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.     

多层结构缺陷检测中的脉冲涡流磁场测量技术

脉冲涡流技术是一种可以对飞机多层结构中缺陷实施有效检测的方法。交变磁场测量技术是一种精确测量表面裂纹的非接触式无损检测方法。提出了脉冲涡流磁场测量（PECFM）技术,并对其进行了理论分析。在设计了相应传感器的基础上,对多层铝板结构中的缺陷进行了检测实验,实验结果与理论分析相一致。实验证明PECFM技术可以有效地实现多层结构中缺陷的识别与定量检测。可以预见,PECFM技术将会在无损检测领域中发挥很大的作用。     

铆接结构缺陷检测中的低频脉冲涡流技术

脉冲涡流是一种可以对飞机多层铆接结构中缺陷进行有效检测的无损检测技术。本文通过研究低频涡流与脉冲涡流检测技术,设计和实现了圆柱形差分检测传感器,对铆钉周围出现的缺陷进行了检测。通过轴向扫描时获得的峰值曲线对缺陷的轴向宽度进行了定量检测。通过缺陷的瞬态感应电压信号,利用峰值、过零时间等特征量对缺陷造成的不连续性和损耗程度进行了检测分析。试验结果证明文中设计的圆柱形差分传感器可以对多层铆接结构中的缺陷进行有效检测,低频脉冲技术在飞机铆接结构缺陷的检测中具有很好的使用前景。     

飞机结构腐蚀检测中的脉冲涡流无损检测技术

对脉冲涡流无损检测技术的工作原理进行了分析，建立了脉冲涡流的检测系统对加工的模拟飞机多层结构的试件进行了测试，提取其时域瞬态感应信号的峰值和过零时间作为特征量，对出现在飞机多层结构第二层中的腐蚀缺陷进行了定量检测，试验结果和理论分析相一致，证明了脉冲涡流检测方法的有效性，由于其具有快速和定量化的优点，因而在飞机结构的腐蚀检测中具有广阔的应用前景．     

铁磁性平板中不同走向裂纹脉冲远场涡流检测的仿真研究

远场涡流技术克服了传统涡流检测受集肤效应限制的不足，在铁磁性管道的检测中得到了广泛的应用。本文采用脉冲方波来激励探头，形成了铁磁性平板脉冲远场涡流检测新技术。首先分析了脉冲远场涡流的检测原理，然后采用ANSYS仿真软件建立了其仿真模型，仿真分析不同走向缺陷对空间磁场的扰动规律，对比分析了脉冲远场涡流技术对不同走向裂纹的检测灵敏度。研究结果对于深入明晰脉冲远场涡流的检测机理及传感器设计具有重要的理论价值。     

某型航空发动机篦齿盘裂纹的原位涡流检测

针对某型航空发动机篦齿盘上产生的裂纹缺陷,在不拆分发动机的前提下,提出采用涡流检测的方法对篦齿盘进行原位无损检测．设计完成了一套可用于篦齿盘裂纹原位检测的涡流无损检测系统．采用正交型锁相放大器对涡流检测信号进行处理,提高了信号检测精度同时达到了抑制干扰的作用．在标准检测试件和模拟试件上分别进行了试验,试验结果表明,该涡流检测系统可以实现航空发动机篦齿盘裂纹缺陷的原位检测,并且可以定性判断裂纹的深度．     

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.     

角焊缝表面裂纹的涡流热成像检测研究

压力管道中由于部分焊缝结构复杂、所处位置特殊,导致缺陷检测漏检率较大,对压力管道安全运行带来严重隐患.该文采用电涡流热成像技术研究带腐蚀层角焊缝表面裂纹检测的可行性.实验通过对T型角焊缝两道自然裂纹的检测,证明该方法对角焊缝表面裂纹检测有效.为进一步提高涡流热成像技术的检测灵敏度,利用主成分分析算法增强原始图像中的缺陷...     

基于电磁差动涡流传感器和FPGA的金属板探伤研究

为了研究电磁涡流无损检测技术在金属板损伤探测上的应用,根据电涡流检测原理,设计了基于电磁差动传感器和FPGA的检测系统,实现对涡流传感器的正弦激励和阻抗分析.对不同长度、深度和材质的缺陷金属板进行了实验探测.通过对采集信号的相敏解调发现了阻抗变化的特征值与金属缺陷特征的对应关系.理论分析和实验测试表明该系统能较准确地检测出金属表面及内部的损伤.     

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。     

Methodology of short fatigue crack detection by the eddy current method in a multi-layered metal aircraft structure

The field of non-destructive inspection (NDI) is an integral part of aircraft maintenance and service. It is optimal to apply the eddy current (EC) method on the complex multi-layered metal aircraft structure to detect cracks and other damage. A range of standard eddy current probes giving satisfactory results with respect to crack detection are available. However, these EC probes are not always suitable for the detection of short fatigue cracks hidden under a rivet head. This article presents a new methodology for eddy current inspection of a critical area on the wing. The development of the new methodology was inspired by a catastrophic glider accident in 2010. Because of this accident, all glider service was prohibited. The critical area is located in the structure of the wing spar, which consists of six layers. The position of the critical area is hidden under the countersunk rivet head in the third layer of the spar flange and under two layers of metal sheets. Thus, the actual location of the area is in the fourth layer, created by the countersunk rivet head. In addition, another rivet of a smaller diameter is inserted into the rivet in the flange. This article presents the work related to the development of a special EC probe that is able to measure in an operating frequency range between 200 Hz and 100 kHz with a single-value interpretation of the individual EC signals.     

Techniques for depth-selective,low-frequency eddy current analysis for SQUID-based nondestructive testing

Conventional eddy current techniques are widely used for detection of surface-breaking cracks in metal structures. These techniques have limited success in the detection of deep, nonsurface-breaking flaws that require low frequency eddy currents, for which inductive pick-up probes have drastically reduced sensitivity. High resolution, Superconducting QUantum Interference Device (SQUID) magnetometers, which are very sensitive to do or low frequency magnetic fields, have been developed for detection of subsurface flaws. We have now extended SQUID NDE by utilizing a sheet inducer to produce an extended eddy current parallel to the surface in a conducting plate. The magnitude of the induced current density inside the plate reduces with the depth; however, the current component at a certain phase angle may increase with the depth. At a particular phase angle, the current density on the surface becomes zero, while the current inside the plate is large, so that the magnetic signal at that phase angle due to the surface structures can be minimized. With this method, we have detected simulated cracks in the sides of plugged holes in a thick plate, a hidden corrosion area in a specimen which consisted of two painted aluminum plates joined with sealant, as well as crack defects adjacent to fasteners in the second layer of lap joined aluminum plates. We present a theoretical model for simulation of the phase-related magnetic signal due to a flaw, which shows the relation between the phase angle and the depth of the flaw. The theoretical phase analysis is compared with the experimental results.     

Eddy Current Probability of Detection for Mid-Bore and Corner Cracks in Bolt Holes of Service Material

Fatigue cracks are prone to develop around fasteners found in multilayer aluminum structures on aging aircraft. Probability of detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. Signal response to corner and mid-bore cracks by eddy current testing using standard split-D differential probes has been examined for in-service material from the horizontal stabilizer of a Hercules aircraft. Results are compared to data obtained from laboratory samples with drilled holes. Based on a logistic regression analysis, the results show no significant difference for a_90/95 (90% of the cracks of size a will be detected 95% of the time) for mid-bore crack length of 0.60 mm in this study compared to 0.62 mm in earlier work on drilled holes. However, there was a substantial loss of sensitivity for corner cracks. In this study on in-service material, the a_90/95 for corner cracks was 0.82 mm compared to 0.31 mm obtained from drilled holes. Decrease in sensitivity was attributed to damage at the hole’s corners of the in-service material, including rounding, folded metal, and burrs. Hole damage also significantly increased the risk of a false call.     

A Permeability-Measuring Magnetic Flux Leakage Method for Inner Surface Crack in Thick-Walled Steel Pipe

It is difficult for traditional magnetic flux leakage (MFL) methods to detect inner surface cracks of thick-walled steel pipe or plate due to magnetic shielding of the wall and strong magnetic background noise, and for eddy current testing (ECT) as well due to its skin effect. On the basis of the nonlinear magnetic permeability of ferromagnetic materials, a new non-destructive testing method (NDT) permeability-measuring magnetic flux leakage (P-MFL) is proposed, in which the magnetization is perpendicular to the inner surface crack, and the surface layer permeability distortion caused by magnetic field distortion is measured by differential pick-up coils. Afterwards, its detection mechanism is presented and analyzed, and its feasibility is verified by simulations and experiments. Finally, some application cases for steel pipe are also realized effectively. Meanwhile, its testing characteristics for cracks are given and effects of crack size, specimen thickness, scanning paths to testing signal amplitude are briefly analyzed. Finally, the proposed P-MFL method compared to traditional MFL method is discussed in detail.     

金属材料缺陷的电磁超声/涡流复合检测技术研究

电磁超声检测和涡流检测因其非接触、检测速度快、对试件表面要求低等优点而被广泛应用于金属材料的缺陷检测中,但电磁超声检测存在近表面的检测盲区,涡流检测对内部深层缺陷灵敏度不高。基于电磁超声和涡流的复合检测方法,设计了能同时满足电磁超声检测和涡流检测的复合式探头,建立了电磁超声和涡流复合检测有限元模型,并对金属试件中不同类型的缺陷进行了检测实验。仿真和实验结果表明,该复合探头不仅能快速检测表面裂纹,而且可激发出具有明显指向性的纵波,一定程度上削弱了波形转换产生的干扰波,可实现对内部缺陷的准确定位、识别,为电磁超声和涡流复合式检测技术在板材的复杂缺陷检测中的应用提供了基础。     

轨道车辆焊缝缺陷远场涡流检测系统设计及试验研究

轨道车辆工作环境恶劣,车体焊缝区域易出现缺陷,对车体焊缝开展无损检测工作,可有效保障行车安全.该文设计并研制轨道车辆焊缝缺陷远场涡流检测系统,该系统包括激励模块、信号调理模块、信号采集模块组成的硬件电路和基于LabVIEW编制的上位机软件;基于该系统开展轨道车辆铝合金焊缝、不锈钢焊缝远场涡流检测试验研究,研究结果表明:...     

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.     

空气耦合斜入射非线性检测方法研究

针对金属板结构微观缺陷难以检测的问题,提出一种基于空气耦合超声斜入射非线性微观缺陷的检测方法.首先通过数值分析的方法分别对垂直入射钢板与斜入射钢板时的透射率进行对比,并对3?mm厚钢板进行不同入射角的透射率对比试验.试验证明在斜入射条件下,超声波在钢板中因发生模态转换导致透射率增大.其次,利用空气耦合激励斜入射方法,对...     

钢坯表面裂纹的检测技术

表面裂纹的检测是生产高质量钢材的重要保证。目前,冶金企业已经开始应用一些检测技术对钢坯表面裂纹进行在线检测或离线检测。介绍了目前常用的几种钢坯表面裂纹检测技术的原理、特点、应用实例及其检测效果,这些技术包括涡流检测法、漏磁检测法、红外检测法和机器视觉检测法。在此基础上,总结了钢坯表面裂纹缺陷检测技术的发展方向。     

Enhancing Probability of Detection and Analysis of Bolt Hole Eddy Current

Fatigue cracks are prone to develop around fasteners found in multi-layer aluminum structures on ageing aircraft such as the CC-130 Hercules and CP-140 Aurora (P-3 Orion). Probability of Detection (POD) studies using eddy current techniques within the bolt holes contribute to risk assessments used in evaluating the serviceability of these aircraft. Improving POD by optimizing the inspection system can reduce the required frequency of inspections, since assurance of detection of smaller crack sizes extends the interval for which growth of cracks to a critical size may occur. In this work signal analysis and POD of laboratory grown fatigue cracks in the corners of bolt holes of 7075-T6 aluminum is examined. A number of parameters that enhance crack detection are identified, including the use of intimate contact probes versus steel sheath (non-contact), higher frequencies and the use of C-Scan display. Results demonstrate better detectability at 1600 kHz, than at the normally used 400 kHz, and enhanced recognition and assurance of identification of peak crack signal for data recorded and displayed in a C-Scan format. Results are compared with a previous POD study, which used current field techniques for detection.