Experimental determination of the mechanical properties of highland barley grains

Background The aim of this study was to investigate the conventional and viscoelastic mechanical properties of highland barley grains to provide a foundation for optimizing harvesting and processing equipment. Methods The triaxial dimensions, 1,000-grain weight, and unit weight of three highland barley varieties (Beiqing-7, Kunlun-5, and Yunqing-8) were determined at different moisture contents (9.0–22.9%). The friction coefficients and angles of repose of the grains were measured using an inclined plane instrument and an angle-of-repose measuring device. Stress relaxation and creep tests were conducted using a dynamic thermomechanical analyzer (Q800). The stress relaxation and creep data were fitted and analyzed using the Maxwell and Burgers models, respectively. The shear mechanical properties of the grains were measured using a texture analyzer. Results As the moisture content increased, the length, width, height, 1,000-grain weight, arithmetic mean diameter, and geometric mean diameter of the grains increased significantly, whereas the unit weight decreased. Moreover, the highest friction coefficient was observed between the grains and a Q235 steel plate. The friction coefficient and angle of repose decreased as the moisture content decreased. Furthermore, the shear failure force and shear failure stress of the grains increased gradually as the moisture content decreased. The Burgers model accurately described the creep behavior of the grains, whereas the three-element Maxwell model described their stress relaxation behavior. The model results indicated that increasing moisture content led to a decrease in elastic modulus and an increase in creep deformation. The triaxial dimensions, 1,000-grain weight, and unit weight of Beiqing-7 grains were the largest, and their mechanical properties were the most favorable. The friction coefficient of Yunqing-8 grains was the largest; however, their angle of repose was the smallest. Conclusion The findings of this study provide a scientific basis for the development of mechanized harvesting and processing equipment (peeling, flour milling, and storage) and for parameter optimization in highland barley production.