Research on Exploratory Development of Nondestructive Methods for Crack Detection. Part III.
Annual rept. 1 Oct 68-30 Sep 69,
ARVIN SYSTEMS INC DAYTON OH
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Results of a research study devoted to exploratory development of a nondestructive method for crack detection are reported. The method investigated is based upon an Acoustic Impact Technique AIT, which consists of the analysis of the vibrations in the test specimens produced by mechanical pulses. The time-to-damp of these vibrations was the primary factor evaluated. General design considerations for the test probes are discussed. The possibility of improving the accuracy and sensitivity of the AIT by a Damping Decrement Computer was investigated and a breadboard model constructed. Fatigue crack investigations were performed and the AIT-measurements correlated with fatigue cycles, crack detection and crack growth. The test results presented indicate that changes in the material are detected before a microscopic crack can be observed on the surface of the fatigue sample. During a fatigue life time test on a specimen with Taper-Lok fasteners, cracks in the hole walls were indicated by the AIT and later verified after removing the fasteners. Tests on adhesively bonded interfaces in honeycomb, dual and multilayer assemblies proved that defects can be detected with the AIT and that the spatial location and the nature of defects can be determined through use of the appropriate frequencies. Author
- Test Facilities, Equipment and Methods
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