induce a fatigue problem. Many mechanical joining techniques have been 

 proposed for this application. A few are considered here. The following 

 discussion presents several typical ideas and some of their strengths and 

 weaknesses . 



The rings could be held in place by tension wires or rods secured 

 at the bulkheads (Figure 5a) . This method has the advantage of low 

 weight since very high-tensile-strength steel may be used. One problem 

 involves the location of the rods. They cannot pierce the frames or webs 

 since, this would introduce severe stress concentrations particularly for 

 nonductile materials. If they are inboard of the frames, they are less 

 efficient structurally and consume valuable interior space. Ideally, they 

 would be placed outside the hull, but there they are subject to mechanical 

 damage and to corrosion. 



Bolts might be used to secure the rings (Figure 5b). This technique 

 is being considered for ALUMINAUT. An important problem here is the 

 stress concentration in the bolt holes. Large, round taper pins might 

 overcome the stress-concentration problem of the holes (Figure 5c), but 

 they would be loaded in shear and would have a stress-concentration problem 

 under longitudinal loading. 



Clamps and similar devices carry no hydrostatic load and may be 

 prohibitively heavy for joining individual shell and frame rings. However, 

 sections consisting of several frame and shell sections could be joined 

 by a system as shown in Figure 5d. The sections could be assembled by one 

 of the other techniques considered here or, for small diameter hulls, 

 could be machined. This procedure is being considered for deep-running 

 torpedoes . The clamping ring may be formed in several segments which are 

 joined by bolts. 



In the technique of composite construction, the rings are inserted 

 into a jacket of weldable or otherwise easily fabricated material (Figure 

 5e). The jacket yields during the initial submergence, holds the rings in 

 place, and provides watertight integrity and corrosion protection. The 

 main difficulty with this technique is in the repair of the jacket. Some 

 materials, particularly aluminum and glass -re in forced plastics, are heat 

 sensitive, and heat applied in welding the jacket might seriously weaken 

 the inner rings. This problem could be overcome by using an epoxy or 



