Determination of the restitution coefficient of seeds and coefficients of visco-elastic Hertz contact models for DEM simulations

J. Horabik, M. Beczek, M. Molenda, M. Ryzak, P. Parafiniuk, R. Mazur
Biosystems Engineering
Hertz contact, impact, restitution coefficient, seeds, visco-elastic model

In this study, we determine the coefficients of restitution (CoRs) of seeds coming from three plants, namely the pea (Pisum sativum L. cv. Piast), soybean (Glycine max (L.) Merr. cv. Annushka) and rapeseed (Brassica napus L. cv. Licosmos), at three levels of moisture content for an impact velocity V0 ranging from 0.17 to 8.8 m s−1. We obtain high-speed camera measurements as well as single-drop and repeated-bounce tests. We record the impact force–time relationships Fn(t) using a piezo-ceramic pressure sensor. The results show that the rate of decrease of the CoR with an increase in V0 was the highest for rapeseed having the highest moisture content (MC), and it was the lowest for pea seeds having the lowest MC. We perform experiments to model the relationships CoR(V0) using visco-elastic contact models based on Hertz contact theory. The impacts of dry seeds for three crops were best illustrated using three different contact models, for pea – Kuwabara and Kono (1987), soybean – Alizadeh et al. (2013) and rapeseed – Hu et al. (2011). For higher MC, models which provide a more nonlinear CoR(V0) relationship appeared to be more appropriate, i.e. Kuwabara and Kono (1987) for the pea and soybean, while the model of Alizadeh et al. (2013) better described the behaviour of rapeseed. Visco-elastic contact models which were selected using the least-square method provided a very good approximation of CoR(V0) and impact time tc(V0) relationships, and a sufficiently good approximation of the shape of Fn(t) relationships.

Keywords: restitution coefficient, impact, seeds, hertz contact, visco-elastic model.

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