In this investigation, an efficient fatigue life computation method under variable amplitude loading of structural components has been proposed. Attention in this study is focused on total fatigue life estimation of aircraft structural components. Flat specimens with central hole made of quenched and tempered steel 13H11N2V2MF were tested as representatives of different structural components. Total fatigue life of these specimens, defined as sum of fatigue crack initiation and crack growth life, was experimentally determined. Specimens were tested by blocks of positive variable amplitude loading. Crack initiation life was computed using theory of low-cycle fatigue (LCF) properties. Cyclic stress-strain curve, Masing's curve and approximate Sonsino's curve were used for determining stress-strain response at critical point of considered specimens. Computation of crack initiation life was realised using Palmgren-Miner's linear rule of damage accumulation, applied on Morrow's curves of LCF properties. Crack growth life was predicted using strain energy density method. In this method, the same LCF properties were used for crack initiation life and for crack growth life computations also. Computation results are compared with own experimentally obtained results.KEY WORDS: crack growth, crack initiation, FEM, strain energy density method, total fatigue life prediction Ó

A submodeling technique is applied in the framework of this study on a Tjoint fillet weld example in order to check finite element mesh sensitivity as well as to obtain more accurate temperatures, displacements and residual stress fields in the weld and its vicinity where the temperature and stress gradients are very high. The submodeling procedure of the welding process is demonstrated step-by-step. The obtained results of the temperature, residual stress and displacement distributions correspond very well with the experimental measurements and analytical solutions from the literature.

This work consideres the buckling and postbuckling behaviour of axially compressed layered composite panels including initial failure analysis. For determination stresses in layered composite panels Finite Element Method (FEM) used. A series of experiments were conducted to verify the FEA-results, but also to address the stability and strength of the composite structure. Combining a geometric nonlinear finite element analysis (FEA) based on the von Karman theory and High Order Shear Deformation Theory (HOST) are used to study the first-ply failure behavior as well as the postbuckling behavior of laminated type composite panels. For this purpose and for the investigation of the failure responses improved 4-node layered shell finite elements are used. The finite element formulation is based on the third order shear deformation theory with four-node shell finite elements having eight degres of freedom per node. A simple method is proposed to predict buckling loads and the post-buckling behaviour together with initial failure analysis of layered composite panels. The experiments carried out on SCHRENK system. Comparisons between numerical and experimental results show quite a good agreement.

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This work considers the numerical computation methods and procedures for the fatigue crack growth predicting of cracked notched structural components. Computation method is based on fatigue life prediction using the strain energy density approach. Based on the strain energy density (SED) theory, a fatigue crack growth model is developed to predict the lifetime of fatigue crack growth for single or mixed mode cracks. The model is based on an equation expressed in terms of low cycle fatigue parameters. Attention is focused on crack growth analysis of structural components under variable amplitude loads. Crack growth is largely influenced by the effect of the plastic zone at the front of the crack. To obtain efficient computation model plasticity-induced crack closure phenomenon is considered during fatigue crack growth. The use of the strain energy density method is efficient for fatigue crack growth prediction under cyclic loading in damaged structural components. Strain energy density method is easy for engineering applications since it does not require any additional determination of fatigue parameters (those would need to be separately determined for fatigue crack propagation phase), and low cyclic fatigue parameters are used instead. Accurate determination of fatigue crack closure has been a complex task for years. The influence of this phenomenon can be considered by means of experimental and numerical methods. Both of these models are considered. Finite element analysis (FEA) has been shown to be a powerful and useful tool1,6 to analyze crack growth and crack closure effects. Computation results are compared with available experimental results. [Projekat Ministarstva nauke Republike Srbije, br. OI 174001]