ENGINEERING PROPERTIES OF LAMINATES 



5-3 



RELATIONSHIPS BETWEEN REINFORCEMENTS, 

 MOLDING METHODS AND PROPERTIES 



There exists definite relationships between reinforcements, molding methods and 

 engineering properties (1, 3,4). In general, increased molding pressure decreases laminate 

 thickness and increases glass percentage. Strength properties are improved in proportion 

 to increases in the glass content, Fig. 5-3. 



The different types of fiberglass reinforcements vary widely in thickness and weight 

 per ply in a finished laminate, when molded by the same method. Differences in shop 

 practices or molding techniques also produce variations in laminate thickness, weight and 

 strength properties for any particular type 

 of reinforcement. This variation due to 

 shop practices can be materially reduced by 

 quality control. Fabricators experienced in 

 working with a specific type of reinforcement, 

 resin system and molding method can con- 

 sistently produce high quality laminates. 



Table 5-1 presents the relationship 

 between reinforcements, molding methods, 

 physical and mechanical properties. The 

 values given in Table 5-1 are over -all 

 averages presented for comparison only and 

 should not be used for design unless verified 

 by qualification tests. Fabricators should 

 investigate the effects of the important vari- 

 ables to establish the most efficient and 

 economical relationship for each specific 

 application. There are a number of other 

 minor causes of variability in laminate pro- 

 perties, such as, humidity, temperature and 

 improper storage and handling of basic 

 materials which should be considered in the production of fiberglass laminates. 



TEST PROGRAM TO OBTAIN PROPERTIES - CONTACT MOLDED 



WEIGHT PERCENT GLASS 

 REFERENCE (l) 



Fig. 5-3. Strength Properties Im- 

 prove with Increased Glass Content 



Purpose 



Due to practical limitations of the pressure molding methods, the greatest percentage of 

 fiberglass boats are presently being produced by the contact molding method. All of the 

 larger sizes of fiberglass boats are being made by the contact molding method. Unless new 

 molding methods are developed, the contact molding method is the most suitable for con- 

 struction of the larger fiberglass boats to be built in the near future. With further improve- 

 ment of the basic materials and techniques for contact molding, an increase in the construc- 

 tion of these larger sizes of boat hulls is expected (5). 



Since the contact molding method is the most widely used for boat construction, this 

 extensive test program (6) was conducted to obtain necessary properties data for fiberglass 

 mat, woven roving and cloth reinforced polyester laminates molded by this method. Also, 

 since marine applications were of primary consideration, all mechanical properties were 

 obtained from tests of laminates in the "wet" condition or immersed in water at room 

 temperature for 30 days. 



