Fatigue Life Calculation with the Use of the Energy Parameter for the Elastic Material State in the Spectral Method

The problem with the use of the energy parameter lying in its indirect definition in frequency domain is discussed. Modification of the fatigue life assessment method defined in the frequency domain with the use of the energy parameter (stress-strain relation) is presented. The modification is based on the direct use of power spectral densities (PSD) of stress and strain in the process of the estimation of the stress-strain relation. The PSD’s are used to calculate individual probability density functions (PDF) with the use of the Benasciutti-Tovo model. The obtained probability densities are used to create a joint probability distribution that for the elastic state of material is basically a one dimensional degenerated PDF. The authors explain the process of transformation and normalization of the obtained PDF and compare the obtained PDF to other forms of PDF calculation. The results of calculations are compared to experimental results and presented in fatigue life comparison graphs and are discussed.