Residual Stress Pattern Prediction in Spray Transfer Multipass Welding by Means of Numerical Simulation

One of the main problems of gas metal arc welding (GMAW) process is the generation of residual stresses (RS), which has a direct impact on the mechanical performance of welded components. Nevertheless, RS pattern prediction is complex and requires the simulation of the welding process. Consequently, most of the currently used dimensioning approaches do not consider RS, leading to design oversized structures. This fact is especially relevant in big structures since it generates high material, manufacturing and product transportation costs. Nowadays, there are different numerical methods to predict the RS generated in GMAW process, being Goldak’s method one of the most widely used model. However, the use of these methods during the design process is limited, as they require experimentally defining many parameters. Alternatively, in this chapter, a new methodology to define the heat source energy based on the spray welding physics is exposed. The experimental validation of the methodology conducted for a multipass butt weld case shows good agreement in both the temperature pattern (9.16% deviation) and the RS pattern (42 MPa deviation). Finally, the proposed methodology is extended to analyse the influence of the thickness and the number of passes in the RS pattern of thick T-joint welds

A numerical analysis of multiaxial fatigue in a butt weld specimen considering residual stresses

Residual Stress (RS) pattern changes considerably depending on the width of the plates and the welding parameters, having effect on the fatigue strength. Most of the standards do not consider them and in some works, yield stress is taken as residual stressvalue. It results in a very conservative estimation of fatigue life. Authors developed recently a numerical model to predict more properly the value of RS pattern depending on the plate thickness. In a welded joint, considering the RS and alternating axial loads, the evolution of the stresses is multiaxial, becoming necessary its study. Therefore, the aim of this work is to analyse different fatigue indicator parameters (Smith-Watson-Topper, Fatemi-Socie, and Critical Plane implementation of the Basquin equation) in order to predict the fatigue behaviour of butt-weld components. For that purpose, the numerical model to predict the RS pattern in welded joint developed by this research group is used

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

The authors acknowledge Fundacao para a Ciencia e Tecnologia (FCT) for its financial support through the project UID/EMS/00667/2019. Fundo Regional para a Ciencia e Tecnologia and Projeto de I&DT for companies in copromotion SLM-XL, (Ref 3346), funded by Fundo Europeu de Desenvolvimento Regional (FEDER) through Programa Operacional Regional de Lisboa.Additive manufacturing technologies based on melting and solidification have considerable similarities with fusion-based welding technologies, either by electric arc or high-power beams. However, several concepts are being introduced in additive manufacturing which have been extensively used in multipass arc welding with filler material. Therefore, clarification of fundamental definitions is important to establish a common background between welding and additive manufacturing research communities. This paper aims to review these concepts, highlighting the distinctive characteristics of fusion welding that can be embraced by additive manufacturing, namely the nature of rapid thermal cycles associated to small size and localized heat sources, the non-equilibrium nature of rapid solidification and its effects on: internal defects formation, phase transformations, residual stresses and distortions. Concerning process optimization, distinct criteria are proposed based on geometric, energetic and thermal considerations, allowing to determine an upper bound limit for the optimum hatch distance during additive manufacturing. Finally, a unified equation to compute the energy density is proposed. This equation enables to compare works performed with distinct equipment and experimental conditions, covering the major process parameters: power, travel speed, heat source dimension, hatch distance, deposited layer thickness and material grain size.publishersversionpublishe

Investigating mechanical properties of MIG reinforced steel sheets using Titanium Alloy powder

Abstract: Mild steel is one of the commonest materials used in the metal industry due to its weldability, malleability and hardness properties. Consequently, there is always a need for joining processes of mild steel, with welding techniques such as Metal Inert Gas (MIG) welding being a popular choice. However, the complex physics involved in welding such as phase changes, metal deposition, and inhomogeneous heating and cooling rates across the weld zone often results in the compromise of structural integrity in mild steel welds. Improving weld integrity has since become an area of interest, with process parameter optimization and post-weld heat treatment being the most popular solutions as discovered in the literature...M.Eng. (Mechanical Engineering

Τρισδιάστατη Θερμομηχανική Ανάλυση της Συγκόλλησης Ανοξείδοτων Ωστενιτικών Χαλύβων

367 σ.Περιλαμβάνει εκτεταμένη ελληνική περίληψη σε ξεχωριστό τεύχος.Στην παρούσα διατριβή μελετάται η αριθμητική μοντελοποίηση της διαδικασίας συγκόλλησης ανοξείδωτων ωστενιτικών χαλύβων με τη μέθοδο των πεπερασμένων στοιχείων. Για την πραγματοποίηση αριθμητικών μοντελοποιήσεων απαραίτητη είναι η μελέτη της διαδικασίας συγκόλλησης αλλά και του υλικού. Η γνώση και κατανόηση της συμπεριφοράς του υλικού κατά τη θέρμανσή του, από το τόξο της συγκόλλησης, αλλά και κατά την ψύξη του είναι απαραίτητες για την κατασκευή του μοντέλου, την ακριβή εφαρμογή του θερμικού φορτίου και την πρόβλεψη της θερμομηχανικής ανάδρασής της συγκολλητής κατασκευής. Συνεπώς, καταστρώθηκαν και πραγματοποιήθηκαν μετωπικές συγκολλήσεις ελασμάτων, διαφόρων διαστάσεων, ανοξείδωτων ωστενιτικών χαλύβων και μετρήθηκαν κατά τη διάρκεια της συγκόλλησης οι θερμικοί κύκλοι, οι παραμορφώσεις και κατόπιν οι παραμένουσες τάσεις, ενώ ακολούθησε μεταλλογραφική μελέτη του προφίλ της συγκόλλησης. Η ολοκληρωμένη διερεύνηση της διαδικασίας συγκόλλησης επιτυγχάνεται κυρίως με την κατασκευή τρισδιάστατων μοντέλων. Η θερμομηχανική επίλυσή τους όμως με τη μέθοδο των πεπερασμένων στοιχείων απαιτεί αρκετό χρόνο σε σχέση με την αντίστοιχη δισδιάστατη ανάλυση, λόγω του αυξημένου αριθμού στοιχείων και κόμβων. Ο χρόνος επίλυσης έχει μειωθεί επιτυχώς χάρη στους σύγχρονους ισχυρούς υπολογιστές, αλλά οι προσπάθειες σήμερα επικεντρώνονται στη μείωση του χρόνου επίλυσης με διάφορες τεχνικές χωρίς όμως την πιθανότητα απώλειας της ακρίβειας των αποτελεσμάτων. Συνεπώς στην παρούσα διατριβή πραγματοποιούνται μια σειρά από αριθμητικές αναλύσεις που αποσκοπούν στη μείωση του χρόνου επίλυσης, ενώ ταυτοχρόνως ελέγχεται και η ακρίβεια των αποτελεσμάτων τους. Τελικώς, η εφαρμογή της τεχνικής «ομαδοποίησης» των περασμάτων επιτυγχάνει μείωση του χρόνου επίλυσης κατά 35% και εξαιρετική ακρίβεια των αποτελεσμάτων της.In the present thesis the numerical simulation of the austenitic stainless steel welding process is investigated via the finite element method. In order to proceed to the simulation of the thermo-mechanical process of austenitic stainless steel, the process itself and the material must be carefully studied. The knowledge and understanding of the material behavior during the heating by the welding arc, but also upon cooling, is crucial for the construction of the model, the accurate implementation of the thermal load and the prediction of the thermo-mechanical response of the welded joint. In order to acquire such knowledge, a series of welding experiments were conducted through the butt-welding of austenitic stainless steel plates with various dimensions. In-situ measurements of the thermo-mechanical response, along with stress measurements and metallographic investigation in the as-welded condition, provided sufficient information, thus allowing the accurate numerical modeling of the welding process. The complete insight in the case of the welding process investigation is achieved mostly with the construction of three-dimensional models. The thermo-mechanical analysis of solid models with the finite element method is a time-consuming process in comparison to two-dimensional analyses, since a much larger number of nodes and elements are required for the construction of the solid model. The required time for a solution to be achieved has been decreased with the ongoing improvement of computational efficiency of personal computers. However, efforts are focused on various techniques that would decrease computational time of three-dimensional analyses mostly in multi-pass welding simulation, without any sacrifice in the accuracy in prediction capability. Thus, in the present thesis a series of numerical welding simulations are presented where the accuracy of the predicted results is evaluated and techniques to minimize the computational time are employed. The employment of the “Grouping” technique clearly shows that accurate results can be acquired with a 35% reduction of computational time.Ανδρέας Π. Κυριακόγγονα

Thermal modelling of gas metal arc welding using finite element analysis

Thesis (M.E.Sc.) -- University of Adelaide, Dept. of Mechanical Engineering, 199

Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding

Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated

Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding

Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated

Mechanical characterization and fatigue assessment of wire and arc additive manufactured HSLA steel parts

Additive manufacturing is one of the main foundations of Industry 4.0. It aims, particularly, to increase productivity, reducing material waste due to machining and bring many advantages that overcome the conventional manufacturing processes. Wire and Arc Additive Manufacturing (WAAM) is an additive manufacturing process that employs an electric arc as heat source in order to melt and add material. It shows great versatility and freedom to fabricate parts using a layer-by-layer method of deposition. Despite the clear advantages presented, there still needs more progress in order to make it industrially feasible. One of the main challenges it faces is studying the mechanical properties bet on the desired geometry, type of material and the adopted parameters before employing these components in critical operational loading conditions. This dissertation aimed to assess the mechanical properties and fatigue resistance of HSLA parts manufactured by this technology. In this way, two type of samples were produced – one of low heat-input and another of high heat-input, in which the changing variable was the travel speed. For each type, three thin walled parts were obtained, measuring 180 x 100 mm each. After manufacturing all the required samples, three different regions were analysed – bottom, middle and top. Next, all parts were assiduously prepared in order to proceed with material characterization as well as testing, specifically, waviness, microstructure, electrical conductivity, microhardness, uniaxial tensile tests and lastly fatigue tests, with subsequent fracture surface observation through Scanning Electron Microscope (SEM). Fatigue tests were performed at room temperature on low heat-input samples with constant stress amplitude, stress ratio R=0.1 and frequencies between 12 Hz and 15 Hz. The S-N curve of the experimental results is presented along with an explanation within the context of the other characterization techniques results

Thermal and residual stress analysis of welded joints in cladded pipelines

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonThe approach employed in this research in resolving the challenge of welding induced stresses on the dissimilar material joints of cladded pipes and the aftermath of weld is unique in approach compared to other researchers in that the transient heat recorded with high temperature thermocouples (positioned at strategic points) and Pico logger uncovered the trend and rate of heat transmitted throughout the dissimilar material welded joint during welding. This further revealed that the rate depended on the nature of the material, the distance from the weld line, weld axis, weld start, the thermal conductivity of material, phase change and not just the assumed proximity to the heat source. Hence the thermocouple closest to the heat source was not necessarily the first to receive the heat neither received the highest amount of heat compared to the rest of the thermocouples, most especially those placed farthest. This was further validated with the aid of finite element analysis of the welded joint of dissimilar materials and was confirmed for different clad thicknesses. Butt welding of two dissimilar materials: stainless steel of grade AISI 316 and mild steel of grade CR4 was carried out with the aid of the tungsten arc weld at a voltage of 240v using metal filler elements of A15 copper wire and 304/316 SS filler metals for the carbon steel and stainless steel sections of the weld, at the Brunel University laboratory. In this thesis different thicknesses (2mm and 12mm) of stainless steel clad in the dissimilar material clad joints has been investigated using scanning electron microscope (SEM), EBSD, XRD and EBSD to examine the dissimilar interface region and carbides in adjacent clads to generate the diffusion interface occurring in the dissimilar welded joint in order to guarantee the structural integrity of the structures for improved product quality and reliability. This resulted in generation of diffusion representation of the microstructural occurrences by reason of the results obtained from the microscopic and macrostructural analysis which stands out from all other authors. The approach of resolving the thermally induced weld stresses using the Gaussian theorem also differs from the approaches of other researchers and proved effective in the FEA of modelling and validation of both thermal and stress models and with respect to the weld direction. It was discovered from the weld induces direction, the radial and axial shrinkage effects radial shrinkage increase with increasing angle of inclination whereas the axial shrinkage at lower increments differs from those at higher increments of the axial length – cause of creep effect experienced at higher shrinkages.Petroleum Technology Development Fun