Directional crack propagation of granular water systems

Abstract

Pattern dynamics of directional crack propagation phenomena observed in drying process of starch-water mixture is investigated. To visualize the three-dimensional structure of the drying-fracture process two kinds of experiments are performed, i.e., resin solidification planing method and real-time measurement of water content distribution with MR instruments. A cross section with polygonal structure is visualized in both experiments. The depth dependency of cell size is measured. The phenomenological model for water transportation is also discussed.

Morphometric analysis of polygonal cracking patterns in desiccated starch slurries

“…In contrast, L φ for the corn starch is believed to be less than 11 mm, and as a result, P (S) did not show significant dependence on L th . Our speculation of L φ ≤ 11 mm for corn starch is consistent with the existing studies based on X-ray tomography 34 and destructive sampling 37 , which unveiled the presence of a sharp dry front with a thickness of a few millimeters. To further examine the validity of the estimation that L φ for potato starch should be larger than that for corn starch, we have measured the spatial distribution of the water content within potato starch samples with 50 mm in slurry thickness; see Appendix B for the method of measurement.…”

“…As evaporation continues, φ w near to the top, air-exposed surface decreases with time, while the corresponding value far below the top surface remains at the initial value. This gives rise to the development of an intermediate zone that is sandwiched by the top drying surface and the far-below fully wet slurry, through which φ w (z) undergoes a gradient with respect to z from φ w ≃ 0 at the top surface to φ w = φ max w at the bottom 34,37 . The vertical limits of the intermediate zone depends on the magnitude of the local diffusivity D(φ w ) of the water content in the slurry.…”

“…[34] that the peak located at 120 • -130 • for corn starch and all the measurement data of joint angles fell into the range from 90 • to 180 • . As well, the standard deviation of the joint angles, σ θ , estimated by the present analysis shows a certain deviation from the earlier one; it was reported in Ref.…”

“…The two types of cracks can be differentiated in a visual way 2,34,38 . Primary cracks appear successively and they typically meet at T-shaped junctions, since a later crack will preferentially meet an earlier one in a normal direction.…”

“…Of the many candidates, corn starch slurry (i.e., a dense mixture of corn starch powder with distilled water) [33][34][35][36][37][38] can exhibit heterogeneous crack network characteristics consisting of two distinct types, namely primary cracks and secondary cracks. Primary cracks are long and nearly straight cracks, and they emerge in advance of the appearance of secondary cracks.…”