Analysis And Application Research For Fatigue Strength Under Random Loading

This paper studies the effect of fatigue damage of structures. In time domain, existing fatigue life estimation sample method is improved and random fatigue life analysis method based on inverse discrete Fourier transform is Proposed. With the power spectral density(PSD) of random loading, the corresponding amplitude and the random phase can be got, then loadings in time domain can be simulated by inverse Discrete Fourier Transform(DFT), the life of structure with counting method can be estimated. In frequency domain, this paper presents a way by which the peaks and valleys are sellected with the power spectral density of the random loading to estimate fatigue life of the structure. Comparing with the earlier methods relying on peaks and valleys, this method is more precise.Later, in this paper fatigue failure analysis method is used in the case of iced transmission conductor galloping. Firstly, the movement of iced transmission conductor is analysed, together with the aerodynamic theory and galloping theory, a transmission galloping model is established. In order to solve the galloping equations,this paper use MATLAB to simulate the process of transmission conductor. Results show that galloping in Vertical direction is more substantial than that in horizontal,as well the dancing locus of points on the transmission line is roughly oval.This paper conductes a fatigue life estimation for galloping transmission line and analysed the rigid and flexible transmission wire. In addition, axial dynamic stress and dynamic bending stress are anslysed in order to calculate the damage with the wind direction-velocity joint probability density, linear cumulative damage theory and the Wohler’s curve.Finally, influence of the initial wires tension, transmission tower span, wire static sag and dancing magnitude on fatigue damage is also studied. The simulation results can show the way to improve the fatigue life of the transmission lines.