管壁缺陷的电磁超声检测技术实验研究

设计了一种基于电磁超声技术的管壁缺陷检测实验系统。系统激励并接收电磁超声信号,通过分析信号幅值的衰减实现管壁缺陷的检测及定位。介绍了系统的工作原理,收发分开的电磁超声换能器设计方法,硬件电路构成,软件设计方法及实验结果分析。该系统具有无需耦合,对试件表面质量要求不高等优点。     

点探头涡流无损检测中磁介质作用机理研究

结合实际涡流无损检测应用中的含磁介质点探头的特点,分析了探头中磁介质引入的各种附加效应及其对缺陷阻抗的影响。通过引入等效电流的概念,讨论了磁介质对涡流场的作用,建立含磁介质点探头涡流无损检测模型,并给出含磁介质探头周围的电磁场方程,求得均匀半无限导体系统的磁矢量势分布和导体中涡流、电场强度分布。通过实例,计算了非铁磁性导体中无缺陷时探头信号与提离高度的关系、存在缺陷时探头阻抗变化的特点。理论计算与实验结果基本吻合。     

亚表面缺陷的实时成像检测

提出一种适合于金属亚表面缺陷的可视化无损检测方法——磁光/脉冲涡流成像方法。该方法以脉冲信号激励产生涡流,以激光对被检测物体的照射取代传统涡流检测的线圈探头,通过磁光传感元件将缺陷引起的磁场变化转换成相应的光强度的变化,由传统的显微镜、照明系统、偏振器和CCD图像传感器组成的光学系统将光强变化转换为“明”或“暗”图像,实现了对缺陷的实时成像检测。本文论述了磁光/脉冲涡流实时成像检测机理,给出了一种实验装置。通过对金属表面/亚表面缺陷实验,表明该检测方法快速、准确,可实现微/纳米级缺陷的成像检测。     

铁磁性管道腐蚀远场涡流检测性能的改进

远场涡流检测由于信号微弱、探头过长等缺点限制了其进一步应用.本文结合有限元仿真和实验方法,研究了改进远场涡流技术性能的几种方法,即: 采用电磁屏蔽、磁路进行传感器优化设计以缩短探头长度、增大信号强度;改进信号调理电路以提高细微缺陷检出能力;利用同态滤波、小波变换以及误差修正等数字信号处理技术确保检测结果的可靠性.实验结果表明,采用上述方法后系统性能得到很大提高,可以有效检测出管道外壁的细微缺陷.     

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.     

跑道型差动式涡流探头设计及其性能研究

针对传统差动式涡流探头几何尺寸大、缺陷检测灵敏度低的问题,在传统差动式涡流探头的基础上,设计了一种跑道型差动式涡流探头。它由激励线圈包裹2个尺寸相同、反向连接的感应线圈而构成。首先,利用COMSOL Multiphysics仿真软件建立了跑道型差动式涡流探头模型,比较了跑道型差动式涡流探头与传统差动式涡流探头涡流场分布的差异,并研究了在不同缺陷深度、不同扫查角度下2种差动式涡流探头的检测灵敏度。接着,制作了跑道型差动式涡流探头实物和碳钢板缺陷试件,利用试验测试的方法比较了跑道型和传统差动式涡流探头的检测灵敏度。试验结果表明,与传统差动式涡流探头相比,跑道型差动式涡流探头具有更紧凑的结构、更高的缺陷检测灵敏度。研究结果可为小尺寸、高精度差动式涡流探头的优化设计提供参考。     

细铜棒内部缺陷超声自动检测研究

叙述了用超声纵波探头和表面波探头两组探头对细铜棒内部缺陷进行检测，纵波探头采用双探头垂直入射，接收，表面波探头采用单探头进行补检，同时采用棒料周向转动和组合探头装置轴向步进扫描方式完成整个铜棒的全面检测实验。     

复合构件粘合质量超声多次脉冲反射检测方法

本文介绍了复合构件粘合质量的超声多次脉冲反射检测方法,该方法可以无损地检测出复合构件内部的脱粘或灌胶不到位等缺陷。所能检测的最小缺陷是:面积大小为探头直径的1/2、间隙厚度的量级为10~(-2)mm。在实际检测中所术用设备为CIS-36型全数字式超声波探伤仪和Φ10mm的2.5MHz直探头。     

基于矩形脉冲涡流传感器的表面缺陷定量评估及成像检测技术研究

本文介绍利用矩形脉冲涡流传感器的自差分特性来提高缺陷检测能力,并最终实现对表面缺陷的成像检测.采用ANSYS软件建立了矩形脉冲涡流传感器的仿真模型,对铝板表面涡流分布进行了仿真分析,结果表明:矩形传感器能够在铝板表面激励出均匀的感应涡流,当有缺陷存在时,提取Z向和Y向感应信号的幅值扫描曲线可以实现对表面缺陷长度和深度的定量.并对仿真结果进行了实验验证,得到了表面缺陷的成像结果.研究结果表明,该矩形脉冲涡流传感器可以很好的实现对表面缺陷的定量评估及成像检测.     

阻抗电压变换法无线涡流探头研究

研究的是一种无线涡流探头的设计。将探头线圈、激励源、信号调理电路集成于探头中,通过无线收发传输信号至仪器主机,可大大降低仪器的设计成本和体积,并提高涡流检测主机的探头兼容性,实现一套涡流仪接上各种不同探头就可对大多数工件探伤。解决传统涡流探伤仪在管材螺纹等环形工件检测的不便。检测电路采用阻抗电压变换法,检测涡流探头阻抗变化。使用该探头检测铁、铝两种材料缺陷,实验结果表明:经过调试之后发现,在提离效应和在对缺陷扫查过程中,本探头输出数据的变化很明显,并且这些变化可较容易将提离和缺陷区分出来,而且在对不同材料的工件进行检查时变化趋势及大小也有不同,这将为我们以后分析不同材料及缺陷提供帮助。     

飞机多层金属板隐藏缺陷远场涡流探头设计及试验研究

由于飞机多层金属板结构厚度大、复杂等特性,现有检测方法无法发现原位内部缺陷,对于多层板金属缺陷的检测一直都是航空无损检测的难题。远场涡流检测技术因打破趋肤效应的限制,涡流能量可穿透较厚的被测试件,对金属板结构中隐藏缺陷的检测具有潜在优势。该文针对飞机多层金属板隐藏裂纹的原位检测,建立多层金属板构件隐藏裂纹平面远场涡流检测有限元仿真模型,研究不同角度、不同深度裂纹检测幅值、相位的变化规律。为验证该仿真模型的正确性,开展远场涡流检测多层金属板的试验。试验结果表明:设计开发的远场涡流探头可检测埋深13 mm的裂纹缺陷,当裂纹倾斜角度为0°时,检测灵敏度最高,当裂纹倾斜角度为90°时,检测灵敏度最低,与仿真结果保持一致,且能够对缺陷进行精准定位,可为飞机多层金属板构件隐藏裂纹的定量检测提供依据。     

利用电磁超声横波检测二冷区尾端连铸坯壳厚度

使用电磁超声横波对二冷区尾端的连铸坯壳厚度进行检测,并建立了有限元仿真模型.选取Q235连铸小钢坯作为被测对象.为减小永磁铁的提离距离、在被测体内部生成更大的感应涡流,文章利用多物理场有限元仿真软件建立了一种不同于一般结构的电磁超声换能器仿真模型:圆柱形永磁体两侧并行排列螺旋线圈.分析了永磁铁尺寸对磁场涡流的影响以及电...     

Ultrasonic fatigue testing on notched and smooth specimens of ultrafine-grained steel

Ultrasonic and conventional electromagnetic resonance fatigue tests were conducted on notched and smooth specimens of ultrafine-grained steels. The notched specimens developed no internal fractures but showed a fatigue limit. In this case, ultrasonic fatigue testing showed good agreement with the electromagnetic resonance. The smooth specimens showed internal fractures after ultrasonic fatigue testing, but not during electromagnetic resonance testing. In the smooth specimens, ultrasonic fatigue testing showed a longer fatigue life. These results show that the frequency effect is negligible in surface fractures of notched specimens but not in smooth specimens. The frequency effect causes a change in type of fracture from surface fracture to internal fracture. Concerning the gigacycle fatigue properties, the ultrafine-grained steel shows a fatigue limit with notched specimens, whereas the fatigue limit can disappear with smooth specimens because of the internal fracture.     

A monitoring system for contact fatigue crack testing

A new monitoring system is developed to detect crack initiation and propagation in the surface layer during contact fatigue running. The magnetic head of a commercial tape recorder is used as a probe. A combination of leakage and eddy current methods is ussed for the contact roller specimen on the JPM-1 machine. Experimental results show that this system is very sensitive to artificial defects and can distinguish defects on the surface from those beneath the surface. The defect signals agree well with their positions. Testing of an ion-nitrided specimen shows that a tiny subsurface crack (∼ 1 μm), which can only be examined under a microscope with 200 × magnification, is observable with this system.     

复合材料层压板分层缺陷超声相控阵检测与评估

针对碳纤维增强树脂基复合材料分层缺陷的无损检测与评估问题,通过制备预埋分层缺陷的标准试样,利用超声相控阵技术对缺陷进行无损检测与定量评估,并对测量误差进行分析。首先,在层压板铺层中间埋入聚酰亚胺薄膜制备分层缺陷试样;然后,对试样进行超声相控阵检测,通过超声S扫和C扫图像对缺陷进行定性分析与定量测量,并结合声场仿真对检测误差进行分析。结果表明:所制备试样内分层缺陷形状规则、埋深及大小与预设一致;超声相控阵步进方向检测尺寸比较准确,而扫查方向尺寸误差较大;超声相控阵技术能够准确识别分层缺陷的形状、尺寸及位置,具有很高的检测精度,对较小缺陷具有很好的检测效果。     

Characterizing the performance of eddy current probes using photoinductive field-mapping

We present a new method for characterizing the performance of eddy current probes by mapping their electromagnetic fields. The technique is based on the photoinductive effect, the change in the impedance of an eddy current probe induced by laser heating of the material under the probe. The instrument we developed maps a probe's electric field distribution by scanning an infrared laser beam over a thin film of gold lying underneath the probe. Measurements of both photoinductive signals and flaw signals for a series of similar probes demonstrate that the impedance change caused by an electrical-discharge-machined (EDM) notch or a fatigue crack is proportional to the strength of the photoinductive signal. Thus, photoinductive measurements can supplant the use of artifact standards to calibrate eddy current probes. Furthermore, the shape and symmetry of the probe's field pattern can reveal defects in probe construction. By combining photoinductive measurements of a probe's field strength with a theoretical model, we are able to quantitatively predict the probe's performance under hypothetical conditions. To model commercial eddy current probes with ferrite cores, we developed a procedure to treat them as effective air-core probes. We obtained good agreement between the flaw signals calculated using this effective-coil approach and actual fatiguecrack signals measured with commercial probes. We also calculated probabilities of detection for target flaws in titanium alloys for a series of commercial probes. The results reveal how probe sensitivity can affect the reliability of an eddy current inspection.This article is dedicated to Professor Bertram A. Auld on the occasion of his 70th birthday and his retirement from Stanford University.     

Geometrically anisotropic probes: an improved eddy current technique

Geometrically anisotropic eddy current probes are a type of separate function probes especially fit to the detection of defects showing a preferential direction. This kind of flaw induces a coupling between the transmitter and the receiver by guiding eddy currents from the one to the other. On the other hand, this coupling will be almost non-existent in the presence of defects or spurious effects not displaying this geometrical particularity. Basic studies on an elementary two-coil set-up allow the acknowledgment of the intrinsic qualities of such probes: good signal-to-noise ratio, influence field practically constant on the whole defect length, ability to detect bridged defects, insensitivity to lift off. These results can be improved by achieving multicoils probes adapted to different kinds of problems. An application to continuous casting slabs testing yields very interesting results in the detection of cracks, while getting rid of the effect of oscillation marks with no need of any signal processing. These achievements are promising for the improvement of eddy current testing, in terms of detection sensitivity as well as of rapidity to obtain information.     

Theoretical Analysis and Numerical Simulation of the Feasibility of Inspecting Nonferromagnetic Conductors by an MFL Testing Apparatus

ABSTRACT

It has been widely accepted that the magnetic flux leakage (MFL) testing system can be applied only to the inspection of ferromagnetic materials. The possibility of using the MFL testing apparatus to inspect nonferromagnetic metals is discussed in this article. According to Faraday’s law of induction, eddy current rises in the conductor passing through the MFL magnetizer. The perturbation of eddy current and its corresponding magnetic field caused by defects are theoretically analyzed. Then, the finite element method is carried out to verify the theoretical analyses and extract the perturbed magnetic field signals. Furthermore, the influences of specimen conductivity and moving velocity on the detection signal amplitude are also simulated. The results show that the nonferromagnetic conductors are possible to be inspected by the MFL apparatus, and higher conductivity or inspection speed will facilitate the inspection.     

水利工程中金属焊缝缺陷的超声检测方法比较研究

为研究基于超声的无损探伤方法在水利工程金属结构焊缝缺陷识别中的应用,利用常规超声检测技术、超声相控阵技术、衍射时差法(Time of Flight Diffraction, TOFD)超声检测技术对水利工程金属结构焊接试块缺陷进行识别,分析了各种缺陷在超声无损探伤技术中的特征显示。研究结果表明:常规超声检测技术、TOFD检测技术均能对各种缺陷实现信号显示,超声相控阵检测技术对气孔和横向裂纹的显示不够明显,但对其它缺陷的检出效果较为明显;常规超声检测技术对操作人员的要求较高,对缺陷的定性困难,精度不高;TOFD检测结果中气孔和横向裂纹的显示呈现出一种特殊的弧形,有一定高度的内部裂纹和未熔合的信号由上下尖端衍射波组成,根部未焊透上下尖端信号不够明显;相控阵检测结果直观,可以较精确地测量缺陷的埋藏深度、自身高度、长度等,但在扫查点状缺陷或者与超声声束平行的裂纹缺陷时,检出率极低。     

纺织复合材料预制体成型过程无损检测技术研究进展

纺织复合材料多为各向异性材料,其力学性能很大程度上取决于成型后预制体内纤维的取向。为确保预制体成型后纤维的取向符合产品设计的要求,目前已有多种无损检测技术为纺织复合材料预制体成型过程及质量的检测提供服务。本文结合纺织复合材料预制体织造技术的发展趋势及预制体成型过程对无损检测的需求,就目前广泛用于科研和产业化生产当中的多种无损检测技术(包括接触式测量技术、光学检测技术、热成像检测技术、涡流检测技术、射线检测技术)进行了综述,总结各方法所具有的技术特点、应用情况与存在问题。最后,讨论了纺织复合材料预制体成型过程无损检测技术的发展趋势和面临的挑战。