| Due to historical reasons, Chinese aviation manufacturing has been a lot of help and guidance of the Soviet Union in the early stage of development. Therefore, the standard of high-lock bolt assembly is still used in the Soviet Union. Due to the lack of relevant theoretical and experimental study, the standard and the assembly of Chinese military aircraft have demonstrated a serious non adaptability, in the assembly of large interference caused by the excessive amount of bolt bending and even fracture.In this paper, the fatigue gain mechanism on the interference of high-lock bolt in different thickness of the structure is studied, which is based on the structure of the aircraft aluminum alloy. In order to guarantee the assembly quality of a certain type of aircraft, make the most reasonable high-lock bolt interference connection installation specification for a series of ai craft and subsequent models of aluminum alloy material about the thickness of the structure characteristics. The main contents are as follows:(1)The mechanism of anti fatigue strengthening of aircraft structure with interference fit and according to the fatigue life and the fatigue test method, determine the fatigue test of the high-lock bolt structure with different interference are introduced.(2) A method for predicting the crack initiation life is proposed. According to the experimental results and the mechanism of crack propagation, a formula of crack growth law is derived and in the experiment, the results show that the change of the stress in the simulation and test data is in good agreement with the experimental data. The crack initiation life of 0.8mm under high lock bolt with different interference is obtained by the formula. The results show that: in the same case that the thickness is 10 mm, the pore size is 9.4mm, and the maximum stress is 170 Mpa, the crack initiation life of the test specimen with the interference of 1.19% is much higher than that of the interference of0.75%. When the reliability life is less than 150 thousand times, the optimal interference of the structure of which thickness is 6mm, the pore size is 7.8mm should be around 0.87%, and the gain of the structure is the largest, and the optimum interference of which the reliability life is more than 150 thousand times is close to 0.65%.(3) Using the finite element software to construct the three-dimensional model of the structure of the different high-lock bolt interference, simulate the fatigue test process and deal with numerical simulation analysis. The results show that: Although the increase of the interference can make the structure more to reduce the Y to the stress level, but more than a certain extent, the increase in theamount of interference is not obvious. Moreover, in practical engineering application, the increase of interference will lead to the difficulty of the whole assembly process. For example, the bolt is difficult to break into the structure, the bolt hole in the process of large deformation, so that the structure is scrapped, and sometimes even into the process of bolt fracture, etc. Therefore, according to the finite element simulation results and the actual assembly conditions, it is suggested that the interference of the structure of which thickness is 10 mm, the pore size is 9.4mm is between 1%~1.5%, and the interference of the structure of which thickness is 6mm, the pore size is 7.8mm is between 0.5%~1%,which is more consistent with the actual situation of the project. And, this is also consistent with the experimental results. |
PDF Full Text Request