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Magneto resistive (MR) sensors are suited for a wide range of different applications. Especially due to their small sizes and their frequency-independent behaviour, they are eligible candidates for non-destructive testing methods where high spatial resolution is required. The use of specialized magnetic field probes enables not only a defect evaluation, but also a localized characterization of ferromagnetic materials.
This paper presents some NDT (non-destructive testing) examples concerning magnetic flux leakage applications (MFL) and eddy current testing (ET). For MFL-testing we used an NDT-adapted GMR (Giant MR) sensor array for the detection of small inclusions in thin steel sheets. We also investigated the effects of microstructure on magnetic properties using GMR sensors. The ET-example describes an MR array probe consisting of 32 MR-elements, an ASIC, subsequent readout components and a one-wire excitation to generate eddy currents inside the material (developed in the EU-funded IMAGIC-project, 2011-2014, 7th Framework Programme). Using this MR-probe we achieved results with a better spatial resolved defect detection of neighbouring boreholes compared to “conventional” ET-probes.
Magneto resistive (MR) sensors are suited for a wide range of different applications. Especially due to their small sizes and their frequency-independent behaviour, they are eligible candidates for non-destructive testing methods where high spatial resolution is required. The use of specialized magnetic field probes enables not only a defect evaluation, but also a localized characterization of ferromagnetic materials.
This paper presents some NDT (non-destructive testing) examples concerning magnetic flux leakage applications (MFL) and eddy current testing (ET). For MFL-testing we used an NDT-adapted GMR (Giant MR) sensor array for the detection of small inclusions in thin steel sheets. We also investigated the effects of microstructure on magnetic properties using GMR sensors. The ET-example describes an MR array probe consisting of 32 MR-elements, an ASIC, subsequent readout components and a one-wire excitation to generate eddy currents inside the material (developed in the EU-funded IMAGIC-project , 2011-2014, 7th Framework Programme). Using this MR-probe we achieved results with a better spatial resolved defect detection of neighbouring boreholes compared to “conventional” ET-probes.
Since 1999 there has been a continuous development of non-destructive head check inspection. Especially in case of modern rail inspection systems, high demands on a fast, detailed detection and classification of defects called for improved testing methods. Due to the large amount of different rail types and profiles, the adaptation and optimization of algorithms is still in progress. Additional data analysis is under devel-opment for combined eddy current and ultrasonic inspection methods. This presentation gives an over-view of further enhancement and linking of testing systems as well as data processing. Main foci of the development are an improved sensitivity and an increased reliability of the testing results. Also, additional information can be obtained like determination of local hardness and roughness of the rail as well as an enhanced resolution for locating of defects which will be part of the presented work.
Since 1999 there has been a continuous development of non-destructive head check inspection. Especially in case of modern rail inspection systems, high demands on a fast, detailed detection and classification of defects called for improved testing methods. Due to the large amount of different rail types and profiles, the adaptation and optimization of algorithms is still in progress. Additional data analysis is under devel-opment for combined eddy current and ultrasonic inspection methods. This presentation gives an over-view of further enhancement and linking of testing systems as well as data processing. Main foci of the development are an improved sensitivity and an increased reliability of the testing results. Also, addi-tional information can be obtained like determination of local hardness and roughness of the rail as well as an enhanced resolution for locating of defects which will be part of the presented work.
Composite pressure vessels consist of an internal liner (Steel, aluminum, or plastic) which stores the liquid or gas and CFRP (carbon fiber reinforced plastics) which serves as pressure resistance. These vessels comprise some advantages compared with conventional vessels made of steel or aluminum and their application grew strongly over the last decade. The reason for this trend is the tremendous weight saving.
However, the long-time behavior for filling and discharging cycles and the creep strength of composite vessels is not fully understood. Therefore, BAM started an internal project to investigate degradation of these material systems. Normally, high-frequency eddy current testing (HF-ET, f > 10 MHz) is deployed for CFRP due to the low conductivity of the fibers, which is in the order of 0.01 MS/s, and the capacitive coupling between them. Nevertheless, in some cases conventional ET can be applied.
Some first results using conventional ET for detecting leakages in the internal liners are already presented. This contribution gives an update of our investigation using both conventional and high-frequency ET. Therefore, we developed an ET equipment based on a vector network analyzer using frequencies between 300 kHz and 2 GHz. The focus concerns the study of the aging effects.
This paper discloses two high-sensitivity probes for Eddy Current Nondestructive Test (NDT) of buried and surface defects. These probes incorporate eight and 32 magnetoresistive sensors, respectively, which are optimized for high sensitivity and spatial resolution. The signal processing and interfacing are carried out by a full-custom application-specific integrated circuit (ASIC). The ASIC signal chain performs with a thermal input-referred noise of 30 nV/√Hz at 1 kHz, with 66 mW of power consumption, in a die with 3.7 × 3.4 mm 2 . NDT results are presented, showing that there is an increase in spatial resolution of surface defects when contrasted to prior art, enabling the probes to resolve defects with diameters of 0.44 mm, pitches of 0.6 mm, and minimum edge distance as low as 0.16 mm. The results also show that the probe for buried defects is a good all-round tool for detection of defects under cladding and multiple-plate flat junctions.
With rising popularity and availability of additive manufacturing (AM), companies mainly in the aerospace sector, set high requirements on quality control of AM parts, especially produced with selective laser melting (SLM). Since it was shown that those parts are prawn to flaws like pores or cracks, every part needs to be tested. Therefore, NDT Methods, like eddy current testing (ET), could help to characterize SLM parts. Research on ET has shown, that offline ET with high spatial resolution MR (magneto resistive) sensor arrays is possible and that flaws as small as 50 µm could be detected while significantly reducing testing time. A first approach on automated online ET method for testing SLM parts is proposed in this contribution.
Composite pressure vessels for transporting dangerous goods and for hydrogen and natural gas vehicles consist of a load-bearing composite and a gas-tight, metallic or polymeric barrier layer (liner). To investigate the aging behavior of such composite pressure vessels, BAM carried out the interdisciplinary project COD-AGE. The aim of the project was the development of methods and models for the description and determination of the aging behavior of carbon fiber composites using the example of pressure vessels in order to better predict aging and safe working life. One focus of this project was the provision of suitable NDT methods. These included both test-related tests and the possible development of test equipment for later practical use.
In the lecture, test results of the age-related eddy current test on composite pressure vessels are presented.
In aging tests, pressure vessels made of an approximately 4 mm thick aluminum liner and approx. 8 mm thick CFRP layer were examined. Typical application of such pressure vessels are respiratory protective devices of the fire department. The pressure vessels were tested using conventional eddy current technology from the outer and inner side as well as with high-frequency eddy current technology. Both damage to the metallic liner and structures of the CFRP could be detected. A particular mechanical challenge was the inspection of the inside of the liners, since a cylindrical surface with an inside diameter of 150 mm has to be tested with an access of only 15 mm diameter.
Non-destructive testing for surface crack detection and head check depth quantification at the gauge cor-ner of railway tracks can be achieved using eddy current methods. With the extension of the tested zone to the running surface, rail defect signal types other than head checks can be measured. Due to their most-ly irregular shape, a quantitation based on a calibration against regular test cracks of varying depth may not be linear. Estimates of the expected influence of more complex crack patterns may be obtained by a finite element simulation of sufficiently simple limiting cases, like two displaced or intersecting cracks or a simply branched or flexed crack. As a first step, a 3D finite element model of the HC10 eddy current probe distributed by Prüftechnik Linke und Rühe (PLR), Germany was built and verified against meas-ured results from an (easily fabricated) reference block with isolated long cracks.