静止轴肩对FSW温度与应力影响的数值模拟

目的研究外部辅助静止轴肩对搅拌摩擦焊接过程温度场以及应力场的影响。方法建立有限模型并采用热机耦合的方法分析常规与静止轴肩辅助工艺下7075-T6铝合金搅拌摩擦焊接过程,得出不同工艺下的焊接温度与应力分布状态。对比常规与静止轴肩工艺下的温度与应力结果,得出静止轴肩对焊接过程中温度与应力的影响规律。结果焊缝横截面的高温区域均呈现出上宽下窄的碗型分布。相比于常规工艺,静止轴肩辅助工艺的焊缝区域温度具有上升速度较慢、下降速度较快的特点,且温度峰值低了55.7℃。静止轴肩具有随焊碾压的作用,在焊接过程中为焊缝区域提供一个额外的压应力,抵消焊接过程中产生的拉应力,焊后残余应力降低了17.4%。结论静止轴肩辅助工艺对焊缝区域的温度峰值以及残余应力峰值的降低均具有明显效果。     

铝合金加筋壁板搅拌摩擦焊接残余应力及变形分析

目的对民机用铝合金加筋壁板搅拌摩擦焊接残余应力及变形进行研究。方法采用热-力耦合数值模拟方法,分析民机用铝合金加筋壁板搅拌摩擦焊接过程,分别模拟了采用3种焊接顺序进行蒙皮-长桁焊接时,壁板温度场分布规律及焊后残余应力及变形情况。结果铝合金壁板搅拌摩擦焊接后,沿焊缝方向残余应力为拉应力,由此导致长桁及与其连接的蒙皮产生向上的挠曲变形,垂直焊缝方向,焊缝两侧的壁板向上翘曲。结论对于3种焊接顺序,采用"先两侧、后中心"由外向里的焊接顺序,得到的壁板残余变形最小。     

TC4钛合金激光焊接应力变形有限元分析

基于ANSYS有限元分析软件,采用三维移动热源,对TC4钛合金激光焊接残余应力和变形进行了数值模拟和实验研究.结果表明:钛合金激光焊接产生很大的纵向残余应力,而横向残余应力较小.激光焊接线能量增加时,纵向残余应力拉伸区域变宽,峰值应力降低;而横向残余应力随线能量的增加而升高.在临界焊透规范以上焊接时,随焊接线能量的增大,角变形随之而减小,而横向收缩变形增大.焊件被完全穿透时,线能量对角变形的影响作用降低.钛合金激光焊接变形和残余应力实验结果与数值计算结果吻合性较好.通过焊缝金相实验分析了焊接残余应力和变形与线能量的内在关系.     

6061铝合金无倾角搅拌摩擦焊工艺及性能

目的 为了适应空间曲面构件的搅拌摩擦焊,开展6061铝合金无倾角搅拌摩擦焊工艺及性能的研究。方法 采用无倾角搅拌摩擦焊用的搅拌头,对5 mm厚6061-T6铝合金板材进行试验,研究焊缝成形及接头力学性能,并分析接头组织特征。结果 零倾角搅拌摩擦焊接头从组织上可区分为5个不同区域：焊核区(WNZ)、热力影响区(TMAZ)、热影响区(HAZ)、轴肩影响区(SAZ)和母材(BM);随着搅拌头转速增加,焊缝宽度和焊核尺寸均先变大后变小;随焊接速度增加,焊缝宽度和焊核尺寸均逐渐变小;当焊接速度固定时,随搅拌头转速增加,接头拉伸强度先增加后减小;当搅拌头转速固定时,随焊接速度增加,接头拉伸强度逐渐增大。结论 采用无倾角搅拌摩擦焊接方法,能够实现对5 mm厚6061-T6铝合金板材的有效焊接。     

钛合金薄板带热沉钨极氩弧焊的应变场

采用数值模拟和试验相结合的方法对比研究了钛合金常规钨极氩弧焊(GTAW)及带热沉的钨极氩弧焊,即动态控制低应力无变形(DC-LSND)GTAW焊接过程中纵向应变场的形态与发展历史.DC-LSND GTAW焊接过程中,由于紧随热源之后热沉冷却介质的急冷作用,使得热沉作用部位产生强烈收缩,热源与热沉之间的极大温度梯度,对高温金属产生较强的拉伸作用,使得焊缝中拉伸塑性应变增大,近缝区压缩塑性应变减小,焊缝与近缝区的不协调应变减小.DC-LSND焊时,不但可以降低残余应变,减小变形;而且,在所选用的焊接条件下,DC-LSND GTAW焊缝中甚至还可获得拉伸的不协调应变.     

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。     

铝合金氩弧焊与搅拌摩擦焊残余应力对比分析

铝合金材料由于其重量轻、耐腐蚀等优点被广泛应用于石油海洋工程中。铝合金的焊接及焊接接头的性能,备受关注。不同的焊接方法和焊接工艺产生的焊接残余应力对接头的疲劳寿命影响极大。以氩弧焊和搅拌摩擦焊工艺,选用不同的铝合金材料,采用小盲孔法测试焊接残余应力。比较了两种焊接方法、工艺所产生的接头焊接残余应力值,为今后铝合金焊接接头中,疲劳性能的计算提供初步的数据。试验结果表明,在铝合金的氩弧焊和搅拌摩擦焊对接接头中,残余应力的最大值均出现在焊缝中心到热影响区的范围内,随着与焊缝中心距离的增加,残余应力的数值逐渐减小。     

轨道车辆型材结构搅拌摩擦焊残余状态研究

目的 研究轨道车辆中典型的箱型和V筋结构型材搅拌摩擦焊残余状态。方法 采用顺序热力耦合方法进行了搅拌摩擦焊残余应力及变形的仿真研究。结果 给出了上下壁板焊缝区域的残余应力大小及分布规律，阐述了两种结构的横向和纵向残余变形特征。对V筋结构型材，分析了不同筋板角度对焊接残余状态的影响。结论 残余应力方面，主要表现为纵向残余应力，上下壁板两条焊缝的残余应力峰值相近，高应力分布区域宽度差别较大。残余变形方面，箱型结构呈马鞍形，V筋型材呈下凹形。V筋型材筋板夹角的变化对残余应力没有显著影响。筋板角度增大，纵向残余变形减小而横向残余变形增大。     

转速对 7075-T651 铝合金搅拌摩擦焊接件内部残余应力分布的影响

目的掌握铝合金搅拌摩擦焊接板内部残余应力的分布,为控制焊接残余应力、改进焊接工艺和提高焊接件质量。方法以13.6 mm厚的7075-T651铝合金为研究对象,用短波长X射线衍射技术,对在不同搅拌头转速下搅拌摩擦焊接板内部的残余应力进行了无损测试,并对焊接接头在板厚中心层上的微观组织和显微硬度进行了研究。结果在垂直于焊缝截面上的显微硬度均呈"W"型分布,焊核区的显微硬度高于其两侧的热机械影响区和热影响区,但低于母材区的硬度;随着转速的增大,接头硬度的最小值减小,低硬度区的范围越大。横向残余应力绝对值整体小于焊接方向;焊核区为正应力,热机械影响区残余应力减小且变化梯度最大;残余应力的极大值位于热影响区和热机械影响区的交界处;残余应力极大值与硬度最小值的位置重合。结论通过残余应力的无损检测分析,不仅可以直接获得加工件内部应力分布,还可以间接获得加工件内部的加工缺陷情况,为改进加工工艺、提高成形精度提供依据。     

铝锂合金电子束焊接数值模拟分析及工艺优化

采用组合热源模型对Al-Li合金电子束焊接温度场分布进行数值模拟分析,通过热-力耦合,模拟计算得到接头区域的残余应力分布.结果表明,Al-Li合金电子束焊接温度场沿焊接方向呈椭圆形分布,电子束热源中心的温度最高,其附近区域的等温线分布密集,随着与热源中心的距离增大,等温线分布逐渐稀疏,焊缝区存在较大的温度梯度,较好地模拟出了电子束焊缝的钉形分布特征.接头的残余应力分布模拟结果显示,残余应力主要集中于焊缝区,由于修饰焊的热作用,焊缝上部具有相对较大的应力值.利用模拟计算得到的结果进行焊接工艺及参数优化,焊接工艺试验表明,试验焊缝形貌与模拟熔池形貌相吻合,进一步验证了模拟计算结果的可靠性.     

Finding irreducible and primitive polynomials

In the paper some new fast constructions of irreducible and primitive polynomials are presented. For instance, it is shown, that for anyQ large enough one can design a finite field _q withq=Q + o(Q) elements in polynomial time (log Q) ^o (1).     

电场磁场对电流变液体减振器性能影响的研究

由于电流变液和磁流变液具有良好的可控性能和力学性能而在工程上具有广阔的应用前景.本文将其用于环形间隙通道外置的双缸电流变液体减振器.同时,对电流变液减振器在同时外加电场和垂直磁场作用下阻尼力的变化进行了理论研究和台架实验研究.结果表明,在外加电场和垂直磁场作用下,电流变效应得到加强,改善了减振器的示功特性.     

Methods of Measuring the Low-Frequency Electric and Magnetic Fields of Ships

Methods of recording low-frequency electric and magnetic fields in an aqueous medium, generated by ships and other moving objects, are considered. The history of the development of instruments for measuring such fields is described, their characteristics are presented, and the main areas of development of future instruments for this type of measurement are determined. __________ Translated from Izmeritel'naya Tekhnika, No. 11, pp. 68–71, November, 2005.     

A new efficient factorization algorithm for polynomials over small finite fields

We present a new deterministic factorization algorithm for polynomials over a finite prime fieldF _p . As in other factorization algorithms for polynomials over finite fields such as the Berlekamp algorithm, the key step is the linearization of the factorization problem, i.e., the reduction of the problem to a system of linear equations. The theoretical justification for our algorithm is based on a study of the differential equationy ^(p –1)+y ^p =0 of orderp–1 in the rational function fieldF _p(x). In the casep=2 the new algorithm is more efficient than the Berlekamp algorithm since there is no set-up cost for the coefficient matrix of the system of linear equations.     

3rd-order Spectral Representation Method: Simulation of multi-dimensional random fields and ergodic multi-variate random processes with fast Fourier transform implementation

This paper introduces a generalized 3rd-order Spectral Representation Method for the simulation of multi-dimensional random fields and ergodic multi-variate stochastic processes with asymmetric non-linearities. The formula for the simulation of general $d$-dimensional random fields is presented and the method is applied to simulate 2D and 3D random fields. The differences between samples generated by the proposed methodology and the existing classical Spectral Representation Method are analysed. The formula for the simulation of multi-variate random processes is subsequently developed. An important feature of the methodologies is that they can be implemented efficiently with the Fast Fourier Transform (FFT), details of which are presented. Computational savings are shown to grow exponentially with dimensionality as a testament of the scalability of the simulation methodology. Examples highlighting the salient features of these methodologies are also presented.     

Modern computer assisted methods in metallurgy

Image analysis systems have been used in metallurgy for over two decades and play a vital role in quality assessment for the steel industry. One major application is the characterization of steel by counting and measuring the non-metallic inclusion content. Visual steel assessment, relying on the comparison with idealized ‘charts’ of varying inclusion content, for example as defined byastm andsep, is the most common manual method employed. However, this has proved to be most difficult to automate due to the degree of subjectivity associated with the manual methods. This has previously restricted the acceptance of image analysis systems for routine quality control. The increased software power of the more modern instruments has enabled the installation of systems which satisfactorily mimic the skilled observer in a reproducible manner. These work with an economically attractive throughput and produce results in the accepted standard format. A limitation of these systems is that they grade a field on the basis of the majority inclusion type present. This can lead to significant but lesser inclusions being ignored altogether and presenting a false picture of the sample. This paper describes a new method which separately identifies individual inclusions in a field. The grade number of a field can then be determined for each inclusion type. This is known as the mixed field method. This paper describes this method and its implementation on the Cambridge Instruments’quantimet 920 image analysis system.     

Single‐camera special stereo‐digital image correlation applied for accurate virtual fields method identification

A single‐camera special stereo‐DIC (SS‐DIC) is proposed for accurate virtual fields method (VFM) identification. The single‐camera SS‐DIC allows accurate surface 3D deformation measurements using a single colour camera and a specially designed colour separation device. It not only effectively eliminates the unavoidable out‐of‐plane movement/rotation due to unideal in‐plane loading but also delivers uniformly distributed measurement points that brings great simplicity and convenience for internal virtual work calculation in VFM. In addition, since only a single camera is used for stereovision, the proposed SS‐DIC system requires no complicated synchronisation devices. The effectiveness and practicality of the proposed method are evaluated by heterogeneous deformation experiments of a holed aluminium alloy and 304 stainless steel plate. Combined with a high‐speed colour camera, the proposed method is expected to be a simple and practical method for the calibration of material constitutive model under intermediate and high strain rate conditions using VFM.     

Some results on permutation polynomials over finite fields

This paper deals with two questions concerning permutation polynomials in several variables. Lidl and Niederreiter have considered the problem of when a sum of permutation polynomials in disjoint sets of variables is itself a permutation polynomial, and in the case of prime fields have shown that it is necessary and sufficient that at least one summand be a permutation polynomial. They also showed that in the case of non-prime fields this condition is not necessary. In this paper, a necessary and sufficient condition is obtained for the general case which specialises to the previous result for prime fields. The second part extends a criterion of Niederreiter for permutation polynomials over prime fields to any finite field.     

Construction of irreducible polynomials using cubic transformation

The transformationf(x)f(x ³–3x) is studied. We show that for allF _q of characteristic >3 andn1, there existsf(x)F _q [x] of degreen which generates an infinite sequence of irreducible polynomials of degree 3 ⁱ n by the iteration of this transformation.