  The different thermo-elastic properties of glass fibers and polymer matrices
can generate residual thermal stresses in injection-molded fiber-reinforced
plastic (FRP) objects. During cooling from mold to room temperature, these
stresses can be relaxed by large deformations resulting from an instability of
the unwarped configuration (i.e., buckling). This article investigates the
thermal buckling of thin FRP disks via an analytical formulation based on the
Foppl-von Karman theory. Expanding on our previous work, cylindrical orthotropy
with material parameters varying over the disk thickness is assumed in order to
account for thickness dependency of the glass fiber orientation distribution. A
disk parameter generalizing the thermal anisotropy ratio for homogeneous
orthotropic disks is introduced and its relation with the occurrence and
periodicity of buckling is discussed. This is done for a skin-coreskin model,
for which the core-to-total thickness ratio is defined. For fiber orientation
distributions typical of injection-molded disks, it is found that there exists
a value of the thickness ratio for which no buckling occurs. It is also
demonstrated that the periodicity of the first buckling mode is described by
the generalized thermal anisotropy ratio, thus extending the results obtained
for a homogeneous fiber orientation distribution. Improvements in the accuracy
of the predictions for experimental data available in the literature when using
the skin-core-skin model are shown. Finally, we study the relation between
buckling temperature and disk thickness and propose an expression for the
dependence of the normalized buckling temperature on the thermal anisotropy
ratio. Results of FEM simulations are used to validate the proposed expression,
proving its applicability and accuracy.
