Yunpeng Jiang

A micromechanics-based incremental damage theory of bulk metallic glass matrix composites

Based on the Mori–Tanaka’s mean field concept, a micromechanics-based incremental damage theory was developed to investigate the mechanical performance of bulk metallic glass matrix composites under tension. Firstly, the shear band was considered to be a microcrack, and therefore a spherical fictitious inclusion-containing microcracks and the surrounding bulk metallic glass matrix were constructed. Based on the equivalence between the effective elasticity of microcrack-containing media and porous material, the volume fraction of the fictitious inclusion could be determined by the density of microcracks generated during a strain increment. The stress-based Weibull probability distribution function and percolation theory were applied to describe the microcrack evolution that results in the progressive damaging of bulk metallic glass composites. Based on the present model, the impact of shear bands on the tensile ductility was discussed for the composites with various microstructures. The predictions are in fairly good agreement with the experimental data, demonstrating that the developed analytical model is capable of successfully capturing the main features, such as yield strength, strain hardening, and stress softening elongation, of particle-toughened bulk metallic glass. The main conclusions will shed some light on optimizing the microstructures in effectively improving the tensile ductility of bulk metallic glass composites.

Ultrasonic dispersion of SiO2 particles in glassy epoxy resin

In this work, ultrasonic waves generated by an ultrasonic horn were used to disperse nano- and micrometer SiO2 particles into glassy epoxy resin. Many processing conditions, such as dispersion time, cooling, and materials volume, were varied systematically with an aim of achieving an optimum dispersion of particles. The glassy epoxy resin was reinforced by using spherical SiO2 powders with diameters of 0.7 μm and 1.6 μm and volume fraction of 0–20%. Dog-bone-shaped specimens were fabricated and measured under uniaxial tension for determining the fundamental material properties. Experimental results revealed that (1) increasing dispersion time resulted in more homogeneous dispersion, but excessively long dispersion could not further improve the dispersion effect; (2) the influence of dispersion time to neat epoxy is negligible; and (3) fracture surface of glassy polymer is very smooth, which is a viscous flow process different from metals. Finally, ultrasonic wave has proved to be a good technique for effectively dispersing SiO2 powders in glassy epoxy resin.

Micromechanical Modeling the Plastic Deformation of Particle-Reinforced Bulk Metallic Glass Composites

A micromechanics model was employed to investigate the mechanical performance of particle-reinforced bulk metallic glass (BMG) composites. The roles of shear banding in the tensile deformation are accounted for in characterizing the strength and ductility of ductile particle-filled BMGs. For the sake of simplicity and convenience, shear band was considered to be a micro-crack in the present model. The strain-based Weibull probability distribution function and percolation theory were applied to describe the equivalent micro-crack evolution, which results in the progressive failure of BMG composites. Based on the developed model, the influences of shear bands on the plastic deformation were discussed for various microstructures. The predictions were in fairly good agreement with the experimental data from the literatures, which confirms that the developed analytical model is able to successfully describe the mechanical properties, such as yield strength, strain hardening, and stress softening elongation of composites. The present results will shed some light on optimizing the microstructures in effectively improving the tensile ductility of BMG composites.