Acoustic Emission Study on Hydrogen-Induced Delayed Cracking Propagation in High Strength Steel

Abstract

quantitative acoustic emission analysis has been applied to study crack propagation modes of hydrogeninduced delayed cracking. Two experiments are conducted; they are weld cracking of small y grooved bud joints and tearing of linear comliance specimens. In the latter case, hydrogen is charged thermally to attain uniform hydrogen concentration.
The acoustic emission method is suited to detect weld cracking behaviour which changes in accordance with pre -and post- heating. Total counts of acoustic emissions can be used as an index to cross-sectional cracking percentage, and one can determine pre-heating temperature for crack free weld by using this index only.
Fundamental experiments on the crack propagation behaviour in linear compliance specimens show that the crack propagation speed is influenced by the amount of hydrogen introduced and the stress-intensityfactor at crack tip, where logarithms of acoustic emission count rate and crack propagation speed are found to be linearly related. This relationship is independent of hydrogen content level. Further the energy release rate as emissions is dependent on the stress-intensity-factor and hydrogen level. It increases in accordance with the increase of both the stress-intensity-factor and hydrogen level.