Ramp hold unload scheme would significantly reduce

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ramp-hold-unload scheme would significantly reduce the burst pressures. Results The acoustic emission test data from the first fiberglass epoxy bottle 24,25,33 were of no use because the thresholds for the four acoustic emission analyzer channels were set too low and the pressurization rate was too high. Consequently, the event rate was so large that the acoustic emission analyzer was unable to distinguish one event from the next and the output was recorded as one continuous event rather than a series of discrete events. The thresholds were subsequently increased to 60 dB and the pressurization rate was reduced to 70 MPa·s –1 (600 lb f ·in. –2 ·min –1 ). This allowed the internal microprocessor to operate just below its saturation point, which was about 40 hits per second per channel. Figure 28 is a plot of burst pressure versus high energy acoustic emission events (more than 500 counts) up to 5.17 MPa (750 lb f ·in. –2 gage), 25 percent of the design burst pressure, for the remaining 11 bottles. The low temperature data points are indicated by the hollow squares and the room temperature data points are plotted as triangles. A multiple linear regression analysis was performed using the variables listed in Table 4 to find a burst pressure prediction equation. The number of high energy acoustic emission events is a continuous variable and, as such, was represented by the appropriate numerical values for each bottle; the dummy variables 0 and 1 were used to describe the pressurization scheme, the burst 385 Aerospace Applications of Acoustic Emission Testing F IGURE 28. Burst pressure versus high energy acoustic emission events for 146 mm (5.75 in.) diameter bottles. Burst pressure, MPa (10 3 lb f ·in. –2 ) High energy acoustic emission events (>500 units) up to 5.17 MPa (750 lb f ·in. –2 ), 25 percent of design burst pressure 5 10 15 20 25 30 20 (2.9) 19 (2.8) 18 (2.6) 17 (2.5) 16 (2.3) 15 (2.2) 39-45 57-66 72-78 165-187 33-35 27-28 18-20 78-112 22-24 8-8 15-17 Legend = 0 °C (32 °F) = 21.1 °C (70 °F) = 43.3 °C (110 °F) T ABLE 4. Variables in multiple-regression analysis for 146 mm (5.75 in.) diameter bottles. Variable Class Specific Variable Detail Value Dependent (continuous) burst pressure (BP) Independent (continuous) high energy acoustic emisson events (HEE) Independent (categorical) pressurization scheme (PS) load-hold-unload 1 ramp to failure 0 transducer configuration (XDCR) four transducers 1 two transducers 0 burst temperature (T1 and T2) 273.2 K = 0 °C = 32 °F 0, 0 294.3 K = 21.1 °C = 70 °F 1, 0 316.5 K = 43.3 °C = 110 °F 0, 1
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temperature and the transducer configuration because these are categorical variables. 29 Numerical values were not assigned to the manufacturing discontinuities because it was assumed that their effect would be manifested in either an increase or a decrease in the number of high energy acoustic emission events. The data used in the linear regression are summarized in Table 5.
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  • Fall '19
  • Fighter aircraft, Nondestructive testing, Acoustic Emission, Acoustic Emission Testing

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