DESIGN OF LAMINATES 6-45 



t 3 t t 



r 



xx 



12 x t 2 x i/3~ 3.U6U 



L 36 x 3.U6U = 12U.70 



r t t 



P = -~ x 12t = 7500 lbs. 



Assume t = 1 in.: then - = -, - n = 12u.r0 

 J r 1.00 



From Figure 6-26, F cr = 1550 psi 



For a FS =2; f Q = 32§2 = 775 psi 



P = 775 x 12 x 1.00 = 8600 lbs. Greater than required. 



From Figure 6-26 F cr = 1350 psi 



1320 

 For a FS of 2 j f c = -5 — = 675 psi 



P = 675 x 12 x .9375 = 759U lbs. 

 Use a 15/16 in. thick laminate. 



Composite laminates made of several laminae of different materials have properties 

 which are different from the physical properties of any of the individual laminae. These 

 properties for composite laminates have to be computed before the ultimate compressive 

 stress can be determined. The properties for a composite laminate can be found by means 

 of the following equations: 



I E i A i x i 



Neutral Axis x = = , , (6. 24) 



L i A i 



Stiffness Factor EI = £ E i I j _ (6. 25) 



Modulus of Elasticity E = 7 X EiAi (6.26) 



Shear Modulus 



G = 1 X^iAj (6.27) 



