AE07.pdf

Two wide band differential integrated amplifier

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Two wide band differential integrated amplifier transducers were used along with the digital signal processing card to record the repair weld acoustic activity. During all weld repairs, the acoustic emission system timing, threshold and location parameters were set to the values provided in Table 1. The acoustic emission transducers were arranged to provide linear location capabilities along the length of each repair zone while allowing adequate room for the welder to work and enough separation from the weld zone to prevent heat damage to the transducers. The three transducer location sets are defined as A, B and C in Fig. 10. The transducers were bonded with hot melt glue 15 mm (7 in.) apart and 75 mm (3 in.) off the weld centerline as previously mentioned. The hot melt glue provided an added degree of protection from the weld heat by softening and releasing before the transducers could be damaged. Pencil breaks of 0.5 mm (0.02 in.) diameter graphite were performed after resetting the transducers for each repair zone to ensure that transducer coupling was consistent for each repair cycle. A good transducer bond was defined as one where graphite breaks that were 15 mm (0.6 in.) from the transducer produced a peak amplitude of 70 to 80 dB. In addition to the reweld test objects, diamond saw notched tensile test objects were low cycle fatigue loaded to generate clean crack signals, free from background weld noises, for comparison with the reweld network model. Here, the acoustic 236 Acoustic Emission Testing F IGURE 10. Transducer placement for weld repairs. 175 mm (7 in.) Transducer A(A) Transducer A(B) Transducer B(C) 100 mm (4 in.) 75 mm (3 in.) Position A Position B Position C 75 mm (3 in.) Transducer B(A) Transducer A(C) 600 mm (24 in.) Legend A, B, C = transducers (A), (B), (C) = transducer placements 175 mm (7 in.) 175 mm (7 in.) 75 mm (3 in.) 75 mm (3 in.) 75 mm (3 in.) 100 mm (4 in.) 100 mm (4 in.) Transducer B(B) 250 mm (10 in.) T ABLE 1. Acoustic emission system initialization settings for repair welds. Type Parameter Setting Acoustic emission peak definition time 1000 μs Acoustic emission hit definition time 2000 μs Acoustic emission hit lockout time 2000 μs Acoustic emission transducer gain 40 dB Acoustic emission threshold 45 dB Location wave speed 4.7 km·s –1 (5.55 × 10 7 ft·h –1 ) Location lockout 175 mm (7 in.) Location overcalibration 13 mm (0.5 in.)
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activity from five tensile coupons, cut from an aluminum lithium repair panel, were monitored with a single wide band differential integrated amplifier transducer connected to a signal processing card during the low cycle fatigue loading. The transducer was centered just above the weld line and again bonded to the test object with hot melt glue. The tensile test objects were made from a weld repair panel by cutting 25 mm (1.0 in.) wide strips perpendicular to the weld. A 2 mm (0.08 in.) deep notch was cut through the thickness of the test object with a diamond wheel saw to provide a crack initiation point. The test objects were gripped in a 138 MPa (2 × 10 4 lb f ·in. –2 ) tensile test machine and cycled to failure. The tensile tester was configured to provide a positive, tensile, sinusoidal loading of 0.2 Hz. The system
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