Polytetrafluoroethylene (PTFE) is a polymeric material with excellent self-lubricating properties. In this study, in order to improve the wear resistance of PTFE, the PTFE matrix was filled with soft-phase polyetheretherketone (PEEK) particles and hard-phase nano-ZrO₂ particles in varying volume ratios. A linear reciprocating friction tester was used to test the tribological properties of the PTFE composites. Optical microscopy (OM) and scanning electron microscopy (SEM) were utilized to observe the formation and evolution of the transfer film on the surface of the counterpart metal during the friction process. Molecular dynamics simulation software (Materials Studio MS) was used to simulate and analyze the frictional behavior between the molecular structures of PTFE composites and the counterpart iron atoms on a microscopic scale. The results showed that the uniformity and firmness of the transfer film had an important influence on the wear resistance of the material. PEEK and ZrO₂ nanoparticles were able to improve the firmness and formation rate of the transfer film, respectively, resulting in significant improvement in the wear resistance of PTFE (volume wear rate reduced from 7.7 × 10⁻⁴ mm³/Nm for pure PTFE to 1.76 × 10⁻⁶ mm³/Nm for nano-ZrO₂/PEEK/PTFE). Molecular dynamics simulations revealed that the poor wear resistance of PTFE was due to significant interlayer slippage within its molecular chains. PEEK molecular chains could effectively adsorb PTFE molecular chains and formed a strong bond. ZrO₂ nanoparticles also contributed to the overall stability of the PTFE matrix. Both soft and hard fillers significantly inhibited interlayer slippage between PTFE molecular chains, enhancing the shear deformation resistance of the material and thus improving the wear resistance of PTFE composites.

Determination of the coefficient of rolling friction of irregularly shaped maize particles by using discrete element method

Autonomous navigation for agricultural machinery has broad and promising development prospects. Kalman filter technology, which can improve positioning accuracy, is widely used in navigation systems in different fields. However, there has not been much research performed into navigation for sprinkler irrigation machines (SIMs). In this paper, firstly, a self-developed SIM is introduced. Secondly, the kinematics model is established on the platform of the self-developed SIM, and the updated Sage–Husa adaptive Kalman filter, which is an accurate and real-time self-adaptive filtering algorithm, is applied in the navigation of the SIM with the aim of improving the positioning accuracy. Finally, experiment verifications were carried out, and the results show that the self-developed SIM has good navigation performance. Besides this, the influence of abnormal observations on the positioning accuracy of the system can be restrained by using the updated Sage–Husa adaptive Kalman filter. After using the updated Sage–Husa adaptive Kalman filter for the SIM, the maximum deviation between the SIM and the predetermined path is 0.18 m, and the average deviation is 0.08 m; these deviations are within a reasonable range. This proves that the updated Sage–Husa adaptive Kalman filter is applicable for the navigation of sprinkler irrigation machines.

The materials tribology community has identified that the transfer film attached to the surface of the counterpart metal during the friction process is not only closely related to the filler modification material but also a key factor affecting the tribological properties of polymer composites; however, there is a lack of feasible methods to quantify the characteristics of the transfer film. In this study, Nano-ZrO₂ and polyetheretherketone (PEEK) were filled into a PTFE matrix in order to enhance the wear resistance of polytetrafluoroethylene (PTFE). The tribological properties of the modified PTFE composites were tested using a linear reciprocating friction and wear tester, and the entire friction experiment was designed in seven separate stages. Morphological features were extracted and analyzed from photographs of the transfer film acquired by optical microscopy at each friction stage using an image processing program. The thickness and roughness of the transfer film sections were measured using a non-contact profilometer. Abrasive debris were collected, and their morphological features were observed with an electron microscope. The results showed that the synergistic addition of soft PEEK and hard Nano-ZrO₂ particles effectively inhibited interlayer slippage between PTFE molecular chains, dramatically reducing the size and yield of abrasive debris, and facilitated the improvement of the thickness and firmness of the transfer film, which significantly enhanced the wear resistance of the PTFE composites (the lowest volumetric wear rate for Nano-ZrO₂/PEEK/PTFE was only 1.76 × 10⁻⁴ mm³/Nm). Quantitative analyses of the morphological characteristics of the transfer films revealed that the coverage and roundness of the transfer films gradually increase with the friction stroke, while the aspect ratio and texture entropy subsequently decrease gradually. The coverage, area, mean, third-order moments, and consistency of the transfer film strongly correlated with the volumetric wear rate (correlation coefficient |r| > 0.9).

The coefficient of static friction (SF), the coefficient of rolling friction (RF) for particles are two key parameters affecting the repose angle formation and flow characteristics. In this paper, the interaction effects of SF and RF on the formation process of corn repose angle was investigated by the discrete element method. Firstly, five shape kinds of corn models (horse tooth, spherical cone, spheroid, oblate, and irregular shape) were established. Secondly, aluminum cylinder and organic glass box were used to conduct the simulation experiments with taking SF and RF as independent factors and seeing the repose angle as dependent value. Based on simulation results the regression equations were established. Simulation results showed the relation between two factors and the rotational kinetic energy is not nonlinear, and SF does not significantly restrict the flow of corn models after increasing the flow direction, and the effect of SF on the contact number between corns and the bottom plate is remarkable, while the effect of RF on the contact number is not remarkable. Finally, the interaction effect of two factors on the repose angle was analyzed by variance analysis and results showed SF and RF all have a significant impact on the repose angle. Moreover, their interaction effect has an impact on the repose angle. Keywords: corn kernels, coefficient of static friction, coefficient of rolling friction, repose angle, interaction influence DOI: 10.25165/j.ijabe.20211405.4357 Citation: Shi L R, Yang X P, Zhao W Y, Sun W, Wang G P, Sun B G. Investigation of interaction effect between static and rolling friction of corn kernels on repose formation by DEM. Int J Agric & Biol Eng, 2021; 14(5): 238–246.

The translational sprinkler irrigation machine is widely used because of its high degree of automation, less manual investment, and convenient movement. However, when using the sprinkler irrigation machine, the power supply is difficult to be guaranteed in some remote power shortage areas. Solar energy has become one of the best choices for the power source of sprinkler irrigation machines. An important issue is the optimal sizing of the stand-alone photovoltaic system for a solar-powered translational sprinkler irrigation machine. This work conducts the optimal sizing of the stand-alone photovoltaic system for a solar-powered translational sprinkler irrigation machine considering the loss of power supply probability. Firstly, the self-developed translational sprinkler irrigation machine is introduced. The load power, which includes the driving power of the translational sprinkler irrigation machine, water intake pressure driving power, and the loss power of the controller and sensors, is considered in the calculation process. Subsequently, the photovoltaic generator model and the battery storage model are established. Then, the stand-alone photovoltaic system is optimized considering the loss of power supply probability (LPSP) and the life cycle cost (LCC). After the solar irradiance and ambient temperature of a typical sunny day in the test area are given, the optimal combination of the PV module and battery is obtained. The optimal sizing result is verified using the PV power, state of charge (SOC), and load power. The presented optimal sizing method is also compared with an existing method. Besides, the operation test of the sprinkler irrigation machine is also carried out to verify the optimal sizing result. The optimal sizing result is proved to be effective and applicable.