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Effect of internal defects on the dynamic fatigue strength behaviour of friction-welded joints
Abstract
This paper investigates the effect of internal defects on the fatigue behaviour of friction-welded joints with an alternating torsion load. To that end specimens of St 52-3 and 42 CrMo 4 with defined and reproduceable defects will be tested. Recommendations for the extension of the calculation code for friction-welded joints will be derived from the experimental findings.
... Since a considerable amount of the friction welded (FW) structures work under cyclic loading of variable amplitude, it's important to investigate experimentally the fatigue behavior, in order to develop the predicting method of fatigue life of the FW structure. Some work [1][2][3][4][5][6][7][8][9][10][11][12] has been devoted to the cyclic fatigue of FW joints, and the focus was laid on the effects of materials, the friction welding procedures and the service conditions (such as weld flash and corrosive environments) on the fatigue behavior of FW joints, which is important and essential for engineering applications of FW struc-tures. To the knowledge of the authors, most of the FW structures are used for the mechanical elements under variable-amplitude loading (VAL), nevertheless, no expression of the S-N curve of FW joints could be found in the available literature [1][2][3][4][5][6][7][8][9][10][11][12], and there is no report on the fatigue life of FW joints under VAL. ...
... Some work [1][2][3][4][5][6][7][8][9][10][11][12] has been devoted to the cyclic fatigue of FW joints, and the focus was laid on the effects of materials, the friction welding procedures and the service conditions (such as weld flash and corrosive environments) on the fatigue behavior of FW joints, which is important and essential for engineering applications of FW struc-tures. To the knowledge of the authors, most of the FW structures are used for the mechanical elements under variable-amplitude loading (VAL), nevertheless, no expression of the S-N curve of FW joints could be found in the available literature [1][2][3][4][5][6][7][8][9][10][11][12], and there is no report on the fatigue life of FW joints under VAL. No investigation of the procedures for predicting fatigue life and its probability distribution of FW joints under VAL could be found in the literature. ...
... According to the F-distribution [30], F 0.05 (9,4) =6.00, so, FϽF 0.05 (9,4) , this means that under a significance level of 5%, there is no significant difference between the two variations mentioned above. ...
In the present study, fatigue tests under constant-amplitude loading (CAL) and variable-amplitude loading (VAL) are carried out on the notched friction welded (FW) joints of 45 (0.45%C) carbon steel, which is similar to the AISI 1045 steel. Statistical and regression analysis on the fatigue test results under CAL shows that the fatigue life of 45 steel notched FW joints with small size can be expressed as the function of the equivalent stress amplitude, and the values of the fatigue resistant coefficient and threshold are thus obtained. From the probability distribution of fatigue resistant coefficient and threshold, the expressions of the fatigue life with given survivability, i.e., the so-called P–S–N curves of 45 steel notched FW joints are obtained, which can cover the whole life region, in particular, the long life range and are used to determine the probability distribution of fatigue strength of 45 steel notched FW joints. Furthermore, the so-obtained expressions for P–S–N curves and Miner's rule are directly applied to predict the fatigue life and its probability distribution of 45 steel notched FW joints considering that 45 steel is of non-continuous strain-hardening characteristic and thus nil overloading effect. The prediction procedures for fatigue life with given survivability of 45 steel notched FW joints under VAL by using Miner's rule and the expressions of P–S–N curves are outlined. The fatigue life and the critical cumulative fatigue damage of 45 steel notched FW joints under VAL predicted by using the above procedures follow the log-normal distribution, and checked by test results under one type of programmed block loading and the statistical analysis. The procedures mentioned above may be applicable in predicting the probability distribution of fatigue life of the notched elements of metals with non-continuous strain-hardening characteristic, including the notched friction welded joints under VAL.
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