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.