DESIGN OF LAMINATES 6-61 



various section moduli the required laminate may be obtained. The largest number of plies 

 would control the construction of the laminate. 



The composite laminate problem in Design Example 6-19 will now be done by using the 

 graphs, to obtain the minimum resisting moment of the laminate. 



From the graph in Fig. 6-31 for a Type A laminate: 



The equivalent moment of inertia for woven roving: 



I' = 0.00079 in^ 

 and the section moduli are: 



Cloth Z c = 0.0060 in 3 



Mat Z M = 0.0156 in 3 



Woven Roving Z^ = 0.0077 in 3 



These values are approximately equal to the values previously calculated and the final 

 resisting moments should be the same. 



Stiffener and Plate Construction 



Beams of reinforced fiberglass can be molded in numerous shapes with various combi- 

 nations of reinforcements and core materials. To list all the possibilities would be a 

 voluminous task beyond the scope of this manual. For this reason only a few sections have 

 been chosen as representative. 



To expedite the work of the designer the graphs of Figs. 6-37 through 6-40 have 

 been prepared. 



Figs. 6-37 and 6-38 give the section modulus, Z, and moment of inertia, I, for hat 

 stiffeners made up of woven roving. Fig. 6-37 is for hat stiffeners in conjunction with type 

 A laminate, where the number of plies of woven roving in the laminate is the same as the 

 number of plies in the stiffener. Fig. 6-38 is for hat stiffeners in conjunction with type B 

 laminate, where the number of ounces of mat in the laminate is approximately one and one- 

 half times the number of plies of woven roving in the stiffener. The exact relationship used 

 is indicated on each Figure. In all cases the effective width of the plate laminate assumed 

 acting with the stiffener is taken as twice the width of the top of the stiffener. Similar to 

 the laminates Figs. 6-31 to 6-33, the section moduli given for the cloth face of the laminate 

 and the woven roving face of the stiffener are corrected so that stress values may be calcu- 

 lated without modification for moduli values of the different reinforcements. The moment of 

 inertia, I, values are based on woven roving equivalence with a tension modulus of elasticity 

 approximately equal to 2. 06 x 106 psi. The tension moduli have been used since it is 

 questionable which moduli will control. Tests of these hat sections are necessary to ascertain 

 the correct moduli. The stiffener laminate faying, or touching flange has been taken as 

 twice the width of the top of the stiffener to ensure that the horizontal secondary bond shear 

 stress at the interface is never critical. 



