the glass) resists this attack and is all-important in maintaining 

 strength under prolonged immersion. 



Durability 



Fried and Graner°^ discuss the utilization of glass-reinforced 

 plastics (GRP's) in marine structural applications. Information is given 

 on the durability of a large reinforced plastic structure, a submarine 

 fairwater (sail), after 11 yr of service. The sail was a 1/4-in. -thick 

 reinforced plastic laminate fabricated of a high-strength glass cloth. 

 The cloth was a satin woven bidirectional textile treated with a special 

 finish to improve resin bond and water resistance. The plastic matrix was 

 a general-purpose room temperature curing polyester resin, blended with 

 10 percent of a flexible resin for increased toughness. It was manufac- 

 tured by a conventional vacuum-bag molding process which resulted in a 

 high-quality laminate having a high glass content and a void content of 

 less than 1 percent. The data obtained after the 11-yr exposure. Table 6, 

 show that the mechanical properties of the GRP material did not differ 

 substantially from the original. 



TABLE 6 - EVALUATION OF GRP FAIRWATER AFTER 11 YEARS OF SERVICE 



Property 



Condi- 

 tion 



Original* 

 Value 



Aft 



er Exposure | 



Panel 1 



Panel 2 



Average 



Flexural Strength, psi 



Dry 



52,400 



51,900 



51,900 



51,900 





Wet*''^ 



54,300 



46,400 



47,300 



46,900 



Flexural Modulus, psi x 10" 



Dry 



2.54 



2.62 



2.41 



2.52 





Wet 



2.49 



2.45 



2.28 



2.37 



Compressive Strength, psi 



Dry 



Not 

 determined 



40,200 



38,000 



39,100 





Wet 



Not 

 determined 



36,000 



35,200 



35,600 



Barcol Hardness 



Dry 



55 



53 



50 



51.5 



Specific Gravity 



Dry 



1.68 



1.69 



1.66 



1.68 



Resin Content, % 



Dry 



47.6 



47.4 



48.2 



47.8 



"Average of three panel 



s. 











**Two-hour boil. 













25 



