EVALUATION OF RESIDUAL STRESSES IN CERAMIC AND POLYMERMATRIX COMPOSITES USING FINITE ELEMENT METHOD

摘要

The aim of the study was to evaluate the residual stresses in polymer – ceramic composites using the Finite Element Method (FEM).The effect of the composite structure on the residual stresses built up was also analyzed. The ceramic matrix composites were made of porous SiO2 ceramic infiltrated with urea – urethane elastomer.In the infiltration process liquid mixture of the substrates is incorporated into ceramic pores using the vacuum pressure and elevated temperature.This results in thermal stresses being generated since the thermal expansions of the elastomer and ceramics are different upon cooling to ambient temperature. A bis-glycidylmethylmethacrylate (bis-GMA) polymeric matrix with the ceramic fillers, which is used for dental restoration, was also investigated.During the restoration the matrix polymerizes and shrinks.The shrinkage again results in strains, which lead to restoration failure by de-bonding at the composite-tooth interface.The fillers are added to the polymeric matrix to reduce the material shrinkage.The effect of the fillers on the residual stresses at composite-tooth and resin-ceramic filler interfaces has been evaluated in the present study. Both composite materials were analysed using the Finite Element Method employing the Ansys software.A linear and isotropic properties have been assumed for the ceramic and polymer components.For infiltrated composite (CMC) the simulations of both thermal and external loading of material were carried out.The models were subjected to thermal load simulating the cooling from fabrication (120oC) to room temperature (20oC), followed by compressive straining.For the dental restoration polymer matrix composite (PMC) the polymerization shrinkage of the composite was modelled using temperature-dependent expansion. The analysis of distribution of principal stresses in the CMC shows that a change of temperature leads to buildup of high tensile stresses in elastomeric phase and both tensile and compressive stresses in the ceramic pre-form.It was found that the thermal stresses present in composite mostly reduce the maximum values of tensile stresses in ceramics.It can be advantageous and result in an increase of composite toughness. The FE results obtained for the PMC show the effect of the resin shrinkage on the residual stresses at the resin-ceramic filler interface, which can cause de-bonding.Various fillers have been examined in terms of the efficiency in the reduction of these residual stresses. In more general sense, the present studies show the potential application of the finite element method in investigation of the residual stresses in different types of the composite materials.The future work will be concentrated on the experimental validation of the numerical results.