Effects of temperature and moisture content on mechanical properties of brown rice

Abstract

Investigations were conducted on the ultimate tensile and compressive strengths, modulus of elasticity, proportional limit and modulus of toughness of individual brown rice kernels at moisture equilibrated conditions involving three temperatures and four relative humidities. Other observations of the mechanical properties of brown rice were made after grains were exposed to a moisture absorbing environment. The results indicate that the mechanical properties of rice are dependent on moisture, variety and temperature. Moisture had the greatest effect on the mechanical properties of rice. In general, all strength values decreased as moisture content of the grains increased. Long grain brown rice yielded higher maximum stress, modulus of elasticity and modulus of toughness than did medium grain rice. The temperature effect was dependent on variety and type of mechanical force which was applied to the grains. Core specimens, prepared by cutting off both kernel ends, were subjected to uniaxial compression by mess of parallel plates at a constant loading speed until failure occurred. Breaking force, deformation and energy were measured directly from the force-deformation curves. Ultimate compression strength, modulus of elasticity and modulus of toughness were calculated from data obtained from the force-deformation diagrams. Compressive strength was affected by the environmental condition at which the grains were equilibrated. Nato brown rice required more force but generally less energy to cause failure under uniaxial compression. For a given temperature, ultimate compressive strength, modulus of elasticity and modulus of toughness depended on moisture content of the grains.