Mechanical response of nanoporous gold

We report the results of computational tensile and compressive tests for model bi-continuous nanoporous gold structures using atomistic simulations with empirical many-body potentials and molecular dynamics. The results are compared with the predictions of scaling laws for coarser-scale foams and with available experimental data. We find a surprising substantial tension/compression asymmetry in yield due to the surface stress that sets the filament under compression, providing a bias favoring yielding in compression. We provide a model for our results based on a ligament strength value close to the theoretical strength of Au, and the surface stress. The model predicts a significant tension/compression asymmetry for ligament sizes below ～10 nm and pore collapse for ligament sizes below 1 nm. We also observe an unexpected compaction tendency under tension characterized by a decrease in the total volume of the sample of 15% for samples deformed under tension by 30%. The mechanism of the compaction involves a decrease in the average pore size and pore collapse resulting from plasticity within the ligaments.     

基于ANSYS有限元法的某型车床主轴振动频率响应分析

Making an analysis for vibration modal and frequency response of the lathe spindle, respectively by using finite element method based on ANSYS and experiment of CA6140 type lathe in machining, and the calculation results are compared and analyzed, which verified the accuracy of ANSYS method. Numerical simulation and experimental results show that: Spindle in the first order and fifth order are prone to resonance, but did not reach resonance, the low order natural frequency have more effect than the high order natural frequency of the spindle vibration; by the experiments can conclude that the maximum vibration of the main shaft in the working state is mainly concentrated in the vicinity of its two ends, therefore, the improved bearing is an important way to reduce the vibration of the main shaft and ensure the machining accuracy, and the research results can provide a theoretical reference for the structural optimization design of the lathe.     

Optical response of a single gold nanoparticle

Optical detection and spectroscopy of single gold nanoparticles using the spatial-modulation spectroscopy technique is described, focusing on the connection between the nanoparticle and environment parameters with the measured linear optical extinction spectrum. Characterisation of the size, shape and orientation on the substrate of a nanoparticle through quantitative determination of its optical extinction cross-section spectrum is illustrated in the case of gold nanospheres and nanorods. Extension of this technique to ultrafast nonlinear spectroscopy of a single gold nanoparticle is also discussed.     

The determination of initial blank shape by using the one-step finite element method and experimental verification

Many process parameters have an effect on the sheet metal forming process. A well-designed blank shape causes the material to flow smoothly, reduces the punch force, and yields a product with a uniform thickness distribution. Therefore, the determination of an initial blank shape plays the important role of saving time and cost in the sheet metal forming process. For these reasons, some approaches to estimate the initial blank shape have been implemented. In this paper, the one-step approach using a finite element inverse method will be introduced to predict the initial blank shape. The developed program is applied to several sheet metal forming examples for the demonstration of its validity. Moreover, the usefulness of the developed one-step approach program is investigated as compared with the FAST-3D program, which is a commercial package that is commonly used. Finally, the verification will be performed by comparing the predicted and experimental results.     

焊接残余应力求解的边界元数学模型

焊接残余应力和变形之间存在着确定关系,二者可通过焊接过程中产生的非协调应变联系起来,文中以焊接初应变为基础,利用边界元的直接法,推导出了通过焊接变形求解二维焊接残余应力的数学模型.给定焊缝中初应变的初值,根据焊接构件边界上已知的位移信息,可由边界积分方程求出边界上所有未知的位移分量和表面力分量.在边界位移已知的条件下,应用该模型可对焊接构件内部残余应力进行求解.构件边界上的应力可由弹性体的边界应力和边界面力的关系,通过物理方程和几何方程求出.通过计算实例,验证了模型的可行性.     

响应曲面法优化NaClO浸出贵州难浸金矿中的金

采用响应曲面法(RSM)优化NaClO浸出贵州难浸金矿中的金,探究了Na ClO浓度、温度、液固比、p H值4个因素之间的交互作用及其对金浸金率的影响,并进行了参数优化。RSM分析表明,各因素对金浸出率的显著程度为：NaClO浓度>液固比>p H>温度,NaClO浓度和p H之间的交互作用较为显著;得到较优的浸金工艺条件为：反应时间3 h,Na ClO浓度0.9 mol/L,初始pH=13.4,液固比8.2,温度27℃,在此条件下金的浸出率为93.4%。     

Colorimetric assay of lead using unmodified gold nanorods

Lead poisoning in adults can affect the peripheral and central nervous systems, the kidneys, and blood pressure. Thus, the development of environment-friendly and simple methods for Pb²⁺ detection is of great importance. Herein, a label-free colorimetric method has been developed for the detection of Pb²⁺ based on the conformational switch from single-stranded DNA to G-quadruplex. The electrostatic interactions between DNA probe and gold nanorods (GNRs) induce GNRs to space closely. However, the electrostatic interaction is not strong enough to change the suspension state of GNRs. In the presence of Pb²⁺, the formation of G-quadruplexes increases the surface charge density around DNA, which is expected to strengthen the electrostatic interaction between the GNRs and the DNA. Therefore, the longitudinal absorption of GNRs decreased because the stronger interaction induced aggregation of GNRs. Importantly, the decrease in longitudinal absorption is proportional to concentration of Pb²⁺. By monitoring the change of absorbance, Pb²⁺ can be detected at a level of 3 nM with a linear range from 5 nM to 1 μM. The overall test only takes a few minutes and very little interference is observed from other metal ions. The major advantages of this method are its low cost, convenience, simplicity, sensitivity, and specificity.     

Electroless synthesis of nano-structured gold particles using conducting polymer nanoparticles

In this study, gold nanoparticles were synthesized by electroless recovery of [AuCl₄]⁻ from an acidic aqueous solution using nano-structured conducting polymer, polypyrrole nanoparticles, as active surface. The formation of gold nanoparticles was confirmed by TEM, SEM and EDX measurements. The effects of the initial Au(III) concentration on the gold uptake was examined. The recovery capability and gold particle morphology prepared from polypyrrole nanoparticle were compared to that from cast PPy film counterpart.     

Practical determination of friction coefficient of Al 3003 for forming of backward extruded part using simple tip test and inverse finite element analysis

The friction coefficient for aluminum alloy 3003 was determined from a specially designed tip test and finite element (FE) simulations. Measured radial tip distance after the tip test was compared to the FE simulations by iteratively changing friction coefficient and the best fitting friction coefficient was determined. To consider strain rate effect on flow stress response during large plastic deformation, a new combined Hollomon- Voce hardening law was proposed. The friction under three different surface conditions was considered by the proposed inverse FE analysis. The results showed that there was obvious strain rate effect on the predicted punch load in the tip test. Moreover, the different friction coefficients were numerically determined for punch/workpiece and die/workpiece interfaces. Two possible causes of this difference were discussed by the analysis on contact normal pressure and slip velocity distributions of the two interfaces.     

金电极自组装基因分子膜的制备及电化学检测

采用分子自组装技术制备巯基修饰的基因分子膜修饰金电极,用于竞争式杂交检测黄孢原毛平革菌木素过氧化物酶编码基因。通过差分脉冲伏安法、循环伏安法、交流阻抗法和电流—时间曲线法优化自组装时间和信号探针的最佳响应浓度,研究目标基因的线性检测范围和再生性能。结果表明:修饰金电极最优自组装时间为15 h,信号探针的最佳响应浓度为0.51×10-6 mol/L,目标基因的线性检测范围为7.51×10-12-1.05×10-9 mol/L,检测下限为7.51×10-13 mol/L。该修饰电极具有良好的再生性能。     

用ICP-AES法快速测定Al-Ti中间合金和AlTiB晶粒细化剂中的Ti含量

建立了一种快速测定Al-Ti中间合金、AlTiB晶粒细化剂中Ti元素含量的分析方法。采用铝基体进行匹配,通过与分光光度法进行对比试验。结果表明,本方法可以达到快速测定Ti含量的目的。两种方法的绝对误差和相对误差均在允差范围内。     

板带轧制过程的三维耦合有限元分析

对板带轧制过程进行严密的三维分析是研究轧制参数对轧后板带尺寸、板形和机械性能的影响 ,从而实施有效控制的基础。本文简要回顾了板带轧制过程三维数值模拟的研究进展 ,提出了一个分析板带轧制过程的耦合有限元模型 ,其中 ,轧件塑性变形采用刚塑性有限元法计算 ,辊系弹性变形采用弹性有限元法计算。计算实践表明 ,该模型具有良好的精度和较高的效率。     

台阶式凸模精冲工艺分析及数值模拟

采用平面压板的无齿圈精冲,可以有效降低模具制造成本,提高精冲材料利用率。但采用常规平面压板精冲很难获得较好的冲裁面质量。文章对常规平面压板精冲模具进行改进,通过采用台阶式凸模结构实现无齿圈精冲;采用DEFORM 2DTM软件对C20E-EN钢圆盘的台阶式凸模精冲过程建立轴对称模型进行有限元模拟,分析凸模台阶高度、台阶宽度和冲裁间隙等工艺参数对零件冲裁面光洁带高度和塌角高度的影响规律,获得了相对最佳工艺参数的配合方式。将模拟结果与台阶式凸模精冲实验结果进行比较表明,模拟结果和实验结果具有较好的一致性。     

A factorial analysis of input parameters using finite element techniques

A two-level factorial design was performed to evaluate the effect of three key input parameters in a finite element analysis of a forging process. A series of “computer experiments” were performed that simulated the forging of a subscale jet engine disk, and these results were then compared with an actual disk forging.     

Stochastic modelling of abrasive waterjet footprints using finite element analysis

The proposal of erosion models to predict the jet footprint during abrasive waterjet machining is a key element for the development of this technology, but it is very challenging because of the inherent fluctuations of the process. This issue becomes critical when the size of the cutting systems is reduced, since the relative size of these deviations increases. The present paper considers for the first time a modelling framework capable of predicting the average shape of AWJM footprints and, of great novelty, the variability along the trench, combining finite element analysis and Monte Carlo methods, and verifying the model using different feed speeds and tilt angles. For that purpose, the relevance of each random parameter, such as shape (sharpness), size and relative orientation of the abrasive particles, has been investigated through parametric studies on these variables. Multiple particle simulations with randomly generated input were performed to determine the effect of operating parameters in the overall variability of the jet footprint. The process was simulated using Abaqus 6.14 as multiple garnet particles hitting a target of Ti–6Al–4V at very high velocity, eroding the target by plastic deformation and material removal. The model shows successfully the influence of single particle parameters, such as the shape, on the surface variability. The results for the footprint variability show that stochastic methods are suitable to model these fluctuations, and it is also shown that this approach yields accurate estimates of the average profile after multiple jet passes with error less than 5%.     

Analysis of stresses in micro-drills using the finite element method

The trend towards higher density printed circuit boards requires smaller holes down to 0.1 mm diameter to be drilled through the board layers. Drills of this size are inherently more susceptible to drill breakage and must be used with restricted operating parameters. In order to analyse the stresses occurring in microdrills, finite element methods are used. Three-dimensional models of drills are defined by setting node points of the drill geometry. Measured forces from experimental tests are used to determine drill loading. Principal stress isograms on drill cross-sections are presented for different drill geometries and correlation with actual drill life is made.     

直齿圆柱齿轮精锻成形工艺及三维有限元模拟

本文在齿轮分流锻造法的基础上 ,提出了闭式模锻———向内分流法两步成形的直齿圆柱齿轮的精锻工艺方案。采用三维刚塑性有限元法模拟了此工艺的成形过程 ,并且和传统的闭式模锻工艺进行了比较分析。从模拟结果可以看出 ,两步成形工艺不仅工作载荷低 ,而且齿形充填良好 ,是适用于直齿圆柱齿轮精锻的有效工艺方案。     

Development of a thermo-viscoplastic cutting model using finite element method

In this paper, a cutting model is developed by applying the thereto-viscoplastic FEM (finite element method) to analyze the mechanics of steady state orthogonal cutting process. The model is capable of dealing with free chip geometry and chip-tool contact length. The coupling with thermal effects is also considered. In calculating temperature distributions, the “upwind” scheme is employed to remove spurious oscillations that occur in the solution and therefore it is possible to analyze high speed metal cutting. Orthogonal cutting experiments are performed for 0.2% carbon steel to validate the cutting model. Tool forces are measured and the results are discussed in comparison with the results of the FEM analysis.     

环件轧制过程的显式有限元模拟分析

用于金属成形模拟的有限元方程的求解方法 ,主要有隐式和显式积分两种方法。对于复杂的三维变形分析 ,如环件轧制 ,隐式方法需要很长的运行时间。而利用显式方法 ,可以达到很好的效果。本文利用Abaqus /Ex plicit通用有限元程序对径向环轧进行了模拟。