EMAT and Eddy Current Dual Probe for Detecting Surface and Near-Surface Defects

2006 ◽  
Author(s):  
R. S. Edwards
Keyword(s):  
Eddy Current ◽  
Surface Defects ◽  
Near Surface ◽  
Dual Probe

Limitations of eddy current inspection in railway rail evaluation

2016 ◽  
Vol 232 (1) ◽  
pp. 121-129 ◽  
Author(s):  
Juho Rajamäki ◽  
Minnamari Vippola ◽  
Antti Nurmikolu ◽  
Tuomo Viitala
Keyword(s):  
Eddy Current ◽  
Surface Defects ◽  
Great Sensitivity ◽  
Rolling Contact ◽  
Electromagnetic Properties ◽  
Depth Of Penetration ◽  
Railway Network ◽  
Near Surface ◽  
Eddy Current Inspection ◽  
Deep Inspection

At the moment, one of the most cost-effective ways to inspect a whole railway network for rolling-contact fatigue is to carry out an eddy current inspection. It has a great sensitivity to even the smallest near surface defects, but this can also be a downside as it can lead to indications of deep damage from an array of tiny cracks. This can lead to overestimation of damage severity. Moreover, sizing of cracks in rails is unreliable due to the large number of parameters that affect the eddy current inspection response. The depth of penetration is of major importance in eddy current inspection, since cracks that are over this limit cannot be sized reliably. Deep inspection is desirable, but it is unattainable in practice, since signal-to-noise ratio decreases while penetration increases. Also, deep inspection is more affected by variations in steel’s electromagnetic properties. Furthermore, increasing inspection velocity will lead to decreased inspection depth. Most of the problems with eddy current inspection are related to the surface microstructure of the rail, and thus could be mitigated with a preliminary rail grinding. Therefore, eddy current inspection is best suited for maintenance quality control. However, eddy current inspection carried out with conventional equipment and without support from other methods gives only coarse estimate of the rails condition.

Limitations of eddy current inspection for the characterization of near-surface cracks in railheads

2021 ◽  
pp. 095440972110295
Author(s):  
Rayendra Anandika ◽  
Jan Lundberg
Keyword(s):  
Eddy Current ◽  
Surface Defects ◽  
Crack Depth ◽  
Surface Cracks ◽  
Important Conclusion ◽  
Near Surface ◽  
Eddy Current Inspection ◽  
Signal Response ◽  
Crack Profile

Eddy current (EC) testing is the most commonly used method to inspect near-surface cracks in railheads. Monitoring surface defects periodically is important to assess the track quality for serving daily operations. Nevertheless, despite being used in many countries, this method has limitations when characterizing cracks under the rail surface. Theoretically, EC testing is unreliable for the inspection of many cracks situated too close to each other in a concentrated location. This study has aimed to prove these limitations. EC signals from inspected cracks were compared with real crack profile parameters, i.e. depth and area, which were delivered by slicing the inspected cracked spots into 0.65 mm-thick pieces. The results show that the EC signal responses to the parameters of area and depth may lead to misleading measurements of the near-surface crack depth in the railhead. For instance, a shallower crack with a larger area can generate a higher EC signal response than a deeper crack with a smaller area. Another important conclusion is that the EC testing in this experiment could not be used to measure densely located cracks, which are those near-surface cracks which are typically found in a rail track.

Electron Channelling Contrast Imaging of Dislocations

1990 ◽  
Vol 48 (1) ◽  
pp. 600-601
Author(s):  
J.T. Czernuszka ◽  
N.J. Long ◽  
P.B. Hirsch
Keyword(s):  
Field Emission ◽  
Secondary Electron ◽  
Surface Defects ◽  
Spot Size ◽  
Beam Divergence ◽  
Contrast Imaging ◽  
Scattered Electron ◽  
Near Surface ◽  
Filter System ◽  
Electron Channelling

In the 1970s there was considerable interest in the development of the electron channelling contrast imaging (ECCI) technique for imaging near surface defects in bulk (electron opaque) specimens. The predictions of the theories were realised experimentally by Morin et al., who used a field emission gun (FEG) operating at 40-50kV and an energy filter such that only electrons which had lost no more than a few 100V were detected. This paper presents the results of a set of preliminary experiments which show that an energy filter system is unneccessary to image and characterise the Burgers vectors of dislocations in bulk specimens. The examples in the paper indicatethe general versatility of the technique.A VG HB501 STEM with a FEG was operated at 100kV. A single tilt cartridge was used in the reflection position of the microscope. A retractable back-scattered electron detector was fitted into the secondary electron port and positioned to within a few millimetres of the specimen. The image was acquired using a Synoptics Synergy framestore and digital scan generator and subsequently processed using Semper 6. The beam divergence with the specimen in this position was 2.5 mrads with a spot size of approximately 4nm. Electron channelling patterns were used to orientate the sample.

Direct Plan View FIB Liftout for Near-Surface Defect Analysis in TEM

2013 ◽  
Author(s):  
Max L. Lifson ◽  
Carla M. Chapman ◽  
D. Philip Pokrinchak ◽  
Phyllis J. Campbell ◽  
Greg S. Chrisman ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Silicon Germanium ◽  
Focused Ion Beam ◽  
Surface Defects ◽  
Ion Beam ◽  
Misfit Dislocations ◽  
Tem Analysis ◽  
Plan View ◽  
Near Surface ◽  
Straightforward Method

Abstract Plan view TEM imaging is a powerful technique for failure analysis and semiconductor process characterization. Sample preparation for near-surface defects requires additional care, as the surface of the sample needs to be protected to avoid unintentionally induced damage. This paper demonstrates a straightforward method to create plan view samples in a dual beam focused ion beam (FIB) for TEM studies of near-surface defects, such as misfit dislocations in heteroepitaxial growths. Results show that misfit dislocations are easily imaged in bright-field TEM and STEM for silicon-germanium epitaxial growth. Since FIB tools are ubiquitous in semiconductor failure analysis labs today, the plan view method presented provides a quick to implement, fast, consistent, and straightforward method of generating samples for TEM analysis. While this technique has been optimized for near-surface defects, it can be used with any application requiring plan view TEM analysis.

Reemitted positron spectroscopy of near-surface defects

1990 ◽  
Vol 42 (4) ◽  
pp. 1910-1916 ◽  
Author(s):  
T. McMullen ◽  
M. J. Stott
Keyword(s):  
Surface Defects ◽  
Near Surface ◽  
Positron Spectroscopy

Influence of Geometrical Features of Material Defects on the Identification Level by the Eddy Current Method

2015 ◽  
Vol 237 ◽  
pp. 136-141
Author(s):  
Wojciech Jóźwik ◽  
Tomasz Samborski
Keyword(s):  
Eddy Current ◽  
Surface Defects ◽  
Roller Bearing ◽  
Current Method ◽  
Eddy Current Method ◽  
Cross Sectional ◽  
Tapered Roller Bearing ◽  
Geometrical Features ◽  
Inner Surface ◽  
The Face

The article presents the results of the influence of geometrical features of defects in materials on the level of identification by the eddy current method. The study involved the inner ring of the tapered roller bearing. Four test defects, located at a constant distance from the inner surface, and a subsurface marker defect were performed in the treadmill of the tested ring. The test defects had a constant cross-sectional area in a perpendicular direction to the surface of the eddy current head. The geometrical features of each defect were the following: shape, the perimeter of the defect projected onto the surface of the ring, and the width and height of the defect projected on the face of the measuring head. The study involved an inner surface (subsurface defect detection) and external surface (the study of surface defects). It has been shown that the shape of the defect affects the level of detection using the eddy current method.

Near-surface defects in hydrogen-plasma-treated boron-doped silicon studied by positron beam spectroscopy

1999 ◽  
Vol 68 (6) ◽  
pp. 643-645 ◽  
Author(s):  
C.E. Gonzalez ◽  
S.C. Sharma ◽  
N. Hozhabri ◽  
D.Z. Chi ◽  
S. Ashok
Keyword(s):  
Surface Defects ◽  
Hydrogen Plasma ◽  
Positron Beam ◽  
Near Surface ◽  
Boron Doped ◽  
Doped Silicon

Passive Thermography for Detection of Damaging Events during Quasi-Static Tensile Testing

2019 ◽  
Vol 809 ◽  
pp. 581-586
Author(s):  
Vitalij Popow ◽  
Martin Gurka
Keyword(s):  
Test Specimen ◽  
Surface Defects ◽  
Influencing Factor ◽  
Tensile Tests ◽  
Fiber Reinforced Polymers ◽  
Failure Behavior ◽  
Fiber Reinforced ◽  
Near Surface ◽  
Fiber Reinforced Materials ◽  
Static Tensile

In order to determine the material properties of anisotropic continuous fiber-reinforced polymers, such as stiffness and strength, quasi-static tensile tests are carried out, in which the test specimen is subjected to a controlled load until failure. In opposite to ductile metals, exact localization of the failure on the test specimen or observation of the initial or final failure in time is not possible because of the brittle failure mechanism. The sample often breaks down into many small fragments. In order to get a deeper understanding of the failure behavior and to optimize the material and the design of the specimen, a characterization of the damage progress under load by passive thermography was implemented. This is a suitable method for the detection of near-surface defects and provides very promising results, especially in combination with sophisticated evaluation methods of active thermography. An important influencing factor is the analysis of the amount of energy released during a micro-damaging event. In this paper, we show an approach to increase the contrast of single damaging events and a possibility to visualize the damaging progress, especially for near-surface defects. The measurements were realized with continuously fiber-reinforced materials.

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