| During the process of engineering structure service, the endurance of varying load leads to crack initiation,crack propagation and even validation,this process is named fatigue .Statistical analysis shows that over 80 percent of all the mechanical failure is fatigue failure. Thus it can be seen that it is very important for the assessment of material's antifatigue ability, the design of antifatigue engineering part , the estimate of part's fatigue life and the seek of new way to improve material antifatigue ability to study material mechanics response under varying load,crack initiation and crack propgaion. The mechanical structure design improves with the development of technology and society,it had developed from empirical design to the combination between design and mechanical analysis,up to modern optimized design of structure,but as to strength,the structure design is still based on static criterion, then measures are adopted to control the vibration level, even the serious vibration problems have come out. Practise has proved that this method is costly and less effective .thus,the traditional mechanical structure design method based on static criterion can't meet the needs of modern product design,as to the structure which endures dynamic load, dynamic design method is an effective method as to modern product design because it can control the vibration level of mechanical structure, improve the quality of product, increase its reliability and so on.this dynamic method suits the internal and international direction of design technology of mechanical structure.The dynamic design is defined as:at the design stage, the structure is designed according to the function, strength and the dynamic environment, the structure has excellent dynamic property and our purpose which control the vibration level is achieved. High cycle fatigue is one kind of testers which measures the material's fatigue life and fatigyuproperty. This tester has lots of properties such as simple structure, easily to operate,high efficiency and so on.It can be used to measure various material fatigue life and test S-N curve. If given special fixture, it can be used to measure various parts'fatigue life.Presently ,the labs of many universities, institutes and industry enterprise all adapt high cycle fatigue tester to do fracture toughness test and get the metal material's crack propagation rate and the material threshold. With the development of electronics and computer technology and with the perfectness of test way, its use is gradually extending. The feature of this machine is that the whole machine utilizes machine's natural frequency at certain frequency range when it is working,and under this frequency it generates sympathetic vibration , and at the same time it needs a same frequency vibration source to compensate the energy loss generated by damp. This demands that the whole machine's natural frequency accords with the test frequency to the greatest extend, so during the design phase,I included the tester's dynamic character. By adjusting the structure parameters I got excellent dynamic character . It is very difficult to build the mathematical model of the tester according to the vibration theory because of its complicated structure. This paper carries out the modal analysis and harmonic response of high cycle fatigue tester. In the modal analysis I got the initial steps natural frequency and corresponding vibration modal, and at the same time I have got the influence trend and influence degree of the main structure to base frequency. In the harmonic response analysis,the analysis steps is as follow: I first observed the whole machine's situation when the excitation force was a special given value . Then I let excitation force frequency varied in a certain range From this I observed the selected frequency area's response situation on which the users pay attention and Igot the sympathetic vibration point and got the special parameter of displacement response range under various vibration force frequency. All of the work provides guide for the engineer who design tester, and it saves cost of new product emplorder, and it reduces the design period ,and at the same time it provides reference for product improvement and seriation. In the first chapter of this paper I introduce the background of this project,then the basic theory of vibration,at last I explain the content and method of this project;In the second chapter I introduce the dynamic anlysis section of ANSYS in detail including mode anlysis and harmonic analysis.the point focuses on the application field and analysis steps;In the third chapter I introduce the second development of Ansys which is based on Apdl;The fourth chapter I introduce mode analysis of the high cycle fatigue tester, natural frequency and vibration modal of specified tester are got,and I get the rules which the main parameters give to the natural frequency.In the harmonic analysis,the resonance point is found,all of these provide the reference for the design and improvement of this kind of tester.
|
PDF Full Text Request