4-4 



MATERIALS AND MOLDING METHODS 



The physical characteristics of woven roving are not only different from those of mat 

 but are also different from the properties of woven cloth. 



Woven roving reinforcements cost more than mat, but are less expensive than cloth re- 

 inforcements. 



The advantages of woven roving reinforcements are: 



Good drapeability and handling characteristics in the contact or hand lay up 

 molding method. 



Provides a thicker build-up per ply of laminate than cloth. 



Provides a high glass content per ply when molded by the contact molding method. 



Has high directional physical strength and moduli for orientation in highly 

 stressed areas. 



Has extraordinary resistance to impact because of the greater number of 

 untwisted strands in the individual bundles. 



The disadvantages of woven roving reinforcements are: 



The fine, tightly compacted filaments of glass strands in the woven roving are 

 difficult to wet out or impregnate with resin. This can lead to insufficient bond 

 between filaments within the individual bundles of rovings. 



The coarse weave of woven roving can entrap air bubbles and form voids which 

 tend to make the laminate porous and penetrable by water. This effect is especially 

 noticeable in thinner laminates. 



The coarse weave of woven roving can also cause 

 resin rich areas between the individual bundles 

 and layers of rovings. Resin rich areas are 

 subject to brittle cracking, crazing, poor shear 

 strength and poor interlaminar bond. 



The high directional properties of woven roving 

 are, for some considerations, a disadvantage. 

 As the main directions of reinforcement in woven 

 roving are in the warp and fill directions of the 

 weave, the strengths at angles between these 

 main directions are reduced as indicated in 

 Chapters 5 and 6. 



Spun Roving: Under development, but not included 

 in the test program, is a new type of reinforcement 

 designated "Spun Roving". Essentially this is one con- 

 tinuous filament strand entangled or looped around upon 

 itself to give the equivalent weight of a standard parallel 

 strand roving. Fabrics made from this spun roving re- 

 semble standard woven roving in appearance except that 



Fig. 4-4. Fabric made 

 from Spun Roving 



