International CAE Conference 2014 27-28 October. 2014 1 An innovative approach for CAE based analysis of complex fatigue loadings Alessandro Cristofori a , Denis Benasciutti b a Università di Ferrara, Dipartimento di Ingegneria, Ferrara, Italy b Università di Udine, Dip. Ingegneria Elettrica Gestionale e Meccanica (DIEGM), Udine, Italy Email: alessandro.cristofori@unife.it Web: http://endif.unife.it/it Summary This paper presents an approach, called "Projection-by-Projection" (PbP) criterion, which is suitable for the CAE-based fatigue analysis of complex structures subjected to random loadings. The method framework allows a time domain, as well as a frequency domain analysis of random multiaxial stress. A CAE-based design of a structural component is discussed as an example, to show the capabilities of PbP method. Keywords multi-axial fatigue, FEM analysis, random stress, Power Spectral Density, spectral method Introduction Mechanical components and structures are often subjected to random loadings (some examples are shown in Fig. 1), which often lead to multiaxial random stresses in the most critical point of the structure. Contrary to deterministic loading, which are exactly known from present or past values, random loadings (or stresses) are inherently uncertain and future values can only be estimated in terms of probability. For example, typical questions in structural durability could be: which is the probability that a load will exceed a given threshold "x" in future time T? How many cycles have amplitudes higher than a given value? How many cycles will eventually lead to final fatigue failure? The probabilistic approach to fatigue analysis of random loadings can be developed by two different philosophies: time-domain or frequency-domain approach [1,2]. From the designer's point of view, the matter is to understand which approach (time- or frequency-domain) is best suited for fatigue analysis of multi-axial random stresses, especially at the design phase within a FE environment. The time-domain approach is based on consolidated deterministic algorithms (e.g. rainflow counting, Palmgren-Miner damage rule), which are applied to measured or simulated time-histories to estimate the fatigue damage and the component service life. Instead, the frequency-domain approach characterizes the random signals in the frequency-domain and it applies analytical expressions to estimate the fatigue damage and the service life directly from Power Spectral Density (PSD) data.