Design And Research On The Axial Servo Loading Test System

Servo loading system is also called load simulator in the field of engineering. It is to simulate different kinds of loads exerting on the sample under laboratory conditions and has the advantages of high response, high accuracy, high power weight ratio and high power output. Electro-hydraulic servo loading system is a important part of servo loading system. It is significant equipment on structure testing for static performance, fatigue performance, fracture toughness, and so on. These kinds of testings can provide theoretical basis for the design of structures.In this thesis, the axial servo loading test system is designed for the fatigue test of pipe which is used under the sea. Its function is to simulate the axial load exerting on the pipe subsea in order to check whether the performance of sample can meet the design requirement. Thus the classical all-objective experiment will be converted into half-objective forecasting experiment in laboratory to achieve the aims such as shorting developing time, saving developing funds, enhancing reliability and success proportion.The axial servo loading test system is a typical passive electro-hydraulic force servo system. During the test, the tested pipe is also exerted a radial force load. Because of the bending deformation which is caused by radial load, the axial position of pipe moves back and forth continuously and the movement is considered as interfering with the load system. In this dissertation, beginning with the overall design, the servo valve and accumulator united controlled load mode is established via the comparisons of three distinct load projects. The electro-hydraulic system and mechanical support are all designed. The control strategy is optimized and the program is prepared. The control software is organized by powerful Ladder-diagram software FPWIN GR, easy understanded Engineering software EasyBuilder and convenient graphical software Labview, all with well readability and real-time. The experiment on a tested pipe is conducted, and the reliability of experimental result is checked. Each chapter of this dissertation is introduced as follows:In chapter 1, the scheme and characteristics of each kind of servo loading system are introduced, and the advantages and difficulties of development are also summarized. The current situation of research and application on servo loading system is analyzed. Finally, the significance and main research subjects of this paper are presented.In chapter 2, the design tasks of the axial servo loading test system are introduced. The simulation models of three different kinds of load projects are built and the whole scheme of test system is proposed via the comparisons of their advantages and disadvantages. The main characteristics of the test system in this paper are inducted.In chapter 3, each module of hydraulic system is designed based upon compact design and convenient operation, under the context that the functions are fulfilled. the mechanical support of axial servo loading test system is also designed. The force analysis is carried out in details. Stress analysis and strength checkage on the key parts are made taking advantage of finite element analysis software ANSYS, in order to realize the function of stable and reliable support.In chapter 4, The software and hardware of electronic control system are configured taking advantages of programmed logic controller and data acquisition device. The mathematical model of this servo loading test system and the additional force are built. The causes of additional force is analyzed. The control strategy is optimized by using invariance theory. The effect of optimization is checked through the dynamic simulation of MATLAB/Simulink model. Finally, the control program is prepared and the process of axial loading testing is planned properly under the testing standard.In chapter 5, the experimental research on a certain tested pipe is carried out on the basis of the axial loading test system. The test items as well as their realization are analyzed in details. The test results are analyzed combining the characteristics of the system which can provide experimental support for the further research on improving the accuracy of servo loading system.In chapter 6, conclusions in this thesis are summarized and future research proposals are suggested.