6-22 



DESIGN OF LAMINATES 



DESIGN EXAMPLE 6-7. CLOTH LAMINATE UNDER 

 LONG TERM TENSILE LOAD PARALLEL TO WARP 



A 10 ounce cloth laminate, 8 in. wide, is to support a load of 10, 000 lbs. for a period 

 of 1,000 hours. If the load is applied parallel to the warp what should the thickness of the 

 laminate be? Use a factor of safety of 4 on the ultimate. 



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10000 LBS 



10000 LBS 



Fig. 6-18. Cloth Laminate Under 

 Tensile Load 



The ultimate tensile stress of a 10 ounce cloth laminate at degrees, from Table 5-6, 

 is given as 24, 100 psi. Higher values of ultimate strength may be used when verified by 

 qualifying tests. The reduction factor due to long term loading, from Fig. 5-17, for a wet 

 laminate, is 49 per cent. The ultimate design tensile stress is then: 



F t = 214,100 x 0.U9 = 11,809 psi. 

 The allowable design stress based on a factor of safety of 4 is: 

 f + = 11529 = 2952 psi 



j 

 Using equation 6.12b, A = — , 



Area = 8 x t = 



t = 



= 10000 

 lf t 8 x 2952 



0.1+23 in. say 



16 



in. 



Composite Orthotropic Laminates 



Fig. 6-19 shows a composite laminate made of two laminae of differing physical properties. 



When several laminae are combined to form a composite section as shown in Fig. 6-19, 



the basic formula 6.12b relating stress, load and area, f = £ must be modified. 



A 



A member subjected to a tensile load P will stretch a given amount. The amount that a 

 laminate will stretch or elongate can be expressed as: 



