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Javidi Shirvan, A., Choquet, I., Nilsson, H. & Jasak, H. (2018). Coupling boundary condition for high-intensity electric arc attached on a non-homogeneous refractory cathode. Computer Physics Communications, 222, 31-45
Open this publication in new window or tab >>Coupling boundary condition for high-intensity electric arc attached on a non-homogeneous refractory cathode
2018 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 222, p. 31-45Article in journal (Refereed) Published
Abstract [en]

The boundarycoupling high-intensity electricarc and refractory cathode is characterized bythree sub- layers: the cathode sheath,the Knudsen layerand the pre-sheath. A self-consistent coupling boundarycondition accounting for these three sub-layers is presented; its novel propertyis to take into account a non-uniform distribution of electronemitters on the surface of the refractory cathode. This non- uniformity is due to cathode non-homogeneity induced by arcing.The computational model is appliedto a one-dimensional test case to evaluate the validity of different modelingassumptions. It is also applied coupling a thoriated tungstencathode with an argon plasma(assumed to be in local thermal equilibrium) to compare the calculation results with uniform and non-uniform distribution of the electron emitters to experimental measurements. The resultsshow that the non-uniformity of the electronemitters’ distribution has a significant effect on the calculated properties. It leads to good agreementwith the cathode surfacetemperature, and with the plasmatemperature in the hottest region.Some differences are observedin colder plasmaregions, where deviation from local thermalequilibrium is known to occur.

Keywords
Coupling boundary, Thermal plasma, Refractory cathode layer, Gas tungsten arc
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11812 (URN)10.1016/j.cpc.2017.09.010 (DOI)000418969900003 ()2-s2.0-85031753829 (Scopus ID)
Funder
Knowledge Foundation
Note

Founders: ESAB

Available from: 2017-11-20 Created: 2017-11-20 Last updated: 2019-05-28Bibliographically approved
Choquet, I. (2018). Gas tungsten arc models including the physics of the cathode layer: remaining issues. Welding in the World, 62(1), 177-196
Open this publication in new window or tab >>Gas tungsten arc models including the physics of the cathode layer: remaining issues
2018 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 1, p. 177-196Article in journal (Refereed) Published
Abstract [en]

A recent review pointed out that the existing models for gas tungsten arc coupling the electrode (a cathode) and the plasma are not yet complete enough. Their strength is to predict with good accuracy either the electric potential or the temperature field in the region delimited by the electrode and the workpiece. Their weakness is their poor ability to predict with good accuracy these two fields at once. However, both of these fields are important since they govern the heat flux to the workpiece through current density and temperature gradient. New developments have been made since then. They mainly concern the approaches addressing the electrode sheath (or space charge layer) that suffered from an underestimation of the arc temperature. These new developments are summarized and discussed, the modelling assumptions are examined, and important modelling issues that remain unexplored are underlined.

Keywords
Refractory cathode, cathode surface state, cathode boundary layer, plasma column, modelling assumptions
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11809 (URN)10.1007/s40194-017-0513-2 (DOI)000428751000018 ()2-s2.0-85040806998 (Scopus ID)
Funder
Knowledge Foundation
Note

Funders: ESAB

Available from: 2017-11-20 Created: 2017-11-20 Last updated: 2019-01-22Bibliographically approved
Gaudiuso, C., Giannuzzi, G., Volpe, A., Lugarà, P. M., Choquet, I. & Ancona, A. (2018). Incubation during laser ablation with bursts of femtosecond pulses with picosecond delays. Optics Express, 26(4), 3801-3813
Open this publication in new window or tab >>Incubation during laser ablation with bursts of femtosecond pulses with picosecond delays
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2018 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 4, p. 3801-3813Article in journal (Refereed) Published
Abstract [en]

Abstract: We report on an experimental investigation of the incubation effect during irradiation of stainless steel with bursts of ultrashort laser pulses. A series of birefringent crystals was used to split the pristine 650-fs pulses into bursts of up to 32 sub-pulses with time separations of 1.5 ps and 3 ps, respectively. The number of selected bursts was varied between 50 and 1600. The threshold fluence was measured in case of Burst Mode (BM) processing depending on the burst features, i.e. the number of sub-pulses and their separation time, and on the number of bursts. We found as many values of threshold fluence as the combinations of the number of bursts and of sub-pulses constituting the bursts set to give the same total number of impinging sub-pulses. However, existing incubation models developed for Normal Pulse Mode (NPM) return, for a given number of impinging pulses, a constant value of threshold fluence. Therefore, a dependence of the incubation coefficient with the burst features was hypothesized and experimentally investigated. Numerical solutions of the Two Temperature Model (TTM) in case of irradiation with single bursts of up to 4 sub-pulses have been performed to interpret the experimental results. © 2018 Optical Society of America.

Keywords
Electromagnetic pulse; Irradiation; Laser ablation; Stainless steel; Ultrafast lasers, Birefringent crystals; Experimental investigations; Incubation effects; Numerical solution; Separation time; Threshold fluences; Time separation; Two-temperature models, Ultrashort pulses
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12193 (URN)10.1364/OE.26.003801 (DOI)000426268500008 ()2-s2.0-85042108738 (Scopus ID)
Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2019-05-27Bibliographically approved
Gaudiuso, C., Giannuzzi, G., Choquet, I., Lugarà, P. M. & Ancona, A. (2018). Incubation effect in burst mode fs-laser ablation of stainless steel samples. Paper presented at Laser-Based Micro- and Nanoprocessing XII 2018; San Francisco; United States; 30 January 2018 through 1 February 2018. Proceedings of SPIE, the International Society for Optical Engineering, 10520, Article ID 105200A.
Open this publication in new window or tab >>Incubation effect in burst mode fs-laser ablation of stainless steel samples
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2018 (English)In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 10520, article id 105200AArticle in journal (Refereed) Published
Abstract [en]

We report on an experimental study of the incubation effect during irradiation of stainless steel targets with bursts of femtosecond laser pulses at 1030 nm wavelength and 100 kHz repetition rate. The bursts were generated by splitting the pristine 650-fs laser pulses using an array of birefringent crystals which provided time separations between sub-pulses in the range from 1.5 ps to 24 ps. We measured the threshold fluence in Burst Mode, finding that it strongly depends on the bursts features. The comparison with Normal Pulse Mode revealed that the existing models introduced to explain the incubation effect during irradiation with trains of undivided pulses has to be adapted to describe incubation during Burst Mode processing. In fact, those models assume that the threshold fluence has a unique value for each number of impinging pulses in NPM, while in case of BM we observed different values of threshold fluence for fixed amount of sub-pulses but different pulse splitting. Therefore, the incubation factor coefficient depends on the burst features. It was found that incubation effect is higher in BM than NPM and that it increases with the number of sub-pulses and for shorter time delays within the burst. Two-Temperature-Model simulations in case of single pulses and bursts of up to 4 sub-pulses were performed to understand the experimental results. © Copyright SPIE.

Keywords
Ablation; Irradiation; Laser ablation; Stainless steel; Ultrafast lasers, Birefringent crystals; Damage threshold; Incubation effects; Repetition rate; Threshold fluences; Time separation; Two Temperature Model; Ultrafast laser-matter interactions, Pulse repetition rate
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12660 (URN)10.1117/12.2291612 (DOI)2-s2.0-85048541566 (Scopus ID)
Conference
Laser-Based Micro- and Nanoprocessing XII 2018; San Francisco; United States; 30 January 2018 through 1 February 2018
Available from: 2018-07-04 Created: 2018-07-04 Last updated: 2019-05-28Bibliographically approved
Panwisawas, C., Sovani, Y., Turner, R. P., Brooks, J. W., Basoalto, H. C. & Choquet, I. (2018). Modelling of thermal fluid dynamics for fusion welding. Journal of Materials Processing Technology, 252(February), 176-182
Open this publication in new window or tab >>Modelling of thermal fluid dynamics for fusion welding
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2018 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 252, no February, p. 176-182Article in journal (Refereed) Published
Abstract [en]

A fluid dynamics approach to modelling of fusion welding in titanium alloys is proposed. The model considers the temporal and spatial evolution of liquid metal/gas interface to capture the transient physical effects during the heat source–material interaction of a fusion welding process. Melting and vaporisation have been considered through simulation of all interfacial phenomena such as surface tension, Marangoni force and recoil pressure. The evolution of the metallic (solid and liquid) and gaseous phases which are induced by the process enables the formation of the keyhole, keyhole dynamics, and the fully developed weld pool geometry. This enables the likelihood of fluid flow-induced porosity to be predicted. These features are all a function of process parameters and formulated as time-dependent phenomena. The proposed modelling framework can be utilised as a simulation tool to further develop understanding of defect formation such as weld-induced porosity for a particular fusion welding application. The modelling results are qualitatively compared with available experimental information.

Keywords
Keyhole modelling, Fusion welding, Thermal fluid dynamics, Titanium alloys
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11810 (URN)10.1016/j.jmatprotec.2017.09.019 (DOI)000417659800017 ()2-s2.0-85029481172 (Scopus ID)
Funder
European Regional Development Fund (ERDF), 080/P1/010
Note

Funders: Rolls-Royce; Manufacturing Technology Centre, University of Birmingham 

Available from: 2017-11-20 Created: 2017-11-20 Last updated: 2019-05-28Bibliographically approved
Hosseini, V., Karlsson, L., Hurtig, K., Choquet, I., Engelberg, D., Roy, M. J. & Kumara, C. (2017). A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients. Materials & design, 121(May), 11-23
Open this publication in new window or tab >>A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients
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2017 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 121, no May, p. 11-23Article in journal (Refereed) Published
Abstract [en]

This paper introduces a novel arc heat treatment technique to produce samples with graded microstructures through the application of controlled temperature gradients. Steady state temperature distributions within the sample can be achieved and maintained, for times ranging from a few seconds to several hours. The technique reduces the number of samples needed to characterize the response of a material to thermal treatments, and can consequently be used as a physical simulator for materials processing. The technique is suitable for conventional heat treatment analogues, welding simulations, multi-step heat treatments, and heat treatments with controlled heating and cooling rates. To demonstrate this technique, a super duplex stainless steel was treated with a stationary TIG arc, to confirm the relationship between generated steady-state temperature fields, microstructure development, hardness, and sensitization to corrosion. Metallographic imaging and hardness mapping provided information about graded microstructures, confirming the formation of secondary phases and microstructure sensitization in the temperature range 850–950 °C. Modelling of temperature distributions and thermodynamic calculations of phase stabilities were used to simulate microstructure development and associated welding cycles.

Keywords
Stationary arc, Heat treatment, Graded microstructure, Super duplex stainless steels, Physical simulation, Welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-10760 (URN)10.1016/j.matdes.2017.02.042 (DOI)000399625000002 ()2-s2.0-85013031461 (Scopus ID)
Funder
Knowledge Foundation
Note

Funders: EPSRC (EP/L01680X/1) through the Materials for Demanding Environments Centre for Doctoral Training.

Available from: 2017-02-28 Created: 2017-02-28 Last updated: 2019-05-23Bibliographically approved
Chazelas, C., Trelles, J. P., Choquet, I. & Vardelle, A. (2017). Main issues for a fully predictive plasma spray torch model and numerical considerations. Plasma chemistry and plasma processing, 37(3), 627-651
Open this publication in new window or tab >>Main issues for a fully predictive plasma spray torch model and numerical considerations
2017 (English)In: Plasma chemistry and plasma processing, ISSN 0272-4324, E-ISSN 1572-8986, Vol. 37, no 3, p. 627-651Article in journal (Refereed) Published
Abstract [en]

Plasma spray is one of the most versatile and established techniques for the deposition of thick coatings that provide functional surfaces to protect or improve the performance of the substrate material. However, a greater understanding of plasma spray torch operation will result in improved control of process and coating properties and in the development of novel plasma spray processes and applications. The operation of plasma torches is controlled by coupled dynamic, thermal, chemical, electromagnetic, and acoustic phenomena that take place at different time and space scales. Computational modeling makes it possible to gain important insight into torch characteristics that are not practically accessible to experimental observations, such as the dynamics of the arc inside the plasma torch. This article describes the current main issues in carrying out plasma spray torch numerical simulations at a high level of fidelity. These issues encompass the use of non-chemical and non-thermodynamic equilibrium models, incorporation of electrodes with sheath models in the computational domain, and resolution of rapid transient events, including the so-called arc reattachment process. Practical considerations regarding model implementation are also discussed, particularly the need for the model to naturally reproduce the observed torch operation modes in terms of voltage and pressure fluctuations.

Keywords
Plasma spray torch, Numerical model, Two-temperature, Chemical non-equilibrium, Electrode sheath
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10909 (URN)10.1007/s11090-017-9808-8 (DOI)000399165200007 ()2-s2.0-85015150812 (Scopus ID)
Note

Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2019-05-23Bibliographically approved
Hurtig, K., Choquet, I., Scotti, A. & Svensson, L.-E. (2016). A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter. Science and technology of welding and joining, 21(5), 339-350
Open this publication in new window or tab >>A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter
2016 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 21, no 5, p. 339-350Article in journal (Refereed) Published
Abstract [en]

Comprehensive models of heat transfer require specification of the total amount of heat received by the workpiece. The objective of this work was to critically examine the use of a water-cooled stationary anode calorimeter to obtain both arc efficiency and total heat input into the workpiece. For simplicity and clarity, this last quantity is called the gross heat input. The effects of current, material type and water flow rate on the calorimeter performance were determined experimentally. Some measures for reducing errors in calorimetry were evaluated. Improvements were made to reduce heat losses from the top surface of the test coupon and boost heat removal from the opposite surface. A sensitivity test was conducted to estimate the effect of measurement inaccuracies. The results demonstrate the effectiveness of calorimetry for measuring gross heat input in arc welding.

Keywords
Gross heat input, Arc efficiency, Calorimetry, Measurement uncertainties
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9297 (URN)10.1080/13621718.2015.1112945 (DOI)000376608600001 ()2-s2.0-84978388468 (Scopus ID)
Funder
Knowledge Foundation
Note

Published online: 09 Mar 2016

Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2019-02-11Bibliographically approved
Panwisawas, C., Sovani, Y., Anderson, M., Turner, R., Palumbo, N. M., Saunders, B. C., . . . Basoalto, H. (2016). A Multi-scale Multi-physics Approach to Modelling of Additive Manufacturing in Nickel-based Superalloys. In: M. Hardy, E. Huron, U. Glatzel, B. Griffin, B. Lewis, C. Rae, V. Seetharaman och S. Tin (Ed.), Superalloys 2016: Proceedings of the 13th International Symposium on Superalloys. Paper presented at 13th International Symposium on Superalloys, Seven Springs, Pennsylvania, USA, September 11-15, 2016 (pp. 1021-1030). Minerals, Metals & Materials Society
Open this publication in new window or tab >>A Multi-scale Multi-physics Approach to Modelling of Additive Manufacturing in Nickel-based Superalloys
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2016 (English)In: Superalloys 2016: Proceedings of the 13th International Symposium on Superalloys / [ed] M. Hardy, E. Huron, U. Glatzel, B. Griffin, B. Lewis, C. Rae, V. Seetharaman och S. Tin, Minerals, Metals & Materials Society, 2016, p. 1021-1030Conference paper, Published paper (Refereed)
Abstract [en]

A multi-scale, multi-physics modelling framework of selective laser melting (SLM) in the nickel-based superalloy IN718 is presented. Representative powder-bed particle distribution is simulated using the measured size distribution from experiment. Thermal fluid dynamics calculations are then used to predict melting behaviour, sub-surface morphology, and porosity development during a single pass scanning of the SLM process. The results suggest that the pores and uneven surface structure are exacerbated by increasing powder layer thicknesses. Predicted porosity volume fraction is up to 12% of the single track when 5 statistical powder distributions are simulated for each powder layer thickness. Processing-induced microstructure is predicted by linking cellular automatons – finite element calculations indicate further that the cooling rate is about 4400 o C/s and grain growth strongly follows the thermal gradient giving rise to a columnar grain morphology if homogeneous nucleation is assumed. Random texture is likely for as-fabricated SLM single pass with approximately 8 Pm and 6 Pm grain size for 20 Pm and 100 Pm powder layer thickness fabrication. Use has been made of the cooling history to predict more detailed microstructure using a γ" precipitation model. With the short time scale of solidification and rapid cooling, it becomes less likely that γ" precipitation will be observed in the condition investigated unless a prolonged hold at temperature is carried out. Future work on extension of the proposed multiscale modelling approach on microstructure predictions in SLM to mechanical properties will be discussed.

Place, publisher, year, edition, pages
Minerals, Metals & Materials Society, 2016
Keywords
Multi-scale modelling, additive manufacturing, thermal fluid dynamics, IN718, aerospace component
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-10412 (URN)2-s2.0-85008240176 (Scopus ID)978-1-118-99666-9 (ISBN)
Conference
13th International Symposium on Superalloys, Seven Springs, Pennsylvania, USA, September 11-15, 2016
Available from: 2016-12-27 Created: 2016-12-27 Last updated: 2017-01-20Bibliographically approved
Choquet, I., Javidi Shirvan, A. & Nilsson, H. (2016). A predictive model for gas tungsten arc heat source. In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016. Paper presented at 7th International Swedish Production Symposium, SPS16, Lund, Sweden, October 25–27, 2016 (pp. 1-10). Lund: Swedish Production Academy
Open this publication in new window or tab >>A predictive model for gas tungsten arc heat source
2016 (English)In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-10Conference paper, Published paper (Refereed)
Abstract [en]

Gas tungsten arcs are used as heat sources in production processes such as welding and metal deposition.However, the most advanced of the existing gas tungsten arc models still lack predicting the arc temperature observed experimentally, unless imposing a priori the extent of the cathode arc attachment.Possible causes of this problem were investigated. It was concluded that the physical state of the arcing gas tungsten cathode was too simplified by the existing models. This oversimplification results in an overestimation of the cathode arc attachment area and an underestimation of the arc temperature field.An improved model was developed based only on physical criteria. It was tested by comparison with experimental measurements available in the literature. Good agreement with the temperature measured on the cathode surface and within the arc were obtained.

Place, publisher, year, edition, pages
Lund: Swedish Production Academy, 2016
Keywords
Electric arc, temperature distribution, welding heat source, metal deposition heat source
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-10247 (URN)
Conference
7th International Swedish Production Symposium, SPS16, Lund, Sweden, October 25–27, 2016
Available from: 2016-12-08 Created: 2016-12-08 Last updated: 2018-08-12Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2535-8132

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