خواص مكانيكي كششي دانه برنج در رطوبت ها و دماهاي مختلف خشك كردن

Mechanical (Tensile) Properties of Rice Grain at Various Moisture and Temperature Levels during Drying Process

Tensile mechanical properties of brown rice grain were determined for two rice varieties of Hashemi and Khazar at three moisture content levels of 10.2,12.2 and 13.25% (w. b.), and four drying temperature levels of 35,45,55 and 64ʹC. The mechanical testes were conducted in the diametral compression test method, because of the experimental difficulties involved in the uniaxial tension tests. In this method a core specimen of brown rice is pressed in a lying posision between two flat plates. Tensile strength, tensile failure strain and tensile modulus of elasticity were determined for various treatments. Statistical analysis of the results showed that variety, moisture content and drying temperature significantly affected the properties examined. However, variety had no significant influnce on tensile failure strain. In general, all the tensile mechanical properties increased as moisture content and/or temperature of kernel decreased. Moisture content had the greatest effect on different mechanical properties of rice. Analysis of varience of data indicated that variety exerted a significant effect (at %5 level) on tensile strength. Tensile strength of Hashemi variety was greater than that of Khazar. This puts emphasis on stress cracking susceptibility due to variety. At the different experimental conditions of the study, Hashemi and Khazar rice tensile strengths ranged from 3.97 to 10.05 and 3.19 to 8.10 MPa, respectively, emphaizing the stress cracking susceptibility of these varieties.