Papers by Author: Zijah Burzić

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Authors: Ivica Čamagić, Nemanja Vasić, Zijah Burzić, Aleksandar Sedmak
Abstract: The problem of fracture toughness, KIc, determination at a crack tip localized in a welded joint is placed in principle because fracture mechanics assumes homogenous material, not only around the crack tip but on a distance from it, in order to maintain valid theoretical assumptions and importance of the fracture toughness as the property measured by some of the fracture mechanics methods. Welded joint, as an integral part of a structure, represents inhomogeneity by microstructure and mechanical properties, often by geometrical form, and by the stress field as well, which are affected by various factors as well as residual stresses after welding [1]. However, these general difficulties did not disenable experimental determination of the fracture toughness under plane strain, KIc, in certain critical areas of a welded joint, or welded joint as a whole, but rather there are difficulties in interpreting the meaning of the measured values. Specimens for the fracture mechanics parameters determination are specimens with cracks, and cracks appears in welded joints as the most critical defects.
Authors: Ivica Čamagić, Nemanja Vasić, Predrag Živković, Aleksandar Radović, Tamara Sedmak, Meri Burzić, Zijah Burzić
Abstract: Analysis of fracture toughness of high-strength low alloyed steel, Nionikral-70, welded joint constituencies, subjected to variable load is given in this paper, using two parameters. Crack initiation resistance is determined by testing of endurance limit and by designing of Wöhler curves. Crack propagation resistance is determined by testing of crack growth rate, and accordingly determination of Paris equation parameters. Analysis of fracture toughness is given based on testing results, comparing obtained values for base metal, weld metal and heat affected zone.
Authors: D.R. Sekulić, I.M. Djordjević, M.V. Gordić, Zijah Burzić, M.M. Stevanović
Abstract: Unidirectional and angle-ply carbon/epoxy laminates were gamma irradiated up to doses of 12 and 20 MGy. Composites with two different, low and high temperature epoxy matrices have been submitted to irradiation and subsequent mechanical testing. The radiation effects were studied by measuring in-plane, interalminar shear and transverse tensile strength, as well as interlaminar strain energy release rate of tested composites. The immersion of composite plate in water at 80 oC and mechanical measurements at elevated temperatures emphasized irradiation effects on mechanical properties.
Authors: M. Vratnica, Z. Cvijović, K. Gerić, Zijah Burzić
Abstract: The aim of the present work is to determine the role of intermetallic (IM) phases in the fatigue crack propagation behavior of hot-forged Al-Zn-Mg-Cu alloys in T73 condition. To generate differences in the volume fraction and coarseness of various IM particles, the (Fe+Si) impurity level is varied from 0.23 to 0.37 mass%. The fatigue crack propagation tests are conducted in air at ambient temperature and a stress ratio R of 0.1. Characterization of the fatigue fracture surfaces is performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Quantified IM particles data for each alloy are then related to the fatigue properties and fractographic analysis results. It was found that almost all particles of the Fecontaining phases (primarily (Cu,Fe,Mn)Al3 and Al7Cu2Fe) are broken and not effective in hindering fatigue crack propagation. On the other hand, the Mg2Si and soluble phase particles smaller than those of the Fe-containing phases contribute beneficially to fatigue life. These particles increase the tortuosity of the crack path and retard the crack growth rate. The crack growth rate decreases as the volume fraction of coarse Fe-containing particles increases, because more secondary cracks are produced decreasing the effective stress intensity at the main crack tip.
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