Abstract
Hydrogen cracking tests under repeating stress were carried out on specimens hydrogen precharged, and the effect of stress ratio was investigated on the relations between frequency f and the decreasing rate of crack propagation velocity, 1−β={(da⁄dt)S−(da⁄dt)R}⁄(da⁄dt)S, where (da⁄dt)S and (da⁄dt)R were the crack propagation velocity under static and repeating stress, respectively. The results were analyzed by using an asymmetrical internal friction model proposed.
There appear two peaks on 1−β vs. f curve, as do in the delayed failure test under repeating stress in water, i.e. this phenomenon is controlled by the migration and concentration process of hydrogen atoms to triaxially tensile stressed position near crack tip. With increase in stress ratio R=Kmin⁄Kmax, the two peaks approach each other, the height of peaks decreases, and the frequencies at which two peaks appear shift to the higher frequency ranges.
The existence of two peaks on 1−β vs. f curve and the characteristic change in 1−β vs. f curve with change in the stress ratio, can be explained by assuming the interaction between hydrogen atoms and the cyclic moving of triaxially stressed position. Furthermore, 1−β vs. f relations calculated using the asymmetrical internal friction model reveal a good agreement with the experimental tendencies.
