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Here we derive the laminate coefficients hygral expansion, , for symmetric laminates. Let us define the coefficient of hygral expansion for laminate as laminate mid-plane strains to the per percentage change in moisture absorption, . Thus,
(5.121)
For symmetric laminates with hygral loads alone, we can write
(5.122)
Combining Equation (5.121) and Equation (5.122), we get
(5.123)
For a uniform moisture absorption the equivalent hygral force is given as
(5.124)
Thus, the laminate coefficient of hygral expansion becomes
(5.125)
It is known that the and are constant in each lamina in thickness direction. Thus, the integration over thickness can be simplified as summation over laminae thicknesses as
(5.126)
Combining Equation (5.124) and Equation (5.125) we can get the effective hygral force as
(5.127)
Figure 5.15 shows the variation of for laminate along with of a layer of for T300/5208 material from Pipes et al [5]. Similarly, Figure 5.16 and Figure 5.16 show the variation of and .
Figure 5.15: Variation of for lamina and of for laminate
Figure 5.16: Variation of for lamina and of for laminate
Figure 5.17: Variation of for lamina and of for laminate
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, for symmetric laminates. Let us define the coefficient of hygral expansion for laminate as laminate mid-plane strains to the per percentage change in moisture absorption, 
. Thus,
and 
are constant in each lamina in thickness direction. Thus, the integration over thickness can be simplified as summation over laminae thicknesses as
for 
laminate along with 
of a layer of 
for T300/5208 material from Pipes et al [5]. Similarly, Figure 5.16 and Figure 5.16 show the variation of 
and 
.
