Fatigue cracks were grown from notches in large tensile 'specimens by cyclically applied high pressure. The notch was sealed with an 0-ring which was held in place, by a specially designed clamp. Approximately 25,000 cycles with a peak pressure of 18,000 psi were required to produce 0.4 in. of fatigue crack in the bottom of a 2-in.-deep notch. The growth of the crack was monitored with ultrasonics using both the pulse-echo and the sender-receiver method.
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