1. Experimental characterization and phase-field damage modeling of ductile fracture in AISI 316lVladimir Dunić, Nenad Gubeljak, Miroslav Živković, Vladimir Milovanović, Darko Jagarinec, Nenad Djordjevic, 2024, original scientific article Abstract: ) Modeling and characterization of ductile fracture in metals is still a challenging task in
the field of computational mechanics. Experimental testing offers specific responses in the form of
crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack
growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM)
implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model
(PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed,
with a threshold to propose a new relationship between critical fracture energy and critical total
strain value. In addition, the threshold value of potential internal energy—which controls damage
evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel
are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test.
The PFDM model is validated against the experimental results obtained in the fracture toughness
characterization test, with the simulation results being within 8% of the experimental measurements.
Keywords: phase-field damage modeling, ductile fracture, crack-tip opening displacement, crack growth, resistance curve, finite element method, simulations
Published in DKUM: 19.09.2024; Views: 0; Downloads: 9
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2. Fracture toughness of a high-strength low-alloy steel weldmentJelena Vojvodič-Tuma, Nenad Gubeljak, Borivoj Šuštaršič, Borut Bundara, 2006, original scientific article Abstract: The use of high-strength low-alloy steels for high-performance structures, e.g., pressure vessels and pipelines, requires often high-strength consumables to produce an overmatched welded joint. This globally overmatched welded joint contains local mis-matched regions, which can affect the unstable fracture behaviour of the welded joint and the welded structure itself. If local mis-matched regions are present in the vicinity of a crack tip, then the fracture toughness of the weld metal can be significantly lower than that of the base metal. In this paper, the influence of the weld-metal microstructure on the fracture behaviour is estimated enabling an evaluation of the resistance to stable crack growth through different microstructures. The lower bound of the fracture toughness for different microstructures was evaluated using a modified Weibull distribution. The results, obtained using specimens with a through thickness crack front, indicated a low fracture toughness, caused by the strength mis-matching interaction along the crack front. In the case of through-the-thickness specimens, at least one local brittle zone (LBZ) or a local soft region is incorporated into the process zone in the vicinity of the crack tip. Hence, an unstable fracture occurred with small stable crack propagation, or without it. Despite the fact that the differences between the impact toughness of the weld metal and the base metal can be insignificant, the fracture toughness of a weld metal can be significantly lower.
Keywords: fracture mechanics, welded joint, crack-tip opening displacement, resistance curves
Published in DKUM: 16.03.2017; Views: 1500; Downloads: 104
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3. Leak-before-break analysis of a pressurizer - estimation of the elastic-plastic semi-elliptical through-wall crack opening displacementNenad Gubeljak, Jožef Predan, Dražan Kozak, 2012, published scientific conference contribution Abstract: The work presents methods to estimate elastic-plastic semi-elliptical through-wall Crack Opening Displacement (COD) for the Leak-Before-Break analysis of a pressurizer. Usually proposed methods are based on GE/EPRI approach or on the reference stress and J-integral as stress intensity factor (SIF) along the crack tip. J-integral calculation provides the value of SIF ateach node of mesh along the crack tip, where values vary from the surface to middle section of material in respect to material properties. COD value is calculated through thickness along the centre of crack. The COD values are less sensitive to distance from crack tip and material properties. The engineering approach for the calculation of J-integral by using COD values and material full stress-strain data is given. COD values are proportional to surface length of semi-elliptical through wall crack of the pressurizer
Keywords: mehanika loma, semi-elliptical through-wall crack, crack opening displacement, GE/EPRI approach, leak-before-break analysis, reference stress approach
Published in DKUM: 10.07.2015; Views: 1710; Downloads: 43
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4. Determination of lower bound fracture toughness of a high strength low alloy steel welded jointNenad Gubeljak, 2005, original scientific article Abstract: The use of high-strength low-alloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distortion. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along thevcrck front. In the case of through thickness specimens, at least one local brittle microstructure is incorporatedin the process zone at the vicinity of the crck tip. Hence, unstable fracture occurred with small or without stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and that of base metal are insignificant, the future toughness of a weld metal can be significantly lower.
Keywords: welded joints, fracture mechanics, Crack tip opening displacement, high strength seeel weld, mismatch effects, fracture toughness, resistance curves
Published in DKUM: 01.06.2012; Views: 2489; Downloads: 110
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