| Rock mechanics testing machine is an important means to study rock fracture characteristics.It is of great signification in shale gas mining,nuclear waste disposal and earthquake prediction.Researchers can figure out the complete strain-stress curve after the development of precision detection and control technology,however,the process of rock crack initiation and development is not yet known.The rock mechanics testing machine being investigated in this thesis was designed to simulating the environment under deep ground and can carry three axle load to the rock sample,then the CT technology was used to get the image of the cracks in the rock sample from surrounding direction.Then the real-time image of rock failure process is obtained by image 3D reconstruction technology.On the basis of analyzing the stiffness of the testing machine system,the mechanical testing system and displacement detection system of the integrated rock mechanics test machine which does not reduce the stiffness of the test machine are designed in this thesis.In addition,the parameters of displacement testing system,force testing system and friction force in servo cylinder was calibrated.Firstly,the stiffness analysis of the machine was designed.In view of the stiffness and rotation requirements of the machine,the factors affecting the rigidity of the machine are analyzed.The pressure chamber is used as the reaction frame of the testing machine without affecting the CT imaging while ensuring the rigidity of the testing machine and the rotation accuracy of the turntable,and it's the base of the testing system.The main work of this thesis is as follows:Secondly,a new method for measuring the deformation of rock samples which achieve unoccluded imaging was designed.Three high-precision LVDT was put inside the pressure chamber and the tail of the piston rod.On the basis of a large number of data from many experiments,the relationship between deformation of the machine and axial force is established by using least square method and neural network respectively.then the deformation of the rock sample can be detected by the LVDT at the end of piston.This method realizes the universal detection of displacement of different rock samples in this test machine.Thirdly,a method of axial force detection without reducing the rigidity of the whole machine is presented.Because the force sensor could impair the rigidity of the machine,the stress of rock specimen is indirectly calculated by measuring the pressure of the upper and lower chamber of the servo cylinder and the pressure of confining pressure.rod cavity and confining pressure,then consider the influence of the friction,the special device was designed and the experiment was completed,then the accurate axial force was obtained indirectly.Fourthly,the temperature measurement system was designed.According to the base-heating scheme,the system utilizes thermocouple as the temperature detection unit,temperature controller as the control unit,and the temperature of the rock sample can be controlled at 200?,and the error is about 0.415 ?.The maximum nonlinear error of the displacement sensor after calibration is 0.037%,better than the displacement accuracy of 0.5%in the technical index.The data obtained from the deformation measurement of rock samples are processed by least square method and neural network respectively.The mean square error of neural network identification is 8.25 × 10-6,which is smaller than the mean square error of the least square method.It is proved that the accuracy of neural network identification is better than that of least square method.The friction test of servo cylinder measured the friction force of servo cylinder at constant speed of 689.8N,and the standard deviation was 5.9N.The measurement accuracy meets the requirements of rock mechanics testing machine. |
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