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A New Method to Evaluate Surface Defects with an Electromagnetic Acoustic Transducer.

Zhang K, Yi P, Li Y, Hui B, Zhang X - Sensors (Basel) (2015)

Bottom Line: Moreover, it can also reduce the influence of other factors, such as the lift-off, during the testing.Compared with other features, the theoretical and experimental results show that the feature lift-off slope has many advantages prior to the other features for evaluating the surface defect with the EMAT.Meanwhile, it is not essential to measure the signal without defects.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074, China. zhangkang@hust.edu.cn.

ABSTRACT
Characterizing a surface defect is very crucial in non-destructive testing (NDT). We employ an electromagnetic acoustic transducer (EMAT) to detect the surface defect of a nonmagnetic material. An appropriate feature that can avoid the interference of the human factor is vital for evaluating the crack quantitatively. Moreover, it can also reduce the influence of other factors, such as the lift-off, during the testing. In this paper, we conduct experiments at various depths of surface cracks in an aluminum plate, and a new feature, lift-off slope (LOS), is put forward for the theoretical and experimental analyses of the lift-off effect on the receiving signals. Besides, by changing the lift-off between the receiving probe and the sample for testing, a new method is adopted to evaluate surface defects with the EMAT. Compared with other features, the theoretical and experimental results show that the feature lift-off slope has many advantages prior to the other features for evaluating the surface defect with the EMAT. This can reduce the lift-off effect of one probe. Meanwhile, it is not essential to measure the signal without defects.

No MeSH data available.


Related in: MedlinePlus

The signal at lift-off of 0 mm, 1.0 mm and 2.0 mm of a defect depth of 0 mm.
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sensors-15-17420-f005: The signal at lift-off of 0 mm, 1.0 mm and 2.0 mm of a defect depth of 0 mm.

Mentions: When the lift-off increases, the signal decreases. Figure 5 and Figure 6 show the signal at different lift-offs of defect depths of 0 mm and 1.0 mm, respectively. The different lift-offs hr and the corresponding peak-to-peak logarithmic signals log(D) are fitted in the least squares method with MATLAB software. The relationship between hr and log(D) is plotted in Figure 7. Table 1 shows the slope of the fitting line and the correlation coefficient. With the increasing of the lift-off hr, the signal log(D) decreases. As a result, the correlation coefficients are negative. The minimum absolute value of the correlation coefficients is 0.9992, which is bigger than 0.99. This implies that the linearity of the lift-off hr and the logarithmic signal log(D) is very high. Therefore, it is reasonable to regard the relationship between hr and D as an exponential distribution, and this is verified in [15].


A New Method to Evaluate Surface Defects with an Electromagnetic Acoustic Transducer.

Zhang K, Yi P, Li Y, Hui B, Zhang X - Sensors (Basel) (2015)

The signal at lift-off of 0 mm, 1.0 mm and 2.0 mm of a defect depth of 0 mm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541941&req=5

sensors-15-17420-f005: The signal at lift-off of 0 mm, 1.0 mm and 2.0 mm of a defect depth of 0 mm.
Mentions: When the lift-off increases, the signal decreases. Figure 5 and Figure 6 show the signal at different lift-offs of defect depths of 0 mm and 1.0 mm, respectively. The different lift-offs hr and the corresponding peak-to-peak logarithmic signals log(D) are fitted in the least squares method with MATLAB software. The relationship between hr and log(D) is plotted in Figure 7. Table 1 shows the slope of the fitting line and the correlation coefficient. With the increasing of the lift-off hr, the signal log(D) decreases. As a result, the correlation coefficients are negative. The minimum absolute value of the correlation coefficients is 0.9992, which is bigger than 0.99. This implies that the linearity of the lift-off hr and the logarithmic signal log(D) is very high. Therefore, it is reasonable to regard the relationship between hr and D as an exponential distribution, and this is verified in [15].

Bottom Line: Moreover, it can also reduce the influence of other factors, such as the lift-off, during the testing.Compared with other features, the theoretical and experimental results show that the feature lift-off slope has many advantages prior to the other features for evaluating the surface defect with the EMAT.Meanwhile, it is not essential to measure the signal without defects.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan 430074, China. zhangkang@hust.edu.cn.

ABSTRACT
Characterizing a surface defect is very crucial in non-destructive testing (NDT). We employ an electromagnetic acoustic transducer (EMAT) to detect the surface defect of a nonmagnetic material. An appropriate feature that can avoid the interference of the human factor is vital for evaluating the crack quantitatively. Moreover, it can also reduce the influence of other factors, such as the lift-off, during the testing. In this paper, we conduct experiments at various depths of surface cracks in an aluminum plate, and a new feature, lift-off slope (LOS), is put forward for the theoretical and experimental analyses of the lift-off effect on the receiving signals. Besides, by changing the lift-off between the receiving probe and the sample for testing, a new method is adopted to evaluate surface defects with the EMAT. Compared with other features, the theoretical and experimental results show that the feature lift-off slope has many advantages prior to the other features for evaluating the surface defect with the EMAT. This can reduce the lift-off effect of one probe. Meanwhile, it is not essential to measure the signal without defects.

No MeSH data available.


Related in: MedlinePlus