Abstract
In order to study the relationship between cohesion and void volume of cooked rice, two-dimensional assembly of 350 cylinders was set up in the condition of the closest packing within 10×10 cm frame with a constant lateral force. The size of cylinders was 0.5 cm in radius and 5 cm in length. Three kinds of materials for cylinders, polyethylene (PE), silicon rubber (SR) and foamed rubber (FR) were examined. Normal force-deformation curve and the fractional void ratio betweencylinders were determined. PE assembly showed clear V-shaped faulting crack. With the increase in void volume by adding polypropylene straws (PPS), it seems that compressive force was absorbed by voids of PPS and breaking strain was twice as much as that of PE alone. On the other hand, SR assembly showed no clear crack. SR+PPS assembly behaved as if the force-deformation curve of PE+PPS was expanded. FR assembly was compressed mainly into the central part and void parts appeared in both sides. As compressive strength parameters, the angle of internal friction (φ) and apparent cohesion (c), were calculated by the analysis of Mohr-Coulomb curves in various lateral force data. Increasing with void between the assembly, any of these materials decreased in its friction. It was considered that the above mentioned behavior is well reflected in actual cooked rice.
