Kun Ferenc (Debreceni Egyetem, Elméleti Fizika Tanszék)

Controlled fracture patterns in shrinkage induced cracking

Az előadás kivonata: Shrinkage induced cracking is abundant in nature giving rise to the formation of spectacular polygonal crack patterns for instance in dried lake beds, in permafrost regions on Earth and Mars, and in cooling volcanic lava. The simplest realization of such crack patterns can be achieved in the laboratory by desiccating thin layers of dense suspensions such as coffee, clay, or calcium carbonate on a rigid substrate where the gradual solidification leads to shrinkage stresses and cracking. Recently, a promising method of the generation of controlled crack patterns has been suggested by applying mechanical excitation to dense suspensions before desiccation sets in. Due to its technological potential, we investigate such possibilities of crack patterning in the framework of a discrete element model focusing on the temporal and spatial evolution of anisotropic crack patterns as a thin material layer gradually shrinks. In the model a homogeneous material is considered with an inherent structural disorder where anisotropy is captured by the directional dependence of the local cohesive strength. Based on computer simulations and analytical calculations we explore how the structure of the crack pattern and the shape of emerging fragments evolve as the strength of anisotropy is varied, and determine those features of the system, which remain robust at any degree of anisotropy. In particular, we demonstrate that cracking of the layer proceeds in bursts of activity with scale free statistics similar to a broad class of fracture phenomena.

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