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Coefficients of friction of wheat for grain-on-grain and on galvanized corrugated steel sheet were investigated using a modified direct shear apparatus. Tests were conducted under a normal pressure of 20.7 kPa using soft red winter wheat at a moisture content of 11.2% (w.b.) and an uncompressed bulk density of 740 kg/m 3. Three consolidation procedures and three methods of deposition of grain in the test chamber were used. Test results of grain-on-grain friction showed that consolidation procedure markedly influenced the force-displacement relationship, while its influence on the coefficients of friction were small. Shearing to peak strength as a consolidation method erased all effects of loading history and resulted in the highest values of the coefficient of friction. Grain-on-grain coefficients of friction were in a range from 0.47 + 0.007 to 0.56 + 0.004 depending on the method of grain deposition. Friction on two dimensionally different samples of corrugated steel sheet was examined using three methods of grain deposition. Corrugation depths were 13 mm on both samples, while their periods were 67.5 mm (short) and 104 mm (long). Coefficients of friction on the short-period corrugated samples were in a range from 0.42 + 0.0 to 0.46 + 0.004 and were significantly higher (a = 5%) than those on the long-period corrugated sample, which ranged from 0.36 + 0.003 to 0.39 +0.003. The method of grain deposition significantly (a = 5%) influenced the coefficients of friction of wheat on both types of corrugated steel sheet.

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Investigations were performed to verify the applicability of a direct shear method as recommended by Eurocode 1 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 ΔL/D level of the sample diameter. Values for the angle of internal friction were found to range from 22.1°–35.5° 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.

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