的超高周疲劳及热耗散研究

利用超声疲劳试验设备在20kHz频率下研究了一种高强度钢的超高周疲劳性能,试验持续到109次循环,得到了室温环境及不同循环比(R=0.01和R=0.1)的SN曲线,试验结果显示.疲劳强度在105～109次循环范围内随着循环次数的增加而减小.断面表面的SEM检查结果表明,疲劳裂纹的生成导致疲劳损伤,且亚表面裂纹起源在长寿命范围内.试验结果表明,试件全寿命的99.87%贡献于亚表面裂纹的形成.     

Thermographic Analysis of Fatigue Dissipation Properties of Steel Sheets

ABSTRACT:  This paper presents several properties of heat source fields accompanying the high-cycle fatigue of a dual-phase steel grade. Heat sources were derived from thermal data provided by an infrared focal plane array camera. An especially developed image processing estimates separately the thermoelastic coupling source amplitude and the mean dissipation per cycle. Our experiments underline that dissipation sources are heterogeneous and this forms the beginning of the fatigue test. They also point out a linear evolution of the mean dissipation per cycle as a function of the loading frequency for a given stress range and a given loading ratio.     

Fatigue assessment of a marine structural steel and comparison with Thermographic Method and Static Thermographic Method

Fatigue properties are of fundamental importance and extremely time consuming to be assessed. The aim of this research activity is to apply the Thermographic Method (TM) and the Static Thermographic Method (STM) during fatigue and tensile tests to correlate the temperature trend to the fatigue properties of an S355 steel. The material was retrieved from an in‐service port crane. Traditional fatigue tests were performed in order to evaluate the S‐N curve with a scatter band. Step load tests were carried out deriving the fatigue limit and the Energy Parameter of the material. Static tensile tests were performed to obtain the stress at which the temperature trend deviates from the thermoelastic behavior. The fatigue properties obtained by means of the energetic methods were compared to the traditional ones showing a good agreement.     

A Security Sensitive Function Mining Approach Based on Precondition Pattern Analysis

Security-sensitive functions are the basis for building a taint-style vulnerability model. Current approaches for extracting security-sensitive functions either don’t analyze data flow accurately, or not conducting pattern analyzing of conditions, resulting in higher false positive rate or false negative rate, which increased manual confirmation workload. In this paper, we propose a security sensitive function mining approach based on preconditon pattern analyzing. Firstly, we propose an enhanced system dependency graph analysis algorithm for precisely extracting the conditional statements which check the function parameters and conducting statistical analysis of the conditional statements for selecting candidate security sensitive functions of the target program. Then we adopt a precondition pattern mining method based on conditional statements nomalizing and clustering. Functions with fixed precondition patterns are regarded as security-sensitive functions. The experimental results on four popular open source codebases of different scales show that the approach proposed is effective in reducing the false positive rate and false negative rate for detecting security sensitive functions.     

Strength Analysis and Process Simulation of Subway Contact Rail Support Bracket of Composite Materials

An application of composites for construction of subway brackets is a very effective approach to extend their lifetime. However, this approach involves the necessity to prevent process-induced distortions of the bracket due to thermal deformation and chemical shrinkage. At present study, a process simulation has been carried out to support the design of the production tooling. The simulation was based on the application of viscoelastic model for the resin. Simulation results were verified by comparison with results of manufacturing experiments. To optimize the bracket structure the strength analysis was carried out as well.     

基于ANSYS软件模拟冲击接触问题的讨论

在分析接触算法原理及优劣的基础上,研究如何在ANSYS软件平台上实现冲击-接触计算,主要包括接触算法选择、接触刚度的确定,如何实现收敛性和准确性之间的一个最佳平衡。通过上述过程,总结出ANSYS软件处理此类问题的一般方法,并通过某船推力轴承的冲击计算算例进行验证。算例表明采用此方法接触计算较成功,收敛性好,渗透量小,计算结果的整体趋势符合工程经验,说明方法的可行性及有效性。     

真空开关电器中接触触点热过程的仿真研究

金属蒸气是真空开关电弧存在的根源, 基于流体动力学理论, 建立真空开关开断初期分离最终电接触触点由固体、金属液桥到金属蒸气相变过程的完整模型。考虑了金属触点的熔化变形边界, 同时关注金属液桥断裂后金属蒸气的扩散过程, 计算结果表明电触点最高温度点出现在接触触点的中心, 也正是金属桥断裂形成的初始位置。金属液桥相变过程中伴随金属蒸气的蒸发, 并在真空环境中迅速扩散, 在阴极斑点形成之前, 金属蒸气密度高达1.092×10²⁵ m^-3, 并沿着扩散半径迅速降低。计算结果表明, 随着电极加载电流的增大, 金属液桥完全断裂时间大大缩短。     

Failure Analysis of a Cyclic Contact Testing Machine Pin

The goal of this paper is to investigate the failure of a mandrel pin mounted on a rolling contact test bench. For this purpose, different methods of analysis were conducted, including metallography and stress analysis. The stress values in the failed pin were determined by Finite Elements. The high notch effect and the incorrect mounting of the specimens were identified as the failure causes. A pin design change is proposed to reduce the maximum stress even in the case of incorrect specimen mounting.     

印刷机偏心滚子轴承接触应力与变形仿真分析

目的对偏心轴承接触应力与滚子静、动态变形进行研究,得到接触应力与变形和结构与工况因素的关系。方法在Hertz线接触与弹流润滑理论下,建立滚子接触应力模型及静、动态滚子间接触变形的关系模型,利用有限元软件Ansys仿真计算。建立静、动(润滑与转速)态下滚子变形之间的关系公式,分析印刷机偏心双列圆柱滚子轴承的接触应力与变形及相互关系。结果滚子与内外套圈的接触应力均随径向载荷的增大而增大,滚子与内套圈的接触应力大于滚子与外套圈的接触应力;滚子的总接触变形量与径向载荷呈正比关系,滚子的内外接触应力与滚子的总接触变形量也呈正比关系;滚子的边缘出现应力集中,须用设计凸度的方法降低,从而更好地提高偏心轴承的整体性能。结论根据接触应力与变形的关系,可为偏心轴承的设计与优化提供理论依据。     

Probabilistic Analysis and Design of HCP Nanowires:An Efficient Surrogate Based Molecular Dynamics Simulation Approach

We investigate the dependency of strain rate,temperature and size on yield strength of hexagonal close packed(HCP) nanowires based on large-scale molecular dynamics(MD) simulation.A variance-based analysis has been proposed to quantify relative sensitivity of the three controlling factors on the yield strength of the material.One of the major drawbacks of conventional MD simulation based studies is that the simulations are computationally very intensive and economically expensive.Large scale molecular dynamics simulation needs supercomputing access and the larger the number of atoms,the longer it takes time and computational resources.For this reason it becomes practically impossible to perform a robust and comprehensive analysis that requires multiple simulations such as sensitivity analysis,uncertainty quantification and optimization.We propose a novel surrogate based molecular dynamics(SBMD)simulation approach that enables us to carry out thousands of virtual simulations for different combinations of the controlling factors in a computationally efficient way by performing only few MD simulations.Following the SBMD simulation approach an efficient optimum design scheme has been developed to predict optimized size of the nanowire to maximize the yield strength.Subsequently the effect of inevitable uncertainty associated with the controlling factors has been quantified using Monte Carlo simulation.Though we have confined our analyses in this article for Magnesium nanowires only,the proposed approach can be extended to other materials for computationally intensive nano-scale investigation involving multiple factors of influence.     

Surface Tension of Ni-Cu Alloys: A Molecular Simulation Approach

The Monte Carlo (MC) method and the embedded-atom method (EAM) are used to calculate the surface tension and the temperature dependence of the surface tension of nickel-copper alloys. The simulation of the surface tension is performed through the calculation of the cohesive work of the alloy. The calculated surface tensions of the alloys are 30 to 40% larger than experimental values, while the changes in surface tension as a function of Cu composition show similar behavior in both calculated and experimental results. The simulation results for the temperature dependence of the surface tension in the undercooled region appear to be identical with that above the melting point, and for the Ni-Cu alloys, the temperature coefficients decrease with an increase of copper concentration.     

Thermographic studies of a dynamic synthesis product in the C-N system

The results have been considered of the research into an ultradispersed product synthesized in a hyperspeed flow of a carbon electric-discharge plasma in the nitrogen atmosphere using electron scanning and transmission microscopies, thermography, and IR- Fourier spectroscopy. The aim of the studies has been to remove the impurity carbon phases from the product and to estimate the thermostability of covalent carbon nitride.     

商场中庭空调气流组织方案的数值模拟与优化

应用计算流体力学CFD技术对某商场中庭空调的气流组织形式进行了数值模拟计算,并根据模拟结果,确定了气流组织的最优方案。此研究也说明了在类似的大空间气流组织设计中,CFD技术具有巨大的优势。     

Analysis of CdS/CdTe devices incorporating a ZnTe:Cu/Ti Contact

High-performance CdS/CdTe photovoltaic devices can be produced using a ZnTe:Cu/Ti back contact deposited onto the CdTe layer. We observe that prolonged exposure of the ZnTe:Cu and Ti sputtering targets to an oxygen-containing plasma significantly reduces device open-circuit voltage and fill factor. High-resolution compositional analysis of these devices reveals that Cu concentration in the CdTe and CdS layers is lower for devices with poor performance. Capacitance-voltage analysis and related numerical simulations indicate that the net acceptor concentration in the CdTe is also lower for devices with poor performance. Photoluminescence analyses of the junction region reveal that the intensity of a luminescent peak associated with a defect complex involving interstitial Cu (Cu_i) and oxygen on Te (O_Te) is reduced in devices with poor performance. Combined with thermodynamic considerations, these results suggest that oxygen incorporation into the ZnTe:Cu sputtering target reduces the ability of sputtered ZnTe:Cu film to diffuse Cu into the CdTe.     

接触表面摩擦学仿真设计建模研究

利用计算机仿真技术进行摩擦学设计是现代设计方法之一,其中建立合适的关系模型是仿真的重点.本文对接触表面形貌的数学模型和力学模型的建立方法和过程进行了探讨,并在Matlab、有限元分析软件ANSYS中分别实现了表面形貌的模拟仿真和接触应力仿真.分析结果表明,建立正确的仿真模型并辅以参数化设计方法是解决摩擦学仿真问题非常好的实现方法.     

模锻坯料尺寸选择的新方法—反向成形模拟

本文应用上限单元法(UBET)对H型零件模锻的金属成形过程进行了反向流动模拟设计。本文还结合正向流动模拟分析讨论了不同飞边高,不同坯料尺寸对成形能耗的关系和最佳成形过程及最佳坯料尺寸的概念。     

带冠涡轮叶片的接触分析

以航空发动机动力涡轮一级带锯齿形叶冠的转子叶片为例,用有限元接触分析方法对装配和工作状态下的叶冠紧度和叶冠接触力、叶身应力进行了计算和分析,着重考察了工作载荷(温度和离心力)对叶冠接触力的影响。分析结果表明,叶冠的紧度由预扭角和工作载荷决定,离心力对紧度的变化起主要作用。     

Ultrasonic Approach of Rayleigh Pitch-catch Contact Ultrasound Waves on CFRP Laminated Composites

CFRP （carbon fiber reinforced plastics） composite materials have wide applicability because of their inherent design flexibility and improved material properties. However, impacted composite structures have 50%-75% less strength than undamaged structures. In this work, a CFRP composite material was nondestructively characterized in order to ensure product quality and structural integrity of CFRP and one-sided pitch-catch technique was developed to measure impacted-damaged area by using an automated-data acquisition system in an immersion tank. A pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave under defect conditions in the composite.