矩形脉冲涡流传感器参数变化对涡流分布影响的仿真分析

传统的圆柱形传感器在涡流检测中穿透深度较浅,同时检测灵敏度较低.本文采用矩形传感器进行了检测.在分析矩形涡流传感器榆测原理的基础上,采用大型电磁仿真软件ANsYS建立了脉冲涡流榆测模型,通过改变矩形传感器的尺寸参数和时间常数,研究了参数变化对铝板表面涡流分布以及铝板内涡流衰减的影响,仿真结果表明,铝板表丽均匀涡流区域的...     

Detection of the Subsurface Cracks in a Stainless Steel Plate Using Pulsed Eddy Current

The nondestructive method to detect subsurface defects is limited because conventional eddy current are concentrated near to the surfaces adjacent to the excitation coil. The PEC technique enables detection of cracks buried deeper under the surface with relatively small current density. In the present study, an attempt has been made to investigate detection of subsurface cracks using a specially designed double-D differential probe. The tested sample is a SS304 with a thickness of 5 mm; small EDM notches were machined in the test sample at different depths from the surface to simulate the sub surface cracks in a pipe. The designed PEC probe has two excitation coils and two detecting Hall-sensors. The difference between two sensors is the resultant PEC signal. The cracks under the surface were detected using peak amplitude of the detected pulse; in addition, for a clear understanding of the crack depth, the Fourier transform is applied. In time domain, the peak amplitude of the detected pulse is decreased, and in the frequency domain, the magnitude of the lower frequency component has been increased with an increase in the crack depth. The experimental results have indicated that the proposed differential probe has the potential to detect the sub surface cracks in a stainless steel structure.     

Evaluation of Equibiaxial Compressive Stress Introduced into Austenitic Stainless Steel Using an Eddy Current Method

Equibiaxial compressive residual stress is introduced into steel after peening in order to improve both its resistance to stress corrosion cracking and its fatigue strength. Thus, a nondestructive and relatively quick method to evaluate the equibiaxial compressive residual stress in a surface layer modified by peening is required in order to evaluate the peening intensity needed to enhance the integrity of structural components. The purpose of the work reported here is to establish an eddy current method to evaluate equibiaxial compressive stress which can be applied to the residual stress introduced into various non-ferromagnetic materials after peening. To this end, hydraulic jacks were used to elastically deform specimens of the austenitic stainless steel, Japanese Industrial Standard (JIS) SUS316L, thereby introducing an equibiaxial compressive stress. In the case of SUS316L steel, stress-induced martensitic transformation is rare. The electromagnetic properties of these specimens were then measured. In addition, the eddy current signals from peened specimens were compared with these. The results demonstrate that it is possible to establish a method for evaluating the equibiaxial stress utilizing eddy current signals.     

321不锈钢疲劳早期损伤的涡流评估

采用涡流阵列系统对321不锈钢疲劳早期损伤进行了检测与评估。整个疲劳过程中涡流幅值的变化分为快速增长、稳定和加速增长三个阶段。第一阶段的涡流幅值与循环周次对数之间有近似线性关系。在裂纹萌生寿命内,疲劳损伤区的大小与循环周次无关。对不同循环周次下321不锈钢试样的微结构分析表明疲劳早期涡流幅值变化的主要来源是材料内部位错的增殖和运动,而不是马氏体相转变。     

基于集成霍尔传感器的脉冲涡流无损检测装置

脉冲涡流是近几年新发展起来的一种无损检测技术 ,与传统涡流不同 ,脉冲涡流通过测量磁场最大值出现的时间来确定缺陷的位置。本文采用集成霍尔传感器来对脉冲涡流产生的磁场进行测量 ,试验结果证明集成霍尔传感器使用简单、灵敏度高 ,适于在低频时对弱磁场进行定量检测。     

Monitoring the State of Stainless Steel under Cyclic Deformation by the Acoustic and Eddy Current Methods

Measurement Techniques - The effect of the amplitude of deformation on the intensity of the change of the elastic and magnetic properties of austenitic stainless steel 12Kh18N10T was studied. It is...     

Induced Magnetic Field Used to Detect the Sigma Phase of a 2205 Duplex Stainless Steel

Sigma phases are formed due to heat treatments and/or welding processes during the solidification stage, and they are responsible for embrittlement of duplex stainless steels. Only a small amount of this phase promotes unfavorable mechanical properties and liability to corrosion. In this work, a new affordable approach to detect and follow-up the kinetics of the sigma phase transformation is evaluated. The measurements are based on an induced magnetic field generated through the interaction between an external magnetic field and the microstructure under study. To validate this approach, the induced magnetic field values are compared with the values of the Charpy impact energy, and the sigma phase is assessed by optical microscopy. Moreover, surface fractures are analyzed by scanning electron microscopy and X-ray diffraction. The results from the 2205 duplex stainless steel used show that there is a direct relation among the impact energy, fracture mechanism and induced magnetic field. The method proved to be able to follow up the embrittlement of the DSS successfully. Moreover, the results confirm that the presence of a sigma phase can be studied based on an induced magnetic field, even when in low amounts, and that a critical threshold value can be defined to monitor structures in service.     

The Use of Projection Methods of Multivariate Analysis in Eddy Current Thickness Measurement

Measurement Techniques - Multifrequency eddy current measurements of the thickness of non-magnetic metallic materials with dielectric coatings have been carried out. Based on the principal...     

基于脉冲涡流检测技术的缺陷定量检测研究

对飞机多层结构中出现的缺陷进行定量检测具有重要意义.文章将脉冲涡流检测技术应用其中,设计并实现了一套完整的脉冲涡流检测系统.在对检测信号进行分析处理的基础上,提取峰值、峰值时间、过零时间等时域特征量,实现对缺陷的定量检测,并通过进一步的实验加以验证.     

强流脉冲电子束表面处理对不锈钢316L耐蚀性能的影响

利用"Nadezhda-2"型强流脉冲电子束装置,以奥氏体不锈钢316L为实验材料,分别通过金相显微镜、X射线衍射、电子探针及电化学腐蚀仪等手段对处理后的样品进行组织分析和性能测试.结果表明,处理材料表层微晶粒尺寸明显细化(纳米化),同时形成显著的(111)晶面择优取向,表面层成分分布趋于均匀.上述脉冲强流电子束轰击诱发的材料组织、结构及成分分布变化构成不锈钢316L耐蚀性能提高的主要原因.     

强流脉冲电子束对4Cr13不锈钢的表面改性

为了改善4Cr13不锈钢的表面强度和耐磨性,对其进行了强流脉冲电子束表面辐照处理,研究了该处理对4Cr13的形貌、相结构、显微硬度及耐磨性能的影响。结果表明：电子束处理后,不锈钢表面出现多种形态的熔坑,20次脉冲处理时熔坑边缘出现了大量的变形孪晶;脉冲电子柬处理使不锈钢发生了由α相向γ相的转变,表层晶粒细化至纳米尺度;...     

脉冲涡流在飞机铆接结构无损检测中的应用研究

脉冲涡流是近几年发展起来的一种无损检测技术,主要用来对飞机机身多层铆接结构中出现的缺陷进行定量检测.本文采用霍尔传感器作为磁场测量器件,对铆钉周围出现的裂纹缺陷进行了检测,得出了缺陷位置和大小与检测特征量之间的关系,试验结果表明脉冲涡流是一种有效的检测飞机铆接结构缺陷的方法.     

脉冲涡流无损检测系统工作点的分析与研究

脉冲涡流检测技术(PEC)是近几年发展起来的一种新的无损检测方法。本文围绕应用于飞机多层金属结构中缺陷检测的脉冲涡流无损检测系统的工作点进行分析与研究,给出了传感器的参数设定;通过改变激励脉冲信号的重复频率和占空比,对得到检测信号的时域、频域特征量及其变化值进行数据分析和处理;最后给出了最优化的系统工作点,并通过进一步的实验给以验证。     

低频脉冲涡流技术对多层结构中腐蚀的定量检测

传统的涡流检测技术由于集肤效应的影响，很难有效的检测多层结构中的腐蚀缺陷。本文通过研究低频涡流与脉冲涡流技术，设计研制了一套完整的腐蚀缺陷检测分析系统。在对检测信号进行定量分析的基础上，通过峰值、过零时间等特征量实现了多层结构中腐蚀缺陷的定量检测。     

Influence of a Thick Stainless Steel Shell on the Field Waveform of a Pulsed Magnet

The coupling between a pulsed magnet coil and a coaxial stainless steel shell has been modelled by means of PMDS and ANSYS. The cylinder increases the equivalent resistance and reduces the equivalent inductance in the circuit, resulting in a decrease of peak field by up to 5%. Experiments have been carried out for a 10 T coil with and without the steel shell at room temperature. The results are in good agreement with the simulations.     

阵列式脉冲远场涡流管道缺陷检测方法

针对采用单个枪测线圈在管道缺陷检测中存在的检测分辨力较低的问题,研究了管道缺陷定量检测中的阵列式脉冲远场涡流检测技术.利用有限元仿真的方法对阵列传感器结构进行了优化设计,并且分析了不同深度缺陷对感应电压信号的影响规律.最后通过实验对仿真结果进行了验证,实验结果表明本文设计的阵列传感器具有较高的检测精度和灵敏度,可以实现对管道缺陷的定量检测.     

Development of an Eddy Current Inspection Technique with Surface Magnetization to Evaluate the Carburization Thickness of Ethylene Pyrolysis Furnace Tubes

An eddy current inspection system that incorporates a C-core probe and a direct current magnetizer for HP-grade ethylene pyrolysis tubes was developed to estimate the degree of carburization of the tubes. Through the development process, the characteristics of the B?CH curves and the electric conductivities of service-aged tubes were clarified, and a method of counteracting the external magnetism of the tube, which disturbs the accurate detection of the degree of tube carburization, by installing a direct current magnetizer was validated. The influence of tube external magnetism in the oxide/nitride layer was properly canceled by installing a magnetizer with a magnetizing current of 0.5?A on the external surface of the tube. In addition, a calibration curve correlating the carburization depth from the external surface of the tube with the normalized inductance was obtained by finite element analysis simulation. The calibration curve revealed that the degree of carburization could be quantitatively evaluated from the detected normalized inductance of service-aged tubes using the developed inspection system.     

Eddy Current Probe Parameters Identification Using a Genetic Algorithm and Simultaneous Perturbation Stochastic Approximation

This study tries to identify the coil parameters using numerical methods. The eddy current testing (ECT) is used for evaluation of a crack with the aid of numerical simulations by utilizing the identification of these parameters. In this study, a comparison of the performance of the GA and SPSA algorithms to identify the parameter values of the coil sensors are presented. So, the optimization probe geometry is introduced in the simulation with Three-dimensional finite element simulations (FLUX finite element code) were conducted to obtain eddy current signals resulting from a crack in a plate made of aluminium. The simulation results are compared with experimental measurements for the defect present in a plate.     

Investigation of Ablation Efficiency of Stainless Steel Using Pulsed Lasers in Burst Mode

Due to its high corrosion resistance and mechanical properties, stainless steel is commonly used in various industrial applications. Although different types of stainless steel are similar in their chemical composition, they can differ significantly in their thermal diffusivity. This property is relevant in the ability of a material to conduct heat and thus, in laser processing. In this frame, this study compares the ablation efficiency and characteristics of polished stainless steel samples of the alloys AISI 304, AISI 420, and AISI 316Ti. They are irradiated with single ultrashort pulses having pulse durations between 250 fs and 10 ps as well as using GHz burst modii. The goal is to investigate the differences in both the ablation threshold and the ablation rate to improve the ablation efficiency. The results show that shorter pulse durations lead to a more efficient ablation process. On the other hand, GHz bursts are found to be, in general, less efficient. In addition, there is a significant difference in the surface morphology depending on the process parameters. The differences in the thermal diffusivity do not significantly influence the ablation threshold fluence but surface morphology and the ablation rate.     

大长度大功率S304不锈钢护套矿物绝缘加热电缆缺陷分析

某石油勘探公司在对大长度大功率S304不锈钢护套矿物绝缘加热电缆试运行后,发现加热电缆无法在大功率高温度条件下长期作业,检查发现加热电缆不锈钢外护套表面存在线状缺陷。通过对电缆不锈钢外护套的宏观形貌、化学成分、微观组织和力学性能进行分析,确定了缺陷的性质及产生原因。结果表明:由于焊接和热处理工艺操作不当,使不锈钢外护套产生了多种缺陷,临近焊缝钢管咬边,壁厚出现减薄,钢管未焊透,焊缝根部区域存在裂纹;另制作外护套的不锈钢带存在严重敏化现象,并且有过量的冷加工变形。