Study of the Mechanism of Dynamic Ductile Fracture of Two-Phase Materials

摘要

Dynamic ductile fracture of two phase material have been investigated in two stages. The first stage is a model study where an idealized two phase material, single crystal Cu SiO2, was used to study the initiation and growth of voids, the dislocation morphology and the other microscopic behavior that took place in the as-impacted specimen. Important findings are voids were nucleated from only a fraction of secondary particles SiO2, the larger strain has induced the higher void density, and the dislocation cell structures were formed with the average cell size being constant for the range of strain rates investigated. Analytical models were constructed with the aim of simulating the void growth in a two phase material subjected to high strain rate deformation, static void growth model and dynamic void growth model. A comparison of the void density indicated the static void growth model can predict the experimental results reasonably well for the smaller strain, but it fails to predict for the larger strain, while the dynamic void growth model can simulate the void growth well for the entire range of strain and strain rates. The second stage conducts a series of experiments on more realistic two phase materials, Al Si alloy and SiC(w) or SiC(p)/Al composite. The mode of the initiation and growth of voids was observed in the specimens that were impacted by Split Hopkinson bar test. The void density was also measured along the specimen axis and its values were compared with the analytical results by the static void growth model, resulting in a reasonably good agreement.