Mechanical Structure Fatigue Monitoring Method And Device

Modern engineering machineries are working in more and more complex environment, worse and worse conditions the alternating load effecting on the mechanical structure, aggravates the fatigue damage of material structure, eventually lead to material fatigue and fracture failure. As a status quo that there is no effective method of monitoring mechanical structure fatigue, designing and developing a testing apparatus and measuring system to monitor structural fatigue damage is of great significance.In this paper, according to the requirement that the load magnitude is adjustable and that the load frequency is controllable, the appropriate loading scheme and transmission mechanism is chosen. At the same time, we take the load(stress) and strain response of sample as measured object, and built a measurement system whose main components is optical fiber Bragg grating(FBG) sensor and FBG demodulation instrument. In this paper, we design and develop a fatigue monitoring test unit and a measurement system, realize the effective monitoring of bearing structure, solve the problem of mechanical structure’s fatigue monitoring. This topic’s main work is as follows:1 According to the requirement of the subject, we set the performance index of the fatigue monitoring device, and introduce the device’s overall composition. We have determined an appropriate loading scheme and transmission mechanism, design two kinds of fatigue monitoring test apparatus, the vertical and horizontal, and have analyzed their similarities and differences. We also have make related design calculation and checking of the sample structure, the rotary table structure, the structure of the connecting rod, connecting rod installation location and the frame, and have finished the design of the machinery body structure of the testing apparatus.2 The structural fatigue monitoring test’s measurement system have also been constructed. And we have carried on the detailed design specifications respectively from the working principle of the measurement system, system constitution, the function of the system, measurement accuracy, programming process and so on. According to the principle of Fiber Bragg grating sensors, we have put forward the calculating method of the strain, have transformed the wavelength value into the stress and strain values we needed, and have solved the problem of load or stress and strain measurement.The way make the measurement system become simplify.3 The fatigue monitoring experiment is carried out in two different conditions, changing the crank length and loading frequency. And the stress and strain is converted from wavelength data which is collected from the measurement system. Then we draw the ratio of stress and strain and stress cycle number curve. We assess the fatigue damage degree of sample, and provide a basis for testing the reliability and validity of fatigue monitoring test’s measurement system.