Complex Mechanical Behavior And Analysis Method Of The Dynamic Coring Process Of Lunar Soil

One of the key tasks of the third stage of China’s lunar exploration project is to achieve the unmanned sampling on the lunar surface and and to carry the lunar soil samples back to the ground perfectly.Therein,the general scheme of deep sampling is determined as “drilling sampling,soft bag packaging”.The engineering department also carried out ground simulation experiments with the developed prototype.However,some failure cases occasionally occur in the experiments,such as excessive dragging force damaging soft bags,failure of sealing the soft bag,and large disturbance of the bedding information of soil samples.As a result,the sampling mission could be failed completely or partially,which can not meet the requirements of the absolute safety and reliability of the lunar exploration project.In the process of exploring these failure cases,it is found that the failure mechanism can not be revealed only by experimental research.The sampling method of deep lunar soil in the third stage of lunar exploration is coring by turning inward the soft bag without sliding.The device for wrapping and sealing lunar soil samples is composed of soft bag,retaining tube,drill bit and auger,named coring mechanism.So it plays an important role in the success of the task.In view of these,this paper focuses on the dynamic process of the coring mechanism,aiming to reveal the complex mechanical behavior of the force dragging the soft bag in the coring process,investigate the degree and characteristic of the bedding disturbance in the soft bag coring method,and develop the uncertainty analysis method pertinently.The innovative achievements include:(1)The mechanical analysis method integrating theoretical modelling,simulation and testing is established to study the changing trend and influencing factors of the dragging force in the whole coring process,and to reveal the complex behavior of soft bag in the coring process.A mechanical model of the force dragging the soft bag is established by combining theoretical analysis with experimental research.The whole dynamic process of lunar soil coring is simulated by using the coupled FE-SPH method,in which the dynamic behavior of the coring system is close to the theoretical analysis.To testify the validity and precision of the mechanical model and numerical simulation,the lunar soil coring experiment is performed on a dedicated platform.In addition,the stick-slip behavior of the soft bag in the process of inversion is discussed via theoretical analysis.Based on the established theoretical model,the parametric analysis of the stick-slip behavior is performed to quantitatively analyze the effect of parameters on the stick-slip behavior.(2)By using the method of theoretical analysis and modelling,with the help of numerical simulation and experimental verification,an evaluation index for bedding disturbance of lunar soil sample is established.The index quantitatively describes the boundary range between the slightly disturbed part and the damaged part,and qualitatively analyzes the trend and characteristic of bedding disturbance.Through theoretical calculation,numerical simulation and experimental verification,the analysis of bedding disturbance of lunar soil samples in the coring task is performed.A general theoretical model considering the variation of lunar soil cohesion and internal friction angle with depth is established,and a new method is proposed to quantitatively describe the degree of the bedding disturbance of the coring samples at different depths.Using FE-ALE coupling algorithm,the simulation model is established and the simplified experiment is studied to demonstrate the validity of the constructed theoretical model.(3)The interval modelling method of lunar soil uncertainty is developed to realize the high-precision modelling and analysis of lunar soil uncertain parameters in the case of small sample data.A new non-probabilistic convex modelling method is proposed to obtain the interval boundary of uncertain parameters in the case of small sample data,which provides a more advanced research tool for structural design and parameter optimization in practical engineering.The performance of the proposed method is systematically studied and compared with other existing competitive methods through test standards.The results demonstrate the effectiveness and efficiency of the present method.(4)In view of the uncertainty in the process of coring,the corresponding analysis methods are put forward to deal with it effectively.Based on the non-probabilistic convex model and Mohr-Coulomb failure criterion,a new non-probabilistic analysis method is proposed to calculate the ultimate shear stress of lunar soil.Considering the correlation between uncertain parameters related to lunar soil,the traditional Mohr-Coulomb failure criterion is extended to the case of uncertainty.The validity of the method is proved by numerical examples and experimental data,and the range of the ultimate shear stress of lunar soil at 2 m depth is calculated.Besides,a non-random vibration analysis method considering external excitation and time-varying uncertainties of system parameters is proposed to obtain the bounds of dynamic response of the system.Based on the proposed model of soil bedding disturbance,the relationship between the interval range of bedding disturbance of lunar soil sample and system variables is determined,and the features of bedding disturbance are revealed.