A STUDY OF RICE FISSURING BY FINITE–ELEMENT SIMULATION OF INTERNAL STRESSES COMBINED WITH HIGH–SPEED MICROSCOPY IMAGING OF FISSURE APPEARANCE

Finite–element analysis was performed to simulate stress distributions inside a rice kernel during drying. The distributions of radial, axial, tangential, and shear stresses were mapped and analyzed. It was found that during drying, two distinct stress zones existed inside a rice kernel: a tensile zone near the surface, and a compressive zone close to the center. Although as drying proceeded, radial, tangential, shear, and axial stresses all decreased in magnitude after they peaked, the first three (i.e., radial, tangential, and shear) stresses approached zero in magnitude and became neutral (i.e., neither tensile nor compressive) after 60 min of drying at 60 ³ C, 17% relative humidity (RH). Only axial stress remained at a pronounced level even after 60 min of drying at 60 ³ C, 17% RH, which helps explain why most fissures form perpendicular to the longitudinal axis of rice kernels. The results were well supported by the fissure appearance caught in this study with high–speed microscopy imaging and by other evidences on rice fissuring published in the literature.

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