DESIGN OF LAMINATES 6-33 



The elongation of the laminate is given by equation 6. 13, where the factor E is for the 

 entire laminate and has to be determined according to equation 6. 16; 



EA = X E i A i 

 where A = (0.0625 + 0.375 + 0.0625) x 1 = 0.50 sq.in. 

 Therefore 



| = 1.183 x 10 6 x 0.0625 + 0.81 x 10 6 x 0.375 + 1.183 x 10 6 x 0.0625 



■ft 



= 0.h5l5 x 10° lbs. 



and E 



0.1+515 x 10° = c#9 o3 x 10 6 psi 

 0.50 



and the elongation is calculated from equation 6. 13; 



PL _ 2030 x 20 



AE 0.50 x 0.903 x 10° 



= 0.0899 in. 



COMPRESSION 



The behavior of fiberglass laminates in compression such as columns, struts, etc. is 

 complex and many tests are required before definite conclusions can be made as to the ap- 

 propriate method of analysis. Materials that behave isotropically can be analyzed by ana- 

 lytical methods that have been developed for homogeneous isotropic materials. Glass rein- 

 forced laminates however may fail by interlaminar shear or at the bond between the glass 

 fibers and resin. Therefore any compressive design criteria is dependent on the behavior 

 of the laminate and precautions should be taken in the compression analysis of reinforced 

 plastic laminates whether they are isotropic or orthotropic. 



The data presented here is primarily for laminates that are used individually or as part 

 of a member in compression. The compression buckling of plates is discussed later in 

 this Chapter. 



Short Members 



For laminates whose dimensions are such that buckling is precluded, the basic relation 

 of equation 6. 12, P = A f , can be applied. These laminates will usually fail under ultimate 

 axial compressive loads by crushing or delamination. 



DESIGN EXAMPLE 6-14. WOVEN ROVING LAMINATE 

 IN COMPRESSION WITHOUT BUCKLING 



A woven roving reinforced laminate, 1/2 in. thick, is to support a load of 35, 000 lbs. 

 Find the width of the laminate. The length is such that the laminate will not buckle. Use 

 a factor of safety of 2 on the ultimate compressive strength. See Fig. 6-2 3. 



