DESIGN OF LAMINATES 



6-17 



The relation between stresses at degrees, 90 degrees, and at any other angle can be 

 found from the expression (9): 



1 



i, 

 cos 4 a 



r L 



sin' 1 a sin'' g cos 2 q 



(6.11) 



In equation 6. 11 it is best to determine F s the shear stress, by assigning values Fj, at 0° 

 Ft at 90°, and Fi at U5° , which can be obtained from test results. This is advisable because 

 of the difficulty encountered in obtaining good shear test results in the laboratory. Knowing 

 F s j the right side of the equation can be completed and the stress at any angle to the warp, 

 F-ii can be computed. Design Example 6-3 illustrates the application of this equation. 



DESIGN EXAMPLE 6-3. TENSILE STRESS AT 30 DEGREES 

 TO WARP FOR WOVEN ROVING LAMINATE 



The following high range ultimate tensile values are given for a woven roving laminate. 

 See Table 5-6. 



F L at 0' 



= ).!l,800 psi 

 = 11,800 psi 

 = 37,800 psi 

 Find the ultimate tensile strength ?2 at 30° to the .warp. 



F t at 1,5 c 

 F T at 90 c 



v 



\ 



'°-, 



DIRECTION OF WARP 



Fig. 6-14. Woven Roving Laminate 

 in Tension at 30 Degrees to Warp 



Rearranging equation 6-11 to solve for F s and using U5° values 



1 cos^ a sin^ a 



sm' a. cos" 1 a 



(6. 11a) 



sin' 



h$° 



O.U998 



cos2 h$° = O.U998 



