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NON DESTRUCTIVE TESTING Flaw Detection Flaw Localization Type of Flaw Determination Flaw Dimension Estimation

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Flaw Detection Face AV=Front wall echo (FWE) Face AR=Back wall echo (BWE) d1d1 =Dimension of first flaw d2d2 =Dimension of second flaw CRT Display

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Flaw Localization The transducer is scanning until the maximum echo is obtained - The flaw is exactly below the transducer

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If the flaw is not perpendicular to beam wave direction : - The flaw can not be detected by using straight beam probe - The flaw can only be detected by using angle beam probe

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The transducer position must be changed for obtaining an echo If the flaw is perpendicular to the object surface - Use two transducers

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Type of Flaw Determination Planar flaw (cracks) more dangerous Volume flaw (voids, inclusions) less dangerous Change transducer orientation 10 o and observe the echo

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Flaw Dimension Estimation Amplitude Analysis - 6 db Drop Method - Comparison Method - DGS Method Time Analysis - TOFD Method Frequency Analysis - Ultrasonic Spectroscopy

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6 dB Drop Method - Flaw dimension > transducer diameter

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Comparison Method - Flaw dimension < transducer diameter - Using block references with flat bottom hole (FBH) - Flaw dimension is estimated by amplitude comparison - If the amplitude of flaw echo equal to the amplitude of FBH Flaw dimension diameter of FBH

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Distance Gain Scale (DGS) Method - D is distance of the flaw - A is amplitude of the echo - G is the ratio between flaw dimension and transducer diameter DGS graphic for far field

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DGS graphic for near field

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Time of Flight Diffraction (TOFD) Method - Measure the time propagation of diffraction waves from the crack tips V=Wave velocity d=Crack depth 2S=Transducer distance 2a=Crack dimension t 1, t 2 =Time propagation of diffracted waves

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TOFD method for oblique crack Using tandem transducer Measure time propagation for two positions of transducer Calculate the position of the crack tips Estimate the crack depth and orientation

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Problem No. 1 A surface crack is detected in a steel material. For estimating its dimension (h) and orientation ( ), a tandem system is used which consists of one transducer as transmitting transducer (T) and two transducers (R 1 and R 2 ) as receiving transducer. These transducer are transversal transducers with wave velocity of V T. The distances between them are a, b and c as shown at figure below. The time propagation from T to R 1 is t 1 whereas the time propagation from T to R 2 is t 2. a). Express the crack dimension and orientation as function of the wave velocity V T the distances (a, b and c) and the time propagation (t 1 and t 2 ). b). Calculate h and , if V T = 3230 m/s, a = 40 mm, b = 60 mm, c = 110 mm, t 1 = s and t 2 = s. Steel T R 1 a b h c R 2 x y z

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Steel T R 1 a b h c R 2 x y z

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Steel T R 1 a b h c R 2 x y z

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T(0,50)R1(80,50)R2(100,50) O(0,0) Assignment No. 1 An oblique crack is detected inside an aluminum material. For estimating its dimension (h) and orientation ( ), three transversal transducer with wave velocity of 3100 m/s are used. When these transducers are located at (0, 50), (80,50) and (100, 50) the time propagation measured are : t 1(T-R1) = 20.9 S, t 2(T-R1) = 24.6 S t 1(T-R2) = 21.8 S, t 2(T-R2) = 26.1 S. a). Design a computer program using MatLab for estimating the crack dimension and orientation. b). Calculate h and using the computer program.

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