DESIGN OF LAMINATES 



6-7 



mination of these constants is to test the laminate at degrees, 45 degrees and 90 degrees to 

 the warp. The two basic values at degrees and 90 degrees can be used to compute, by 

 means of mathematical identities, the values at the intermediate angles. The test value at 

 45 degrees can be used to verify the calculated value. Once the basic values at degrees 

 and 90 degrees are obtained, graphs can be developed which will give at a glance, the value 

 of any constant for a specific angle. 



The following graphs, Figs. 6-7 to 6-12, which are typical of those that can be esta- 

 blished, are based upon Fig. 6-6 and the following equations: 



L = Dl RECKON OF WARP 

 T = Dl RECTI ON OF Fl LL 



Fig. 6-6. Orthotropic Laminate 



The modulus of elasticity, E]_, due tc a stress applied in the 1-1 

 direction at an angle a with the warp direction is obtained from: 



E L I E L I 



— = cos^a + — sin^ft + 



Ex E T 



1 E L 



H a 



2a 



LT 



LT 



sin^2a 



(6.2) 



Poisson's Ratio is obtained from: 



J 12 



El 



E L 



-*(*♦* 



LT I 



Li Em ^TT 



sin^2a 



(6.3) 



The shear strain is obtained from: 



12 



m f l 

 1 — 



E L 



(6.4) 



where : 



m = sin 2a 



E I 1 G L 

 a + — _ - 

 LT E T 2 G LT 



cos 



?a (l + 2 a^!L_EL\ 



(6.5) 



