Experimental study on the fatigue damage of designed T-type specimen with high-low frequency superimposed loading

摘要

The nonlinear synthetic bending moment caused by springing and whipping can be simplified as the superposition of high-frequency load components and low-frequency load components. In order to investigate the influence of this high-low frequency superimposed loading on the fatigue performance of hull structure, the high-low frequency superimposed fatigue tests under different frequency ratios, amplitude ratios and mean stresses were carried out for the time domain response characteristics of nonlinear vertical bending moments in the wave load model test of River-Sea-Going-Ship. Combined with the rain-flow counting method and Goodman correction method, the cumulative damage of small loads under fatigue limit and the effect of high-low frequency coupling damage on the fatigue life were analyzed, a fatigue life prediction model suitable for high-low frequency superimposed loading was proposed. The analysis results show that the high-frequency, small-amplitude loads have a significant impact on the fatigue life of the structure. The threshold that the high-low frequency coupling damage causes the reduction of fatigue life is closely related to the combined effects of the amplitude ratio and the frequency ratio.