On applicability of a direct shear test for strength estimation of cereal grain

Investigations were performed to verify the applicability of a direct shear method as recommended by Eurocode I for testing the strength of cereal grains [2]. Tests on rye without preconsolidation have shown that stress-strain characteristics depend on the method of sample deposition. However, consolidation of the sample by twisting the top plate, as recommended by the code, neutralizes the influence of the grain packing structure on values of the angle of internal friction. Determination of the strength parameters for grain of six genera, under normal reference pressure of 100 kPa, and five levels of moisture content in a range from 10% to 20%, confirmed the applicability of the test. The only necessary modification of Eurocode procedure was elongation of the shear path up to the 0.1 DeltaL/D level of the sample diameter. Values for the angle of internal friction were found to range from 22.1degrees-35.5degrees and were dependent on the grain genus and moisture content. The majority of dry grain samples showed low cohesion (below 4 kPa), and thus, should be treated as free flowing material. The increase in moisture content resulted in an increase of cohesion up to the highest observed value of 12 kPa. Triaxial compression tests were performed on wheat of five levels of moisture content, and gave results that were in close agreement with the results of the direct shear test.