AN ACCELERATED TEST METHOD FOR DETERMINING NEAR-THRESHOLD STRESS INTENSITY VALUES IN HSLA STEELS

A new method for accelerating the collection of near-threshold corrosi on fatigue crack propagation data, using local hydrogen embrittlement in the crack tip region, has been investigated for ASTM A710 HSLA stee l. Fatigue tests were conducted at 10 and 0.2 Hz (stress ratio, R = 0. 1) on ''constant K'' contoured double cantilever beam (CDCB) specimens , to establish near-threshold crack growth rates in a locally hydrogen charged region at the crack tip. Hydrogen charging was then discontin ued and crack growth rates were monitored in the uncharged material. N ear-threshold fatigue crack growth rates were found to be 100 times fa ster in the locally hydrogen charged specimens than in the uncharged m aterial. Fatigue thresholds, Delta K-th, were defined in less than one fifth the time required for load shedding tests in air at 0.2 Hz. Alt hough demonstrated for HSLA steels, the technique is applicable to any material which can be embrittled by hydrogen.