| The development level of the rock mechanics testing machine determines the depth and breadth of many fields.Most of the existing rock mechanics testing machines can only obtain the macroscopic mechanical properties such as the stress-strain curve of rock,and can not get the evolution mechanism of meso-structure rupture and the law of internal material movement.This thesis is devoted to the development of a new rock mechanics testing machine,which can carry out real-time imaging of the fracturing process by means of high energy accelerator CT technology.This requires that the testing machine precisely rotate while loading.According to the working condition of the new type testing machine,the thesis presents a new mechanical structure,and completes the design of the electro-hydraulic servo system of the testing machine for the new structure.Through the modeling and simulation of the system,the feasibility of the scheme is proved.Finally,the testing machine is processed,assembled,debugged,and the loading experiment is carried out.The new type of testing machine abandon the traditional testing machine's pillar-type reaction frame structure,and use the pressure chamber wall to act as an integrated reaction frame structure.This structure makes the axial load become the internal force of the testing machine,thus ensuring the rotation accuracy,making the CT imaging possible.We complete the design of mechanical structure,hydraulic circuit,pump station,liquid supply system,electronic control system,seals,etc.We process and assemble the servo cylinder,pressurized cylinder,pressure chamber,liquid plate,fluid flange,hydraulic integrated plate,electro-hydraulic rotary joints and other important parts.We complete the selection and debugging of electro-hydraulic servo valves,displacement sensors,pressure sensors,controllers and other devices.Aiming at the characteristics of the testing machine,a method for detecting post-peak curve of rock's stress-strain has been proposed.Aiming at the problem that the axial loading servo cylinder and the confining pressure loading cylinder are asymmetric cylinders,a zero opening valve controlled asymmetric cylinder system based on the weighted average of the pressure bearing area and the hydraulic spring stiffness theory is proposed.We use parametric weighted averaging methods to unify the different system models in both directions.We conducted theoretical modeling + Simulink simulation,AMESim-Simulink joint simulation and AMESim integrated modeling and simulation.The results show that the response speed of axial loading is 0.4s and the dynamic response frequency is 5.4Hz.Finally,we carry out static loading and dynamic loading experiments.The static experiment obtain the stiffness data with and without the confining pressure.The result shows that 20MPa confining pressure has no effect on the machine stiffness,which is 0.32GN/m.In the dynamic test,the axial load system input is 0.5Hz to 5Hz sinusoidal signal.According to the input and output curve,low frequency tracking is good,and 5Hz output phase lag is only 54 degrees,whose amplitude has no significant attenuation.In the position control mode,the steady-state error of the step response is less than 0.001mm and the sinusoidal input of 1Hz is well tracked,which basically match the simulation results.The prototype can be qualified for ten-ton class rock mechanics testing machine's requirements. |
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