Since it was known that both PS-18 and PS-30 adhesive joints 

 deteriorate in strength with age when exposed to atmospheric environment, 

 it was questioned whether immersion in seawater accelerates this aging pro- 

 cess further. To answer this question, a bonded acrylic plastic block was 

 placed in the Pacific off Point Mugu at a depth of 120 feet. After 13 months 

 of continuous submersion, the acrylic plastic block was retrieved, and material 

 test specimens were machined from it. Because the block was rather small, 

 and only a limited number of test specimens could be machined from it, only 

 tensile and compressive test specimens were cut from it. These test specimens 

 were tested at 70°F to establish the ultimate tensile and compressive strength 

 of the PS-18 and PS-30 cast joint after 1 year's exposure to seawater. 



When the test specimens were tested to destruction, it was found 

 (Table 3) that the average tensile strength of the 0.125-inch-wide, adhesive- 

 filled joints was 8,890 psi for PS-18 and 5,710 psi for PS-30 joints. Since no 

 control block was bonded at the time when the ocean test specimen was 

 fabricated and placed in the ocean, no accurate comparison can be made 

 with test specimens exposed for 1 year to atmospheric environment. A 

 general comparison, however, can be made with tensile and compressive 

 strengths of PS-18 and PS-30 adhesive-bonded joints tested several days 

 after bonding. The comparison between strengths of the fresh joints and 

 those Tyear old but kept submerged in the ocean showed that no statisti- 

 cally significant decrease in tensile or compressive strength occurred for 

 PS-18 or PS-30 adhesive-bonded joints. As a matter of fact, it appears that 

 the strength of a PS-18 adhesive-bonded joint increased somewhat because 

 of long-term immersion in the ocean (Table 3). 



Tests were conducted also on grade G Plexiglas material after 

 immersion in the ocean for 13 months to verify tests conducted by others 19,20 

 indicating that there is no statistically significant degradation of material pro- 

 perties in acrylic plastic after long-term immersion in the ocean even at depths 

 in excess of several thousand feet. Taking into consideration the experimental 

 findings that neither the acrylic plastic nor the PS-18 adhesive joints deterio- 

 rated in strength during a l-year immersion in seawater, it was decided to 

 proceed with the construction of the full-scale acrylic plastic capsule utilizing 

 PS-18 adhesive. 



Although no particular problems were encountered during bonding 

 of PS-18 joint test specimens, it remained to be seen how well this bonding 

 technique would work in practice while bonding the spherical pentagons in 

 a capsule. For this reason it was decided to discontinue bonding model cap- 

 sules with the solvent-cement technique and to bond all the subsequent model 

 capsules with PS-18 cement. 



71 



