On Applicability of a Direct Shear Test for Strength Estimation of Cereal Grain

Abstract

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.

Mechanical properties of some granular agricultural materials used in silo design

“…It is believed that the average particle size to the specimen size ratio had an influence on the test results. The results were similar to those reported by Molenda and Horabik (2004) for barley using direct shear tests. Nevertheless, the results reported by these authors from direct shear tests were approximately 1.5°and 6°higher than those obtained here using triaxial tests for wheat and corn, respectively.…”

“…The results obtained for this material property were similar to those provided by other authors such as Zhang and Britton (2003), Molenda and Horabik (2004), Lebegue and Boudakian (1989), Muir and Sinha (1988) or Molenda and Horabik (2004) for wheat and barley, corn, sunflower, and oats, respectively. It should be noted that the results for wheat were approximately three degrees smaller than those obtained by Molenda et al (2002b) and by Molenda and Horabik (2004) using direct shear tests, whereas the results for barley were about two degrees smaller than those reported by the same authors. These differences could be attributed to either the type of the shear box or the manner in which these tests were conducted.…”

“…In this case, for the low values of normal pressure, a curve instead of a straight line could have been obtained for the Morh-Coulomb failure envelope, thus reducing the values obtained for the apparent cohesion. The results for wheat, barley, corn, and oats were similar to those reported by Molenda and Horabik (2004) using direct shear tests. In the case of wheat, the values obtained here were slightly higher, at least by 2 kPa, than those provided by Molenda et al (2002b).…”

“…It should be noted that barley did not have any apparent cohesion, which differed from the trend observed for the same material by Molenda and Horabik (2004) using direct shear tests. However, even when the types of tests carried out were different, the results obtained for wheat and corn were similar to those reported by these authors.…”

A relationship between friction plate roughness and the external friction angle of wheat kernels

“…According to Molenda et al, [5] Frączek, [1] Horabik, [6] Molenda and Horabik, [7] Afzalinia and Roberge, [2] Sharobeem, [8] Ibrahim [9] and Bakun-Mazor et al, [10] the frictional properties of seeds are influenced by frictional conditions (normal load, sliding distance, sliding velocity, seed orientation relative to the direction of movement), the parameters of the friction surface (type, roughness), seed properties (moisture content, species, variety, ripeness, variations in shape) and external conditions (temperature and humidity). The frictional properties of seeds have been extensively studied, but most researchers have identified only the type of tested friction materials (e.g.…”