Acoustic emission and prefracture processes in high-strength steels

Author / Creator

Baker, G. S., Dr., author

Available as

Online

Summary

A program was conducted to investigate the practical application of stress-wave monitoring techniques to the detection of crack initiation and/or growth by determining the correlation between stres...

A program was conducted to investigate the practical application of stress-wave monitoring techniques to the detection of crack initiation and/or growth by determining the correlation between stress-wave emission and prefracture mechanical processes occurring in high strength steels under stress as affected by material properties and test conditions. D6aC steel in two heat treatment conditions (600F temper and 1075F temper) and grade 200 and grade 300, 18% nickel maraging steel were investigated using standard accelerometer techniques at a sensitivity level of approximately 0.01g. It was found that stress wave activity at this level was a positive indication of nucleation of cracks of greater than 0.00001-sq in. the growth of existing cracks by a similar area. The effects of varying test temperature from -100F to 250F and varying strain were investigated. The stress-wave activity was found to be little affected by test temperature for temperatures above the material brittle-ductile transition region and to vary roughly proportionally with strain rate. For test temperatures in the ductile-brittle transition region the stress wave activity decreases rapidly with decreasing temperature. The application of stress-wave monitoring techniques to the monitoring of the hydrotest of solid rocket chambers is discussed. It is concluded that the techniques provide a means of non-destructively detecting and locating propagating flaws in structures under stress, allowing test or service termination prior to catastrophic failure.

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