Research On The Law Of The Stiffness Degradation And Strength Degradation Of The Bolt Under Fatigue Loads

The Road header is used to cut the rock, coal or semi coal-drift for any shapes, it works under the ground and the working condition of the it is poor, it subjected to many vibrations and random loads besides service loads caused by the rock splashing or disintegration. The rotary table bolt serve as the key components in the Road header which is used to connect the upper and the under part of it, subjected to the same loads. These are much lower than the strength limit of the bolt, under these loads, the bolts becomes fatigue and their stiffness and strength degrade, which leads to the lager dynamic load by the stiffness degradation and lower strength resistance capacity to the external loads by the strength degradation, when the strength equals to the external loads, the bolt fractures. The maintenance of it is difficult and time wasted. Therefore the research on the law of the stiffness degradation and strength degradation of the bolt under fatigue loads is meaningful.In this paper, combining theoretical analysis method and experimental research method, the residual strength and the residual stiffness under fatigue loads of mechanical components is studied systematically. The researches are shown in details as follows:(1) The research of the fatigue test is conducted on the material of 45 steel. In this paper, two different stress level is selected and the loading mode is tensile and compressive load. The fatigue life of different stress level is obtained and the residual stiffness and the residual strength on different cycles is also tested.(2) Build the power degradation model of strength degradation of the material on constant loading and the test results shows good agreements with the model results. The common feasibility of the model is validated with the test results of 35CrMo steel which is usually used on the 10.9 grade bolt, which shows that this model can be used to access the strength degradation of the bolt. The model can better fit the strength degradation process when compare with the other strength degradation models. Based on the assumption that the damage caused by the fatigue loads can be described by the strength drop, and represent the damage caused by different loads by one loads, then the strength degradation model on random loads is built.(3) Build the stiffness degradation model of the material on constant loading through the test results. Under the hypothesis that the residual stiffness and the residual strength at the same time is decides by the same damage mode, the coupled model of the residual stiffness and the residual strength is built, the stiffness model and the coupled model are validated by the test results and little errors are achieved.(4) Apply the strength degradation model built in this paper to access the strength degradation process of the rotary table bolt on the Road header, the ANSYS software is used to calculate the stress of the bolt on different stiffness level and learn the effect of the stiffness degradation on the working property of the bolt, the results show that the lower the stiffness, the lower carrying capacity of the bolt and lager deformation of the bolt.