6-24 DESIGN OF LAMINATES 



Referring to Table 5-7, the folio-wing values for tensile moduli are obtained: 



(a) Mat Laminate E t =0.90 x 10° psi 



(b) 10 Ounce Cloth Laminate Et = 1.95 x 10° psi 



(c) Woven Roving E t = 2.06 x 10° psi 

 Substituting the given values in equation 6. 13: 



, x 5o,ooo x 36 . 



(a) Mat e - g - ^ - gg = 0.U02 in. 



(b) 10 Ounce Cloth e = 50,000 x 36 = Q ^ Qh ± ^ 



5 x 1.95 x 10° 



f \ TT D • 50,000 X 36 - -_.; . 



(c) woven Roving e = e 7 = 0.17? in. 



5 x 2.06 x 10° 



Design Example 6-8 illustrates the effect of the tensile modulus on the ability of a 

 material to stretch or elongate. The mat laminate stretches approximately 2. 25 times 

 as much as the 10 ounce cloth laminate and the woven roving laminate. 



In a composite laminate, such as the one shown in Fig. 6-19, the total elongation must 

 be the same for all the laminae that make up the composite laminate. For this condition 

 not to be true would imply that the mat lamina would have to shear away from the cloth 

 lamina. Therefore sufficient shear stress between the laminae must exist. Equation 6. 13 

 can be rearranged to indicate the strain or the elongation per inch in a laminate: 



Total elongation: 



Ek = £t (6.13a) 



AE E 



IT .. . . . _ e f (6. 13b) 



Unit strain: e - — - — 



L E 



where e = strain; inch per inch and the other terms are as previously defined. Referring 

 to Fig. 6-19 and using equation 6. 13b, the strain in the various laminae are as follows: 



(a) 10 Ounce cloth: 1 



(b) Mat: e 2 



£cl 

 Ecl 



£m 



In order for the mat and cloth laminae to be compatible in the same composite laminate, 

 it follows that the strain in the mat lamina must be the same as the strain in the cloth lamina 

 or e. = e , The following identity therefore is established: 



