Micro-Kinetics of Hydrogen Assisted Cracking by Inverse Processing of Acoustic Emission

概要

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An advanced monitoring and inversion processing system of elastic waves was applied to elucidate the microkinetics of hydrogen assisted cracking (HAC) of low alloy steel. The developed system enables the source waves to be obtained by the de-convolution integral of detected surface displacement by the theoretical second kind Green’s function. Absolute calibration of displacement-type sensor, the radiation pattern of P-wave and the waveform distortion by the reflected waves were carefully examined. It was found that about sixty percent of the detected waves during HAC test were produced by a pure Mode-I cracking, and could be inversion processed in time domain. The obtained source waves suggested that the transgranular cracks with diameter of a few ten micrometers were generated within a few micro-seconds. The growth rate of brittle micro-cracks in segregated MnS band sandwitched by dimple fracture, in front of advancing macro-scopic crack where the highest hydrostatic pressure exists, was estimated to be 30 m/sec at the maximum.