Composite materials are being more frequently used in a wide variety of industries. Their high strength to weight ratio makes them a desirable material in many applications. In some specific cases, polymer based composites can be subjected to large changes in temperature causing undesirable amounts of expansion. To reduce the composite's thermal expansion, materials that have negative coefficients of thermal expansion are used as a filler material. Zirconium tungstate (ZrW2O8) is a metal oxide which exhibits thermal behaviors not seen in most other materials. When subjected to a positive temperature change, ZrW2O8 will decrease in volume as opposed to most other materials which show an increase in volume. This makes ZrW2O8 an ideal candidate to be used as filler material in these polymer composites to reduce their overall thermal expansion.
While experimental research on ZrW2O8 composites has previously been completed, this research looked at the finite element modeling of these composite materials and tried to gain a better understanding of their possibilities. Initial two-dimensional models were created using COMSOL Multiphysics with basic geometries for both the matrix and filler. The results from these tests showed that the filler geometry had little effect on the expansion results and volume fraction was the most important factor. To further test this, more complex models were created using three-dimensional geometries with the same volume fractions. These results confirmed the findings of the two-dimensional tests by showing similar expansion. These results were then compared to published experimental data where it was found that all the models showed less expansion than the physical experiments of the same volume fraction.
The difference between the finite element analysis (FEA) and experimental results was attributed to the interaction between the filler and matrix materials. In the models, the bond between the two was considered perfect, with no voids or separation, leading to the filler material having more effect on the overall properties of the composite. In real-world testing, this perfect bond would be nearly impossible to achieve. To build on this idea and gain a better understanding of how the experimental testing compared to the FEA, models with no bond between the filler and matrix were created. Using the results from these models, as well as the models with a perfect bond, an upper and lower bound of expansion were able to be created. All published experimental data looked at was contained within these FEA-created bounds. This showed that while some bond was likely made between the filler and matrix materials, there was room for improvement if less expansion was desired.