Development of eddy current probes based on magnetoresistive sensors arrays

Conference of 40th Annual Review of Progress in Quantitative Nondestructive Evaluation, QNDE 2013, Incorporating the 10th International Conference on Barkhausen and Micro-Magnetics, ICBM 2013 ; Conference Date: 21 July 2013 Through 26 July 2013; Conference Code:105840International audienceEddy Current Technique is a powerful method for detection of surface notches and of buried flaws during inspection of metallic parts. Recent EC array probes have demonstrated a fast and efficient control of large surfaces. Nevertheless, when the size of flaws decreases or the defect is rather deep, traditional winding coil probes turn out to be useless. Magnetoresistive sensors present the advantages of flat frequency response and micron size. These sensors are hence very attractive for the detection of buried defects that require low frequencies because of skin depth effect. An optimization of the probe with magnetoresistive sensors as receivers has been made by simulations using CIVA software and finite elements methods with OPERA. EC probes for buried flaw detection have been designed. Experimental results have been compared with simulations

Evaluation of High Spatial Resolution Imaging of Magnetic Stray Fields for Early Damage Detection

Metal magnetic memory (MMM) technique with associated ISO 24497-1:3 [1] is gaining considerable interest in the magnetic NDT community. In contrast to traditional Magnetic Flux Leakage (MFL) testing, the inspection objects are not intentionally magnetized by an external magnetic field [1,2]. Due to the physical coupling between mechanical stress and magnetization of ferromagnetic materials [3], it is assumed that the distribution of the residual MFL correspond to the internal stress of the specimen [2,4], or in the most general sense, to a degradation of the material [1,2]. Usually, MMM measurements are performed by relatively bulky magnetic inspection sensors [2]. The evaluation of local magnetic field distribution is limited thereby. High precision GMR (Giant Magneto Resistance) measurements in the micrometer regime can provide a higher degree of information due to better spatial resolution [5]. We present a concise summary of studies on the correlation of magnetic structure and microstructure of steels. In particular, we compare residual stress measurements in S235JRC steel welds by means of neutron diffraction with high resolution magnetic field mappings. Results indicate a qualitative correlation between residual stresses and local stray field variation. In addition, stray field measurements of plastically deformed specimens for quasi- static and cyclic loading cases are discussed. The present study concludes that GMR sensors can detect inhomogeneous plastic deformations of S235JR steel in a very early stage, without specific signal processing according to the ISO 24497-1:3

Influence of the Microstructure on Magnetic Stray Fields of Low Carbon Steel Welds

This study examines the relationship between the magnetic mesostructure with the microstructure of low carbon steel tungsten inert gas welds. Optical microscopy revealed variation in the microstructure of the parent material, in the heat affected and fusion zones, correlating with distinctive changes in the local magnetic stray fields measured with high spatial resolution giant magneto resistance sensors. In the vicinity of the heat affected zone high residual stresses were found using neutron diffraction. Notably, the gradients of von Mises stress and triaxial magnetic stray field modulus follow the same tendency transverse to the weld. In contrast, micro X ray fluorescence characterization indicated that local changes in element composition had no independent effect on magnetic stray field

Astrocytic expression of the chemokine receptor CXCR7/ACKR3 in the diseased CNS

Fulltext: Based on our previous demonstration of CXCR7 as the major mediator of CXCL12 signalling in cultured astrocytes, we have now characterized astrocytic CXCR7 expression in the diseased CNS and compared that to the expression of the second CXCL12 receptor, CXCR4. In the intact brain of adult rats CXCR7 and CXCR4 were expressed by GFAP-immunoreactive astrocytes forming the superficial glia limitans. Outside the glia limitans scattered and faint immunolabelling for CXCR7 and CXCR4 was present in very few additional GFAP-expressing astrocytes. In contrast to the restricted expression in the healthy CNS, a striking increase in CXCR7 expression was detectable in reactive astrocytes in rats with experimental brain infarcts (MCAO), in the spinal cord of rats with experimental autoimmune encephalomyelitis (EAE) as well as after mechanical compression. None of these pathologies was associated with substantial increases in astrocytic CXCR4 expression. Together, our findings favor the hypothesis of a crucial role of astrocytic CXCR7 in the progression of various CNS pathologies

Astrocytic expression of the chemokine receptor CXCR7/ACKR3 in the diseased CNS

Fulltext: Based on our previous demonstration of CXCR7 as the major mediator of CXCL12 signalling in cultured astrocytes, we have now characterized astrocytic CXCR7 expression in the diseased CNS and compared that to the expression of the second CXCL12 receptor, CXCR4. In the intact brain of adult rats CXCR7 and CXCR4 were expressed by GFAP-immunoreactive astrocytes forming the superficial glia limitans. Outside the glia limitans scattered and faint immunolabelling for CXCR7 and CXCR4 was present in very few additional GFAP-expressing astrocytes. In contrast to the restricted expression in the healthy CNS, a striking increase in CXCR7 expression was detectable in reactive astrocytes in rats with experimental brain infarcts (MCAO), in the spinal cord of rats with experimental autoimmune encephalomyelitis (EAE) as well as after mechanical compression. None of these pathologies was associated with substantial increases in astrocytic CXCR4 expression. Together, our findings favor the hypothesis of a crucial role of astrocytic CXCR7 in the progression of various CNS pathologies