共查询到20条相似文献，搜索用时 15 毫秒
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Sub-surface cracks present difficulties for eddy current methods as the skin effect causes currents to flow preferentially near the surface. This work examines graphite as a case study for the qualitative assessment of sub-surface cracks and employs multi-frequency eddy current techniques. The research has particular relevance to Advanced Gas-Cooled Reactors (AGR׳s) as during their operation there is the potential for cracks to develop within moderator bricks. This work reports that subsurface slots of 18% brick thickness can be detected. This work confirms these results with a parametric 3D finite element study. 相似文献
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利用有限元方法，对涡流检测中的电磁场问题进行数值计算，有助于涡流检测线圈的优化设计、检测缺陷的识别与定量，从而提高涡流检测的效果与精度。为验证有限元数值计算结果的有效性，对TEAM（Testing Electromagnetic Analysis Methods）组织提出的Workshop问题（Problem 15）进行了求解与分析。利用解析方法计算了空芯线圈的阻抗，然后通过二维有限元模型进行了阻抗求解，对比结果有较好的一致性。针对厚板上裂纹的涡流检测，建立了三维有限元计算模型，对影响计算结果的因素进行了分析，得到了比较好的数值模拟结果。 相似文献
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This paper proposes a novel method for accurately evaluating the depth of a defect using electromagnetic phenomena. The novel method induces AC currents inside a conductive medium and detects the disturbance of the currents. Whereas the principle itself has been utilized in conventional methods, the uniqueness of this new method lies in realizing a current distribution in which there is a region where currents near the surface and those deeply inside the specimen flow opposite to each other. The novel method provides a clear indication corresponding to the depth of the inspected defect. In addition, it enables one to evaluate the depth of a defect that is much deeper than the depth of penetration. After the physical background of this new method is explained, the results of experimental verifications and subsequent numerical simulations are presented. 相似文献
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Pingjie Huang Guangxin Zhang Zhaotong Wu Jinhui Cai Zekui Zhou 《NDT & E International》2006,39(7):578-584
The forward problem of eddy current detection of defects by scanning conductive multi-layered structures is investigated and the change of the probe coil impedance is modeled by using finite element analysis method. Based on the ANSYS software a fast simulating program is developed and then the coil impedance changes due to the existing of defects in different lengths, shapes and at different locations in conductive multi-layers are calculated. An experimental eddy current testing system combined with a scanner is established and scanning testing experiments are carried out. The simulation and experimental results are compared. The agreement of them shows that the technique studied is promising and can help us to understand the probe responses and can be applied to the inversion model to determine the defect parameters in many important fields ranging from aerospace to energy and transportation industries. 相似文献
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Saeed Kahrobaee Mehrdad KashefiAlireza Saheb Alam 《Surface & coatings technology》2011,205(16):4083-4088
From practical point of view, determining the decarburizing depth is important in quality control of steel parts as it has undesirable effects on the mechanical properties such as hardness, wear and fatigue resistance. Traditional destructive methods of determining the depth of decarburized layer include metallographic and hardness test which are time-consuming and costly. Since response to eddy current is sensitive to chemical composition as well as microstructure of the material under consideration, the non-destructive method can be used in determining the depth of the decarburized layer in steel parts. It is mainly due to the difference in the microstructures, and as a result, in the magnetic properties of the decarburized layer with other parts of the specimen. In the present study at the first step, the magnetic properties of decarburized carbon steel bars (0.45 wt.% C) were evaluated using an electromagnetic sensor and correlated with the microstructure changes from surface to the core of the sample. At the second step the steel bars were held in 900 °C for different period of times and the depth of decarburizing layers were measured using hardness testing. Finally, the non-destructive eddy current technique was used and the response of test samples to the induction current including primary and secondary voltages, normalized impedance, phase angle and harmonic analysis parameters were investigated. Results show an acceptable accuracy in comparison to the destructive method. 相似文献
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