Utilization of random process spectral properties for the calculation of fatigue life under combined loading

Jaroslav Svoboda, Miroslav Balda, Vladislav Fröhlich


The contribution includes the results of experimental works aiming to find a new methodology for the calculation of fatigue life of structures subjected to operational loading from a combination of forces and moments of random character. Considering the fracture mechanics theory, then the damaging of material is both in the micro- and macro-plastic area connected with the rise of plastic deformation and hence with the plastic transformation rate which depends on the amount of supplied energy. The power spectral density (PSD) indicating the power at individual frequencies in the monitored frequency band yields information about the supplied amount of energy. Therefore, it can be assumed that there is a dependence between the PSD shape and the size of damage and that the supplied power which is proportional to the value of dispersion s^2 under the PSD curve could be a new criterion for the calculation of fatigue life under combined loading. The searching for links between the spectral properties of the loading process and the fatigue life of structure under load is dealt with by new Grant GA No. 101/09/0904 of the Czech Technical University in Prague and the Institute of Thermomechanics of the Academy of Sciences of the Czech Republic, v.v.i.


power spectral density; random process; combined loading; plastic deformation; fatigue life

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