Assessment of the effect of existing corrosion on the tensile behaviour of magnesium alloy AZ31 using neural networks

A concept has been devised to assess the effect of existing corrosion damage on the residual tensile properties of structural alloys and applied for the magnesium alloy AZ31. The concept based on the use of a radial basis function neural network. An extensive experimental investigation, including metallographic corrosion characterization and mechanical testing of pre-corroded AZ31 magnesium alloy specimens, was carried out to derive the necessary data for the training and the prediction module of the developed neural network model. The proposed concept was exploited to successfully predict: the gradual tensile property degradation of the alloy AZ31 to the results of gradually increasing corrosion damage with increasing corrosion exposure.     

Laser shock welding of aluminum/aluminum and aluminum/copper plates

This work describes an advanced technique for metal welding and composite production, namely laser shock welding. A series of laser shock welding experiments were conducted to verify the welding ability of aluminum/aluminum and aluminum/copper plates. Two kinds of interface morphologies were observed by metallographic investigation on cross-sections of the joint areas, including the linear and wavy interfaces. Besides, micro-hardness testing results show the welded interface has a much greater hardness than the base metals. The lap shearing test was used to characterize the joint. According to the experimental results, it can be imply that this kind of technique shares the same bonding mechanism with explosive welding and magnetic welding.     

Failure analysis of a natural gas pipeline

In the present work, the failure investigation of a 30 in. diameter gas transmission pipeline (API 5L X-60 grade steel) has been described. The failure was due to a longitudinal crack developing in the centerline of longitudinal weld joint. Mechanisms and morphology of crack initiation and propagation were studied through different tests including: thickness measurement, chemical composition analysis, metallographic inspection, mechanical property testing, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The experiments resulted to the conclusion that some factors associated with Sulphide Stress Cracking (SSC) and metallurgical defects cause the failure of weld joint pipe. Detailed examination revealed that these factors are inappropriate welding parameters, pitting corrosion on longitudinal weld, and hydrogen permeation to the weld metal.     

仪表金属功能材料低倍缺陷的检测

分析了仪表金属功能材料在超声检测中出现的低倍缺陷，讨论了在既定的条件下，采用宽频带窄脉冲超声检测方法对仪表金属功能材料低倍缺陷的检测。实践表明，采用宽频带窄脉冲超声检测与金相检验相结合的方法可有效地检测仪表金属功能材料的低倍缺陷。     

A study on micro-mechanical deformation behaviour of heat-treated 20MnMoNi55 steel

Several heat treatment procedures are designed considering critical temperatures of phase transformation evaluated through dilatometric testing of 20MnMoNi55 steel to transform low carbon bainitic as-received material into ferrite-martensite dual-phase steels consisting of varied martensite fractions. A thorough metallographic study correlated with the micro-hardness of constituent phases ensures morphological characteristics along with its fractional variations in as-received and dual-phase steels. The impact of fractional variation in constituent phases on the uniaxial monotonic deformation characteristics of dual-phase steels has been observed with a correlation study between experimental tensile and finite element simulated results. Therefore, a physical-based model with a 2-dimensional representative volume element has been established, addressing actual morphological characteristics obtained from metallographic studies. Moreover, the constitutive flow behaviours of ferrite and martensite are also derived from the dislocation-based hardening model to address the actual deformation phenomenon. Finally, an inhomogeneous deformation behaviour among constituent phases and localization of plastic strain in ferrite matrix has been observed with von-Mises stress, and equivalent plastic strain distribution through finite element simulated results. This phenomenon is again confirmed with kernel average misorientation mapping and geometrically necessary dislocation density evaluation through electron backscattered diffraction of tensile samples subjected to different degrees of plastic strain.     

Failure analysis of an aircraft nose landing gear piston rod end

A failure investigation has been conducted on a piston rod end used in a hydraulic actuating cylinder of an aircraft landing gear. The failed piston rod end was found to be broken. An evaluation of the failed piston rod end was undertaken to assess its integrity that included a visual examination, photo documentation, chemical analysis, hardness measurement, tensile testing, and metallographic examination. The failure zones were examined with the help of a scanning electron microscope (SEM) equipped with EDX facility. A stress analysis is also carried out by the finite element technique for the determination of highly stressed regions on the piston rod end. The results indicated that the piston rod end failed by fatigue with cracks initiated at the surface close to the mechanically damaged region due to high stress concentrations.     

Microbiologically Influenced Corrosion of Galvanized Steel by a Metalworking Lube

This article investigated the corrosion failure of galvanized steel that had been exposed to a metalworking lube. The investigation included metallographic preparation (sectioning, mounting, and polishing), microstructural analysis, optical microscopy, zinc coating thickness measurements, fluid pH measurements, microbiological testing, and Fourier Transform InfraRed spectroscopy. The results from this investigation showed that the failure that occurred was due to microbial corrosion.     

The influence of salt fog exposure on the fatigue performance of Alclad 6xxx aluminum alloys laser beam welded joints

Laser welding is increasingly used for the fabrication of lightweight and cost-effective integral stiffened panels in modern civil aircraft. As these structures age in service, the issue of the effect of corrosion on their damage tolerance requires attention. In this work, laboratory data on the influence of salt fog corrosion on the fatigue behavior of cladded 6156 T4 aluminum alloy laser welded specimens are presented. The experimental investigation was performed on 6156 T4 laser butt welded sheets. Prior to fatigue testing the welded joints were exposed to laboratory salt fog corrosion exposure for 720 h. The results showed that the clad layer offers sufficient corrosion protection both on base metal and the weld. Fatigue testing was followed by standard metallographic analysis in order to identify fatigue crack initiation sites. Crack initiation is located in all welded samples near the weld reinforcement which induces a significant stress concentration. Localized corrosion attack of the clad layer, in the form of pitting corrosion, creates an additional stress concentration which accelerates crack initiation leading to shorter fatigue life relative to the uncorroded samples. The potency of small corrosion pits to act as stress concentration sites has been assessed analytically. The above results indicate that despite the general corrosion protection offered by the clad layer, the localized attack described above leads to inferior fatigue performance, a fact that should be taken under consideration in the design and maintenance of these structures.     

烧结金属材料的金相制样

详细论述了烧结金属材料金相样品的制备方法和金相样品制备过程中可能产生的总理２以及控制和消除它们的方法信此方法可确保获得一个平整的、能反映烧结金属材料起初显微组织和结构的金相样品。     

CTODi MEASURED BY MEANS OF A MODIFIED CHARPY-V-SPECIMEN

Abstract— Measurements of CTOD_i on Charpy-V-specitnens of mild steel St 37 and pressure-vessel steel 22NiMoCr37 have been carried out. Slotted and precracked specimens have been used besides the original V-notched ones. A definition of CTOD = 2(R – R_o) has been proposed which corresponds to δ₄₅, defining the CTOD of fatigue cracks. The symbols R_o and R represent the original and the actual crack tip radii respectively. Additionally, this definition presents the opportunity to measure CTOD and CTOD_i by a direct metallographic method. It is demonstrated that COD testing, based on the hinge model, can also be applied to slotted bars, delivering CTOD and CTOD_i values which are equal to those evaluated by direct metallographic measurements.
The results obtained on four different tip radii, R_o, show a linear increase of CTOD_i as a function of R_o, which is steeper for the softer material St 37. The extrapolation to the tip radius R_o=0 gives a CTOD_i, which is equal to those determined from precracked specimens.     

超超临界机组T92钢高温受热面管爆管原因分析

某电厂的后屏过热器T92钢管段发生爆管。通过宏观检验、化学成分分析、硬度检验、拉伸性能测试、金相检验以及相关计算分析了爆管的原因。结果表明：管段发生短时过热后,其显微组织为Acl-Ac3相变产物,失去了原典型的回火板条马氏体组织特征,材料强度大幅度降低,从而使得强度不足以抵抗管子的使用应力而发生爆管。另外,通过检验获得了不同状态下的组织与性能的对应关系,有利于长期运行中的金属监督检验。     

ZM6尾减机匣开裂失效分析

某型号飞机尾减机匣试验过程中出现异常,荧光检查发现裂纹.通过故障机匣外观检查、裂纹断口宏微观观察及能谱分析、材料硬度检测、金相检查等试验得出结论,尾减机匣失效属低周疲劳开裂,机匣表面Nd元素偏析是导致机匣疲劳裂纹形成的直接原因,材料韧性不足一定程度上促进了裂纹的疲劳扩展,根据分析结果,给出提高尾减机匣受力部位的疲劳抗力,避免故障再次发生的有效方法.     

Microstructural evaluation of arc-melted Al-Li-Be alloys

A microstructural investigation has been carried out on a series of small castings of arc-melted Al-Li-Be alloys. The alloy composition included amounts of lithium up to 3wt% and beryllium up to 10wt%. Optical metallographic examination has revealed gross macrosegregation in the highly alloyed compositions. On the microstructural level, the structure consists of primary beryllium particles in a matrix of primary aluminium containing eutectic structure at the cell walls. A detailed Auger electron spectroscopy examination has been carried out on a section of an Al-3Li-10Be arc-cast alloy to determine the precise compositional variations. This approach is demonstrated to be a necessary prerequisite for selection of material for rapid solidification processing by techniques such as splat quenching.     

Modeling electrowinning process in an expanded bed electrode

A theoretical model has been developed to describe the flow behavior of conducting particles in a fluidized bed electrode for electro winning of metal ions present in the dilute solution. Model equations have been developed for potential and current distributions and mass transfer rates. The influence of operating parameters on particle growth has been critically examined. It has been observed from the present investigation that the particle size increased with electrolysis time. The present model simulations have been compared with the experimental data reported in the literature and observed that the model predictions satisfactorily match with the reported experimental findings.     

Effect of Notch Location on Fatigue Life Prediction of Strength Mismatched HSLA Steel Weldments

Welding of high strength low alloy steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) than the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the fatigue crack growth behaviour of weld metal (WM) and heat affected zone (HAZ) regions of under matched (UM), equal matched (EM) and over matched (OM) joints has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded metal arc welding (SMAW) process has been used to fabricate the butt joints. Centre cracked tension (CCT) specimen has been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading (R=0). A method has been proposed to predict the fatigue life of HSLA steel welds using fracture mechanics approach by incorporatin     

锅筒斜拉杆焊接接头失效原因分析

通过现场勘查及资料查阅,利用宏观检查、无损检测、金相检验、力学性能试验、化学成分分析、扫描电镜分析、电子能谱分析对锅炉缺陷试样的外观、裂纹状况、金相组织、强度、硬度、冲击韧性、塑性、化学元素含量、高倍显微形貌、裂口晶粒能谱等状况进行了分析。结果表明,这是一起罕见的低碳钢由于非金属硅元素含量超标,形成非金属夹杂物,导致焊接时在热影响区发生纵向热裂纹的质量事故。     

汽车定子盘开裂原因分析

某汽车制动系统定子盘使用不到六个月即在焊接热影响区部位发生开裂,采用金相检验、化学成分分析、硬度测试及断口分析等方法对该定子盘开裂的原因进行了分析。结果表明:引起开裂的主要原因是焊接区域及母材应力集中严重,加上焊缝与母材熔合不良,定子盘在使用过程中承受扭力,最终造成了疲劳开裂。     

金属增材制造中微观组织相场法模拟研究进展

金属增材制造技术是近30年发展起来的一项具有战略意义的先进制造技术。目前对增材制造的研究主要集中在制造装备与控制系统研发、产品性能测试等方面,对构件内微观组织的形成以及宏微观结构性能的关系研究较少。本文简要介绍了金属增材制造发展现状以及在微观组织演化方面研究的不足,揭示了微观组织演化研究的重要性和迫切性。针对相场法的基本原理和优势,着重分析相场法应用于金属增材制造中的模型选取、非材料物性参数的确定等问题及解决方法,从相场数值模拟的角度来探讨工艺参数对微观组织的影响。文章最后指出利用相场法模拟金属增材制造过程中微观组织演化符合未来的发展趋势。     

轴承套圈开裂原因分析

采用金相检验、断口分析和化学成分分析以及硬度测试等试验方法对某大型设备上的轴承套圈的开裂原因进行了分析。结果表明：该轴承套圈材料100CrMo7-3成分符合标准要求,基体硬度约60HRC,在使用过程中由于接触应力和循环应力场的共同作用,导致该轴承套圈发生接触疲劳开裂。     

K418B合金细晶铸造整体涡轮真空热处理工艺研究

通过力学性能评估和金相组织观察，研究五种热处理制度，两个周期的试验结果，确定了Ｋ４１８Ｂ合金细晶铸造整体涡轮的真空热处理工艺。