新型小载荷冲击磨损试验机的研制及其实验研究

设计并研制出新型小载荷冲击磨损试验机,介绍了该试验机的工作原理、结构及其主要技术参数,并采用所研制的试验机对TC4钛合金进行了8个不同周次的3组冲击磨损试验.结果表明:TC4钛合金的冲击坑形貌规整,具有明显的表面特征和累计损伤特征;在相同试验条件下试验结果的重现性较好,数据最大误差小于6%;试验机所加载荷稳定,长时运行无过流过温现象,能够满足小载荷冲击磨损试验的要求.     

A New Fatigue Testing Machine for Investigating the Behavior of Small Shear-Mode Fatigue Cracks

Experimental Techniques - The investigation of the behavior of small shear-mode fatigue cracks in the high-cycle fatigue regime is essential to understand the mechanism of rolling-contact fatigue...     

结构试验机的神经网络内模自适应跟踪控制系统

针对结构试验系统的非线性和不确定性特性，研究了一种基于神经网络的非线性内模自适应加载控制方法。引入的神经网络内模可跟踪学习对象的时变动力学，控制器的设计较少依赖于对象的先验知识，控制参数的调整是基于被控过程的测量信息，利用导出的神经网络算法来实现的。实验结果证明该系统具有良好的控制效果。     

Prediction of Porosity and Permeability Alteration Based on Machine Learning Algorithms

Transport in Porous Media - The objective of this work is to study the applicability of various machine learning algorithms for the prediction of some rock properties which geoscientists usually...     

基于机器学习对三角堰流量系数的预测研究

为了准确高效得出三角堰泄流系数的大小,本研究基于广义神经网络、最小二乘支持向量机和遗传规划对三角堰流量系数进行智能建模．将无量纲参数堰顶角、弗劳德数、堰顶长与堰高之比、堰顶长与堰顶水深之比作为模型输入参数,流量系数作为模型输出参数．研究表明,最小二乘支持向量机性能优于广义神经网络和遗传规划．在测试阶段,均方根误差为0.000 73,散射指数为0.001 02,决定系数为0.999 59,最大误差为1.7 %．该模型精度较高,预测值较准确,具有较强的工程适用性．本研究通过对三角堰流量系数进行智能建模,采用机器学习对非线性物理关系进行高精度拟合,准确高效得出三角堰流量系数的大小,可为水利水电工程设计人员和我国灌区精确量水用水提供一种新的方法和思路．     

Low-Cycle Fatigue Testing of Ni Nanowires Based on a Micro-Mechanical Device

Despite extensive research on the mechanical properties of one-dimensional (1-D) nanomaterials such as nanowires and nanotubes in the past two decades, experimental data on the fatigue behavior of 1-D building blocks are still very limited. Here, we demonstrate the first quantitative in situ tensile fatigue testing of individual nanowires inside a high-resolution scanning electron microscope (SEM), based on the nanoindenter-assisted “push-to-pull” dynamic tensile straining mechanism. With the robust micro-mechanical devices and independent quantitative nanoindenter for actuation and force sensing, we achieved both stress- and strain-controlled cyclic tensile loading on nanowire samples with variable loading frequencies up to 10 Hz, and demonstrated the low-cycle fatigue behavior of pristine single crystalline nickel (Ni) nanowires.     

直流磁场下销盘摩擦接触区的电磁感应现象

为了研究直流磁场对45钢销盘摩擦副的摩擦磨损特性的影响,根据磁场销盘摩擦试验机的结构和销盘摩擦副在摩擦过程中的实际接触情况,建立了二维微凸峰接触静态磁场和瞬态磁场有限元模型,分析了销盘摩擦接触区的电磁感应现象,得出以下结论:磁感应强度B在摩擦接触区分布不均,在微凸峰接触点区域的磁感应强度B值较大;摩擦试验中,在销盘磨痕和磨屑的微凸峰接触区将产生较高频率的动态磁化,同时在微凸峰上产生较大的感应电流,这些现象促进了销盘磨痕表面和磨屑的氧化.     

直流磁场下销盘摩擦过程中的电磁感应力矩分析

为了研究磁场对材料摩擦磨损性能的影响,本文分析了直流磁场下销盘摩擦过程中的涡流和电磁感应力,并通过积分得到感应力矩的计算公式.在销盘0.1 mm间隙时检测了磁吸力和在不同试验条件下盘试样所受的感应力矩,利用试验数据对感应力矩公式中的修正系数进行了最小二乘法拟合,所得感应力矩公式的计算结果与不同电流和转速下的试验数据很好地吻合.在摩擦磨损过程中,可利用感应力矩公式计算出相应试验条件下盘所受的感应力矩,分析其对摩擦系数的影响.     

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A New Testing Machine for the Dynamic Characterization of High Strength Low Damping Fiber Materials

This work describes a novel method for measuring the damping, the elastic modulus and the non-linear behavior of high strength low damping fiber materials such as para-aramids, silicon carbide (SiC) and carbon. The method is based on resonant response characterization of a spring-mass system excited by a sine-wave forcing term which is applied as a vertical force to the suspended mass. The damping is obtained from the measured resonance quality factor Q, the elasticity modulus is calculated from the resonance frequency, and the non-linear coefficient is obtained with the backbone approach from resonance profile variations as a function of the forcing term amplitude. It is argued that the method is very sensitive, to the point that a maximum excitation amplitude of the order of a few percent of resistance is sufficient to obtain an estimate of the non-linear coefficient. This claim is supported by experimental results. A testing machine is also discussed, which provides the necessary sensitivity at such small excitation amplitudes and the capability of evaluating very small damping values, as expected in high strength low damping fiber materials. The sensitivity is guaranteed by an optical position sensor with sub-micron resolution. To evaluate small damping values, particular care has been taken to ensure that energy dispersions in the generator are much smaller than energy dispersions in the fibers themselves. Examples of dynamic characterization are shown for para-aramid, silicon carbide, and carbon fibers.     

Stress Wave Analysis and Optical Force Measurement of Servo-Hydraulic Machine for High Strain Rate Testing

Based on fundamental mechanical principles, a force measurement method for a servo-hydraulic tensile machine at strain rates from quasi-static up to 10³/s is proposed in this paper. Analytical and numerical stress wave analyses were performed at first to understand the principles of the force signal oscillation. The result of this FEM simulation indicates that the elastic vibration within the tensile specimen has a higher frequency and much lower amplitude than at the piezoelectric force sensor of the test machine. Based on this finding, a noncontact optical force measurement method was developed, which provides a fast and reliable force measurement directly on the specimen with little disturbance from the system ringing effect at strain rates up to 10³/s.     

Development of a Closed-Loop High-Cycle Resonant Fatigue Testing System

In this paper, a vibration-based testing methodology to assess fatigue behavior of a metallic structure is presented. To minimize the testing duration, the test setup is designed for a base-excited multiple-specimen arrangement driven in a high-frequency resonant mode, which allows completion of fatigue testing in an accelerated period. The shaker operates in closed-loop control with dynamic specimen response feedback provided by a scanning laser vibrometer. A test coordinator function is developed to synchronize the shaker controller and the laser vibrometer and complete the closed-loop scheme: the test coordinator monitors structural health of the test specimens throughout the test period, recognizes change in specimen dynamic behavior due to fatigue crack initiation, terminates test progression, and acquires test data in an orderly manner. The test methodology is demonstrated with cantilever specimens that are clasped on the shaker armature with specially-designed clamp fixtures. Experimental stress evaluation is carried out to verify the specimen stress predictions. A successful application of the experimental methodology is demonstrated by validation tests with Al 6061-T6 aluminum specimens subjected to fully-reversed bending stress.     

基于神经网络的机械磨损故障光谱定位诊断法

在分析常用光谱定位诊断方法的基础上提出了基于神经网络的光谱定位诊断法;将机械摩擦副材质的元素含量作为神经网络输入,将材质所对应的部件作为神经网络输出,建立了相应的神经网络训练样本;通过整理训练样本和训练神经网络,利用神经网络超强的非线性映射能力和容错性实现了磨损故障部位诊断;通过算例分析验证了所提出的诊断方法的可行性和准确性．结果表明,所建立的方法简洁有效,并具有很高的诊断精度．     

Large and Small Scale Materials Testing of HT-9 Irradiated in the STIP Irradiation Program

The Fuel Cycle R&D (FCRD) initiative is investigating methods of burning minor actinides in a transmutation fuel. To achieve this goal, the fast reactor core materials must withstand very high doses. Small scale materials testing methods in addition to large scale materials testing allows one to gain more insight by providing more data on the same sample while being able to probe areas of interest which are not accessible otherwise. Furthermore, the sample volumes were so small that the tests could be considered a non destructive test since the amount of material needed is so small that a macroscopic structure would not be affected. Tensile testing, micro hardness testing and micro compression testing on focused ion beam (FIB) microscope manufactured pillars were performed on remaining parts of tensile test specimens tested and irradiated in the Spallation Target Irradiation Program (STIP). It is shown that the increases of yield strength measured by tensile testing, micro compression testing and micro hardness testing all showed the same trend. In addition FIB based techniques also allowed fabrication of LEAP samples of such a small size that their residual activity was below detectable levels thus allowing them to be handled and analyzed in a manner comparable to inactive specimens.     

光纤陀螺捷联系统标定测试软件的设计与开发

基于 windows 平台,采用 VC 6.0 开发了光纤陀螺捷联惯组标定测试软件,着重阐述了该软件的设计思想和关键技术的实现。该软件实现了对光纤陀螺捷联组合误差系数的标定与测试,为光纤陀螺捷联系统标定测试提供了方便,具有很强的工程实用价值。     

A Commentary on the NIH Consensus Development Statement 'Genetic Testing for Cystic Fibrosis'

A NIH Consensus Development Statement recommends implementation of a cystic fibrosis carrier screening in the general pregnant and pre-pregnant population. This suggestion is discussed in the light of missing or insufficient data about the reasons for high uptake rates in pilot projects, psychological and social risks, and optimal educational and counselling settings. It is concluded that the recommendation is not defendable and, at best, premature.     

以能量密度为参量的管中导波无损检测参数选择

一般情况下，检测管状结构时采用位移分布或应力分布来选择超声无损检测的导波模式及其频厚积，这在有些情况下是不合适的。本文用总能量密度来选择检测管状结构的最佳导波模式及其频厚积，并用位移分布进行了比较，最后用混合边界元法进行了数值模拟，对其结果的有效性进行了验证。结果表明，总能量密度能有效的选择检测管材的最佳导波模式及其频厚积范围的检测的最佳位置。     

Development of Dominating Waves From Small Disturbances in Falling Viscous-Liquid Films

For wavy liquid films, the principle of selection of the periodic solutions realized experimentally as regular waves is justified. By means of numerical methods, the bifurcations of the families of steady periodic waves and the attractors of the corresponding nonstationary problem are systematically studied. A comparison of the bifurcations and the attractors shows that, when several periodic solutions exist for a given wave number, the solution with the maximum wave amplitude and the maximum phase velocity develops from small initial disturbances (the dominating wave regime). With wave number variation, near the bifurcation points the attractor passes discontinuously from one family to another. This passage is accompanied by the appearance of two-periodic solutions in small neighborhoods of these points. The relations between the calculated parameters of the dominating waves are in a good agreement with all the available experimental data.