The work presented here evaluates the validity of using the load at the point of linearity on the displacement load curve, as suggested by Elber, as an experimental measure of the crack-tip-opening Displacement-load behavior was investigated for a fatigue-cracked modified compact specimen of a nickel-base superalloy. Displacements were determined at the notch mouth using a standard clip-on gage, along the crack sufrace using a laser-interferometric displacement gage and, in the plastic zone ahead of the crack, using an optical- interferometry technique. Acoustic-emission monitoring was employed as a means to detect potential crack extension during measurement-load cycles and to detect physical- crack closure. The magnitude of the crack-tip-opening as determined from these measurements, is dependent on the distance from the crack tip at which the measurement is made. As an additional means of evaluating the crack-tip-opening load, crack-surface profiles are constructed from the displacement- load measurements made behind the crack tip. A discussion is given concerning the significance of these results in evaluating the validity of using the toad at the point of linearity as a para- meter to quantify crack closure.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/43930/11340_2006_Article_BF02324983.pdf;sequence=1

On the variation of fatigue-crack-opening load with measurement location

Simultaneous monitoring of acoustic emission and ultrasonic attenuation during fatigue of 7075 aluminium

This bibliography is comprised of approximately 1200 reference citations related to the mechanics of failure in aerospace structures. Most of the references are for information on life prediction for materials exposed to monotonic and cyclic loading in elevated temperature environments such as that in the hot end of a gas turbine engine. Additional citations listed are for documents on the thermal and mechanical effects on solar cells in the cryogenic vacuum environment; radiation effects on high temperature mechanical properties; and high cycle fatigue technology as applicable to gas turbine engine bearings. The bibliography represents a search of the literature published in the period April 1962 through April 1974 and is largely limited to documents published in the United States. It is a companion volume to NASA CR-134750, Life Prediction of Materials Exposed to Monotonic and cyclic Loading - A Technology Survey.

https://ntrs.nasa.gov/api/citations/19750013596/downloads/19750013596.pdf

Life prediction of materials exposed to monotonic and cyclic loading: Bibliography

A preliminary investigation was conducted to assess the feasibility of monitoring acoustic emission signals from fatigue cracks during cyclic bend tests. Plate specimens of 6A1-4V titanium, 2219-T87 aluminum, and 18-Ni maraging steel were tested with and without crack starter notches. It was found that significant acoustic emission signals could be detected in the frequency range from 100 kHz to 400 kHz. Cracks emanating from starter notches were monitored by the ultrasonic pulse-echo technique and periodically measured by micro-optical examination. Methods used to reduce the effects of extraneous noises (i.e., machine noises, fretting) are described. A frequency spectrum analyzer was used to characterize the emissions and to evaluate methods used to acquire the signals (i.e., transducer location, bandwidth selection). The investigation indicated that it was possible to extract meaningful acoustic emission signals in a cyclic bend machine environment.

A. Vary

Papers

A potential means of using acoustic emission for crack detection under cyclic-load conditions