Abstract:

The multiple frictional contact dynamics of the flexible threshing tooth against grains were presented using an addition-deletion constraints approach. During threshing， the grains undergo impacts and rubbing as they fall from straw to become free particles， thus， they experience a serious of frictional collisions and mutual sliding with tooth. An accurate model of a flexible threshing tooth was established on the basis of high-order rigid-flexible coupling theory. The threshing process was characterized by load-off， multiple sliding-stick collisions and separation. An addition-deletion constraints approach was used to solve the dynamic equations for separation， initial contact， stick， and slip. The contact detection and prediction were made with every integral step. Once contact-pairs between threshing tooth and grains were detected through searching algorithm， the multiple contact constrains as well as constrains equations were activated. Corresponding computational strategy software in the C programming language was developed with explicit solution method. It can obtain the vibration and deformation of threshing teeth， as well as the normal impact force and the tangential stick-slip kneading force of threshing teeth against grains. EDEM software simulation and experimental verification were carried out on the longitudinal flow flexible threshing drum model. The results show that the flexible tooth exerts a less impactful kneading force than the rigid pole tooth on cracked grains or seed， thereby reducing the rate of grain damage， and is thus favorable for increasing the combined benefits to paddy production.

Key words: agriculture engineering, rigid-flexible coupling theory, Lagrange multipliers approach, flexible threshing tooth, stick-slip