6-28 DESIGN OF LAMINATES 



f f 



(b) 17,900 psi = 1.U0 x 10 6 x 2 T = i.^o x 10 6 x — , 



0.90 x 10 6 1.3U x 10 6 



fron which f = 11,507 psi 

 f WR = 17,133 Psi 



(c) ^3,8no psi = 1.3-'; x 10 6 x 5 = 1.3U x 10 6 x cl 



0.90 x 10 6 ' mo x 10 6 



from which f^ = 15,995 psi 

 f cl = 2b, 866 psi 



Part (a) states that if the mat ultimate stress of 6, 600 psi is assumed as the controlling 

 stress then the ultimate stresses obtained in the cloth and woven roving laminae are 10, 267 

 psi and 9, 827 psi respectively. Since all values do not exceed the ultimate, part (a) stresses 

 can be used. 



Part (b) states that if the cloth ultimate stress is assumed as the controlling stress then 

 the ultimate values for the mat and woven roving laminae would be 11, 507 psi and 17, 133 psi 

 respectively. Since the mat stress of 11,507 psi exceeds the ultimate of 6, 600 psi this 

 combination cannot occur without failure. 



Part (c) also indicates an ultimate value for mat of 15,985 psi which cannot occur. 



Therefore Part (a) is the only condition under which the laminate will be stable without 

 overstressing an individual lamina. The final stresses to be used are therefore: 



The total ultimate load P that the composite laminate can carry is now found as the sum 

 of the individual carrying capacity of each lamina: 



P = fjnAn, + fdAcl + fwRAWR (6. 15) 



= 6600 psi x 0.25 + 10,267 psi x 0.0625 + 9,627 x 0.125 

 = 1650 + 602 + 1228 

 = 3520 lbs. per in. of width 



