Numerical modelling of welding process of two cylindrical tubes subjected to cyclic loads of constant amplitude is presented. For that purpose the Finite Element Method (FEM) was used for determination of thermo-mechanical behaviour and evaluation of welded joint residual stresses. In this investigation an efficient computation method for initial fatigue life estimation of welded structural components has been developed. Computation method with corresponding computation procedure is based on finite element numerical simulations of the thermal and stress analyses. As measure of fatigue resistance of welded structural elements, estimated values of low cycle fatigue life were used. Estimation of damages up to crack initiation in the welded joints of two cylindrical tubes was performed using SWT (Smith-Watson-Topper) relations. Present computation results are compared with corresponding experimental results of welded structural components. Obtained computation results of initial fatigue life estimation of welded structural element are in good agreement with experimental results.

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This work deals with fatigue behaviour of cracked aircraft structural components under cyclic loads of constant amplitudes and load spectrum. This investigation is focused on developing efficient and reliable computational methods for fatigue life estimation of cracked aircraft lugs under cyclic loads of constant amplitude and load spectrum. For crack growth analyses and residual lives of damaged lugs two approaches are used: the Strain Energy Density (SED) method and the conventional Forman`s method. A special attention has been focused on the determination of the fracture mechanics parameters of structural components such as stress intensity factors of aircraft cracked lugs. The effects of the shape of lug surface cracks on the residual fatigue life are investigated as well. The SED method uses the low-cycle fatigue (LCF) properties of the material, which are also used for the lifetime evaluation until the occurrence of final failure. Therefore, the experimentally obtained dynamic properties of the material such as Forman`s constants are not required when this approach is concerned. The complete computational procedure for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the cracked structural elements. To determine analytic expressions for stress intensity factors (SIF), singular finite elements are used. The results of the numerical simulations for crack propagation based on the strain energy density method have been compared with the authors' experimental results.

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