Cylindrical structures have been applied in various pressure vessels and weapon systems, which may be subjected to harsh environmental conditions such as large mechanical stresses and thermal stresses. As a result, non-destructive evaluation of such structures is critical in quality control. Among the various defects that may be generated during fabrication, transportation, operation/firing, and so on, surface crack is a critical one and needs to be quantitatively and accurately evaluated. In this study, both ultrasound phased array technique and eddy current technique are applied for the inspection of 120 mm steel test cylinder. In the cylinder, a total of nine sets of surface defects of various size, depth and orientation are fabricated and quantitatively evaluated.

In ultrasound phased array evaluation, simulations and experiments on standard aluminum block were carried out first to calibrate the system parameter setup. During this calibration, ultrasound propagation and its interaction with defects were simulated and studied. The dependence of ultrasound field on the ultrasound parameters and on the characteristics of defects was analyzed and optimized. Then simulations and experiments on steel test cylinder were carried out for the detection of the smallest detectable defects. Results showed that the optimization of the number of active elements can improve the distortion of defect images; the steering angles and the beam focusing laws may change the ultrasound beam intensity and uniformity, which has a significant influence on the sensitivity and resolution of the phased array technique; the geometry and material properties of cylindrical structures could distort the ultrasound beam, and as a result, calibration is necessary and important during practical inspections. Frequency is a key factor for phased array technique to improve its sensitivity.

In eddy current evaluation, a prototype for wireless eddy current system was designed, and an eddy current probe interface and a main unit interface were developed. The main advantages of such wireless probe are safety, economic benefits and maneuverability when compared to conventional wired probe. During testing, the signal at the probe interface was activated, measured, digitized and transmitted wirelessly to the main unit interface. Experimental results showed that the eddy current signals can be wirelessly communicated with main unit, and the results are comparable with the wired eddy current tester. Testing results also showed that the wireless signal is about 8 dB lower compared to wired signals and phase difference exists between the wired and wireless signals.

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