sixties put to rest a number of "can'ts" and 

 "undesirables" in regard to materials for 

 pressure hulls. Let us look at two examples: 



1. Aluminum was considered by many to 

 be unacceptable as a pressure hull ma- 

 terial because it is unweldable and sub- 

 ject to stress-corrosion cracking. How- 

 ever, ALUMINAUT''s designers simply 

 bolted its cylindrical sections and hemi- 

 spherical endcaps together, and placed 

 sacrifical anodes at various locations 

 about the hull; ALVMINAUT performed 

 successfully for several years before its 

 retirement in 1970 (3). 



2. Bernstein (4) relates that tests at the 

 Naval Applied Science Laboratory in 

 early 1965 disclosed that the titanium 

 alloy Ti-721 was also susceptible to 

 stress-corrosion at high tensile stress 

 levels, but in 1973 ALVIN was fitted 

 with a titanium pressure hull using an 

 alloy insensitive to this problem. 



A major innovation in pressure hull mate- 

 rials grew out of the introduction of acrylic 

 plastic viewports by Piccard, which has since 

 led to complete pressure hulls of this mate- 

 rial. Dr. Jerry Stachiw, the leader in the 

 research and development efforts leading to 

 the acceptance of acrylic plastic by the U. S. 

 Navy, presents a quasi-technical account of 

 the development and fabrication of acrylic 

 pressure hulls from NEMO through to the 

 JOHNSON SEA LINK (5). More technical and 

 detailed accounts are presented in refer- 

 ences (6-10). 



Equally innovative and promising is the 

 introduction of glass as an endcap for DEEP 

 VIEW. This application grew out of the early 

 work with HIKINO under Mr. Will Forman 

 at China Lake, California. Though DEEP 

 VIEW is only certified to 100 feet, its design 

 is experimental for the purpose of overcom- 

 ing some of glass's shortcomings, such as its 

 brittleness, high sensitivity to surface abra- 

 sion, and considerable strength degradation 

 at joints (11). The advantages of both acrylic 

 plastic and glass are a low weight/displace- 

 ment ratio and panoramic visibility. Figure 

 5.3a shows the variations of collapse depth 

 for spherical hulls of various materials 

 against W/D ratio; the advantages in this 

 area are clearly in favor of glass and glass 

 reinforced plastic (GRP) for deep diving. 



While some materials are clearly favored 

 in some areas, others offer advantages of 

 their own which must be weighed against 

 the favorite. Figure 5.3b compares five candi- 

 date materials and their advantages and dis- 

 advantages. 



While titanium, glass and GRP will un- 

 doubtedly see a future in manned submers- 

 ibles, provided the material development 

 cost is not prohibitive, steel continues to be 

 the prime candidate; according to Ballinger 

 and Garland (13) the best of these steels are 

 HY-100, HY-140, HP9-4-20 and 18 percent 

 nickel maraging steel, the chemical analyses 

 and mechanical properties for which are 

 given in Table 5.4; both are taken from the 

 same report. 



TABLE 5.4 CHEMICAL ANALYSIS OF STEELS 

 FOR SUBMERSIBLE VEHICLE PRESSURE HULLS [FROM REF. (131) 



Uo 



Co 



HV 100 0,20 Ma> 10/0.40 0.25 Ma« 25 Ma, 0.15/0.35 2.25/3.50 100/180 20/0 60 0.03 Max -- 02 Max 



HY 140 1? Ma. 0.60/0.90 0.01 Ma> 0.01 Max 0.20/0.35 4.75/5.25 0,40/0 70 0.30/0.65 05/0 10 — 0.02 Max — 



HP94.20 0.17/0.23 0.20/0.30 0.01 Max 0.01 Max 10 Max 8 5/9.5 0.65/0.85 0.90/110 006/0 10 4 25/4 75 — — 



18%NI 003Max O.lOMax 0.01 Max 0.01 Max 10 Max 1750/1900 - 3 50/4 50 -.. 7 00/8 00 0,05/0 25 005/0,15 

 Maraging 



249 



