共查询到20条相似文献,搜索用时 15 毫秒
1.
We have used three-dimensional (3D) magnetic finite element analysis (FEA) to simulate the MFL signal from a circular dent geometry with associated residual stresses. Strain distribution information around the dent was obtained from an earlier work using finite element structural modeling. In the magnetic FEA dent model, the localized residual stresses were simulated by assigning appropriate values of magnetic anisotropy to the relevant magnetic regions. The simulated flux leakage patterns were found to be in good agreement with the experimentally observed MFL patterns associated with dent shape as well as with the stress effects from the dent. 相似文献
2.
根据最新力磁理论,使用微型霍尔探头对R3碳钢进行漏磁检测。分析了在弱磁场和强磁场下施加应力后材料的漏磁信号变化。指出残余应力作用下中碳钢的漏磁信号会发生剧烈变化以及应力和漏磁信号之间的联系。预言了对应力集中进行漏磁检测的可行性。 相似文献
3.
The effects of uniaxial stress on the normal (radial) component of the magnetic flux leakage (MFL) signal induced by blind-hole defects for depths of 25%, 50% and 75% of the thickness of the pipe wall were investigated with a pipe wall flux density of 1.24 T. These three defects were on the same surface as the magnetizer and sensor for the MFL signal (near side). A fourth 50% defect was on the pipe wall surface opposite the sensor (far side). Changes of as much as 47% in the MFL signal due to stresses of up to 300 MPa were observed. Increased changes in the stress dependent MFL signal were observed with increasing defect depth. Comparison of the near side and far side 50% defects indicated similar changes in the MFLpp signal as a function of stress, although the shape of the MFL signals was qualitatively different. The stress dependent MFL signal was also investigated for the near side 50% defect for pipe wall flux densities between 0.65 T and 1.24 T. A linear increase in the effects of stress on the MFL signal with increasing flux density was observed. Results demonstrated that the variation of the MFL signal with stress is primarily a bulk stress effect, although the effect of defect-induced stress concentrations upon the various MFL signals investigated could also be observed. 相似文献
4.
5.
Magnetic flux leakage (MFL) is the most used technique for pipeline inspection, being applied through the use of instrumented PIGs. The pipe wall is magnetized and when metal loss or other irregularities occur, a larger fraction of the magnetic flux “leaks” outwards from the wall and is detected by sensors. MFL presents some limitations since it requires magnetic saturation of the pipe wall. Therefore, it is difficult to inspect small diameter and thick wall pipelines. Internal corrosion sensor (ICS) has been developed as a solution for internal corrosion measurements of thick walls. The technique, also called “field disturbance”, is based in a direct magnetic response from a small area of the wall. It is not necessary to achieve the magnetic saturation of the pipe material, and thus ICS performance is not affected by the thickness of the pipe wall. In the present work, finite element calculations are performed and the best resultant configuration of the sensor is proposed. Experimental tests with a prototype were carried out and the results give a strong indication of the validity of the theoretical model proposed for sizing. 相似文献
6.
7.
8.
The results of a study comparing residual magnetic field measurements to magnetic flux leakage (MFL) measurements as methods to detect broken pre-stressing steel are presented. Analysis of two- and three-dimensional magnetic field plots shows that the residual magnetic field technique has strong potential in this application, with detectable signals from a single broken wire on a seven strand cable being found up to 70 mm from the cable surface. MFL measurements with the same yoke produced detectable signals only when the cable was completely severed, indicating that the yoke was not driving the cable into saturation during the magnetisation process. However, the residual field technique was also found to be very sensitive to the technique used to magnetise the object being inspected, indicating that considerable care would be necessary to use the technique successfully in the field. 相似文献
9.
Magnetic easy axis predicted by the orientation distribution of the maximum amplitude of magnetic Barkhausen emission (MBE), which is obtained by magnetization in radial directions from the center of the specimens has been applied to determine the magnetic anisotropy on cold rolled and aged 304 SS in two sets of specimen. The maximum of the MBE has been found to orient along the rolling direction (RD) compared to the transverse direction (TD), indicating the presence of magnetic easy axis along the rolling direction for both sets. The strain induced martensite phase transformation has been determined using X-ray diffraction technique. The orientation distribution function (ODF) analysis has been carried out to obtain the crystallographic texture with cold rolling. ODF analysis revealed the 110 texture as the major. The magnetic anisotropy factor has also been determined with cold deformation and noticed that the strength of magnetic anisotropy decreases above 50% deformation for both the sets. Results have been explained considering two competitive effects, formation of crystallographic texture in the martensite phase and presence of compressive residual stresses along RD during cold rolling. 相似文献
10.
《Acta Materialia》2001,49(16):3231-3242
The role of crystallographic texture in determining the fracture behavior of a highly anisotropic ceramic, iron titanate, has been examined. By exploiting the anisotropy in its single crystal magnetic susceptibility, crystallographically textured and untextured iron titanate microstructures were formed by gelcasting in the presence and absence of a strong magnetic field, respectively. The magnetic field-assisted processing imparted a fiber-like texture to the processed ceramic material in which the crystallographic b-axes of the grains aligned parallel to the applied field. Triaxial residual stress and lattice parameter measurements showed that both the untextured and textured materials had undergone significant stress–relaxation, presumably due to spontaneous microcracking. Further, ‘aggregates’ of non-textured material were discovered within textured material that led to a population of meso-scale cracks (meso-cracks) in the microstructure oriented normal to the direction of alignment. Both crack populations were examined using a finite element simulation and confirmed by small angle neutron scattering measurements, and for meso-cracks, by X-ray tomography. Bend strength and R-curve behavior were evaluated as a function of texture and orientation in the magnetically processed materials. Strengths remained within 20% of that of the control material, except for one orientation, for which the strength decreased with increasing degree of texture due to favorably oriented meso-cracks. The R-curve behavior was highly anisotropic, with the peak fracture toughness of the magnetically processed material ranging from approximately equal to 2.5 times that of the control material. Additionally, the peak fracture toughness of each orientation increased with the degree of texture. Anisotropic fracture properties were related to interactions between the test crack and the population of meso-cracks. 相似文献
11.
Fernando Jose Gomes Landgraf 《JOM Journal of the Minerals, Metals and Materials Society》2012,64(7):764-771
The physical origins of the magnetic properties of nonoriented electrical steels; its relations to microstructural features like grain size, nonmetallic inclusions, dislocation density distribution, crystallographic texture, and residual stresses; and its processing by cold rolling and annealing are overviewed, using quantitative relations whenever available. 相似文献
12.
Experiment and simulation study of 3D magnetic field sensing for magnetic flux leakage defect characterisation 总被引:1,自引:0,他引:1
Magnetic flux leakage (MFL) testing is widely used to detect and characterise defects in pipelines, rail tracks and other structures. The measurement of the two field components perpendicular to the test surface and parallel to the applied field in MFL systems is well established. However, it is rarely effective when the shapes of the specimens and defects with respect to the applied field are arbitrary. In order to overcome the pitfalls of traditional MFL measurement, measurement of the three-dimensional (3D) magnetic field is proposed. The study is undertaken using extensive finite element analysis (FEA) focussing on the 3D distribution of magnetic fields for defect characterisation and employing a high sensitivity 3-axis magnetic field sensor in experimental study. Several MFL tests were undertaken on steel samples, including a section of rail track. The experimental and FEA test results show that data from not only the x- and z-axes but also y-axis can give comprehensive positional information about defects in terms of shape and orientation, being especially advantageous where the defect is aligned close to parallel to the applied field. The work concludes that 3D magnetic field sensing could be used to improve the defect characterisation capabilities of existing MFL systems, especially where defects have irregular geometries. 相似文献
13.
14.
K. H. Wang L. A. Blunt K. J. Stout 《International Journal of Machine Tools and Manufacture》1998,38(5-6)
Engineering surfaces are produced by a large number of manufacturing processes and once the processing is complete they are left with a surface texture which reflects the machining operation. Boring, turning, milling, grinding, lapping and honing are typical machining process, whilst roller burnishing and ballizing are typical of processes where improved surface finish as well as modified surface properties are required. These latter two processes, which have been in common usage for many years, have advantages which have not yet been fully explored. This includes the ability to deliberately impart negative residual stresses into the surface which are advantageous in improving the functional life of often stressed components as well as improved surface texture.The main purpose of this paper is to investigate the trends of roughness and residual stress related to the parameters of the ballizing process. This paper uses the 3-D surface evaluation techniques to characterise the ballized (engineered) surface and uses the ring cut-off method to calculate the residual stress on its circumference. This experimental methodology and analysis are used to show that: 1) The wall thickness of the ballized component and the interference amount are significant causes of roughness and residual stress. 2) The speed of the ball (velocity) going through the holes has a little effect on the roughness and residual stress. 相似文献
15.
针对由某公司生产首次应用到核电设备上的SA508-3钢,为了获得焊接残余应力分布及规律,采用ANSYS有限元软件对60 mm厚圆筒纵焊的焊接接头进行温度场及残余应力数值模拟,并将模拟结果与相同工艺条件下焊接试验结果进行比较验证.结果表明,模拟结果与试验结果基本吻合;焊接时热源周围极窄区域温度高,梯度大,远离热源温度峰值急剧下降;圆筒外表面残余应力大于内表面残余应力;焊缝及近焊缝区的残余拉应力值较大,远离焊缝中心残余拉应力值逐渐减小;圆筒两端和中部的残余应力在方向上或数值大小上不同;这对控制圆筒残余应力提供了理论依据. 相似文献
16.
Laser Powder Bed Fusion is a leading additive manufacturing technology, which has been used successfully with a range of lower melting point materials (titanium alloys, nickel alloys, steels). This work looks to extend its use to refractory metals, such as those considered in this paper where the behaviour of pure tungsten powder is investigated. A strategy for fabricating high density parts was developed by creating a process map in which the effect of laser energy density was studied. The process quality was assessed using different techniques including light optical microscopy, XCT, SEM and EBSD. The results showed that the laser energy density was adequate to process tungsten to produce functional parts. The bulk density and optically determined densities, under different process conditions, ranged from 94 to 98%, but there was evidence of micro cracks and defects in specimens due to micro- and macro-scale residual stress. Analysis of the microstructure and local crystallographic texture showed that the melt pool formed under the laser beam favoured solidification in a preferred orientation by an epitaxial growth mechanism. The EBSD local texture analysis of the tungsten specimens showed a <111>//Z preferential fibre texture, parallel to the build direction. 相似文献
17.
18.
19.
A hydraulic pressure vessel simulation of an operational length of pipeline was constructed to investigate the effects of line pressure stress conditions on Magnetic Flux Leakage (MFL) signals from elongated corrosion pits in API X70 steel line pipe. Two axially elongated corrosion pits were electrochemically milled into the pipe at different circumferential stress levels. Axially excited radial MFL fields were measured. The behaviour of both individual measurements and data trends were correlated with magnetic Barkhausen noise measurements around the perimeter of each defect. Results differ between the defect milled without an applied stress and the defect milled under an applied circumferential tension of 220 MPa. This indicates the need to account for the ambient stress conditions during defect formation in any MFL tool calibration technique. 相似文献
20.
The microstructure, texture, residual stress, and tensile properties of Mg–6 Zn–2 Y–1 La–0.5 Zr(wt%) magnesium alloy were investigated before and after extrusion process, which performed at 300 °C and 400 °C. The microstructural characterizations indicated that the as-cast alloy was comprised of α-Mg, Mg–Zn, Mg–Zn–La, and Mg–Zn–Y phases. During homogenization at 400 °C for 24 h, most of the secondary phases exhibited partial dissolution. Extrusion process led to a remarkable grain refi nement due to dynamic recrystallization(DRX). The degree of DRX and the DRXed grain size increased with increasing extrusion temperature. The homogenized alloy did not show a preferential crystallographic orientation, whereas the extruded alloys showed strong basal texture. The extrusion process led to a signifi cant improvement on the compressive residual stress and mechanical properties. The alloy extruded at 300 °C exhibited the highest basal texture intensity, the compressive residual stress and hardness, and yield and tensile strengths among the studied alloys. 相似文献