AP1000核电站主管道自动焊接头残余应力分析

采用X射线衍射法对AP1000核电站主管道自动焊接头进行应力演变及焊后残余应力测试。分析讨论管道内壁及外壁的环向及轴向残余应力分布。结果表明:管道内壁近缝处环向残余应力值先增大后减小并逐渐稳定,而远缝处残余应力则保持缓慢上升并逐渐稳定。焊后状态下,管道外壁轴向残余应力随着远离焊缝,先减小后增大至母材水平,而环向残余应力则先上升后下降。     

不锈钢管焊接残余应力与变形仿真分析

基于计算机仿真技术,定义随温度变化的材料热物理属性,建立316不锈钢连续油管对接焊接轴对称模型,分析焊接速度对焊后油管接头的残余应力和变形的影响。结果表明,在连续管道焊接过程中,焊接速度影响焊接温度场和焊后残余应力的分布;油管内壁最大残余压应力出现在距离焊缝中心22 mm接近母材的位置处,且轴向应力和环向应力的变化同步,油管外壁环向应力和轴向应力变化不同步;随焊接速度的增加,油管外壁残余应力逐渐增大,内壁残余应力和焊接变形逐渐减小,焊接变形可释放部分焊接残余应力,在一定程度上可降低焊后残余应力。     

海洋平台导管架Y形节点焊接冷裂性评价

海洋平台结构的不均匀性与焊接技术的局限性导致焊接接头位置易产生焊接冷裂纹等缺陷进而导致开裂。针对该问题,文中基于SYSWELD软件对海洋平台E36高强钢材质的导管架典型Y形管节点位置处的焊缝进行建模并对其焊接过程进行了数值模拟。根据焊后应力场获得焊后拘束应力,从而实现对其冷裂性的定量评价。通过热源校核得到的热循环曲线实现热源模型的施加,进而分别对管内壁焊根处和管外壁焊趾处的轴向、周向及径向拘束应力沿着相贯线的变化进行了分析,并将各方向的危险点拘束应力与材料的临界拘束应力进行了对比。结果表明,导管架Y形管节点的焊后最大拘束应力为492 MPa,小于E36高强钢的临界拘束应力,即导管架Y形管节点的焊根和焊趾处均不会发生焊接延迟开裂。     

换热器管与管板接头焊接残余应力的有限元分析

基于ANSYS平台对换热器伸出管板角接头和平焊接头的焊接残余应力进行数值模拟,获得了焊接接头的残余应力分布.有限元分析结果表明,接管环焊缝的残余应力分布具有局部性的特点,最大等效应力出现在焊根处.本文焊接条件下管接头环焊缝在焊接热影响区位置上径向为压应力,环向为拉应力,这种径向受压,环向受托的应力状态下更容易引起径向裂纹的萌生和扩展.     

锆管环焊接头残余应力有限元模拟及分析

应用ABAQUS大型有限元计算软件,建立了锆管单道环焊接头的三维有限元模型,采用热-力顺序耦合、生死单元等技术对锆管焊接的温度场和残余应力场进行了模拟,模拟过程中考虑了相变潜热、材料非线性等因素的影响;研究了不同焊接线能量和不同约束条件对焊接残余应力的影响规律,获得了残余应力分布特征规律。有限元分析显示:焊接等效应力主要存在于焊缝及热影响区,峰值接近锆的屈服强度。环向和轴向应力峰值均达到120 MPa,约为屈服应力的60%。焊件内外壁上,轴向应力对称分布,等效应力大小与线能量大小呈正比,不同约束条件下,等效应力在约束密集方向明显增大。     

吸附塔支撑圈结构焊接残余应力有限元分析

采用有限元分析软件Abaqus对吸附塔支撑圈结构焊接残余应力进行有限元分析,讨论了不同焊接热输入、焊后热处理温度、预热温度对焊接残余应力的影响规律。结果表明:在焊接接头角焊缝处产生了较大的纵向残余应力,这是引起疲劳失效的主要原因。焊接热输入越大,筒体外壁热影响区残余应力越大。焊后热处理能够有效降低残余应力。较高的预热温度有利于降低焊接残余应力,但预热温度也不能太高,应控制在150~200℃。为保证吸附塔支撑圈结构完整性,应综合考虑预热、焊接工艺及焊后热处理等因素,以充分降低焊接结构的残余应力。     

X70管线钢厚板多层多道焊残余应力数值分析

基于逐层激活建模方式实现对多层多道焊接过程中焊缝金属填充的模拟,分别以半椭球体电弧热源模型和均匀柱体分布的熔滴热源模型为热源模型,建立了不等厚X70管线钢板多层多道焊接有限元计算模型,数值计算并分析了焊接过程中温度场和应力场演变、焊后残余应力状态。结果表明,经过多次焊接热循环后先形成的焊缝的应力状态与母材中焊接热影响区的应力状态接近;接头焊根处的残余应力要比盖面焊趾处的残余应力高,根焊两侧焊根的残余应力大小未受两侧板厚的差异影响,数值均达到468 MPa,焊缝焊趾与焊根处残余应力均低于母材屈服强度。计算结果与试验结果吻合良好,证明了模型的可靠性和准确性。     

空心圆柱件内孔的淬火应力

为了分析空心圆柱件淬火时内孔开裂的原因,通过二次开发在Abaqus软件平台上建立了空心圆柱件淬火时温度场、组织场和应力场的三场耦合模型。基于数值模拟对空心圆柱件淬火时的热应力及相变应力(组织应力)进行了分析,并对冷却介质换热系数对内孔淬火应力的影响进行了研究。结果表明：薄壁件在水淬后内壁表层及次表层的残余应力均为拉应力,厚壁件在经水淬后内壁和外壁表面残余应力均为压应力,内外壁的中间位置为拉应力;厚壁件内壁的最大拉应力在冷却过程中出现;引起薄壁件和厚壁件内壁开裂的原因是相变应力。通过分析空心件内孔淬火应力的影响因素并结合实际情况,提出了降低圆柱件内壁淬火应力的工艺方法。生产实践表明：基于数值模拟设计的淬火工艺未出现淬火开裂现象,并且材料的各项力学性能满足要求。     

超临界循环流化床锅炉高温过热器管开裂原因分析

某超临界循环流化床锅炉TP347H钢膜式壁高温过热器管频繁发生开裂,通过宏观检查、光谱分析、力学性能试验、显微组织分析以及运行情况分析等对其失效原因进行了研究。结果表明,取样管化学成分、力学性能均满足标准要求,显微组织未见异常;裂纹起源于管子与鳍片焊趾处,并从外壁向内壁扩展;管子开裂原因为:高温过热器管为大屏膜式壁结构,加之锅炉启动过程中,相邻管壁温度差较大且不断变化,造成管子在轴向方向的膨胀差较大并形成交变热应力,从而在焊趾应力集中部位产生热疲劳裂纹,同时管子与鳍片焊缝处的残余应力以及管子外表面存在的直道沟槽促进了裂纹的形成和扩展。     

焊接顺序及热处理对T91/12Cr1MoV异质接头残余应力影响的数值分析

利用ABAQUS有限元软件,对T91/12Cr1MoV钢管道多层多道焊异质接头进行焊接残余应力有限元模拟,分析焊后热处理和两种焊接顺序对接头内残余应力的影响。结果表明,焊接接头在外壁T91侧热影响区存在最高轴向和环向拉应力。焊接各层焊道时,对比从12Cr1MoV侧向T91侧与从T91侧向12Cr1MoV侧依次焊接各焊道所获得的残余应力,后者所获得的残余应力较低,特别是在管道的外壁处尤为显著。热处理后管道焊接残余应力有所降低,但在T91侧热影响区仍存在较大的残余应力。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。