Breaking down chipping and fragmentation in sediment transport: the control of material strength

Abstract. As rocks are transported, they primarily undergo two breakdown mechanisms: fragmentation and chipping. Fragmentation is catastrophic breakup by fracture in the bulk – either subcritical crack growth under repeated collisions, or from a single high-energy (supercritical) collision produces angular shards. Chipping distinct low-energy mechanism of impact attrition that involves shallow cracking; this process rounds river pebbles universal manner bed-load transport. Despite its geophysical significance, transition chipping to not well studied. Here, we examine experimentally measuring shape mass evolution concrete particles varying strength, subject collisions rotating drum. For sufficiently strong particles, occurred was characterized following: products were orders magnitude smaller than parent; rate insensitive material strength; experienced monotonic rounding toward spherical shape. strength decreased, observed onset cracking regime associated with fragmentation: became larger more varied; inversely proportional fluctuated non-monotonic. Our results validate conceptual numerical models for attrition: follows “Sternberg's law” exponential loss through time; fragmentation, lifetime increases nonlinearly consistent “Basquin's fatigue failure. We suggest bedrock erosion must be clarified incorporate mechanisms, pebble bedrock-channel may utilized deduce operative given environment.