FATIGUE ASSESSMENT OF A SEMI-TRAILER USING FE SPECTRAL ANALYSIS COMBINED WITH RANDOM FATIGUE CALCULATION

Abstract. In this work a numerical methodology is proposed to assess the fatigue failure of a semi-trailer under random load. This methodology combines PSD (Power Spectral Density) and FEA (Finite Element Analysis) with equations proposed by Dirlik to evaluate the damage on structures. Instead of using time domain analysis, as the traditional methodologies, a fre-quency domain analysis is adopted. This approach uses the PSD’s of the imposed loads, which are curves of load in frequency domain. Using well-known experimental techniques, the acceleration of the structure is obtained with accelerometers positioned at the suspension region of the semi-trailer, while the strains are obtained with strain gages positioned in criti-cal points of the structure. The measured accelerations are used as input data of the Finite Element Analysis in order to get the PSD of stresses. The experimental strains are used to calibrate and validate de numerical model. The most important advantage of the proposed methodology is its lower computational cost compared with the time domain analysis. This approach seems to be more appropriate mainly in cases of non-deterministic loads, even though its content is statistically constant. Then, with the pertinent PSD of stresses at each node, a PSD cycle counting is performed and combined with the fatigue curve of the material in order to get the cumulative damage according to the Miner Rule. It should be mentioned, however, that this methodology is valid considering the hypothesis of a linear elastic analysis