Theoretical analysis and finite element simulation of a rice kernel obliquely impacted by a threshing tooth

Impact damage is the main form of rice threshing and it is also a significant cause of rice injury. Based on contact mechanics, models of the compressed displacement and the largest pressure distribution were established for the case when the threshing tooth obliquely impacts against the rice kernel. A critical velocity formula for impact damage was developed. A computer-aided design model of a rice kernel comprising of three layered ellipsoids was established. HyperMesh software was used to partition mesh elements and to set material and contact parameters for each element, constructing a finite element model for the analysis. Using LS-DYNA software, the impact between the threshing tooth and the rice kernel was simulated and analysed. The simulation showed that the rice husk was subjected to tensile stresses. Tensile stress was a maximum at the front of the contact zone and shifted continuously. The entire kernel rolled during impact. The critical damage velocity for the kernel, corresponding to the critical von Mises stress was 29.5 m s−1, which was in agreement with experimental results.