A new method for the measurement of the tensile strength of rice grains byusing the diametral compression test

Breakage of rice grains during milling can be attributed to the presence of fissures, caused by stresses related to shrinkage during drying. These fis sures are usually caused by a tensile failure in the center of the grain. V ery few data of the tensile strength of rice grains have been published, wh ich is related to experimental difficulties. An attractive method for the m easurement of the tensile strength is the diametral compression test, in wh ich a cylinder is pressed between two flat plates. In this paper, results a re shown of the application of the diametral compression test on rice grain s. At a temperature of 20 degrees C, a moisture content of 5.7% (w.b.) and a deformation rate of 7.10(-3) min(-1) the tensile strength of rice grains is 10 +/- 2 MPa, the compressive strength is 73 +/- 15 MPa and the Young's modulus is 1.1 +/- 0.1 GPa. The Young's moduli from the diametral compressi on tests are not significantly different from those from uniaxial compressi on tests, which agrees with the theory. The obtained tensile strength value s are in accordance with those from the literature. The repeatability of th e diametral compression tests is of the same order as the repeatability of uniaxial compression tests. (C) 1999 Elsevier Science Ltd. All rights reser ved.