The effect of impact angle and bond strength on fragmentation in laminated materials

Abstract

An experimental study was undertaken to explore the effects of weak laminations on the fragmentation of impacting rocks. In this work, the fragmentation behavior of manufactured disc specimens of laminated travertine marble is described according to variations in the lamination bond strength, the orientation of laminations at impact, and the impact energy. An experimental apparatus and procedure were developed so that the discs, 96mm in diameter and 25mm thick, could be impacted neatly on their circumferential edge, at a selected lamination impact angle, and subject to filming with a high speed camera. The results of the study generally indicated that weaker bonds cause fragmentation from lower drop heights, as expected. However, the results also indicate that the critical height for breakage is relatively lower and insensitive to the impact angle when the laminations are between 45 and 90 degrees relative to the impacting surface, but the critical height for breakage increases significantly (by a factor of between 2 and 4) as the orientation of the laminations becomes parallel to the impact surface. The presence of laminations and their orientation to the impact surface, directly influenced the failure mechanism of specimens upon impact. At low lamination impact angles, failure was by parting along laminations in direct tension (reflected compression). At intermediate impact angles (approximately 45 degrees), the fragmentation of the specimens was more explosive and fractures were a combination of steps across stronger sheets, and splits along weaker bonded laminations. For high impact angles, fragmentation occurred in indirect tension, along weak laminations.