6-56 



DESIGN OF LAMINATES 



p LBS PER IN. 



I i U I 1 I 



1 PLY 10 OZ CLOTH 

 1 PLY 2 OZ MAT 



4 PLIES 25-27 OZ 

 WOVEN ROVING 



0.1 48" 



0.224" 



Fig. 6-35. Bending of Composite Laminate 



The engineering properties for the three laminae are different and the analysis for a 

 composite section must be used. To obtain the necessary properties of the section such as 

 neutral axis, x, stiffness factor, EI, etc. equations 6.24 to 6.27 can be used. 



The section modulus may be obtained from: 



EI 

 V 



(6.35) 



where y = distance from the neutral axis to any point, in. 



Ey = modulus of elasticity of lamina at that point, lbs. /in. 

 EI = y~Ei!i= stiffness factor of the entire section, lbs. -in.' 



And the flexural stress may be obtained from: 



M _ HEyy 

 b Z EI 



(6.36) 



The maximum flexural stress may not occur at the extreme fiber as for isotropic 

 materials but may occur at any fiber in the section depending on its distance from the neutral 

 axis and its modulus of elasticity. 



The maximum shear stress may be obtained from: 



f 



VQ' 

 Elb 



(6.37) 



where V, EI and b are as previously defined. 



Q' = Weighted static moment, ^E ± A ± y { , of the areas 



between the extreme edge and the plane being con- 

 sidered about the neutral axis of the section. 



It is considered advantageous when obtaining the section properties of a composite lami- 

 nate to transform the areas of the different laminae to equivalent areas of one of the lamina. 

 This method will be used in this design example. 



