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Opis: Numerous studies have demonstrated that the initial out-of-plane deflection can significantly affect stress distribution along the web boundaries of steel plate girders, potentially leading to the initiation of fatigue cracks and eventual structural failure over time. Fatigue cracks in thin-walled structures commonly initiate at locations of maximum secondary bending stress, arising from the web imperfections introduced during the complex manufacturing process and further amplified by the interaction of global and local stresses. The secondary bending stress of box girders web plate has been numerically investigated in this article. Several nonlinear static analyses have been performed, using the hybrid parametric FE model, consisting of shell and beam finite elements. Vertical normal stress in the upper web boundary below rail was evaluated under different boundary conditions and geometric modifications. Considering the deflection shape of critical buckling mode 1, the directional effects of initial web imperfection and eccentric moment have been evaluated. Also, a comparison in terms of secondary bending stress at different girder spans, intermediate plate spacing and load positions are discussed. The results of this study offer valuable insights into the most and least favorable scenarios related to geometric modifications and varying loading conditions, while also highlighting existing research gaps in current design codes.
Ključne besede: box girder, initial web imperfection, out of plane deflection, secondary bending stress, wheel loading
Objavljeno v DKUM: 09.07.2025; Ogledov: 0; Prenosov: 15
Celotno besedilo (5,13 MB)
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Opis: The plate heat exchanger (PHE) is a component that provides heat to be transferred from hot water to domestic cold water without mixing them with high efficiency. Over the lifetime of the PHE, cyclic pressures act on the brazing points and the plates, and this may lead to fatigue failure. The fatigue behaviour of the PHE, designed using copper-brazed 316L stainless steel, was investigated in this study. First, the fatigue tests under the load ratio R = 0.1 were performed on the Vibrophore 100 testing machine to obtain the S-N curve of the analysed brazed joint. Based on the obtained experimental results, an appropriate material model of the analysed brazed joint has been created, which was validated with numerical calculation in the framework of a program code Ansys. A validated material model was then used for the subsequent numerical analysis of PHE. In order to carry out a numerical calculation using the finite element method (FEM), a three-dimensional model of the heat exchanger was created based on the previous scanning of PHE-geometry. Thereafter, the geometry was parameterised, which allowed us to perform parametric simulations (monitoring different responses depending on the input geometry). Numerical simulations were carried out in the framework of the Ansys 2023-R1 software, whereby the obtained results were analysed, and the responses were appropriately characterised according to previously determined load cases.
Ključne besede: brazed joint, fatigue, experimental testing, computational analyses, heat exchanger
Objavljeno v DKUM: 31.01.2024; Ogledov: 316; Prenosov: 107
Celotno besedilo (7,44 MB)
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Opis: V tem delu smo določili vrednosti materialnih parametrov lotnih spojev toplotnega izmenjevalca, ki so namenjeni definiranju materialnih lastnosti pri numeričnih simulacijah z metodo končnih elementov. Na podlagi rezultatov statičnih nateznih testov smo določili vrednost modula elastičnosti, meje tečenja in natezne trdnosti preizkušancev lotnih spojev, prav tako pa smo podali tudi nekaj parametrov, ki opišejo plastični del krivulje σ – ε. Poleg statičnih smo izvajali tudi dinamične teste pri vedno enakem obremenitvenem razmerju in s pomočjo le – teh določili vrednosti koeficienta in eksponenta trdnosti pri utrujanju, ki sta veljavna v območju, ko delovne napetosti ne presegajo vrednosti meje tečenja. Vse pridobljene rezultate smo naknadno tudi potrdili z uporabo numeričnih analiz po metodi končnih elementov v programu Ansys, kjer smo pokazali, da se rezultati ujemajo.
Ključne besede: toplotni izmenjevalec, lotni spoj, utrujanje, eksperimentalne raziskave, numerične analize.
Objavljeno v DKUM: 24.08.2023; Ogledov: 571; Prenosov: 0
Celotno besedilo (3,07 MB)