DISCRETE ELEMENT MODELLING OF THE IMPACT PARAMETERS OF A SELECTED FRUIT: MODEL VALIDATION AND EFFECT OF DAMPING

The Discrete Element Method has been applied to numerical modelling of the impact process in fruit with a view to obtain information on damages due to impact. A DE code which incorporated a non-linear viscoelatic contact law, real containing walls and particle deformation developed from an existing code using a linear elastic contact law without containing walls was used. The code was validated with available theoretical and experimental results on impact behaviour of rubber spheres. The parametric variations with different damping coefficients were then simulated for a selected fruit dropped from a height of 10, 15, 20 and 30 cm onto a hard flat surface. The parameters investigated include variation in the force, time, velocity, deformation and the peak force during contact in relation to the height drop. The experimental and the simulated were found to be in good agreement (p>0.05) with no significant differences. The peak forces predicated by the simulation were 42.5, 85.2 and 137.7 N as compared to 40, 87 and 136 N from the experiment for spheres weighting 29.4, 95 and 190.7 g respectively. The predicted time of contact was however slightly lower in all the cases but there is no significant difference between the experimental and the predicted (p>0.05). The study with the fruits also showed good agreement with the existing data, indicated by the features of the curves, which showed that the non-linear viscoelatic contact model is a good approximation for predicating the contact behaviour of viscoelatic materials. Information on the parameters required in the selection of appropriate materials and range of parameters useful in the design of handling equipment were provided. The model is therefore a useful tool in the study of impact process for agricultural particulate (discrete) materials