Mechanical Properties of Sugar Beet Roots under Impact Loading Conditions

Root damages due to mechanical impacts result in deterioration in commercial sugar beet quality. In order to determine the mechanical characteristics of roots, a stand equipped with a pendulum enabling impact investigations of whole beets was used. The roots were stored in a monitored environment for up to 5 days (temperature 15 ± 2 °C, 40 ± 2%). During the tests, the beets were struck against a flat steel resistant surface with the velocities V = 0.5, 1.0 and 1.5 m·s^-1. The measurements of local root curvatures in three chosen impact areas and the deformation (d) allowed modelling of the volume of contact (CV) by means of the ellipsoid cap. These investigations enabled the determination of the relations between the maximal impact force, F, the impact energy, E, and the absorbed energy, E, as well as the contact volume and impact velocity, taking into account the root storage time, S. It was found that the maximal impact force increased with increasing impact velocity and decreased with the storage time for each group of roots. With increasing velocity, there were also increases in the following: impact energy, absorbed energy, contact volume and maximal deformation, as well as absorbed energy, referred to as the mass E from V. The mean values of the stresses (σ), being the quotients of the impact force (F) and the surface area of the ellipsoid cap base (A), were 0.81-1.17 MPa, 1.064-1.59 MPa and 1.45-1.77 MPa for the velocities of 0.5, 1.0 and 1.5 m·s^-1, respectively. It was confirmed that the statistical significance of the mentioned parameters changes depending on the impact velocity.