Microstructural dependence of mechanical properties and their relationship in modern resin-based composite materials

The aim of the study was to determine the influence of the microstructure on the mechanical behavior of resin-based composites (RBC) with little variation in chemical composition, and to verify a possible mutual dependency.

Four RBCs with similar chemical composition of fillers (Ba-Al-B-F-Si-glass, SiO₂), but with different mean (0.7 µm to 1.8 µm) and maximum particle size values (5 µm to 20 µm) were selected. Fracture toughness/K_IC was evaluated in an NTP (Notchless Triangular Prism) test. Flexural strength/FS and modulus/E were measured in a 3-point-bending test. A fractographic analysis determined the fracture mode and origin. Quasi-static and viscoelastic parameters were assessed by a depth-sensing indentation test equipped with a DMA-module. One and multiple-way analysis of variance (ANOVA), Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), and Weibull statistics were applied.

The influence of the microstructure and the chemical composition of the organic matrix is weighted differently in the measured properties. The inorganic filler amount influences highest K_IC (η_P²=0.813), followed by FS (η_P²=0.768) and E (η_P²=0.611). An optimized filler distribution with a high proportion of larger fillers up to 20 µm contributes to high FS and E data. The reliability of the material (Weibull parameter m) did not depend on the origin of fracture. Smaller inorganic fillers and the addition of 1% larger pre-polymer fillers improve the fracture toughness. Analysed RBCs were well adapted to chewing frequencies.

The properties of RBCs can be tuned by little variation in microstructure and monomer matrix.

Reverse engineering of clinically successful materials can be used to better design future RBCs.