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In this paper, the variation of coefficient of friction, which is one of the main and important parameters in fretting fatigue, has been investigated experimentally. Measuring of coefficient of friction has been performed with the designed device by the researchers. The advantage of using the above device is that it can almost accurately measure the contact pressure and friction force and thus the coefficient of friction. Al alloy 2024-T3 has been used as it is the frequently used alloy in aerospace structures. The coefficient of friction is considered here as a parameter which is a function of normal and cyclic axial load. Another important point in performing the test is the variation of frictional stress at different normal and axial loads which is measured. Results show that as the normal load increases, the coefficient of friction reduces but the frictional stress increases. Changing the frictional stress is the main parameter in investigating wear between interfaces. The above results can be applied in numerical analyses such as life prediction and/or predicting joints fracture section such as double shear lap joints which experience fretting fatigue.

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Accumulation of plastic strain during cyclic loading is one of the main reasons for fatigue failure. In order to predict the fatigue life of plates, it is necessary to calculate the accumulated plastic strain and the affecting parameters carefully. In this study, a combination of nonlinear isotropic and nonlinear kinematic hardening model (modified Choboche) was implemented in the commercial finite element code of ABAQUS, by using a FORTRAN subroutine to calculate the accumulation of strain in samples made from thin plates of aluminum. In this regard experimental, strain controlled and stress controlled cyclic tests were carried out, and the required coefficients for simulating the hardening behavior of aluminum alloy 2024-T3 were obtained and the accumulation of plastic strain was simulated at different uniaxial loading condition. The comparison of the experimental and the predicted results shows that, the determination of optimal coefficients for combined nonlinear isotropic and nonlinear kinematic hardening model (modified Choboche), has an adequate ability to predict the experimental results. The obtained results also show that, increasing stress amplitude and mean stress increase the strain accumulation. The results from 4 types of cyclic loading indicate that the stress ratio has a direct influence on the strain rate when the maximum applied cyclic load is kept the same, and an increase in stress ratio increases the accumulation of plastic strain. Moreover, the rate of strain accumulation at the first cycles is high while it is reduced by increasing the number of cycles.

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Interference fit process, as a popular method, is used in aerospace and automotive industries. General investigation of interference fit has been conducted on plain hole extensively. Nevertheless, interference fitted holes are practically subjected to bolt clamping force which may have different fatigue behavior than the plain hole. The objective of the present study is to extend the present knowledge about the fatigue behavior of interference fitted holes by investigating the subsequent bolt clamping force effect based on the experimental and numerical results. In this paper, Al-alloy 7075-T6 is utilized for fatigue test specimens. In relation to fatigue tests, three dimensional finite element analyses were used to explain the experimental results. By using finite element method, the interference fit process; bolt clamping and subsequent remote cyclic loading were simulated. The fatigue critical stresses on bolt clamped interference fitted (BIF) samples were compared with the corresponding stresses for interference fitted samples. The pre-stress distribution due to interference fitted hole, and its redistribution after bolt clamping forec and its interaction with remote loading were estimated The fatigue test results demonstrate that bolt clamping force applied on the interference fit plays positive effect on fatigue behavior and prolongs the fatigue life. The biggest life improvement for bolt preloads of 3409 and 6818 N is 2.5 and 7 times compared to the only interference fitted specimens, respectively.