Finite Element Simulation And Analysis On Hot-Assisted Cutting Of Frozen Soil

The strength of frozen soil is 10~20 times over that of the unfrozen soil, due to the special existing of a significant connection effect, the ice cement of frozen soil. It is difficult to excavate frozen soil with serious tool wear using conventional digging methods and tools. In order to further improve the efficiency of the frozen soil excavation, it is necessary to study the mechanical characteristics of the frozen soil and the new method of frozen ground breaking. Taking into account that the strength of frozen soil is significantly decreased with the increase of temperature, the characteristic of temperature sensitivity is obvious, which can be called hot cutting technology. To the feasibility of research on frozen soil cutting broken regularity and heating assisted cutting frozen soil. In this paper by using explicit finite element code LS-DYNA to carry out the numerical simulation analysis for the frozen soil cutting process and heating assisted cutting frozen soil process.In this paper, the mechanical behavior of frozen soil in the cutting process is simulated by using the HJC model and the model of elastic and plastic heat related materials. Firstly, based on the HJC model and the above model parameters, a simplified 2D finite element model is established using LS-DYNA. The variation of cutting force, frozen soil stress and frozen soil fracture morphology are studied in different cutter velocity, depths of cut and rake angle. Calculation results show: Brittle fracture leads to the main failure of frozen soil during cutting; Cutting forces are volatile;The relationship between the cutting force and the cutting distance follows an obvious fluctuation; The rake angle has significant influence on the fracture morphology of frozen soil; Among all of the cutting parameters, the depths of cut and rake angle have a greater impact on the cutting force compared with the cutter velocity; The cutting force increases slightly with the cutter velocity increase, while approximately linearly increases with the depths of cut increase.Secondly, based on the explicit finite element code LS-DYNA, the finite element simulation of the heat conduction process and the hot-assisted cutting of frozen soil process by heating tool and suspended hot plate is carried out. The simulation results indicates that it requires a lot of heat in order to increase the temperature of the frozen soil per unit volume due to the frozen soil has a larger volumetric thermal capacity. As a poor heat conductor, frozen soil displays low thermal conductivity that results in low heat passage among the frozen soil, and thus the heat affected zone of heating tool and the suspension plate are limited in a very small range. Due to the phase change latent heat of the surface layer of frozen soil, the conducting heat is mainly consumed in the surface layer of frozen soil. The heat transfer from the heating tool and the suspended heat plate to the frozen soil has some specific characteristics, such as slow speed, shallow depth and large latent heat consumption. The following results can be obtained by analyzing the effectiveness and feasibility of the heating assisted frozen soil cutting. For heating auxiliary tool cutting frozen soil, we studied the change of cutting force under different thermal contact conditions and found that the change of cutting force is only decreased about 5%. The result shows that a higher temperature and lower speed is favorable to play the effect in the heating tool assisted frozen soil cutting process. For suspension thermal plate auxiliary cutting frozen soil, with the increase of suspended the hot plate heating time, weakening effect on the cutting strength of frozen soil is not very obvious. The result shows that cutting strength of frozen soil needs longer heating time(5s) to reduce the 20%.