Modeling of setting stresses in particle-reinforced polymer composites using finite element analysis
Boriek, Aladin Mohamed
Akin, John Edward.
Doctor of Philosophy
This work uses three-dimensional Finite Element Analysis (FEA) to investigate the effect of geometric arrangement of particulate reinforcement in highly filled polymer composites (such as polymer concrete) on the setting stresses that develop in these materials during cure due to resin shrinkage during polymerization. These composites were initially modeled by systems reinforced with spherical particles packed in simple cubic (SC) and face-centered cubic (FCC) arrangements within the polymer matrix. A pronounced decrease in setting stresses was observed in the FCC system, which has a greater aggregate to resin ratio and more of resin domains per unit cell. A hexagonal-close-packed arrangement of hexagonal, prism-shaped aggregate was also analyzed and found to develop higher stresses, indicating that aggregate shape has an effect on setting stresses. A second set of models investigated the effect of size gradation and geometric arrangement of spherical reinforcing particles on setting stresses. The maximum stresses occur at the particle-resin interface, underlining the importance of resin/aggregate adhesion. Reduction of setting stresses by a factor of two was observed in systems with efficient packing, achieved with proper size gradation and close-packed geometry. A microstructural model for a polymer composite system based on a fairly random arrangement (FRA) of aggregate particles was also developed. This model gives a realistic representation of actual particle reinforced polymer composites. FEA results were used to develop an empirical equation for maximum setting stresses for Particle reinforced polymer composites. A probabilistic model for the distribution of voids in polymer composites was developed by solving a non-linear constrained optimization problem. The probability distributions of voids was used with a specially developed algorithm to generate the voids distributions in specific composites. The effect of voids on setting stresses in FRA models was discussed. In polymer composites voids tend to act as stress relief. This effect is more pronounced in poorly packed systems. This study provides an understanding of setting stress distribution in polymer composites. This work provides guidelines for optimizing the amount, shape and particle size distribution of the reinforcing aggregate in polymer composites so as to minimize setting stresses, thus leading to composites with significantly enhanced strength.
Engineering; Materials science