Confirmation of Hydrogen Embrittlement Mechanism for Stress Corrosion Cracking of Gas Main Lines

The nature and mechanism of stress corrosion cracking have been studied and modeled in laboratory conditions. It was established that the destruction process develops in three stages: the formation of corrosion defects on the pipe surface, birth and subcritical growth of stress-corrosion cracks, and break. Release bands observed in focal fracture at subcritical crack growth stage indicate that fluctuating stresses are involved in the destruction development. Transcrystalline nature of the fracture at subcritical growth stage implies that SCC in pipelines develops in consonance with the hydrogen embrittlement mechanism.

On-chip environmentally assisted cracking in thin freestanding SiO2 films

An on-chip fracture mechanics method is extended to characterize subcritical crack growth in submicron freestanding films. The method relies on a self-actuated concept based on MEMS fabrication principles. The configuration consists of a notched specimen attached to actuator beams involving high internal stress. Upon release, a crack initiates at the notch, propagates, and arrests. Several improvements are worked out to limit the mode III component and to avoid crack kinking. The method is applied to subcritical crack growth in 140-nm-thick SiO2 films under different humidity conditions. The data reduction scheme relates crack growth rate to stress intensity factor. The static fracture toughness value is ~ 0.73 MPa $$\sqrt{\mathrm{m}}$$ m , with standard error of 0.01 MPa $$\sqrt{\mathrm{m}}$$ m and standard deviation of 0.17 MPa $$\sqrt{\mathrm{m}}.$$ m . Subcritical crack growth rates are much smaller than in bulk specimens. A major advantage is that many test samples can be simultaneously monitored while avoiding any external equipment. Graphic Abstract