7.45 Figures 7.D2 and 7.D4 present the variations of Q and MK with the flaw configuration and show values of 2.3 and 1.1, respectively, for a semicircular flaw. The desired condition is that the stress intensity factor of a surface flaw which has just penetrated the plate thickness be less than the critical stress intensity factor for the plate material. Since the material in this case is 4130 steel, KIC is approximately equal to 70 ksi/In. The leak before break condition is then given by: TT t 1/2 l.lo (2.3) (1.1) < 70 ksi/In This expression reduces to: o (t)1/ 2 < 49.50 where o is given in units of Kilopounds per square inch (ksi). Recall the outer hull hoop stress equation (see Section VII.4.4). For a steel structure: b 0.284 lb/in 3 0.0779 lb/in 3 7.112 lb/in 2 P 0 5.878 psi R 2 = 4134 in 0 8 4 ~~ 4 [0.284t 2 + 0.0779t 2 + 7.112 + 5.878] psi 08 1496t2 + 53,701 ____t_2___ psi
RkJQdWJsaXNoZXIy MTU5NjU0Mg==