7. 60 C. +the point on the stress/thickness curve for outer hull damage that corresponds to the Fail Safe condition. In order to compute the threshold stress levels the procedure of Section VII.5.2.2 was employed. Assuming that 6Kthresh is equal to 5 ksi/In and that the amplitude of the alternating stress is equal to 10% of the mean stress, one can obt ain : 35.3569 = oa 112 if a 0.1" o = 111.8 ksi o 0 } = 37.27 ksi 2.570xl0 8 N/m 2 if a 0 . 2" o = 79.06 ksi o 0 } = 26.35 ksi = l.817xl0 8 N/m 2 To compute the Fail Safe stress level, simply divide the material yield stress by 2.1. l.o 34 xio 9 = 4.924xl08 N/m 2 = 71,400 psi ~FS = 2.1 As may be seen from the positions of points A, B, and Con the stress/thickness plots, a thickness of 4 cm for the inner and outer hulls, and 3 cm for the bulkheads appears to be reasonable if an initial flaw size of 0.1 in can be guaranteed. For the purposes of this analysis, this capability will be assumed and the plate thicknesses will be set accordingly. Inner and Outer Hulls+ t Bulkheads+ t 0.04m 0.03m 4 cm
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