AE13.pdf

Discontinuity that has a relatively large cross

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Discontinuity that has a relatively large cross section in one direction and a small or negligible cross section when viewed in a direction perpendicular to the first. (2) Propagating discontinuity caused by stresses such as heat treating or grinding. Difficult to detect unaided because of fineness of line and pattern (may have a radial or latticed appearance). 10 crack, cold: Crack that occurs after solidification, because of high stresses from nonuniform cooling. 10 crack, cooling: Crack resulting from uneven cooling after heating or hot rolling. Cooling cracks are usually deep and lie in a longitudinal direction but are usually not straight. 10 crack, fatigue: Progressive growth of a crack that usually develops on the surface and is caused by the repeated loading and unloading of the object. 10 crack, forging: Crack developed by forging at too low a temperature, resulting in rupturing of the material. 10 crack, hot: Crack that develops before the material has completely cooled, as contrasted with cold cracks that develop after solidification. 10 crack, quenching: During quenching of hot metal, rupture produced by more rapid cooling and contraction of one portion of a test object than occur in adjacent portions. 10 cumulative bursts: Number of bursts detected from the beginning of a test. 5 cumulative characteristic distribution: In acoustic emission signal processing, a display of the number of times a characteristic meets a preselected criterion. cumulative count: Number of times the amplitude of the signal has exceeded the threshold since the start of the test. 5 cumulative events: Number of events detected from the beginning of a test. D decibel (dB): Logarithmic unit for expressing relative signal power, such as the loudness of a sound, in proportion to the intensity of a reference signal. One tenth of a bel. Decibel in signal amplitude is twice that in signal power. Twenty decibels equals ten-fold voltage amplification. defect: Discontinuity whose size, shape, orientation or location (1) makes it detrimental to the useful service of its host object or (2) exceeds an accept/reject criterion of an applicable specification. 10,17 Note that some discontinuities may not exceed an accept/reject criterion and are therefore not defects. Compare crack; discontinuity; indication. 10 delta ( t ): Time interval between the detected arrival of an acoustic emission wave at two sensors. 5 Also called time differential or difference in time of arrival. differential amplifier: Amplifier whose output signal is proportional to the mathematical difference between two input signals. 10,16 discontinuity: Interruption in the physical structure or configuration of a test object. After nondestructive testing, discontinuities can be interpreted to be flaws or defects. 10 See defect and indication.
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  • Fall '19
  • Nondestructive testing, Acoustic Emission

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