MESOMECHANICAL CHARACTERIZATION OF IN SITU RICE GRAIN HULLS
Mesomechanical properties (those on a scale between micro and macro) of in situ rice grain hulls are of 
fundamental interest in engineering design of cereal postharvest processing equipment. However, their measurement often 
requires new experimental methods. A scheme was developed combining simple tension and three–point bending tests for 
characterizing mesomechanical properties of in situ rice grain hulls. Sample groups were examined at 27_C, 15% wet basis 
moisture content, and at 1 mm/min crossbar speed. The load–displacement curves indicated that the hull fracture was brittle, 
and it appeared to be more so in the longitudinal tension mode than in the transverse (cross) tension mode. The general 
material orthotropy in the hull due to longitudinal or transverse cellular texture had a minor effect on these properties. 
Structural orthotropy was manifested primarily through the overall shape, surface profile, and silicon strengthening 
characteristics of the rice grain hull. The weakest link is at the seam where the lemma and palea interlock into an S–shaped 
“lap–joint,” where the stress concentration factor based on finite element analysis was from 5 to 9. The nominal structural 
orthotropy index (SOI) of rice grain hulls was estimated to be 5 to 7.