6-48 DESIGN OF LAMINATES 



Solving for the radius of gyration, r 



(6. 19) 



(6. 17a) 



(97. 96) 2 



FLEXURE 



As previously stated fiberglass laminates may be homogeneous and isotropic or com- 

 posite and orthotropic depending on the type of reinforcement used. Mat reinforced lami- 

 nates are considered to be isotropic with equal strength and elastic properties in every 

 direction and can be analyzed with the same elastic theories as used for metals. Cloth and 

 woven roving laminates are considered orthotropic with different strength and elastic pro- 

 perties in different directions and the method of analysis will depend on the direction of load 

 in relation to the glass fibers. For laminates reinforced with a single type of reinforcement 

 and for loading parallel to the direction of the glass fibers, the method of analysis will be 

 similar to the method used for mat laminates. For composite laminates reinforced with two 

 or more types of reinforcement and for loading parallel to the direction of the glass fibers, 

 the same type of analysis as used for any other composite section where the moduli are con- 

 sidered is applicable. The method of analysis for stiffener and plate construction is the same 

 as for composite laminates with loading in the direction of the glass fibers. In the develop- 

 ment of stiffeners molded or bonded to the skin laminate, care must be taken to be sure that 

 the horizontal shear stress at the plane between the stiffeners and plate does not exceed the 

 laminate interlaminate or bond stress. 



Simple One-Way Plates 



The differences in analysis for the homogeneous and composite laminates in simple one- 

 way bending will be illustrated in the design examples which follow. A discussion on the 

 bending of plates loaded normal to their surface is presented later in this Chapter. For 

 guidance, graphs of section moduli and moments of inertia have been prepared for several 

 composite laminates, Figs. 6-31 to 6-33, commonly used in boat hull construction. 



