7. 50 VII.5.2.3: Minor Stiffener Sizing for Damage Containment: In section VII.4.3 the minor stiffeners were rough sized in relation to the task of providing added bending stiffness to the major 20m x 20m hull section. Recall that they were designed with a rectangular cross section, the width being equal to the hull plate thickness, t, and the depth being 4t. An added task assigned to the minor stiffeners is that of preventing the propagation of cracks from one of the lm x lm panels to an adjacent panel. The most severe situation encountered in this regard is the assumed corner joint failure and subsequent loss of four panels discussed in Section VII.2.4. The plate/stiffener joint must be designed so that the maximum K 1 aris~ ing from such a failure is less than the critical stress intensity factor of the stiffener material. Unfortunately, this study did not possess the resources to complete a sophisticated analysis of the stress intensity factor occurring at the joint of two elements, differing in both configuration and mechanical properties. In order to estimate the K 1 experienced, however, referen~e is made to a somewhat analogous situation described in (7.16) . Reproduced from this reference is Figure 7.16. As may be seen, the value of K 1 is given by the standard formula for a through crack multiplied by a correction factor, F. This correction factor is a function of the ratios a/b and E~~•. In order to obtain an approximateE~a~ue 1 oft~~ KIC required in the stiffener, assume that a/b + 1, E and h = 4. Kl= orn(.6) The most severe case involves a stress equal to twice the normal mean stress and a crack half length, a, equal to lm or 39.4 in. Thus, one obtains: K 1 = 6.680 = 6.68 (20 8 1 The value of K 1 thus obtained must be less than the KIC appropriate for the stiffener material. If a maximum value of KIC for material used as stiffeners can be determined, then the upper limit of the mean normal stress can be computed as follows:
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