Ultrasonic and Acoustic Emission Detection of Fatigue Damage.
Rept. no. 2 (Annual) 1 Mar 77-31 May 78,
JOHNS HOPKINS UNIV BALTIMORE MD DEPT OF MECHANICS AND MATERIALS SCIENCE
Pagination or Media Count:
The purpose of the present research is to optimize existing ultrasonic and acoustic emission techniques and to investigate new ones for early detection of fatigue damage in aluminum alloys used in aircraft construction. Ultrasonic attenuation measurements made simulataneously with fatigue tests on aircraft aluminum alloy bars and sheets gave warning of crack formation and eminent fracture much earlier than conventional ultrasonic methods. An acoustic emission characterization system has been designed and constructed to record waveform and frequency spectra of the acoustic emission signals obtained at various stages of a test specimens fatigue life. This sytem, which incorporates a capacitance transducer, permits superior characterization of acoustic emission signals unmodified by the detection transducer or by a videotape recorder. Use of an Admiralty Materials Laboratory AML acoustic emission transducer-cable-amplifier system permitted reliable acoustic emission measurements to be made during fatigue testing. The AML acoustic emission system and the ultrasonic attenuation system were used to simultaneously monitor the true rms-voltage of acoustic emission signals and changes in ultrasonic attenuation during fatigue testing of aluminum alloys bars. Author
- Metallurgy and Metallography