斜角 및 位相配列 超音波探賞 信號와 誘導超音波 分散 豫測 技法에 關한 硏究 = (A)study on prediction methods of angle beam and phased array ultrasonic testing signals and guided wave dispersion

다국어 초록 (Multilingual Abstract)

Modeling of ultrasonic testing has been paid a great attention in nondestructive evaluation community since it can provide thorough understanding of underlying physics of ultrasonic testing.
In this study, new approaches to predicting angle beam and phased array ultrasonic testing signals are proposed for the reliable flaw signal identification and interpretation. Specifically, this paper present four new approaches including: 1) to verify the existing modeling method of ultrasonic testing at near critical angles, 2) to predict the angle beam ultrasonic testing signals from a surface breaking crack, 3) to calculate of phased array ultrasonic testing signals, and 4) to invoke guided wave ultrasonic testing dispersion.
The major results obtained from the present study are as follows.
1) Comparison of modeling approaches to ultrasonic testing at near critical angles
This study discusses the modeling of ultrasonic testing with oblique incidence at the near critical angles using two approaches based on either the multi-Gaussian beam or the Rayleigh-Sommerfeld integral. The theoretical models that can predict the reflection signals from side drilled cylindrical holes in solid specimen immersed in water are developed. Then, the theoretical predictions for the oblique incidence at the near critical angles are compared to the experiments for the investigation of model behavior.
2) Prediction of angle beam ultrasonic testing signals from a surface breaking crack
This study proposes a new modeling approach to predict the angle beam ultrasonic pulse-echo signals that can be captured from a surface breaking, vertical crack in a plate specimen in a computationally efficient manner. For this purpose, the 3-D multi-Gaussian beam models are adopted to describe the reflected beam fields from the crack surface and the specimen bottom surface as well as the radiating beam field from the transducer, and the geometry theory of diffraction and 2-D ray methods to calculate the diffracted beam field from the crack tip. In addition, the characteristics of the ultrasonic testing system are considered in terms of the system efficiency factor. By combining these three ingredients, the surface breaking crack signals are predicted at different interrogating positions. The accuracy of the proposed models is verified by the initial experiments.
3) Prediction of phased array ultrasonic testing signals
Very recently, it has been developed the expanded multi-Gaussian beam model that can calculate the radiation beam field from a single, rectangular transducer with great computational efficiency. In this study, this model is adopted to calculate the radiation beam field from phased array transducers with various time delays to achieve steering and/or focusing. The calculation results are compared to those obtained by well known Rayleigh-Sommerfeld integral that provides the exact solution in order to explore the validity of the expanded multi-Gaussian beam model. Also, this study proposes a complete model that can predict the phased array ultrasonic testing signals for a circular crack using the expanded multi-Gaussian beam model in a computationally efficient manner.
4) Prediction of guided wave ultrasonic testing dispersion
In this study, a new approach to obtain the dispersion curves of a bent cylindrical pipe and doughnut-shaped pipe is proposed by the combination of 3-dimensional finite element modeling and 2-dimensional Fourier transform. The transient responses of the bent pipe and doughnut-shaped pipe are calculated by using a general-purpose finite element program, and the displacements are extracted at a series of sequential points as a function of spatial position and time. Then 2-dimensional time domain data are transformed via 2-D FFT to invoke the relation between wave number and angular frequency so that the phase velocity and group velocity can be calculated. In addition, verification of the result is made by the mode identification using wavelet transform. The modes determined by both methods agree very well.

목차 (Table of Contents)

• 목차
• Nomenclature = ⅳ
• ListofTables = ⅶ
• ListofFigures = ⅷ
• 제1장 서론 = 1
• 1.1 연구 배경 = 1
• 1.2 연구목적 및 내용 = 5
• 1.3 연구 동향 = 8
• 제2장 관련이론 = 14
• 2.1 초음파탐상 시험 측정 모델 = 15
• 2.2 초음파 탐촉자 방사음장 모델 = 16
• 2.2.1 Rayleigh-Sommerfeld 적분 = 16
• 2.2.2 다중가우시안 빔 모델 = 18
• 2.2.3 확장 다중가우시안 빔 모델 = 24
• 2.3 결함 산란음장 모델 = 28
• 2.3.1 Kirchhoff 근사법 = 28
• 2.3.2 기하학적 회절이론 = 32
• 2.4 시스템 효율인자 = 34
• 2.5 유도초음파 분산해석 = 37
• 2.5.1 탄성관에서 유도초음파 전파 = 37
• 2.5.2 분산선도 = 42
• 제3장 임계각 근처에서 방사음장 예측기법 비교 = 57
• 3.1 개요 = 57
• 3.2 2차원 원통형 결함에 대한 초음파탐상 신호 예측 = 58
• 3.3 방사음장 비교 = 60
• 3.4 예측신호와 실험신호 비교 = 61
• 3.5 요약 = 62
• 제4장 사각탐상시험의 표면개구 균열 신호 예측 = 73
• 4.1 개요 = 73
• 4.2 균열선단의 회절신호의 모델링 = 74
• 4.3 균열 모서리 신호 모델링 = 78
• 4.4 실험과의 비교 = 79
• 4.5 요약 = 80
• 제5장 위상배열 초음파탐상 신호 예측 = 88
• 5.1 개요 = 88
• 5.2 시간지연 계산 기법 = 89
• 5.2.1 단일매질에서의 시간지연 계산 = 89
• 5.2.2 이중매질에서의 시간지연의 계산 = 93
• 5.3 위상배열 탐촉자의 방사음장 = 96
• 5.3.1 단일 매질에서의 방사음장 계산 = 96
• 5.3.2 이중매질에서의 방사음장 = 100
• 5.3.3 이중매질 내의 전면반사 방사음장 = 102
• 5.4 위상배열 초음파탐상 시험 시스템 효율인자 = 103
• 5.5 위상배열 초음파탐상 시험 신호예측 = 105
• 5.5.1 단일매질에서의 신호예측 = 105
• 5.5.2 이중매질에서의 신호 예측 = 107
• 5.5.3 이중매질 내의 전면반사 신호예측 = 108
• 5.6 요약 = 110
• 제6장 유도초음파 분산선도 예측 = 138
• 6.1 개요 = 138
• 6.2 3-D FEM과 2-D FFT를 이용한 관에서의 유도초음파의 분산 해석 = 139
• 6.3 직관에서 유도초음파 분산예측 = 140
• 6.4 곡관에서 유도초음파 분산예측 = 143
• 6.5 도넛 모양 관에서 유도초음파 분산예측 = 144
• 6.6 요약 = 146
• 제7장 결론 = 163
• 참고문헌 = 166
• ABSTRACT = 173