As the frozen soil in the South Pole region of the Moon is an important water resource, the operation of drilling and retrieving samples of the frozen soil in this region will be a crucial task for us to accomplish in future deep-space exploration. Thus, this paper investigated the effects of the increasing temperature and heat transfer between the drilling tools and the simulated lunar soil to minimize the degradation of the frozen soil samples during drilling due to the increased temperature. Specifically, the discrete element method was adopted and the heat transfer parameters of the discrete element particles were calibrated based on the equivalent heat transfer of the particle system. Moreover, a lunar soil particle system was developed for the simulations. Under the current working conditions with reasonable parameters, the maximum increase in the drill bit temperature was about 60 °C. Overall, the simulation results were consistent with the experimental results, and further analysis revealed that the flow of lunar soil can effectively take away thermal, which is also one of the reasons why the simulated lunar soil particles are in a high-temperature state at the front of the drilling tool.

To improve the kinematic performance of the remote center mechanism for surgical robot, a double space index and kinematic accuracy reliability index are proposed to optimize the dimensional sizes of mechanism. First, the influence of the angular error on the position error and the operability of the remote center in the workspace are analyzed. The position error space and operability space index are weighted to establish the double space index. Second, a kinematic accuracy reliability index is established based on the influence of joint clearance on output position accuracy. Finally, the dimensional sizes of remote center adjustment mechanism and double parallelogram mechanism are optimized based on proposed optimization indices. Multipopulation genetic algorithm is used to obtain the optimal size parameters under the corresponding index. The optimized double space index is 56.7%, which is 56.5% higher than before optimization. The optimized kinematic accuracy reliability is 0.91, which is 22.9% higher than before optimization. The kinematic performance of remote center mechanism has been significantly improved after optimization.

In order to study the influence of scratches on the fatigue life of CRH5 EMU wheels under -40°C servicing condition, a dynamic model of the vehicle-rail system is established along with the contact model of the scratched wheels. Considering the irregular and typical working condition of the railway line, a random load spectrum and a cyclical wheel-rail impact load spectrum are obtained. The S-N character of the wheel material is obtained according to a series of fatigue test in serving environment -40°C. Using the finite element quasi-static superposition method, the fatigue life of the wheels with and without scratch are compared, and then the fatigue life of the scratched wheel is evaluated. The results show when the scratch length L_R ≤ 20 mm, the fatigue life of the scratched wheel is less affected by the wheel-rail impact caused by scratch; when the scratch length L_R > 20 mm, the fatigue life decrease quickly, less than 1e6km, affecting the safety of the EMU.