In viscoelastic behavior of composite material, such as those made of thermo-set
polyester and one layer random fiber glass, the Poisson’s ratio is described in new
function of time and stress. The relaxation stress is obtained experimentally to describe
the non-linear viscoelastic behavior in composite material. The results show that,
Poisson’s ratio increases with an approximate rate of 16% as a result of the increasing
stress from 6.877 MPa to 8.239 MPa and decreases with increasing the time at constant
temperature 30 Co.
The investigation demonstrated that such time dependence is not a necessary
consequence of the theory of viscoelasticity to describe viscoelasticity behavior.