Development of a non-contact stress measurement system during tensile testing using the electromagnetic acoustic transducer for a Lamb wave

In recent years, investigations into the changes in the microstructure of functional metal materials during their processing have been carried out by many researchers. Therefore, it is required that the change in the material characteristics during processing by a nondestructive evaluation method be evaluated. However, conventional technology has been restricted to a static material characteristic evaluation. For example, a strain gauge has the problem that it can influence the measurement conditions of the tensile test and can only evaluate the position at which the strain gauge is attached. We then tried to develop a non-contact stress measurement system for tensile testing using an EMAT with a Lamb wave as the first step for the material characterization evaluation during mechanical testing. The EMAT measures the propagation time of a Lamb wave between the receiver and a transmitter during the tensile testing. The interval between the transmitter and the receiver of the first set is 10 mm and can move in the direction of the tensile load. In this presentation, the specifications of the measurement system and the evaluation results are reported.     

A new electromagnetic acoustic transducer (EMAT) design for operation on rail

Electromagnetic acoustic transducers (EMATs) can emit and receive ultrasound on a conducting sample without contact, but are usually kept within 3 mm lift-off from the sample surface, to achieve a sufficient signal-to-noise ratio (SNR). There are scenarios under which EMATs must scan a sample at high speed, with the EMAT-sample separation varying by more than the standard lift-off range, such as for detection of gauge corner cracks in rail. A new EMAT has been designed that allows the low weight and flexible EMAT coil to skim over the sample surface, while the heavier and bulkier magnet behind the coil has a lift-off that can vary over 10 mm whilst still achieving a reasonable SNR. In experiments conducted with the EMATs mounted on a train, scanning a rail, they were demonstrated as being sufficiently robust, with an SNR sufficient for defect detection.     

电磁超声表面波换能器发射过程的精确建模与分析

针对具有曲折线圈结构的电磁超声表面波换能器模型精度较低问题,以铝合金板材表层缺陷检测为背景,在考虑交变磁场影响前提下,通过将有限元方法与解析法相结合,建立了一个精确描述电磁超声表面波换能器发射过程的三维模型。仿真分析表明,换能器在发射过程中产生的交变磁场可激发出两倍频率成分的表面波;该表面波分量能够有效提高换能器的缺陷敏感度;增加发射电流、降低提离距离均可显著增强该分量。试验验证了所建模型的有效性和精确性。     

Evaluation of stress corrosion cracking phenomenon in an AISI type 316LN stainless steel using acoustic emission technique

This paper deals with the analysis of the acoustic emission (AE) signals to determine the micro-process during stress corrosion cracking (SCC) of AISI type 316LN stainless steel that cause the AE, and thus the mechanism of the SCC process. AE with amplitudes ranging from 27.6 to 46.5 dB with different counts, energy and rise times occurred during SCC of type 316LN stainless steel in 45% MgCl₂ at 413 K. The analysis of the AE signals in conjunction with fractography indicated that a surge in the AE counts and energy indicated initiation of SCC. AE was found to be continuous prior to the initiation. The time gap between AE events increased during initiation. AE events occurred in bursts during crack growth. Plastic deformation ahead of the crack tip was determined to be the major source of AE during propagation of SCC in type 316LN stainless steel. The cracking was found to initiate and propagate in the transgranular mode.     

电磁超声传感器检测不同材质钢管的试验研究

通过试验确定了不同材质钢管的磁致伸缩曲线，得到了不同材质钢管缺陷检测的电磁超声传感器（EMAT）直流电磁铁的励磁电流与超声波幅值的关系，确定了最佳励磁电流，并得出其变化规律与磁致伸缩曲线变化趋势一致的结论。为电磁超声传感器设计和开发提供了依据。     

Optimum excitation signal for long-range inspection of steel wires by longitudinal waves

Optimization of an excitation signal is proposed for long-range inspection of thin steel wires by ultrasonic waves. Due to its sensitivity to flaws normal to the axial direction, a longitudinal wave is a useful tool for flaw detection of wires. We can launch and detect longitudinal waves at arbitrary positions on the wire by using electromagnetic acoustic transducers. The broadband pulse is suitable for achieving high spatial resolution in locating flaws. However, the dispersion of the longitudinal wave distorts the waveform, and consequently decreases the apparent signal amplitude. If the effect of the dispersion is removed, the signal to noise ratio can be expected to be improved and the high flaw detectability can be obtained. In this study, we suggest using the optimum excitation signal, which has been modified to compensate for the dispersion during the propagation of the assumed path length. It is possible that the flaw, which occupies 10% of the cross-sectional area of the wire, can easily be detected from a distance of 10 m.     

脉冲涡流和电磁声换能器双探头无损检测

在许多情况下，只应用一种NDT技术存在不足，这就迫使NDT操作人员使用一种以上的技术以保证检测出危害被检物使用寿命或功能的缺陷。但分别实施多种技术的检测，就会延长检验时间。介绍了一种新的NDT设施，采用两种不同的非接触无损检测技术进行互补，即电磁声换能器（EMAT）和脉冲涡流（PEC）探头。检测结果表明，脉冲涡流和电磁声换能器因是非接触，所以可应用于材料生产过程中的自动在线检验，也可用于在役检验。     

丙烯球罐底部排放阀连接螺栓断裂原因分析

对开裂和断裂的丙烯球罐底部排液阀连接螺栓进行了宏观和微观观察分析,结果表明,螺栓断裂起源于螺栓表面的晶间腐蚀,后以晶间型应力腐蚀开裂(SCC)扩展至断裂,腐蚀介质为SO4^2-和Cr^-对在大气中使用的奥氏体不锈钢螺栓产生SCC的原因进行了分析和讨论,并提出防止该螺栓断裂的工程措施。     

黄铜管开裂失效分析

采用扫描电和Ｘ－射线衍射等技术对黄铜管断口形貌和腐蚀产物等进行了较全面的分析。结果表明,黄铜管的开裂为氯离子引起的穿晶应力腐蚀开裂;为氯离子引起黄铜应力腐蚀开裂提供了实例。     

应力腐蚀机理研究的新进展

首先对近十年来在应力腐蚀机理研究中提出的主要新观点进行了评述,然后以作者近期关于应力腐蚀机理研究的结果为主,重点介绍了在溶解促进位错发射、增殖和运动及在应力腐蚀裂纹形核、扩展的透射电镜研究中取得的最新进展.最后提出了目前应力腐蚀机理研究中尚需进一步研究的问题.     

Stress corrosion cracking and hydrogen-induced cracking of amorphous Fe74.5Ni10Si3.5B9C2

Stress corrosion cracking (SCC) in NaCl solution and hydrogen-induced cracking (HIC) during dynamic charging of Fe_74.5Ni₁₀Si_3.5B₉C₂ amorphous alloy were investigated through sustained load tests. The normalized threshold stress of SCC was σ_SCC/σ_F=0.04, where σ_F is fracture strength in air. Anodic polarization and addition of As₂O₃ into the solution did not change σ_SCC/σ_F, but cathodic polarization increased σ_SCC/σ_F from 0.04 to 0.31. Cathodic polarization increased but anodic polarization decreased the time to failure during SCC at the constant load of σ=0.27σ_F.The normalized threshold stress of HIC, σ_HIC/σ_F, was linearly decreased with the increase in logarithm of hydrogen concentration (C₀) and kept a minimum constant when C₀ was larger than a critical value, i.e., σ_HIC/σ_F=1.58−0.36lnC₀ (C₀?74.4 wppm) and 0.1 (C₀?74.4 wppm). The threshold stress of HIC during dynamic charging with the maximum current was larger than that of SCC at open-circuit potential. Fracture surfaces of HIC were also different with that of SCC. Experiments indicated that SCC of the amorphous alloy in the NaCl solution is controlled by anodic dissolution process instead of hydrogen.     

环境断裂机理及控制措施

依据作者所在集体的研究结果,对材料环境断裂这种事故,仿医学,先简述“机理”,然后从事例介绍“控制措施”,这类似于“病理”及“医治案例”。     

The influence of a corrosive wood-cutting environment on the mechanical properties of hardmetal tools

The influence of a corrosive wood-cutting environment on the strength of hardmetals and on their behaviour under static loading conditions has been investigated. Two commercial hardmetals were tested, which differed in hard phase composition. The results show exposure to this environment to have a highly detrimental influence on the strength of both hardmetals investigated, due to localised corrosive attack which results in the formation of stress raisers. The relative loss in strength as a function of corrosion time is the same for both hardmetals. However, the performance of the two grades differ significantly when a static load is applied in this corrosive environment: the strength of the WC-Co grade remains unaffected by the applied load, while the grade containing a mixed carbide phase exhibits stress corrosion cracking which results in a further reduction in strength.     

富气反应器F316不锈钢变径管接头腐蚀破裂原因分析

用光学显微镜、扫描电镜、俄歇能谱等方法对Ｆ３１６不锈钢变径管开裂件进行了失效原因分析。结果表明,在高温高压的服役条件下,变径管接头焊接热影响在应力作用下,环境介质中Ｃｌ＾－１污染物是引起穿晶应力腐蚀破裂的主要因素。     

双相不锈钢在应力腐蚀开裂过程中的选择性腐蚀

铁素体－奥氏体双相不锈钢在Ｈ２Ｓ－Ｃｌ－Ｈ２Ｏ系统呵发生应力腐蚀开裂行为,为研究其开裂原因,用金相显微镜、电子探针、扫描电子显微镜等手段断裂试样进行分析。结果表明：在应力腐蚀开理解的过程中存在奥氏体相或铁素体相的选择性腐蚀;改变系统的ＰＨ值和Ｃｌ含量可使由铁素体和奥氏体构成的微电池的极性发生转变。     

电磁超声技术在焊缝检测中的应用

电磁超声技术利用洛伦兹力或磁致伸缩原理在金属或磁性材料中激发出超声波,它是一种超声无损检测新技术。相对于其他无损检测技术而言,电磁超声具有所有的超声检测的优势。声波的激发发生在材料的表面而不是在传感器内部。所以它与传统的基于压电换能器的超声检测相比,具有无需耦合剂、可非接触、可适用于超低温或超高温环境、有利于工业自动化以及可方便有效地实现横波检测及导波检测等优势。Innerspec Technologies公司致力于电磁超声技术的研发和应用,在近十几年中开发了150多台工业在线电磁超声检测系统,广泛应用于钢铁、汽车制造、石油天然气管道和压力容器等领域。作为一种超声波技术,电磁超声可以应用于各种厚度测量、缺陷检测以及材料表征。举例讨论了电磁超声在焊缝检测中的应用。第一个应用是利用导波对激光拼焊板的检测。第二个应用是电阻焊钢管的在线检测。利用沿着周向传播的超声导波对焊缝进行检测,克服了由于焊缝位置偏转对传统超声焊缝检测设备带来的困难。第三个应用是水平横波以及多通道电磁超声相控阵技术实现奥氏体不锈钢焊缝的检测。     

H62黄铜锥套的破裂分析

电气化铁道接触网产品接触线终端描固线夹中的锥套要求采用Ｈ６２黄铜材质,在全国大部分地区使用十多年,未见异常破环现象,但是近期在我国南方个别区域使用过程中发现了开裂破损。对这些开裂件进行分析研究,发现它们均是由应力腐蚀造成的破裂,就此提出了改进意见。     

Role of nitrite addition in chloride stress corrosion cracking of a super duplex stainless steel

This paper presents the role of addition of nitrite ions in susceptibility of a super duplex stainless steel, SAF 2507 to stress corrosion cracking (SCC) in chloride environment, which has a particular industrial relevance. Slow strain rate testing (SSRT) in 30 wt.% MgCl₂ solution established SCC susceptibility, as evidenced by post-SSRT fractography. However, the addition of nitrite has interesting influence. At their lower concentrations, nitrite additions seem to decrease SCC susceptibility, whereas, at a higher concentration, it has an accelerating effect on SCC. Attempts have been made to understand this behaviour on the basis of the role of nitrite in passivation and pitting characteristics of SAF 2507 in chloride solution.     

局部腐蚀作用下设备的寿命预测

综术字局部腐蚀和应力腐蚀破裂及点腐蚀作用下设备寿命预测技术的进展,由于局部腐蚀萌生、发展具有的内在的随机特征,以及设备长期服役过程中材料,环境等因素波上入的随机干扰,使得单一腐蚀微缺陷具有随机特征,需引入统计方法研究偶然性缺陷群体作用对材料宏观性能的影响。进行局部腐蚀设备寿命预测时,力学研究中对损伤演化及突变的处理方法值得借鉴。