Crack patterns in layers: effect of the thickness and mechanical properties

Abstract:

The surface of planets is host to many regions displaying cracks patterns that have been identified as potential dessication cracks. Crack patterns can be observed at multi-scales from millimeters in rocks to several kilometers on planetary surface. The mechanisms of cracking usually result from differential shrinkage stress (due to a drying process or temperature change). A large variety of crack morphologies is involved depending on both the microstructure and the thickness of the layer : crack can form isolated junctions or interact each other. In last case cracks can divide the plane hierarchically leading to broken or connected network of cracks, or grow in-depth resulting in the well ordered basalt columns. In particular, crack patterns strongly depend on both the mechanical properties and the thickness of the layer.

To understand the physical process involved, the geometrical characteristics of the crack pattern (crack spacing, crack aperture or crack depth) are analyzed by laboratory testing procedures. In this way, crack patterns can be modeled by the drying layers of aqueous suspensions of nanoparticles (silica particles). During the drying process, advection towards the evaporation surface accumulates particles and leads to a porous structure filled of water. The mechanical properties of the layer are related to the structure of the layer and are measured using indentation testing. Depending on the accumulation rate, solid layers exhibit non-homogeneous mechanical properties in depth. This affect the crack formation and stability of crack propagation.