E l /300\ 1 /400\ + 1 /600 



4.000 1 600 



4,000 \600/ 1,000 \600/ 100\600 



to result in a cumulative fatigue value of 0.01079. So long as the summation 

 of all dive fatigues is 2 < 1 .000 the hull is considered safe. When the sum of 

 the dive fatigue values reaches 1 .000 the hull will be considered to have no 

 further fatigue life and must be replaced. 



4. The fatigue curve of Figure 121 is very conservative as it is based on the 

 appearance of cracks under cyclic proof-test depth loadings to 1,140 feet 

 while the manned operational dives will have a maximum depth limit of 

 only 600 feet. Furthermore, since it is known from the cycling tests con- 

 ducted on models that extensive fracturing of the acrylic/metal plate interface 

 takes place prior to catastrophic fatigue failure, periodic visual inspection of 

 the hull during its service life will prevent premature fatigue failure. 



5. These recommendations also apply to other acrylic plastic capsules that 

 will be fabricated in the future for other systems besides NEMO, provided 

 that: 



a. The capsule design is identical to the one developed in this program. 



b. Acrylic plastic material has the properties specified in Table 1. 



c. Adhesive utilized has a minimum tensile strength of 4,500 psi and 

 service life comparable to PS-18 adhesive in marine environment. 



d. Thickness of material in the finished capsule is 2.285 < t < 2.625 

 inches. 



e. The diameter of the capsule is 65.875 < D< 66.125 inches. 



f. The external radius of the capsule is 32.875 < R < 33.125 inches. 



ACKNOWLEDGMENTS 



Many engineers and scientists have contributed to the development 

 of the NEMO concept and the successful completion of the acrylic plastic 

 capsule structural validation program. Messrs. R. G. McCarty,* J. G. Molden- 

 hauer,* initiated the NEMO concept, while Messrs. K. Tsuji* and D. T. StowelT 

 developed it sufficiently to show its feasibility. The pentagonal acrylic plastic 



Naval Missile Center, Point Mugu, California. 



158 



