Fracture and fragmentation patterns within a single cemented glass bead under impact

Abstract

Dynamic fracture and fragmentation within cemented granular materials play a significant role in controlling industrial comminution and blasting processes. In this study, impact experiments using a Hopkinson bar facility demonstrate that the damage pattern in a system of a single brittle glass bead covered by epoxy cement is highly dependent on the absorbed energy. Under small to moderate impacts the damage preferentially occurs in the cement material, while under stronger impacts the damage is prone to occur in the glass bead. Quantitative analysis using X-ray micro-computed tomography supports the understanding that friction is the most prominent energy dissipation mechanism, particularly during severe fragmentation processes. Using innovative techniques based on Fourier transform, the locality of damage within the cemented bead is then quantitatively analysed, as well as their preferential crack orientation. The resulting analysis shows that damage is most likely to occur along the central loading axis area of the cemented bead and forms cracks propagating through the bead along the impact direction, a pattern that is strikingly different from the failure pattern of non-cemented glass beads. Meanwhile, the central plane normal to the impact direction has the typical coplanar cracks, accompanied by oblique cracks (roughly 45∘ or 135∘ inclined to the loading direction) near the centre of the glass bead.