16 research outputs found
Fracture Patterns Induced by Desiccation in a Thin Layer
We study a theoretical model of mud cracks, that is, the fracture patterns
resulting from the contraction with drying in a thin layer of a mixture of
granules and water. In this model, we consider the slip on the bottom of this
layer and the relaxation of the elastic field that represents deformation of
the layer. Analysis of the one-dimensional model gives results for the crack
size that are consistent with experiments. We propose an analytical method of
estimation for the growth velocity of a simple straight crack to explain the
very slow propagation observed in actual experiments. Numerical simulations
reveal the dependence of qualitative nature of the formation of crack patterns
on material properties.Comment: 37 pages,18 figures,REVTEX,submitted to Rhys.Rev.
Shaking-induced stress anisotropy in the memory effect of paste
When paste of fine granular particles and water is shaken in one direction and then left undisturbed, memory of the direction of shaking is retained for a sufficiently long time to result in a directional crack pattern that appears after drying. Although it has been conjectured that anisotropy in residual stresses caused by plastic deformation is responsible for this memory effect, to this time, no evidence of such anisotropy has been found. We experimentally investigated the stress in drying paste by measuring the bending of elastic plates supporting the paste sample and found stress anisotropy developing in paste. Additional bending tests suggested that paste retains plasticity during the drying process and that plastic deformation is not always frozen in place after initial shaking
Dynamic Scaling of the Growing Rough Surfaces (Mathematical Aspects of Pattern Formation in Complex Fluids)
Erasure of memory in paste by irradiation of ultrasonic waves
Densely packed colloidal suspension, called paste, remembers the direction of applied forces, such as vibration and flow, and these memories kept in paste can be visualized as morphology of desiccation crack patterns. For example, when the paste remembers the direction of vibration, all primary cracks propagate in the direction perpendicular to the direction of initial vibration. On the other hand, when the paste remembers the direction of flow, all primary cracks propagate along the direction of initial flow. These results indicate that external forces imprint easy-breakable direction into paste as memories. Therefore, by controlling memories in paste, we can tune to produce various types of crack patterns, such as cellular, radial, lamellar, ring, spiral and lattice structures. Recently we have found that memories in paste can be erased by the irradiation of ultrasonic waves to paste as we obtain only isotropic and cellular crack patterns without any anisotropy related to memory effect. This method can be applied to increase the breaking strength of dried paste by homogenizing microstructure in paste