8. 54 for proof testing. To avoid local yielding at stress concentration points, a stress concentration factor of 3 is assumed. K 1 is then 43,400 psi/In, assuming a= 0.1 in. This gives a = 1.61. This is low enough to prevent damaging unflawed portions of the hull during the proof test. Stress varies linearly with pressure, so the proof test pressure is simply ap 0 = 65,000 N/m 2 . Stress due to centrifugal forces increases with the square of the rotation rate w, so for a maximum operational w of .314 (3 RPM), the proof test rotation rate is law= .398 (corresponding to 3.8 RPM). The pressure proof test, performed first, involves only static loading and does not fatigue the structure except for a single cycle. From Section VII.5.2.2, da _ C(l>Kl)n rr 1/2 2 25 dN - ~ = C[l.1 (O.lo) (/ 3> l · for normal operations, and 1 ~ for the single zero stress to proof stress cycle. The ratio of proof test fatigue to operational fatigue is then ( 0 ~~ 0 ) 2 " 25 X (0.1) = 0.1 X (10a ) 2 • 25 = 51.9, or the equivalent of 52 operational cycles (about 17 minutes at 3 RPM). Dynamic fatigue during rotational testing is proportional to o 2 · 25 , or a 2 · 25 = 2.92 times as high as normal. Since the number of cycles per unit time is higher by lei, the resulting test fatigue rate is lei a 2 · 25 = a 2 · 75 = 3.71 times the operational rate. So a one week proof test would age the structure the equivalent of one month of operations, which is acceptable for the 30-year design 1ifetime hull.
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