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

Abstract

Finiteelement analysis was performed to simulate stress distributions inside a rice kernel during drying. Thedistributions of radial, axial, tangential, and shear stresses were mapped and analyzed. It was found that during drying, twodistinct 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, thefirst three (i.e., radial, tangential, and shear) stresses approached zero in magnitude and became neutral (i.e., neither tensilenor compressive) after 60 min of drying at 60C, 17% relative humidity (RH). Only axial stress remained at a pronouncedlevel even after 60 min of drying at 60C, 17% RH, which helps explain why most fissures form perpendicular to thelongitudinal axis of rice kernels. The results were well supported by the fissure appearance caught in this study withhighspeed microscopy imaging and by other evidences on rice fissuring published in the literature.