Crack initiation and propagation resistance of hsla steel welded joint constituents

The welded joint is heterogeneous in its microstructure, mechanical and geometrical properties, thus the stress field is affected by different factors as well as by residual stress. Therefore, special procedures are needed for experimentally determining the fracture toughness in plane strain, K-Ic, and the impact toughness, usually associated with difficulties in interpreting the measured values. Notched specimens are tested by instrumented Charpy in order to determine impact energy and crack initiation and propagation energies. The pre-cracked specimens are tested by standard, using three-point bending specimens, as geometrically closest to Charpy specimens. In both cases, the notch and crack are located in all various regions of the welded joint of the high-strength low alloyed steel NIONIKRAL-70. Analysis of the results includes speculations on the ratio of energies for crack initiation and propagation vs. fracture toughness

Crack initiation and propagation resistance of hsla steel welded joint constituents

The welded joint is heterogeneous in its microstructure, mechanical and geometrical properties, thus the stress field is affected by different factors as well as by residual stress. Therefore, special procedures are needed for experimentally determining the fracture toughness in plane strain, K-Ic, and the impact toughness, usually associated with difficulties in interpreting the measured values. Notched specimens are tested by instrumented Charpy in order to determine impact energy and crack initiation and propagation energies. The pre-cracked specimens are tested by standard, using three-point bending specimens, as geometrically closest to Charpy specimens. In both cases, the notch and crack are located in all various regions of the welded joint of the high-strength low alloyed steel NIONIKRAL-70. Analysis of the results includes speculations on the ratio of energies for crack initiation and propagation vs. fracture toughness

Experimental examination of fatigue life of welded joint with stress concentration

This paper presents results of experimental examinations of stress concentration influence to fatigue life of butt welded joints with K-groove, produced from the most frequently used structural steel S355J2+N. One group of experiments comprised examinations carried out on the K-groove specimens with stress concentrators of edged notch type. Specimens with short cracks (limited length of initial crack), defined on the basis of the experience from fracture mechanics by the three points bending examinations, have been examined according to standard for the determination of S-N curve, and aimed to determine fatigue strengths for different lengths of initial crack and Relationship between fatigue strength and crack length. Other group of experiments comprised examinations of specimens with edge notch, prepared in accordance with ASTM E 399 for three points bending, in order to establish regularity between crack growth and range of exerted stress intensity factor aimed to determine resistance of welded joint to initial crack growth, namely fatigue threshold (ΔKth)

FEM simulation of welded joint geometry influence on fatigue crack growth resistance

Fatigue behaviour of welded joints is investigated, in terms of welded joint geometry and the fatigue crack position. It is based on previous work which involved numerical simulation of fatigue crack growth in a welded joint made of micro-alloyed, low-carbon pressure vessel steel P460NL1, with the main focus on fatigue crack growth rate through different welded joint regions. The goal here was to change the size of the heat affected zone, as the region in which the fatigue crack initiated, and to compare the results obtained for new crack length values with the original ones, obtained by creating numerical models based on experimental data. A number of models were created, some of which simulated the case with a bigger heat affected zone (and, consequently, a smaller crack length in the weld metal), and other which simulated the case with a smaller heat affected zone. Due to the micro-structural differences between these two welded joint regions, noticeable differences appeared in the numbers of cycles obtained for each zone with varying fatigue crack lengths, as well as in the total number of cycles for both zones through which the crack propagated

Influence of temperature and exploitation period on the behaviour of a welded joint subjected to impact loading

Presented in this paper is the analysis of the influence of temperature and exploitation period on the measure of fracture resistance of welded joint constituents in both new and exploited low-alloyed Cr-Mo steel A-387 Gr. B subjected to impact load. Exploited parent material was a part of the reactor mantle in exploitation for over 40 years and is currently in the repair stage, wherein a part of the mantle is being replaced with newly built-in material. Performed are impact tests of a notched specimen of new and exploited parent material (PM), weld metal (WM) and heat affected zone (HAZ), at both the exploited and new PM sides, in order to determine total impact energy, and its components, crack initiation-and crack propagation energy. Based on test results, analysis of tendency toward brittle fracture, i.e. toward an increase of in-service brittleness (ageing) represents the comparison of values obtained for characteristic areas of welded joints and the justification of the selected welding technology

Influence of temperature and exploitation period on the behaviour of a welded joint subjected to impact loading

Presented in this paper is the analysis of the influence of temperature and exploitation period on the measure of fracture resistance of welded joint constituents in both new and exploited low-alloyed Cr-Mo steel A-387 Gr. B subjected to impact load. Exploited parent material was a part of the reactor mantle in exploitation for over 40 years and is currently in the repair stage, wherein a part of the mantle is being replaced with newly built-in material. Performed are impact tests of a notched specimen of new and exploited parent material (PM), weld metal (WM) and heat affected zone (HAZ), at both the exploited and new PM sides, in order to determine total impact energy, and its components, crack initiation-and crack propagation energy. Based on test results, analysis of tendency toward brittle fracture, i.e. toward an increase of in-service brittleness (ageing) represents the comparison of values obtained for characteristic areas of welded joints and the justification of the selected welding technology

Impact fracture response of friction stir welded Al-Mg alloy

Ispitivani su uticaji parametara frikcionog zavarivanja mešanjem na ponašanje loma udarom po Šarpiju u leguri Al-Mg 5083. Rotaciona i poprečna brzina zavarivanja su povezane sa dinamičkom inicijacijom prsline i duktilno čupanje. Mehanizam loma je razjašnjen numeričkom i fraktografskom analizom. Rezultati pokazuju da na inicijaciju i na stabilan rast prsline ne utiču toliko parametri postupka zavarivanja, koliko deformaciono ojačavanje ispitane legure. Međutim, konačna nestabilna faza duktilnom cepanja u velikoj meri zavisi od grešaka unutar zone mešanja u metalu šava.Effects of friction stir welding (FSW) variables on the Charpy impact fracture behaviour of Al-Mg 5083 alloy are investigated. Rotational and traversal welding rates are linked to the dynamic crack initiation and ductile tearing. The fracture mechanism is clarified by numerical and fractographic analysis. Results had revealed that initiation and stable crack propagation is not significantly influenced by the applied welding variables. It is attributed to the strain hardening of the investigated alloy. However, the final unstable phase of ductile tearing is strongly susceptible to the imperfections in the stirring zone of the weld

Micromechanical Coupled Study of Crack Growth Initiation Criterion in Pressure Vessel Steel

We present results of the combined design-theoretical investigation of the mechanism of crack growth at the onset of ductile fracture of NPP reactor pressure vessels. Micromechanical approach to the prediction of ductile fracture has been applied, according to which the volume fraction of voids in the deformed material is determined by finite-element method. On the basis of CT-specimen tests and known damage parameters, obtained on smooth spherical specimens, we obtained micromechanical criterion of crack growth initiation for ductile fracture.Представлены результаты комплексного расчетно-экспериментального исследования механизма распространения трещины на начальном этапе вязкого разрушения корпусных сталей АЭС. Использован микромеханический подход к прогнозированию вязкого разрушения, согласно которому объемное содержание пор деформируемого материала определяется методом конечных элементов. На основании проведенных испытаний образцов СТ с трещиной и имеющихся данных о параметрах разрушения гладких сферических образцов установлен микромеханический критерий начала развития трещины в условиях вязкого разрушения материала.Представлено результати комплексного розрахунково-експериментального дослідження механізму розповсюдження тріщини на початковому етапі в’язкого руйнування корпусних сталей АЕС. Використовується мікромеха- нічний підхід до прогнозування в ’язкого руйнування, згідно з яким об’ємний вміст пор деформівного матеріалу визначається методом скінченних елементів. На основі проведених випробувань зразків СТ із тріщиною та відомих даних про параметри руйнування гладких сферичних зразків установлено мікромеханічний критерій початку розвитку тріщини в умовах в ’язкого руйнування

Numerical simulation of the plunge stage in friction stir welding alloys EN AW 2024 T 351 and EN AW 7049A T 652

Tema ovog rada je proučavanje faze probijanja korišćenjem numeričkog modela. Analizirana je promena temperature i sile probijanja u toku faze probijanja postupka zavarivanja trenjem mešanjem za legure aluminijuma visoke čvrstoće EN AW 2024 T 351 i EN AW 7049A T 652, pri različitim brzinama rotacije alata. Numerički rezultati pokazuju da maksimalne temperature u postupku zavarivanja trenjem mešanjem mogu biti povećane sa povećanjem brzine rotacije alata i da su temperature manje od temperature topljenja materijala koji se zavaruje. Pri istim brzinama rotacije alata, registrovana je veća temperatura kod legure aluminijuma EN AW 2024 T 351 i veća sila probijanja - otpor materijala kod legure EN AW 7049A T 652. Sa povećanjem brzine rotacije alata, sila probijanja može biti smanjena. Trodimenzionalni model konačnih elemenata faze probijanja je razvijen korišćenjem ABAQUS programskog paketa za proučavanje termomehaničkih procesa faze probijanja. Spregnuti termo-mehanički model konačnih elemenata koristi proizvoljnu Lagranž-Ojlerovu formulaciju, Džonson-Kukov zakon i Kulonov zakon trenja. U ovoj analizi se temperatura, pomjeranje i mehaničke reakcije posmatraju istovremeno. Generisanje toplote u postupku zavarivanja trenjem mešanjem se može podeliti na tri dela:generisanje toplote trenjem od čela alata, generisanje toplote trenjem od trna alata i generisanje toplote od plastičnih deformacija u blizini trna alata.This paper investigates the plunge stage using numerical modeling. Change of temperature and plunge force have been analyzed during the plunge stage of the FSW procedure for high hardness aluminum alloys EN AW 2024 T 351 and EN AW 7049A T 652, at different speed of tool rotation. Numerical results indicate that the maximum temperature in the FSW process can be increased with the increase of the rotational speed and that temperature is lower than the melting point of the welding material. Higher temperature was registered at the aluminum alloy EN AW 2024 T 351 at the same speed of tool rotation, and higher plunge force - resistance of material was registered at the alloy EN AW 7049A T 652. When the rotational speed is increased, the plunge force can be reduced. A three-dimensional finite element model (FEM) of the plunge stage was developed using the commercial code ABAQUS to study the thermo-mechanical processes involved during the plunge stage. A coupled thermo-mechanical 3D FE model using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and the Coulomb's Law of friction. In this analysis, temperature, displacement and mechanical responses are determined simultaneously. The heat generation in FSW can be divided into three parts: frictional heat generated by the tool shoulder, frictional heat generated by the tool pin, and heat generated by material plastic deformation near the pin region

Numerical simulation of the plunge stage in friction stir welding alloys EN AW 2024 T 351 and EN AW 7049A T 652

Tema ovog rada je proučavanje faze probijanja korišćenjem numeričkog modela. Analizirana je promena temperature i sile probijanja u toku faze probijanja postupka zavarivanja trenjem mešanjem za legure aluminijuma visoke čvrstoće EN AW 2024 T 351 i EN AW 7049A T 652, pri različitim brzinama rotacije alata. Numerički rezultati pokazuju da maksimalne temperature u postupku zavarivanja trenjem mešanjem mogu biti povećane sa povećanjem brzine rotacije alata i da su temperature manje od temperature topljenja materijala koji se zavaruje. Pri istim brzinama rotacije alata, registrovana je veća temperatura kod legure aluminijuma EN AW 2024 T 351 i veća sila probijanja - otpor materijala kod legure EN AW 7049A T 652. Sa povećanjem brzine rotacije alata, sila probijanja može biti smanjena. Trodimenzionalni model konačnih elemenata faze probijanja je razvijen korišćenjem ABAQUS programskog paketa za proučavanje termomehaničkih procesa faze probijanja. Spregnuti termo-mehanički model konačnih elemenata koristi proizvoljnu Lagranž-Ojlerovu formulaciju, Džonson-Kukov zakon i Kulonov zakon trenja. U ovoj analizi se temperatura, pomjeranje i mehaničke reakcije posmatraju istovremeno. Generisanje toplote u postupku zavarivanja trenjem mešanjem se može podeliti na tri dela:generisanje toplote trenjem od čela alata, generisanje toplote trenjem od trna alata i generisanje toplote od plastičnih deformacija u blizini trna alata.This paper investigates the plunge stage using numerical modeling. Change of temperature and plunge force have been analyzed during the plunge stage of the FSW procedure for high hardness aluminum alloys EN AW 2024 T 351 and EN AW 7049A T 652, at different speed of tool rotation. Numerical results indicate that the maximum temperature in the FSW process can be increased with the increase of the rotational speed and that temperature is lower than the melting point of the welding material. Higher temperature was registered at the aluminum alloy EN AW 2024 T 351 at the same speed of tool rotation, and higher plunge force - resistance of material was registered at the alloy EN AW 7049A T 652. When the rotational speed is increased, the plunge force can be reduced. A three-dimensional finite element model (FEM) of the plunge stage was developed using the commercial code ABAQUS to study the thermo-mechanical processes involved during the plunge stage. A coupled thermo-mechanical 3D FE model using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and the Coulomb's Law of friction. In this analysis, temperature, displacement and mechanical responses are determined simultaneously. The heat generation in FSW can be divided into three parts: frictional heat generated by the tool shoulder, frictional heat generated by the tool pin, and heat generated by material plastic deformation near the pin region