Study On Fatigue Life Estimation Of Welded Lap Joints

Currently, the Miner linear cumulative damage model is the one which is applied most abroad. But the Mine's model hasn't considered the influence to cumulative damage caused by the load history and the reciprocity of them. So it will result in error when calculating the fatigue life, and it is significant to study on the variable fatigue life and the cumulative damage theories.In this paper, the difference between constant and variable fatigue life is studied by tests on four welded joints under uniaxial constant or variable amplitude cyclic tensile loadings. By comparing with the data in other literatures, it is found maybe insecure that to estimate variable life by the Miner's model and S-N curve. The strain, distortion, and lives are noted; the strain-loading curves, distortion-cyclic times curves, and loading- distortion curves are portrayed.A non-linear cumulative damage model based on residual stiffness is proposed. The particular expression of this model under the testing condition is proposed by test results. It is found well that to estimate life by this model.Some methods to calculate variable life are discussed with the test results. Stress concentration and fatigue life of the welded joints is analyzed. The results show that the influence to stress concentration and fatigue life produced by the dimensions of the joints is greater than that produced by the shapes of the weld. The results also show that the stress concentration coefficient is the least when the ratio of the main armor plate to the cover board equal to 0.6. A formula is proposed to calculate the stress concentration coefficient. It is proved that the formula is very precise by contrasting the results calculated by the formula and ANSYS.