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Influence of microdefect on fatigue properties in weld fine grain heat affected zone on nickel molybdenum alloy steel : doctoral disertation
Fidan Smaili, 2023, doktorska disertacija

Opis: This research presents two possibilities to prepare and test the Fine Grain of a Heat Affected Zone, which, practically, could be considered as the weakest part of welded joints in the presence of any microdefect. It is a narrow zone located between the fusion zone and the unaffected base material; therefore, only a few methods are suitable to test its mechanical properties. The 18CrNiMo7-6 steel was used as the base material. As this steel is usually used for the production of dynamically loaded components, testing of its fatigue behaviour and fracture toughness was crucial, but also measurement of its hardness and impact toughness. To investigate the mechanical properties of a Fine-Grain Heat-Affected Zone (FG HAZ), two different methods for simulation of as-welded microstructures were used in this research: A weld thermal cycle simulator (WTCS) and austenitising in a laboratory furnace +
Ključne besede: weld joint, Fine Grain Heat Affected Zone, mechanical properties, fatigue crack growth
Objavljeno v DKUM: 06.10.2023; Ogledov: 326; Prenosov: 37
.pdf Celotno besedilo (13,49 MB)

Validation of boundary element method for assessment of weld joints accounting for notch stress : magistrsko delo
Rok Skerbiš, 2022, magistrsko delo

Opis: Robust, automated mesh generation on arbitrary weld joint geometries, using finite element method (FEM) is a problematic task. It was previously discovered, that an arbitrary weld joint geometry can be parameterized inside a CAD environment [1], however when it comes to domain discretization and boundary conditions assignment, the parameterized approach becomes too demanding inside FEM. This results in long FEM model preparation times and sometimes in problems with the parametric model itself, which leads to a need for an additional numerical method - boundary element method (BEM), which overcomes this issue and is beneficial in this case. BEM is a numerical method, that in addition to other applications finds a use in the elasto-mechanic problems, where the only concern is the boundary of the considered geometric domain. Since notch stress calculations of weld joints fall into this category, their calculation can be carried out with it. Since there is not much available information on whether or not such calculations are a suitable alternative for the currently used FEM, this thesis had to be confirmed through a structured and step by step procedure. First, a notch mesh quality study has been made, then other entities followed. It was discovered that BEM is applicable to the problem and capable of calculating results with sufficient quality. Furthermore, the parameter driven approach and automated calculation provide for additional advantageous potentials.
Ključne besede: weld joint, boundary element method, finite element method, spatial discretization, notch stress
Objavljeno v DKUM: 02.11.2022; Ogledov: 467; Prenosov: 0
.pdf Celotno besedilo (4,62 MB)

Flaw acceptability assessment detected in HSLA steel weld joints
Inoslav Rak, 1999, izvirni znanstveni članek

Opis: The flow size in weld joint can be determined by non destructive examination (NDE). Because of different mateials, and loading as well as because of the possible effect of corrosive environment the question arises how to assess reliably the allowable falw size in different weld joint parts. The presence of flaws is obvious but the possibilities of their revealing are limited and not always posssible. The flaw size and distribution are the essential parameters for the structure capacity of bearing under high loading the weld joint. The larger is the allowable flaw size anticipated, the safer is the welded structure, and the easiest is the detection of the flaw size by NDE methods. Thus for assessing the safety of complex loaded welded structure, machine parts or equipment life time, it is obligatory to consider the requirements of different "Fitness for Purpose" systems. The article presents the possibility of assessing the detected flaw by means of NDE if the material fracture toughness of the area where the fatigue crack tip located is known. The fatigue crack represents the severest discontinuity that can occur in a welded joint. The principles of IIW Guidance on Assessment of The Fitness for Purpose of Welded Structures - IIW/IIS-SST-1157-90 and BS PD 6493 and separately ETM that treats mis-matched weld joints are shown and used.
Ključne besede: zvarni spoji, dopustna velikost napake, lomna žilavost, trdnostna heterogenost, primernost za uporabo, weld joint, allowable flaw size, fracture toughness, strength mis-match, fitness for purpose
Objavljeno v DKUM: 10.07.2015; Ogledov: 1630; Prenosov: 25
URL Povezava na celotno besedilo

Measurement of strain caused by residual stresses in a welded joint using neutron diffraction
Nenad Gubeljak, Jelena Vojvodič-Tuma, Hans-Georg Preismeyer, 1999, izvirni znanstveni članek

Opis: The distribution and amount of residual stresses can significantly contrubute to the fatigue fracture behaviour of welded joints in structures. Interior residual stresses, which interact with the plane strain state, are more dangerous than residual stresses at the surface of the welded joint. If the surface of the welded joint is mechanically treated (e.g. shapering), then significant differences between the stress stated at the surface and within the volume occur. Hence, different non-destructive methods (e.g. gamma radiation, neutron diffraction) have been developed to determine strains caused by residual stresses in the volume of polycrystalline materials. However, the measurement of strains caused by residual stresses becomes difficult for large samples. In this paper the measurement procedure on a sample taken from the weld joint is presented and the effecet of residual stresses on fatigue crack propagation is assessed for low and high cycle loading fatigue.
Ključne besede: zaostale napetosti, zvarni spoj, neutronski lom žarkov, utrujenostno širjenje razpoke, neutron diffraction method, residual stresses, fatigue crack propagation, weld joint
Objavljeno v DKUM: 10.07.2015; Ogledov: 1216; Prenosov: 34
URL Povezava na celotno besedilo

Role of residual stresses on fracture properties of under-matched butt weld
Inoslav Rak, Vladimir Gliha, 1999, izvirni znanstveni članek

Opis: Under-matched weld joints were adopted for producing a penstock of 47 mm wall thickness and 4200 mm diameter, to improve the weldability. The isothermal Robertson wide plate test on the under-matched weld joints, were the allowable stress level was 0.6 of the yield stress, proved that the longitudinal stresses caused the crack propagation alog the weld joint to deviate into tough base material where it was arrested. The arrest temperature was between -10 and -20°C. The behaviour of the crack propagation was the reason to omit the thermal stress relieving of the pipe section and on circumferential weld joints executed on this side. One can always take into consideration the role of axial residual stresses when assessing whether to use, or not, under-matched weld joints in severer loaded structures.
Ključne besede: strjeni zvar z nižjo mejo tečenja, zaostale napetosti, potek loma, lastnosti ujetja, lomna žilavost, under-matched weld joint, residual stresses, fracture path, arrest properties, fracture toughness
Objavljeno v DKUM: 10.07.2015; Ogledov: 1489; Prenosov: 44
URL Povezava na celotno besedilo

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