Quasi-static compressive tests to determine the mechanical properties of individual brown rice kernels were conducted on whole kernel rice of Hashemi and core specimens of Khazar varieties. The magnitudes of the failure force, failure deformation, breakage energy and apparent elasticity modulus for Hashemi kernels were determined at two moisture content levels, namly, %11 and %17 (w.b.) at four levels of loading rates ranging from 1 mm/min to 5.5 mm/min. For the Khazar variety, the magnitudes of failure stress and strain, as well as toughness and elasticity modulus were determined at moisture content of %14 (w.b.) for five levels of loading rates ranging from 0.5 mm/min to 1.5 mm/min. Statistical analysis of the test results showed that deformation rates had no significant effect on the mechanical properties. Moisture content had a significant effect on all grain mechanical properties. Decreasing moisture content caused significant increases in all these properties. The failure force and the breaking energy for Hashemi kernels increased more than double, when the moisture content decreased from 17% to 11%. The magnitudes of failure force and breaking energy varied from 56 N to 115.7 N, and from 2.01 mJ to 5.23 mJ, respectively. The means of apparent elasticity modulus for compressive test on the core specimens was calculated to be 1.762 GPa at 17% moisture content and 2.835 GPa at 11% moisture content. Compressive strength and apparent elasticity modulus for Khazar variety were determined to be 36 MPa and 973.4 MPa, respectively. Some of the mechanical properties compared well with the published data.

Keywords: Mechanical properties, rice, Compression test, Failure stress, Elasticity modulus

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