搅拌摩擦焊数值模拟的现状

自搅拌摩擦焊发明以来，对多种不同材料的搅拌摩擦焊实验研究已取得了巨大的进展，但对搅拌摩擦焊工艺过程的计算机模拟直到最近几年才逐渐兴起。简要叙述了搅拌摩擦焊数值模拟研究的3个主要方向（温度场、流场和组织性能）的研究现状。     

钛合金搅拌摩擦焊研究现状

搅拌摩擦焊是目前钛合金焊接技术研究的热点.从搅拌头材料与结构设计、焊接工艺与组织性能关系、焊接过程数值仿真等方面综述了钛合金搅拌摩擦焊国内外研究现状.以现有的研究结果来看,搅拌摩擦焊是实现钛合金高强可靠连接的有效途径,选择合适的焊接参数和焊后热处理工艺可获得高质量钛合金焊接接头;但由于对钛合金用高温高强高耐磨搅拌头研制不足,以及对焊接过程多物理场表征技术、数值仿真、辅助焊接工艺等研究较少,限制了其研究进展和应用.     

钛合金搅拌摩擦焊搅拌头研究现状

搅拌摩擦焊在焊接钛合金这类高熔点金属方面具有很大优势,但是搅拌头的磨损一直是其一大难点。对钛合金搅拌摩擦焊中的搅拌头结构、材料选择进行了讨论,认为圆锥形搅拌针综合性能较好,而在材料选择方面,认为目前应用前景较好的是钨铼合金,但不同材料的组合可能更符合未来发展的方向。为了研究搅拌头的磨损机理及如何减小磨损,列举了几种辅助焊接工艺及目前应用较广的模拟仿真,指出辅助焊接工艺可减小搅拌头磨损,但目前工艺不完善等问题依然存在,需要进一步优化,包括模拟仿真在内,对于钛合金搅拌摩擦焊搅拌头结构、材料优化、磨损机理、辅助焊接工艺等研究均较少,限制了其研究进展及应用。     

搅拌摩擦焊接及其加工研究现状与展望

搅拌摩擦焊是一种新型的固相焊接工艺,在近些年取得了巨大的研究进展.从搅拌摩擦焊的工作原理和特点出发,对搅拌摩擦焊工艺参数、焊缝组织及性能进行了评述;最后简要介绍了搅拌摩擦加工的最新发展及在各工业领域中的应用概况.     

适用于机器人焊接的搅拌摩擦焊技术及工艺研究现状

集绿色化与智能化于一体的机器人搅拌摩擦焊技术具有极高的焊接柔性,在工业生产中受到广泛重视与应用。从减小搅拌摩擦焊接过程中的轴向力方面入手,对一些低轴向力且适用于机器人搅拌摩擦焊的技术方法进行了综述,同时,对能够进一步降低搅拌摩擦焊过程中轴向力的搅拌摩擦焊工艺进行了分析,并对机器人搅拌摩擦焊的发展进行了展望,以期拓宽机器人搅拌摩擦焊的应用范围。     

铝合金搅拌摩擦焊研究现状及应用

搅拌摩擦焊是由英国焊接研究所发明的一种固相连接技术，可以对熔化焊接性差的铝合金进行可靠的连接，又具有诸多优点。介绍了搅拌摩擦焊工艺过程，分析了搅拌摩擦焊技术目前存在的优缺点，综述了铝合金搅拌摩擦焊的国内外研究现状和应用情况，指出搅拌摩擦焊为现代铝合金制造业提供了新的连接方法。     

铝/钢异种材料搅拌摩擦焊研究进展

由于铝、钢的物理化学性质存在巨大差异,铝/钢的连接是焊接领域的难点问题。搅拌摩擦焊是低热输入的固态连接方法,能够有效控制铝/钢金属间化合物的生长,且搅拌针强烈的搅拌作用可增加铝/钢异种材料机械咬合程度,得到高质量的铝/钢焊接接头,铝/钢搅拌摩擦焊已经成为了焊接领域的热点问题。文中综述了铝/钢搅拌摩擦焊国内外研究现状,涉及到接头形式、焊缝成形、焊接工艺和力学性能,着重介绍了铝/钢搅拌摩擦焊接头的连接机制,并围绕铝/钢搅拌摩擦焊存在的两大问题,对铝/钢搅拌摩擦焊新技术进行总结,并进一步提出了铝/钢搅拌摩擦焊的基础研究方向。     

纯铝板搅拌摩擦焊温度场数值模拟

建立了搅拌摩擦焊热源模型,利用有限元分析软件ABAQUS模拟了搅拌摩擦焊的温度场,研究了焊接速度、搅拌头轴肩尺寸和垫板材质对搅拌摩擦焊接过程中试板的温度场的影响。结果表明：随着焊接速度的提高,焊件上各点的峰值温度降低,经历高温区的时间减少;轴肩摩擦热是热输入的主要来源,随着搅拌头轴肩尺寸的增加,焊缝中心高温区同一等温线上宽下窄的分布特征越来越明显;垫板材质明显影响焊件底部的温度和分布;适当的焊接参数、搅拌头尺寸及散热条件对获得较好的焊缝质量极为重要。     

外加能量辅助搅拌摩擦焊技术的研究进展

搅拌摩擦焊接已经成为材料成形领域主要的固相连接工艺技术。在简要回顾搅拌摩擦焊及其衍生焊接技术研发现状的基础上,综述了近年来国内外开展的第二能量辅助搅拌摩擦焊的研究现状,主要包括激光、电弧、感应、电流、超声等能量辅助搅拌摩擦焊技术。进而着重综述了超声振动辅助搅拌摩擦焊的研究进展,介绍了目前出现的3种超声振动在搅拌摩擦焊中的施加方式。最后,对外加能量辅助搅拌摩擦焊下一步的研发方向进行了展望。     

搅拌摩擦焊焊缝塑性流动规律的数值模拟

使用FLUENT流体工程仿真软件对搅拌摩擦焊缝金属的塑性流动进行了数值模拟;初步得出了搅拌摩擦焊焊缝塑性流体流动规律.实验结果表明:随着距轴肩和搅拌针距离的增大,速度场开始减弱,焊缝金属由顶面向底面、由搅拌区向旋转区的流动也随之减弱.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。