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Belgrade, Serbia

Boljanovic S.,Serbian Academy of Science and Arts | Maksimovic S.,Ratka Resanovica
Frattura ed Integrita Strutturale

In the present paper, mathematical models are proposed in order to analyze the strength of pinloaded lugs with semi-elliptical crack and through-the-thickness crack. The crack growth investigation of considered crack configurations tackles the fatigue life evaluation and the crack path simulation of semi-elliptical crack. The residual strength is estimated by applying the two-parameter driving force model. The numerical and analytical approaches are employed for the stress intensity factor calculation. Experimental fatigue crack growth data are used in order to verify efficiency of the developed models. A good correlation between fatigue crack growth estimations and experimental observations is obtained. © 2016, Gruppo Italiano Frattura. All rights reserved. Source

Jovicic G.,University of Kragujevac | Nikolic R.,University of Kragujevac | Zivkovic M.,University of Kragujevac | Milovanovic D.,University of Kragujevac | And 3 more authors.
Archives of Civil and Mechanical Engineering

The paper presents an estimation of the residual life of the power plant high-pressure pipe, which has been in exploitation for years. A crack was noticed in the pipe, thus it was necessary to estimate the pipe material residual life until its eventual failure. The combined methodology for residual life estimation, which consists of experimental and numerical investigations, was developed. The samples were taken directly from the real high pressure pipe and material properties were determined experimentally, both at room and elevated (operational) temperature. The experimental results also served for the verification of the developed numerical methodologies. The FEM and the X-FEM methods were used for the residual life numerical estimation of the high pressure pipe. The stress and strain fields, used for the estimate, were obtained by application of the Paris' law. The final verification of numerical results was realized by comparing the critical crack length to the experimentally obtained value. © 2012 Politechnika WrocŁawska. Source

Boljanovic S.,Ratka Resanovica | Maksimovic S.,Ratka Resanovica
Engineering Fracture Mechanics

In the present paper, a computational model for crack growth analysis under Mode I/II conditions is formulated. The focus is on two issues - crack path simulation and fatigue life estimation. The finite element method is used together with the maximum principal stress criterion and the crack growth rate equation based on the equivalent stress intensity factor. To determine the mixed-mode stress intensity factors, quarter-point (Q-P) singular finite elements are employed. For verification purposes, a plate with crack emanating from the edge of a hole is examined. The crack path of the plate made of 2024 T3 Al Alloy is investigated experimentally and simulated by using the finite element method with the maximum tangential stress criterion. Then, the validation of the procedure is illustrated by applying the numerical evaluation of the curvilinear crack propagation in the polymethyl methacrylate (PMMA) beam and the Arcan specimen made of Al Alloy for which experimental results are available in the literature. In order to estimate fatigue life up to failure of the plate with crack emanating from the edge of a hole, the polynomial expression is evaluated for the equivalent stress intensity factor using values of stress intensity factors obtained from the finite element analysis. Additionally, the fatigue life up to failure of the Arcan specimen is analyzed for different loading angles and compared with experimental data. Excellent correlations between the computed and experimental results are obtained. © 2011 Elsevier Ltd. Source

Boljanovic S.,Serbian Academy of Science and Arts | Maksimovic S.,Ratka Resanovica | Djuric M.,Ratka Resanovica
International Journal of Fatigue

In the present paper, the residual strength of a pin-loaded lug and a finite plate, both with a semi-elliptical crack emanating from a hole, is examined. A new analytical methodology, based on Fracture Mechanics concepts, is proposed to analyse the crack propagation process in terms of life estimation and crack front evolution. Firstly, the stress field and the stress intensity factor are computed by applying both analytical and numerical approaches. Then, the two-parameter driving force model proposed by Kujawski is implemented for the fatigue life estimation and the crack front evolution. The validity of model here employed is assessed through the comparison between crack growth calculations and experimental data available in the literature, such comparison shows a quite good correlation for the crack and geometrical configurations here examined. © 2016 Elsevier Ltd. Source

Stasevic M.,NIS Petroleum | Maksimovic S.,Ratka Resanovica | Geric K.,University of Novi Sad | Burzic Z.,Ratka Resanovica | Maksimovic M.,Belgrade Waterworks and Sewerage

The goal of this paper is the establishment of computation methods for the evaluation of the residual life of structural elements in the presence of initial damage which appears in the form of cracks. Initial cracks appear during the exploitation of structures in stress concentration zones. Therefore in this paper computation method for the evaluation of the residual life of structural elements with initial damage subjected to cyclic loading of constant amplitude is presented. Calculational methods for the evaluation of the residual life of structural elements with initial damage basically rely on crack propagation analysis. In this investigation for crack propagation analysis Strain Energy Density (SED) method will be used. This method uses the low-cycle fatigue properties of the material, which are also being used for the lifetime evaluation until the occurrence of initial damage. Therefore experimentally obtained dynamic properties of the material such as Paris' constants are not required when this approch is concerned. The complete method for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the structural element in the form of a plate with a hole and a single initial crack. Results of numerical simulation for crack propagation based on strain density method have been compared with experimental results. Source

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