This paper aims to promote the engineering application of the metal magnetic memory (MMM) method, which is prone to interference from disturbing external magnetic fields. For this purpose, an enhanced MMM approach is proposed that highlights and enhances the useful magnetic signals through deliberate enhancement of the external field excitation, with the aim of improving the sensitivity and reliability of the detection system. Bearing in mind the non-linearity of the magnetic permeability curves for ferromagnetic materials, the feasibility of the enhanced MMM method is qualitatively analysed from a theoretical perspective and a real-time monitoring system is established to monitor the damage state of bolted joints based on the enhanced MMM method. The established system is then applied to the early prediction of the fracturing positions at the bolt holes. The results show that the enhanced MMM method can effectively and accurately predict the fracturing positions. The research findings lay a solid basis for the engineering application of the MMM method.
Original scientific paper Yield failure is a common failure mode of low carbon steels in practical engineering application, so detecting it timely and accurately is of great significance. Tensile tests were carried out under different loads which covered tensile elastic loads up to plastic deformation. Meanwhile, the normal components of spontaneous abnormal magnetic field, the H p (y) signals, were measured offline using the TSC-1M-4 type instrument. The correlation between the magnetic gradient K and the tension load F is discussed. The results show that the H p (y) signals, which change gradually from negative to positive, approach a straight line and have a unique zero-crossing point in the elastic stage, and the magnetic gradient K fluctuates with the load increasing. However, the distribution curve of the H p (y) signals has a peak and a trough in the yield stage, and the Lüders bands appear and expand as strain increases. The phenomenon of magnetic polarity reversal appears so that the magnetic gradient K changes from positive to negative, thus the mechanical state of the specimens can be judged from the magnetic gradient K.Keywords: magnetic domain; magnetic polarity reversal; metal magnetic memory; residual compressive stress; yield failure Praćenje izostanka popuštanja feromagnetskih materijala spontanim abnormalnim magnetskim signalima Izvorni znanstveni članak Izostanak popuštanja je uobičajena pojava kod nisko ugljičnih čelika u praktičnim inženjerskim primjenama pa je njegovo pravovremeno i točno otkrivanje od velike važnosti. Vlačni pokusi su se provodili pri različitim opterećenjima, od vlačnih elastičnih opterećenja do plastične deformacije. U međuvremenu, normalne komponente spontanog abnormalnog magnetskog polja, H p (y) signali, mjereni su samostalno, instrumentom tipa TSC-1M-4. Razmatrana je korelacija između magnetskog gradijenta K i opterećenja zbog vlaka F. Rezultati pokazuju da se H p (y) signali, koji se postepeno mijenjaju od negativnih do pozitivnih, približavaju ravnoj liniji i imaju jedinstvenu točku presjeka nultog izlaznog napona (zero-crossing point) u stadiju elastičnosti, i magnetski se gradijent K mijenja s porastom opterećenja. Međutim, krivulja raspodjele H p (y) signala dostiže vrhunac kod granice popuštanja i kako se povećava deformacija pojavljuju se i šire Lüders pojasi (Lüders bands). Javlja se fenomen promjene magnetskog polariteta tako da se magnetski gradijent K mijenja iz pozitivnog u negativni te se mehaničko stanje uzoraka može odrediti prema magnetskom gradijentu K.Ključne riječi: izostanak popuštanja; magnetsko područje; promjena magnetskog polariteta; magnetska memorija metala; zaostalo tlačno naprezanje
Aiming at the problems of the in-situ stress monitoring sensor such as susceptibility to lightning strikes and low accuracy, this paper attempts to design one extrinsic pressure sensor based on the optical fiber sensing technology and F-P interferometer. To this end, it first introduces the structural design of the sensor, which is mainly composed of sensitive diaphragm, single-mode fiber and ceramic ring. The use of silver-plated diaphragms in the air cavity can increase the light reflectivity, thereby improving the monitoring accuracy; the insulating anti-electromagnetic interference material can make the sensor less susceptible to lightning strikes and reduce the risk of damage to the sensor due to lightning strikes. Then, the ANSYS simulation software was used to statically analyze the silverplated diaphragm of the sensor, and obtain the ideal radius and thickness values of the silver-plated diaphragm. Furthermore, to verify the accuracy and lightning protection performance of the extrinsic fiber pressure sensor based on F-P cavity in actual stress measurement, an in-situ stress monitoring experiment platform and a simulated lightning strike experiment platform were built. The pressure and temperature calibration experiments and sensor stress loading simulation showed that the sensor has a cavity length change sensitivity of 1677nm/MPa within 0-10MPa and a stress measurement resolution of 60Pa; compared with the common fiber grating method for in-situ stress measurement, the monitoring accuracy of the designed sensor has improved about 3 times; the lightning strike experiment found by using a lightning surge generator that the designed sensor has a stable operating and anti-lightning performance under the test voltage of 0.5kV. The research findings shed light on the further study of F-P cavity-based extrinsic fiber pressure sensor.
Abstract:An integrated non destructive testing system using AMR magnetic sensor is manufactured which contains detection technology of metalmagnetic memory(MMM), magnetic flux leakage(MFL) and Barkhausen(MBN)in order to detect the defects of ferromagnetic materials rapidly. The test of 45 steel specimens with prefabricated cracks in different directions and stress concentration zone was carried out. The results show that the system can detect the defects sensitively and evaluate the stress concentration quantitatively.
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