ENGINEERING PROPERTIES OF LAMINATES 



5-13 



where volatiles would form gas bubbles. Careful placement of the plies in a lay up will 

 eliminate wrinkles which can result in large voids between the plies. 



The following method (8) can be used to calculate the per cent voids in a laminate: 



Per cent voids 



100 



100 a 



_ + _ 

 c b 



= specific gravity of the laminate from Table 5-4 



= specific gravity of fiberglass = 2. 55 



= specific gravity of cured resin = 1. 18 to 1.24 as 

 obtained from manufacturers. 



= resin content, by weight. 



= glass content, by weight. 



= filler content 



= specific gravity of filler 



Table 5-5 contains average values of per cent voids for the test laminates calculated by 

 this method. Since fillers were not included in the test laminates, filler content and 

 corresponding specific gravity were omitted. 



TABLE 5-5. FIBERGLASS POLYESTER LAMINATES - CONTACT MOLDED 



VOID CONTENT 



Laminate 

 Ml - 2 Oz. Mat 

 M2 - 25-27 Oz. Woven Roving 

 M3 - 10 Oz. Cloth 

 M4 - 10 Oz. Cloth - 2 Oz. Mat - 10 Oz. Cloth * 



Average Per Cent Voids 

 in Laminate Volume 



2.51 



1.82 



1. 12 



2.31 



M5 - 10 Oz. Cloth - 25-27 Oz. Woven Roving - 10 Oz. Cloth ** 2.44 



* 2 Oz. mat faced on each side with a single layer 

 of 10 Oz. cloth. 



** Woven roving faced on each side with a single layer 

 of 10 Oz. cloth. 



