Advanced Inspection Methods 2

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Advanced Inspection Methods 2

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Exercise 2 (20 marks) (LO: a-f) (a) For ultrasonic testing, a circular transducer with diameter 14 mm and operating frequency 2 MHz is used at normal incidence on an aluminium test object. i. What is the near field distance of the transducer? (3 marks) ii. The angular divergence of the beam from a circular transducer follows the formula siny = 1.2 The probe was characterised in a zero degree configuration on a aluminium test block 35 mm thick. At what off-axis distance from the probe axis does the acoustic pressure become zero at the back wall of the test block? (3 marks)
(b) A 70° miniature probe, diameter 6 mm, frequency 4 MHz, was used to inspect a steel component (v = 3240 m s´¹). See Figure below. A double V groove butt weld in steel plate 19 mm thick showed a near surface defect at the fusion face of the weld, apparently lack of fusion, at a depth of 3 mm from the opposite surface. Further action was taken to confirm whether the indication was genuine. One action taken was to flush the weld cap so that the weld was level with the surface of the metal. When the ultrasonic test was repeated, the indication had disappeared. Give an explanation of how this false indication could come about. Include a sketch diagram. (8 marks)
Depth: 3mm 100% 80% 60% 40% 20% Sound Path 45mm to 48mm Central sound beam Aeff A- CRT 1 T19mm (c) The effective aperture of a phased array probe on a wedge is given by cos ß cos a where a is the beam angle in the wedge and ß is the beam angle in the specimen, and A is the active aperture. The phased array has 32 elements at pitch of 0.6 mm, and is used on a wedge with an angle of 20°. If the velocity in the wedge is 2700 m s-¹ and the velocity in steel is 5960 m s¹, what is the effective aperture for this array? (6 marks)