Microscopic Mechanism of Environmentally Assisted Cracking by the Inverse Analysis of Measured Data

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For the Acoustic Emission (AE), advanced source location and simulation methods for guided waves (pipe and rod) are developed. Source dynamics of hydrogen blister, delayed fracture and void formation (Ti-Pd) were obtained by the wave form simulation of So and L (0,1) waves by the wave form matching of computed to the measured. Here the wave form was computed by the convolution of assumed crack opening with experimental over-all transfer function determined using the expansion of the compression type PZT element. Micro-cracks of delayed fracture of high tension steel was found to be close to the Rayleigh wave velocity and caused sub-cracks by leaking the wave-energy during fast propagation. Extremely fast micro-crack of delayed fracture was first studied by using the AE sensors at marker and the rod specimen where the dispersive low frequency guided waves were monitored, but was slower than those of mechanical fractures of quenched high carbon steel. It was also first that the strong an … More d fast guided wave Aes were monitored during hydrogen absorbing of Ti-Pd alloy rod, possibly by void formation by hydrogen gas. Such Aes are supposed to be produced by rapid void formation by hydrogen gas emitted from titanium hydride.The author first proposed the AE source location method using very few AE sensors. Source locations of guided wave, both in the longitudinal direction and transverse section, were determined only a single AE sensor. Computer soft ware for velocity dispersion and modal analysis, required for such signal analysis were developed at home and now opened on the internet.Trans-granular APC-SCC does not emit Aes while inter-granular one does emit Aes with sufficient amplitudes. Fluctuation dynamics of corrosion potential during APC-SCC were attempted using the over-all transfer function determined by artificial fracture of PVD-TiN film. However, it could not be studied by the inverse processing of potential fluctuation due to it's too slow response. Wavelet analysis (time-frequency domain analysis) revealed that fluctuation frequency higher than 0.2Hz was dominant during the incubation period, but lower frequency during SCC propagation. Less