Viscoelastic Characteristics of Potato Tissue Based on Stress Relaxation Tests

Stress relaxation tests on cylindrical samples of the Bellarosa potato cultivar were conducted over a wide range of deformation velocities, from 0.0002 m/s to 1.5 m/s. A three-element Maxwell model was applied to describe the response of potato tissue to the applied load. The effect of deformation velocity on the Maxwell model parameters and the values derived from the experimental stress relaxation curves was determined. The viscoelastic behavior of potato tissue was confirmed by the increase in the maximum force response with increasing deformation velocity. The relaxation times τ1 and τ3 decreased as the deformation velocity increased. The minimum force recorded at the end of the test and the elastic modulus E3 were substantially higher under quasi-static than under impact loading conditions. These two parameters provide a good description of the material state after deformation and indicate a greater degree of cellular structure damage during impact loading compared with compression at low deformation velocities. Potato tissue contains approximately 80% water and only 3% air spaces. Therefore, changes in the cellular structure are expected to be associated mainly with water movement within cells and through intercellular spaces, with the intensity of these processes depending on the deformation velocity.