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Compressed gas cylinder example a 470 mm 185 in

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Compressed Gas Cylinder Example A 470 mm (18.5 in.) diameter compressed gas cylinder was instrumented with nine transducers. Transducers 1, 2 and 3 were mounted around the circumference of the cylinder at the head-to-shell interface and equally spaced. A second ring of transducers numbered 4, 5 and 6 was χ 2 2 = ( ) Δ Δ t t i i ,obs ,calc Δ t X X Y Y X X Y Y v i i S i S S S = ( ) + ( ) ( ) + ( ) × 2 2 1 2 1 2 1 132 Acoustic Emission Testing F IGURE 13. Two-dimensional source location using three-hit event definition. 60 (2.4) 50 (2.0) 40 (1.6) 30 (1.2) 20 (0.8) 10 (0.4) 0 (0) Circumferential position in Y axis, mm (in.) 0 20 40 60 80 100 120 140 160 0 (0.8) (1.6) (2.4) (3.2) (4.0) (4.8) (5.6) (6.4) Longitudinal position in X axis, mm (in.) 3 2 6 5 4 1 7 8 9
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mounted 2 m (80 in.) away in the longitudinal direction and equally spaced around the circumference of the cylinder but offset from the first ring of transducers by 1047 mrad (60 deg). A third ring of transducers numbered 7, 8 and 9 was mounted at the other head-to-shell interface, 3.94 m (155 in.) from the first ring, equally spaced around the circumference and in line with transducers 1, 2 and 3. A series of 0.3 mm (0.12 in.), hardness 2, pencil graphite breaks, sometimes called pencil lead breaks (PLBs), were performed starting 250 mm (10 in.) away from the first ring of transducers and then every 125 mm (5 in.) after that to 3.5 m (140 in.) from the first ring of transducers. Two-dimensional source location was performed, restricting the event definition to only the first three hits detected. The results are shown in Fig. 13, where the cylinder is sliced open and laid flat for graphical presentation of the source location analysis. Nine transducers are shown numbered. The X axis represents the longitudinal axis of the cylinder and the Y axis represents the circumferential direction. Event positions are shown as dots. The pencil graphite breaks were performed along a line between transducers 2 and 8. The results are not very good: out of 94 pencil graphite breaks only 14 can be mapped (nine are visible in Fig. 13). The overall error in the source location analysis is caused by two problems. One is the error in the timing measurements and the other is the problem associated with restricting the event definition to just the first three arriving hits. Pencil graphite breaks executed close to the first ring of transducers will be detected first by the ring of transducers including 1, 2 and 3. These three transducers are all in one plane, making it difficult to calculate a source position even if the timing measurement has no error or very small error. This restriction was relaxed by allowing the source location algorithm to use four hits to calculate the pencil graphite break position. The results of this exercise are shown in Fig. 14, where immediate improvement is obvious. All 94 pencil graphite breaks are located for this 133 Acoustic Emission Source Location Circumferential position in Y axis, mm (in.) Longitudinal position in X axis, mm (in.) F IGURE 14. Two-dimensional source location using four-hit event definition, with same transducer locations as in Fig. 13.
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