Laminate Coefficients of Thermal and Hygral Expansions:

We have seen the variation of laminate coefficient of thermal and hygral expansion with the ply orientation. From these variations it is seen that these coefficients vary from positive to negative values. Further, it is observed that the coefficient of thermal expansion depends upon stacking sequence. This fact is very important from laminate designing point of view where it is used in an environment with large thermal gradient. One can choose a laminate sequence for which a coefficient of thermal expansion is zero. Similarly, one can choose the laminate sequence and material parameters to get a desired hygroscopic coefficient of expansion for laminates.

Thermal and Hygral Coefficients of Thermal Expansion in Off-axis Lamina:

The orthotropic materials, like isotropic materials have effects of thermal or hrgral expansion only in principal material directions. They do not have shear effect in principal material directions. However, when the principal material directions are rotated about an axis then there exist a shear effect due to thermal or hygral actions. In such a rotated system one has   or   present in off axis laminae. Thus, a thermal or hygral change gives rise to shear effect in such off-axis laminae/laminate. This phenomenon should be studied carefully so that one can avoid it or harness is according to the design needs.