Spectral analysis techniques are employed to analyze the fatigue damage to the suspension of a six-axle locomotive on tangent track with vertical and lateral random track irregularities. The locomotive is represented by a thirty-nine (39) degrees of freedom linear model. Spectral densities of forces and probability density functions for stress levels in suspension elements are generated. Using a modified definition of transmissibility, the probability density functions of the output/input and mean square values of outputs are obtained for various stiffness ratios. A cumulative linear damage criterion based on Miner’s theory is employed to predict fractional damage per operational second and mean life of the suspension elements. Operational stress cycles/sec. versus operational stress level are plotted for the suspension elements. These operational characteristics in conjunction with fatigue characteristics (S-N curve) can be effectively used as a tool for fatigue design.

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