Thermal buckling of thin injection-molded FRP plates with fiber orientation varying over the thickness

TL;DR

This paper develops an analytical model to predict thermal buckling in thin injection-molded fiber-reinforced plastic disks, accounting for fiber orientation variation over thickness, and validates it with FEM simulations and experimental data.

Contribution

It introduces a generalized thermal anisotropy ratio and a skin-core-skin model to improve buckling prediction accuracy for injection-molded FRP disks.

Findings

Existence of a specific thickness ratio where no buckling occurs

Buckling mode periodicity linked to the generalized thermal anisotropy ratio

Validated predictive expression for buckling temperature dependence

Abstract

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.