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  • 1.
    Abrahamsson, Lena
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Johansson, Jan
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Rask, Kjell
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Fältholm, Ylva
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Bergquist, Bjarne
    Projekt: LUPO - globala länkar2010Other (Other (popular science, discussion, etc.))
  • 2.
    Aidanpää, Jan-Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustavsson, Rolf K.
    Vattenfall, VRD.
    Lundström, Niklas L. P.
    Umeå university.
    Karlsson, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Calleecharan, Yogeshwarsing
    Nässelqvist, Mattias
    Karlberg, Magnus
    Lundin, Urban
    Uppsala University.
    Developments in rotor dynamical modeling of hydropower units2009In: Proceedings of the IUTAM Symposium on Emerging Trends in Rotor Dynamics: held in New Delhi, India, March 23 - March 26, 2009 / [ed] Kshitij Gupta, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2009Conference paper (Refereed)
  • 3.
    Akselsen, Odd M.
    et al.
    SINTEF, Trondheim.
    Wiklund, Greger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Østby, Erling
    SINTEF, Trondheim.
    Sörgjärd, Arve
    Kværner Verdal.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    A first assessment of laser hybrid welding of 420 mpa steel for offshore structure application2013In: 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden / [ed] Alexander Kaplan; Hans Engström, Luleå: Luleå tekniska universitet, 2013, p. 171-182Conference paper (Other academic)
    Abstract [en]

    For many years, laser hybrid welding has been used in various industries to increaseproductivity and reduce costs. One example is the adaption of the hybrid process inshipbuilding. The next natural step is to further develop the process for the oil and gasindustry, where the welded joint properties requirements are more severe, and the ability tohandle tolerance deviations is more critical. As a first attempt to develop hybrid laser processfor the use in offshore structures, the present investigation addresses preliminary weldingtrails carried out with 15 kW fibre laser with appropriate gas metal arc welding equipment,using double Y joint geometry and 20 mm thick 420 MPa steel plates. The subsequent weldtesting included both Charpy V notch impact and CTOD fracture mechanical testing at -30°C.The results indicate that the heat affected zone (HAZ) of the examined steel appeared withsatisfactory Charpy and CTOD toughness (> 200 J, > 0.2 mm) while the weld metal hadinsufficient toughness (20-40 J, < 0.2 mm). With a better welding wire, designed for lowtemperature applications, it is reasonable to suggest that laser hybrid arc welding can be usedfor applications even below a temperature of -30°C.

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  • 4.
    Akselsen, Odd Magne
    et al.
    SINTEF, Trondheim.
    Wiklund, Greger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Østby, Erling
    SINTEF, Trondheim.
    Sørgjerd, Arve
    Kværner Verdal.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Properties of laser hybrid butt welds of 420 MPa steel2013In: The proceedings of the Twenty-third (2013) International Offshore and Polar Engineering Conference: Anchorage, Alaska, June 30-July 5, 2013 : ISOPE-2013 Anchorage / [ed] Jin S. Chung, Cupertino, Calif.: International Society of Offshore and Polar Engineers , 2013, p. 290-294Conference paper (Refereed)
    Abstract [en]

    Laser hybrid welding has been used in European shipbuilding for many years due to its high productivity. In order to qualify the process for the oil and gas industry, an extensive welding and testing programme is needed, and the properties must satisfy more severe requirements than in shipbuilding. This is particularly the case when these activities are moving to the Arctic regions, where low temperature toughness may be the primary challenge. The present investigation addressed preliminary welding trials carried out with 15 kW fibre laser-gas metal arc (GMA) hybrid welding using double Y joint of 20 mm thick 420 MPa steel plates. Both Charpy V notch impact and CTOD fracture mechanical testing were included with test temperature of -30°C. The results indicate that the heat affected zone (HAZ) of the examined steel appeared with satisfactory toughness (> 200 J, > 0.2 mm) while the employed weld metal had insufficient impact properties. The weld metal CTOD toughness approached 0.2 mm. With a better welding wire, designed for low temperature applications, it is reasonable to suggest that laser hybrid arc welding can be used for applications even below -30 to -40°C

  • 5.
    Alam, M. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z.
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, SE-100 44 Stockholm, Sweden.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander F. H.
    Luleå University of Technology.
    Häggblad, Hans-Åke
    Luleå University of Technology.
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 265, no 6, p. 1936-1945Article in journal (Refereed)
    Abstract [en]

    Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by four point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

  • 6.
    Alam, Md. Minhaj
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    A study of the fatigue behaviour of laser and hybrid laser welds2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This licentiate thesis focuses on the fatigue cracking behaviour of laser and hybrid laser-MAG welded structures. Beside the welding process and the resulting weld, several topics related to fatigue of welded structures are treated such as; macro and micro surface geometry, weld defects and their influence on fatigue performance of welded structures, fatigue analysis by the nominal and effective notch stress method, fatigue life prediction using LEFM (Linear Elastic Fracture Mechanics), fatigue testing, metallurgical analysis, elastic and elastic-plastic finite element analysis. The main objective is to gain understanding of the impact of weld defects and weld shape details on the fatigue behaviour of laser and hybrid laser welded joints. The first paper is a literature survey which compiled useful information regarding fracture and fatigue analysis of various welded joints. In the second paper fatigue testing by bending of laser hybrid welded eccentric fillet joints was carried out. The weld surface geometry was measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. The competing criteria of throat depth and stress raising by the weld toe radii and by the surface ripples are explained, showing that surface ripples can be critical.The third paper is the continuation of the second paper, but studying the fatigue crack propagation of laser hybrid welded eccentric fillet joints. Microscopic analysis was carried out to identify internal weld defects. Nominal and effective notch stress analysis was carried out to compare standardized values. LEFM analysis was conducted for this joint geometry for four point bending load in order to study the effect of LOF on fatigue life. In good agreement between simulation and metallurgy, cracking starts and propagates from the lower toe, but for certain geometries alternatively from the weld bead or upper toe, even in case of Lack of Fusion, as was well be explained. Improved understanding of the crack propagation for these geometrical conditions was obtained and in turn illustrated. Lack of fusion surprisingly was not critical and only slightly lowered the fatigue life. Two dimensional linear elastic finite element analyses is carried out in the fourth paper on laser welding of a beamer in order to study the impact of geometrical aspects of the joint design and of the weld root on the fatigue performance. Critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the fatigue behaviour. Stress comparison of full 15 mm and partial 6 mm weld penetration of the beam was done by varying the toe and root geometry to identify the critical details. Generalization of the knowledge by new methods was an important aspect, particularly to apply the findings for other joints. Together the papers provide better understanding of fatigue behaviour for complex geometries and are therefore suitable guidelines for improved weld design.

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  • 7.
    Alam, Md. Minhaj
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser welding and cladding: the effects of defects on fatigue behaviour2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis focuses on weld defects in laser processed materials (for laser welding, laser hybrid arc welding and laser cladding) and their effect on the fatigue life of components. Component properties were studied with particular emphasis on the macro and micro surface geometry, weld defects and clad defects. The influence of these defects on fatigue life was analyzed by; the nominal and effective notch stress method, fatigue life prediction using Linear Elastic Fracture Mechanics (LEFM), fatigue testing, metallurgical analysis, fractography, elastic and elastic-plastic Finite Element Analysis (FEA). A simplified Computational Fluid Dynamics (CFD) analysis was also carried out to better understand the formation of undercuts during the welding process. The main objective is to gain an understanding of the impact of laser weld and clad defects on the fatigue behaviour of components.In the first two papers, fatigue testing involving the bending of laser hybrid arc welded eccentric fillet joints was carried out. Based on measurements of the weld surface geometry the crack initiation location and the crack propagation path were studied, experimentally and in conjunction with FE stress analysis. The competing criteria of throat depth and stress raising by the weld toe radii and by the surface ripples are explained, showing that the topology of surface ripples can be critical to fatigue behaviour. LEFM analysis was conducted to study the effect of Lack of Fusion (LOF) on fatigue life. Cracking starts and propagates preferentially from the lower toe of the top surface for this eccentric weld, even in cases of LOF. In the third paper two-dimensional linear elastic FEA was carried out for laser welding of a high strength steel beam. The impact of the geometrical aspects of joint design and of the weld root geometry on the fatigue performance was studied. Critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the fatigue behaviour. In the fourth paper the melt pool flow behaviour during the laser hybrid arc welding process was analyzed by CFD simulation. The melt velocity behind the keyhole was measured from high speed imaging as a starting value for the simulation. It was found that a high speed flow in the thin topmost layer of the melt transferred its momentum to an underlying flow which is faster than the welding speed and this delays the lifting of the depressed melt.In the fifth and sixth papers FEA of different macro stress fields and of stress raisers produced by defects was studied in laser clad surfaces for four different fatigue load conditions. Defects were categorized into zero-, one- and two-dimensional types. Pores intersecting or just beneath the surface initiated fatigue cracking, accompanied by two circular buckling patterns. For a four-point bending load involving a surface pore on a spherical rod, the critical range of azimuthal angle was identified to be 55º. The performance of as-clad surfaces was found to be governed by the sharpness of surface notches. Planar defects like hot cracks or LOF are most critical if oriented vertically, transverse to the bar axis. A generalized theory was established, showing that the combination of the macro stress field with the defect type, position and orientation, determines whether it is the most critical stress raiser.

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    FULLTEXT01
  • 8.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, Stockholm.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint2011In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, no 10, p. 2246-2258Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser hybrid welded eccentric fillet joints has been studied for stainless steel. Two-dimensional linear elastic fracture mechanics analysis was carried out for this joint geometry for four point bending load. The numerical simulations explain for the experimental observations why the crack propagates from the lower weld toe and why the crack gradually bends towards the root. Lack of fusion turned out to be uncritical for the initiation of cracks due to its compressive stress conditions. The linear elastic fracture mechanics analysis has demonstrated in good qualitative agreement with fatigue test results that lack of fusion slightly (<10%) reduces the fatigue life by accelerating the crack propagation. For the geometrical conditions studied here improved understanding of the crack propagation was obtained and in turn illustrated. The elaborated design curves turned out to be above the standard recommendations

  • 9.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part I2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Welded joints are a major component that is often responsible for causing a structure failure or for being the point at which fatigue cracking initiates and propagates. Despite tremendous research efforts, the understanding of fatigue behaviour is still limited, particularly for new techniques like laser hybrid welding. Beside a comprehensive state-of-the-art study, the paper presents a fatigue study of laser hybrid welded eccentric fillet joint of stainless steel of 10 mm thickness, with 5 mm displacement. Motivation is to study the influence of the surface geometry shape on fatigue performance under a four point bending test. 13 samples were produced, measuring the toe radii and testing under constant amplitude loading with stress ratio R=0. Different techniques have been used to measure local weld geometry, like plastic replica, a 3D optical profiler and a 3D-digitizer. The influence of the local weld geometry, like the toe radii, on the stress concentration was studied by FE-analysis. Occasionally lack of fusion was observed, which was taken into account in the FE-analysis. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. Macro hardness tests were carried out and the crack surfaces were observed in order to detect crack initiation and propagation. Correlations between the toe radii, the corresponding stress maxima and crack initiation locations were studied between the different samples and even along the welds.

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  • 10.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of postulated cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the regions most likely to contain original fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often blamed for causing a structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models/techniques for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments. This literature survey compiled useful information on fracture and fatigue analysis of various welded joints. The present review is divided into two major sections- fracture mechanics and fatigue analysis with widely used models. A survey table is also introduced to get the outlook of research trend on fatigue and fracture over last 3 decades. Although tremendous research effort has been implemented on fatigue and fracture analysis of conventional welding, research on relatively new welding technology (laser welding, hybrid laser welding) is still limited and unsatisfactory. In order to give guarantee or make welding standard for new welding technology, further research is required in the field of fatigue and fracture mechanics including FEM and multi-scale modeling.

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    fulltext
  • 11.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Geometrical aspects of the fatigue behaviour of laser hybrid fillet welds2009In: Proceedings of the Fatigue Design Conference, Cetim , 2009Conference paper (Refereed)
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  • 12.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The effects of surface topography and lack of fusion on the fatigue strength of laser hybrid welds2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics : November 2 - 5, 2009 - Orlando, FL : Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference, poster presentation, gallery, Orlando, Fla: Laser institute of America , 2009, p. 38-46Conference paper (Refereed)
    Abstract [en]

    The geometrical aspects of laser hybrid welding before, during and after the process differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the microgeometry, i.e. the surface ripples can be more critical than the macrogeometry of the weld surface and even than lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface the tendency to LOF can be explained. Stress analysis was carried out by FEA for the complex joint geometry and bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

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  • 13.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Analysis of the rapid central melt pool flow in hybrid laser-arc welding2012In: Physics Procedia, E-ISSN 1875-3892, Vol. 39, p. 853-862Article in journal (Refereed)
    Abstract [en]

    Hybrid laser arc welding creates a long weld pool tail. By high speed imaging the melt velocity behind the keyhole was measured to be very high, of the order of meters per second. Fluid dynamics simulation was carried out locally in the central axial plane of the pool tail. The high speed melt layer redistributes its momentum to slow movement of the deeper bulk. The consequences of initially high melt speed and its mass flow redistribution on the formation of the central reinforcement peak are discussed.

  • 14.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F. H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Tuominen, J.
    Tampere University of Technology, Department of Materials Science, FI-33101 Tampere, Finland.
    Vuoristo, P.
    Tampere University of Technology, Department of Materials Science, FI-33101 Tampere, Finland.
    Miettinen, J.
    Tampere University of Technology, Department of Mechanics and Design, FI-33101 Tampere, Finland.
    Poutala, J.
    Tampere University of Technology, Department of Mechanics and Design, FI-33101 Tampere, Finland.
    Närkki, J.
    Tampere University of Technology, Department of Materials Science, FI-33101 Tampere, Finland; Technology Centre KETEK Ltd., FI-67100 Kokkola, Finland.
    Junkala, J.
    Technology Centre KETEK Ltd., FI-67100 Kokkola, Finland.
    Peltola, T.
    Technology Centre KETEK Ltd., FI-67100 Kokkola, Finland.
    Barsoum, Z.
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, SE-100 44 Stockholm, Sweden.
    Analysis of the stress raising action of flaws in laser clad deposits2013In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 46, p. 328-337Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations.

  • 15. Alam, Md. Minhaj
    et al.
    Karlsson, Jan
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Generalising fatigue stress analysis of different laser weld geometries2011In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, no 4, p. 1814-1823Article in journal (Refereed)
    Abstract [en]

    Two-dimensional elastic-plastic finite element analyses was carried out on a laser welded box beam in order to study the impact of the geometrical aspects of the joint type and weld root on the fatigue stress behaviour. Different experimental and hypothetical weld geometries were studied. Characteristic root shapes, measured by the plastic replica method, and critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the maximum stress. The simulation of hypothetical transition geometries facilitated the identification of trends and the explanation of part of the phenomena. However, quantitative geometry criteria were only partially suitable to describe the relations. The results have shown that the combination of throat depth, local surface radius and its opening angle determines the peak stress value and its location. Beside extended throat depths, particularly larger toe radii and the avoidance of small opening angles and of surface ripples reduces the peak stress. The explanations were developed in a generalising manner, accompanied by illustrative and flow chart description.

  • 16.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Tuominen, Jari
    Tampere University of Technology.
    Vuoristo, Petri MJ J
    Tampere University of Technology.
    Miettinen, Juha S.
    Tampere University of Technology.
    Poutala, J.
    Department of Mechanics and Design, Tampere University of Technology.
    Näkki, Jonne
    Tampere University of Technology.
    Junkala, J.
    Tampere University of Technology.
    Peltola, Tero
    Tampere University of Technology.
    Surface pore initiated fatigue failure in laser clad components2013In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, no 3Article in journal (Refereed)
    Abstract [en]

    A laser clad and machined cylindrical structural steel rod was fatigue tested under four-point bending load. The resulting fracture could be tracked back to a spherical surface pore in the Co-based coating. Due to an oxide inclusion, the pore was not identified by dye penetrant inspection. Two circular buckling strain patterns that were detected beside the pore at the surfaces after fracture confirm local plastic deformation prior to crack initiation. In order to calculate the stress field around the surface pore, linear elastic finite element analysis was carried out. For four-point bending load, a surface pore generally exceeds the maximum stress of a smooth rod as long as the pore is located within an azimuthal angle of ±55°, which was the case for the presented as well as for another pore initiated sample.

  • 17.
    Alhalaweh, Amjad
    et al.
    Luleå University of Technology, Department of Health Sciences, Medical Science.
    Alzghoul, Ahmad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaialy, Waseem
    Chemistry and Drug Delivery Group, Medway School of Pharmacy, University of Kent.
    Data mining of solubility parameters for computational prediction of drug–excipient miscibility2014In: Drug Development and Industrial Pharmacy, ISSN 0363-9045, E-ISSN 1520-5762, Vol. 40, no 7, p. 904-909Article in journal (Refereed)
    Abstract [en]

    Computational data mining is of interest in the pharmaceutical arena for the analysis of massive amounts of data and to assist in the management and utilization of the data. In this study, a data mining approach was used to predict the miscibility of a drug and several excipients, using Hansen solubility parameters (HSPs) as the data set. The K-means clustering algorithm was applied to predict the miscibility of indomethacin with a set of more than 30 compounds based on their partial solubility parameters [dispersion forces , polar forces and hydrogen bonding ]. The miscibility of the compounds was determined experimentally, using differential scanning calorimetry (DSC), in a separate study. The results of the K-means algorithm and DSC were compared to evaluate the K-means clustering prediction performance using the HSPs three-dimensional parameters, the two-dimensional parameters such as volume-dependent solubility and hydrogen bonding , and selected single (one-dimensional) parameters. Using HSPs, the prediction of miscibility by the K-means algorithm correlated well with the DSC results, with an overall accuracy of 94%. The prediction accuracy was the same (94%) when the two-dimensional parameters or the hydrogen-bonding (one-dimensional) parameter were used. The hydrogen-bonding parameter was thus a determining factor in predicting miscibility in such set of compounds, whereas the dispersive and polar parameters had only a weak correlation. The results show that data mining approach is a valuable tool for predicting drug–excipient miscibility because it is easy to use, is time and cost-effective, and is material sparing.

  • 18.
    Al-Mashikhi, S.O.
    et al.
    University of Notttingham.
    Powell, John
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Voisey, K.T.
    University of Notttingham.
    An explanation of ‘striation free' cutting of mild steel by fibre laser2009In: Lasers in manufacturing 2009: proceedings of the Fifth International WLT-Conference Lasers in Manufacturing, LIM 2009 : Munich, Germany, June 15th - 18th, 2009 / [ed] Andreas Ostendorf, Stuttgart: AT-Fachverlag , 2009Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of an experimental and theoretical investigation into the phenomenon of ‘striation free cutting', which is a feature of fibre laser cutting of thin section mild steel. The paper concludes that the creation of very low roughness edges is related to an optimisation of the cut front geometry when the cut front is inclined at angles close to the Brewster angle for the laser - material combination. For purely geometric reasons this particular type of cut front optimisation is not possible for CO2 laser cutting of mild steel.

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  • 19.
    Al-Mashikhi, S.O
    et al.
    Salalah College of Technology, Engineering Department, Salalah, Oman and Faculty of Engineering, University of Nottingham.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Voisey, K.T.
    Faculty of Engineering, University of Nottingham.
    Heat affected zones and oxidation marks in fiber laser–oxygen cutting of mild steel2011In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, no 4Article in journal (Refereed)
    Abstract [en]

    The effect of cutting speed and sheet thickness on surface oxidation and heat affected zones (HAZs) has been investigated for laser–oxygen cutting of mild steel sheet with a fiber laser. Optical and scanning electron micrographs were used to determine the extent of surface oxidation and HAZ from plan and cross-sectional views, respectively. The HAZ is consistently wider at the bottom of the cut compared to the HAZ at the top of the cut. With increasing speed, the width of the HAZ at the top of the cut decreases whereas the HAZ width at the bottom of the cut generally increases. No simple, direct relationship between HAZ width and surface oxidation was seen. However, it is possible to state that in each case considered here, the HAZ would be completely removed if they are machined back by a depth equal to the extent of the surface oxidation.

  • 20.
    Alsyouf, Imad
    et al.
    School of Technology and Design, Växjö University, SE-35195, Växjö, Sweden.
    Alzghoul, Ahmad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Soft computing applications in wind power systems: a review and analysis2009Conference paper (Other academic)
    Abstract [en]

    This paper reviews, analyses, discusses and summarises the recent research and development and trends in the applications of soft computing in the field of wind power systems. We show the usage and the influence of soft computing on the different aspects of wind power systems especially in the field of operation and maintenance. This work provides the state of the art in this area which will be a good guidance for future research work. The main results achieved from the study show that the soft computing techniques are adequate for solving the different challenges at the different phases of the life cycle processes of wind power systems. Using the various soft computing techniques with wind power systems proved to be useful for the wind energy business. Using these tools contribute by improving the robustness of the decisions at different phases of the system's life cycle. Soft computing can enhance the efficiency and effectiveness of the operation and maintenance of offshore wind power systems through improving the availability levels. Thus, providing secure, sustainable and competitive energy supply for the future.

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  • 21.
    Alzghoul, Ahmad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Improving availability of industrial products through data stream mining2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Products of high quality are of great interest for industrial companies. The quality of a product can be considered in terms of production cost, operating cost, safety and product availability, for example. Product availability is a function of maintainability and reliability. Monitoring prevents unplanned stops, thus increasing product availability by decreasing needed maintenance. Through monitoring, failures can be detected and/or avoided. Detecting failures eliminates extra costs such as costs associated with machinery damage and dissatisfied customers, and time is saved since stops can be scheduled, instead of having unplanned stops. Product monitoring can be done through searching the data generated from sensors installed on products.Nowadays, the data can be collected at high rates as part of a data stream. Therefore, data stream management systems (DSMS) and data stream mining (DSM) are being used to control, manage and search the data stream. This work investigated how the availability of industrial products can be increased through the use of DSM and DSMS technologies.A review of the data stream mining algorithms and their applications in monitoring was conducted. Based on the review, a new data stream classification method, i.e. Grid-based classifier was proposed, tested and validated. Also, a fault detection system based on DSM and DSMS technologies was proposed. The proposed fault detection system was tested using data collected from Hägglunds Drives AB (HDAB) hydraulic motors. Thereafter, a data stream predictor was integrated into the proposed fault detection system to detect failures earlier, thus gaining more time for response actions. The modified fault detection system was tested and showed good performance. The results showed that the proposed fault detection system, which is based on DSM and DSMS technologies, achieved good performance (with classification accuracy around 95%) in detecting failures on time. Detecting failures on time prevents unplanned stops and may improve the maintainability of the industrial systems and, thus, their availability.

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  • 22.
    Alzghoul, Ahmad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Mining data streams to increase ‎industrial product availability2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Improving product quality is always of industrial interest. Product availability, a function of product maintainability and reliability, is an example of a measurement that can be used to evaluate product quality. Product availability and cost are two units which are especially important to manage in the context of the manufacturing industry, especially where industry is interested in selling or buying offers with increased service content. Industry in general uses different strategies for increasing equipment availability; these include: corrective (immediate or delayed) and preventive strategies. Preventive strategies may be further subdivided into scheduled and predictive (condition-based) maintenance strategies. In turn, predictive maintenance may also be subdivided into scheduled inspection and continuously monitored. The predictive approach can be achieved by early fault detection. Fault detection and diagnosis methods can be classified into three categories: data-driven, analytically based, and knowledge-based methods. In this thesis, the focus is mainly on fault detection and on data-driven models.Furthermore, industry is generating an ever-increasing amount of data, which may eventually become impractical to store and search, and when the data rate is increasing, eventually impossible to store. The ever-increasing amount of data has prompted both industry and researchers to find systems and tools which can control the data on the fly, as close to real-time as possible, without the need to store the data itself. Approaches and tools such as Data Stream Mining (DSM) and Data Stream Management Systems (DSMS) become important. For the work reported in this thesis, DSMS and DSM have been used to control, manage and search data streams, with the purpose of supporting increased availability of industrial products.Bosch Rexroth Mellansel AB (formerly Hägglunds Drives AB) has been the industrial partner company during the course of the work reported in this thesis. Related data collection concerning the functionality of the BRMAB hydraulic system has been performed in collaboration with other researchers in Computer Aided Design at Luleå University of Technology.The research reported in this thesis started with a review of data stream mining algorithms and their applications in monitoring. Based on the review, a data stream classification method, i.e. Grid-based classifier, was proposed, tested and validated (Paper A). Also, a fault detection system based on DSM and DSMS was proposed and tested, as reported in Paper A. Thereafter, a data stream predictor was integrated into the proposed fault detection system to detect failures earlier, thus demonstrating how data stream prediction can be used to gain more time for proactive response actions by industry (Paper B). Further development included an automatic update method which allows the proposed fault detection system to be able to overcome the problem of concept drift (Paper E). The proposed and modified fault detection systems were tested and verified using data collected in collaboration with Bosch Rexroth Mellansel AB (BRMAB). The requirements for the proposed fault detection system and how it can be used in product development and design of the support system were also discussed (Paper C). In addition, the performance of a knowledge-based method and a data- driven method for detecting failures in high-volume data streams from industrial equipment have been compared (Paper D). It was found that both methods were able to detect all faults without any false alert. Finally, the possible implications of using cloud services for supporting industrial availability are discussed in Paper F. Further discussions regarding the research process and the relations between the appended papers can be found in Chapter 2, Figure 4 and in Chapter 5, Figure 21.The results showed that the proposed and modified fault detection systems achieved good performance in detecting and predicting failures on time (see Paper A and Paper B). In Paper C, it is shown how data stream management systems may be used to increase product availability awareness. Also, both the data-driven method and the knowledgebased method were suitable for searching data streams (see Paper D). Paper E shows how the challenge of concept drift, i.e. the situation in which the statistical properties of a data stream change over time, was turned to an advantage, since the authors were able to develop a method to automatically update the safe operation limits of the one-class data-driven models.In general, detecting faults and failures on time prevents unplanned stops and may improve both maintainability and reliability of industrial systems and, thus, their availability (since availability is a function of maintainability and reliability). By the results, this thesis demonstrates how DSM and DSMS technologies can be used to increase product availability and thereby increase product quality in terms of availability.

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  • 23.
    Alzghoul, Ahmad
    et al.
    Department of Information Technology, Division of Computing Science, Room POL ITC 19134, Box 337, 751 05 Uppsala, Sweden.
    Backe, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Department of Information Technology, Division of Computing Science, Room POL ITC 19111, Box 337, 751 05 Uppsala, Sweden.
    Byström, Arne
    Bosch Rexroth Mellansel AB, SE-895 80 Mellansel, Sweden.
    Liljedahl, Bengt
    Bosch Rexroth Mellansel AB, SE-895 80 Mellansel, Sweden.
    Comparing a knowledge-based and a data-driven method in querying data streams for system fault detection: A hydraulic drive system application2014In: Computers in industry (Print), ISSN 0166-3615, E-ISSN 1872-6194, Vol. 65, no 8, p. 1126-1135Article in journal (Refereed)
    Abstract [en]

    The field of fault detection and diagnosis has been the subject of considerable interest in industry. Fault detection may increase the availability of products, thereby improving their quality. Fault detection and diagnosis methods can be classified in three categories: data-driven, analytically based, and knowledge-based methods. In this work, we investigated the ability and the performance of applying two fault detection methods to query data streams produced from hydraulic drive systems. A knowledge-based method was compared to a data-driven method. A fault detection system based on a data stream management system (DSMS) was developed in order to test and compare the two methods using data from real hydraulic drive systems. The knowledge-based method was based on causal models (fault trees), and principal component analysis (PCA) was used to build the data-driven model. The performance of the methods in terms of accuracy and speed, was examined using normal and physically simulated fault data. The results show that both methods generate queries fast enough to query the data streams online, with a similar level of fault detection accuracy. The industrial applications of both methods include monitoring of individual industrial mechanical systems as well as fleets of such systems. One can conclude that both methods may be used to increase industrial system availability

  • 24.
    Alzghoul, Ahmad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Increasing availability of industrial systems through data stream mining2011In: Computers & industrial engineering, ISSN 0360-8352, E-ISSN 1879-0550, Vol. 60, no 2, p. 195-205Article in journal (Refereed)
    Abstract [en]

    Improving industrial product reliability, maintainability and thus availability is a challenging task for many industrial companies. In industry, there is a growing need to process data in real time, since the generated data volume exceeds the available storage capacity. This paper consists of a review of data stream mining and data stream management systems aimed at improving product availability. Further, a newly developed and validated grid-based classifier method is presented and compared to one-class support vector machine (OCSVM) and a polygon-based classifier.The results showed that, using 10% of the total data set to train the algorithm, all three methods achieved good (>95% correct) overall classification accuracy. In addition, all three methods can be applied on both offline and online data.The speed of the resultant function from the OCSVM method was, not surprisingly, higher than the other two methods, but in industrial applications the OCSVMs' comparatively long time needed for training is a possible challenge. The main advantage of the grid-based classification method is that it allows for calculation of the probability (%) that a data point belongs to a specific class, and the method can be easily modified to be incremental.The high classification accuracy can be utilized to detect the failures at an early stage, thereby increasing the reliability and thus the availability of the product (since availability is a function of maintainability and reliability). In addition, the consequences of equipment failures in terms of time and cost can be mitigated.

  • 25.
    Alzghoul, Ahmad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Backe, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Data stream forecasting for system fault prediction2012In: Computers & industrial engineering, ISSN 0360-8352, E-ISSN 1879-0550, Vol. 62, no 4, p. 972-978Article in journal (Refereed)
    Abstract [en]

    Competition among today’s industrial companies is very high. Therefore, system availability plays an important role and is a critical point for most companies. Detecting failures at an early stage or foreseeing them before they occur is crucial for machinery availability. Data analysis is the most common method for machine health condition monitoring. In this paper we propose a fault-detection system based on data stream prediction, data stream mining, and data stream management system (DSMS). Companies that are able to predict and avoid the occurrence of failures have an advantage over their competitors. The literature has shown that data prediction can also reduce the consumption of communication resources in distributed data stream processing.In this paper different data-stream-based linear regression prediction methods have been tested and compared within a newly developed fault detection system. Based on the fault detection system, three DSM algorithms outputs are compared to each other and to real data. The three applied and evaluated data stream mining algorithms were: Grid-based classifier, polygon-based method, and one-class support vector machines (OCSVM).The results showed that the linear regression method generally achieved good performance in predicting short-term data. (The best achieved performance was with a Mean Absolute Error (MAE) around 0.4, representing prediction accuracy of 87.5%). Not surprisingly, results showed that the classification accuracy was reduced when using the predicted data. However, the fault-detection system was able to attain an acceptable performance of around 89% classification accuracy when using predicted data.

  • 26.
    Alzghoul, Ahmad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Karlsson, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Data stream mining for increased functional product availability awareness2011In: Functional Thinking for Value Creation: Proceedings of the 3rd CIRP International Conference on Industrial Product Service Systems, Technische Universität Braunschweig, Braunschweig, Germany, May 5th - 6th, 2011 / [ed] Jürgen Hesselbach; Christoph Herrmann, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2011, p. 237-241Conference paper (Refereed)
    Abstract [en]

    Functional Products (FP) and Product Service Systems (PSS) may be seen as integrated systems comprising hardware and support services. For such offerings, availability is key. Little research has been done on integrating Data Stream Management Systems (DSMS) for monitoring (parts of) a FP to improve system availability. This paper introduces an approach for how data stream mining may be applied to monitor hardware being part of a Functional Product. The result shows that DSMS have the potential to significantly support continuous availability awareness of industrial systems, especially important when the supplier is to supply a function with certain availability.

  • 27.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling2009In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, no 21, p. 8917-8925Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to study the effect of the laser spot diameter on the shock wave generated in the ablation process of an Nd:YAG laser pulse on a Zn target under atmospheric pressure. For different laser spot diameters and time delays, the propagation of the expanding vapour and of the shock wave were recorded by intensity maps calculated using the recorded digital holograms. From the latter phase maps, the refractive index and the density field can be derived. A model was developed that approaches the density distribution, in particular the ellipsoidal expansion characteristics. The induced shock wave has an ellipsoid shape that approaches a sphere for decreasing spot diameter. The ellipsoidal shock waves have almost the same centre offset towards the laser beam and the same aspect ratio for different time steps. The model facilitates the derivation of the particle velocity field. The method provides valuable quantitative results that are discussed, in particular in comparison with the simpler point source explosion theory.

  • 28.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shaer, M. El
    Department of Engineering Physics and Mathematics, Faculty of Engineering, Zagazig University.
    Comparison of the laser ablation process on Zn and Ti using pulsed digital holographic interferometry2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 14, p. 4633-4641Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to compare the laser ablation process of a Q-switched Nd-YAG laser pulse (wavelength 1064 nm, pulse duration 12 ns) on two different metals (Zn and Ti) under atmospheric air pressure. Digital holograms were recorded for different time delays using collimated laser light (532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. Intensity maps were calculated from the recorded digital holograms and are used to calculate the attenuation of the probing laser beam by the ablated plume. The different structures of the plume, namely streaks normal to the surface for Zn in contrast to absorbing regions for Ti, indicates that different mechanisms of laser ablation could happen for different metals for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism.

  • 29.
    Amundsdotter, Eva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Andersson, Susanne
    Stockholms Universitet.
    Developing innovative organisations: using action-orientated gender research2012In: Promoting innovation: Policies, Practices and Procedures, Stockholm: Vinnova , 2012, p. 310-327Chapter in book (Refereed)
    Abstract [en]

    Lack of gender awareness affects not only the conditions under which people work, itis also an obstacle to organisations’ ability to produce, develop and organise for innovation.This article presents an approach called action-orientated gender research, amerger of two theoretical perspectives: a) the doing-gender perspective, with its understandingof gender as formed in on-going relational activities and b) learning theorywithin the action research tradition, which focuses on reflection, learning and especiallyreflective learning for transformation. Gender theory and learning theory are combinedinto joint learning processes in networks of participants from different organisationswithin innovation systems. This makes it possible to uncover taken-for-grantedassumptions and gendered power relations which constrain the development of newinnovative possibilities in organisations.This article will present basic theoretical characteristic of the action-orientatedgender research approach, plus examples of how we have worked with this approachin a network of middle managers. Moreover, we will elaborate on the important considerationswe have discovered for organising transformative learning aimed at developinggender-aware, innovative organisations. The empirical material in the articlecomes from two meetings. One in which co-research was conducted with two managersworking in the same organisation. The other meeting took place one month laterwhen all the managers in the Gender network were present. During this second meeting,observations from the earlier co-research were presented and discussed using theconcentric circle method.

  • 30.
    Amundsdotter, Eva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gunnarsson, Ewa
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Westerberg, Mats
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    GAAL: a model for practical equality work in an engineering environment2013Conference paper (Other academic)
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  • 31.
    Andersson, Anders
    et al.
    Luleå University of Technology.
    Engström, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Wiklund, Greger
    Påsvetsning, upplegering och ytomsmältning (glasering) med högeffektlaser1983Report (Other academic)
  • 32. Andersson, Börje
    et al.
    Karlsson, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Thermal stresses in large butt-welded plates1981In: Journal of thermal stresses, ISSN 0149-5739, E-ISSN 1521-074X, Vol. 4, no 3-4, p. 491-500Article in journal (Refereed)
    Abstract [en]

    In shipyard panel-production lines several rectangular plates ae butt welded to form large panels. One problem is the tendency of hot cracking in the end portion of the butt weld. In this paper transient temperature fields and stress fields in butt-welded plates are calculated using the finite-element method. The calculations are performed for different welding speeds, for different heat inputs, and for one-sided and two-sided welding.

  • 33.
    Andersson, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Hur kan akademi organisera samverkan för tillväxt?: Deliberativ Organiserad Samverkan, DOS, en ny styrningsmodell2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Within research and education policies of later decades, a clear trend can be seen in expanded attempts to stimulate growth-concentrated cooperation between government, academia and industry. With economic financing, channelled to academia through different kinds of research and development councils, follows a responsibility to operationally organize the actors' cooperation. This task is rather complex. The cooperative process is expected to be equal, provided that the participating actors have different professional identities, belong to different organizations, have different values and ideas of norms, and satisfy different interests. With present research and education policies, follows the idea of academia acting as a potential growth engine that should be directly used to develop society's innovation system, production system and markets. In connection with this, discussions regarding academic capitalism, commercialisation of research results, incubation processes, etc., are being conducted. The traditional role of academia as a research university has also been complemented by the roles of organizer for growth-concentrated cooperation and entrepreneur.Pursuing independent research, being an organizer for similar cooperation, and satisfying their personal interests all at the same time is contradictory. A way for academia to prevent their own interests from getting out of hand during cooperation is to avoid all forms of external management, and instead focus on stimulating the participating actors to evaluate, develop and manage their cooperation themselves. Conventional education, research and project models are developed for purposes other than this. Desipte this, their usage with the cooperative task is rather widespred. For cooperative actors to understand and handle their activities in an aware, collective and flexible manner, they need to use some form of management model that allows for communicative coordination, evaluation and development of organizational action. As an alternative to those conventional models, a new management model has been developed in this thesis, called Deliberative Organized Cooperation, DOC. The model is developed with inspiration from deliberative theory. Simply put, the actors' cooperation is expected to occur through repeated dialectic movements between deliberative phases (management process), where actors produce valid action alternatives and legitimate interpersonal and systematic relations, and systematic phases (operational activities), where the actors transform the gained validity and legitimacy in systematic action and resulting factuality. While the deliberative phase corresponds to evaluation and development orientated logic with open rationality conditions, the systematic phase corresponds to production orientated logic with closed rationality conditions.The primary empirical results of the thesis are collected from activities that have been driven or are driven within or closely connected to two competence centres located at Luleå Univeristy of Technology. The first competence centre, the Polhem Laboratory, is presently being phased out and replaced by the Faste Laboratory. Both operations can be described with help from the Triple Helix model. Simply stated, the government contributes with direct economic funding for R&D as well as the overall rules of the game regarding the actors' cooperation, the industry with supplementary economic funding and direct turnover of the developed knowledge. The economic funding also goes to academia with an organizing of the cooperation process, knowledge development and commercialisation of interesting spin-off knowledge. An essential element in the operations of the Polhem and Faste Laboratories constitutes the so-called Sirius Project, an industrially oriented product development project conducted by fourth year students in the mechanical engineering program. This project is primarily conducted in cooperation between academia and large companies. Closely connected to this activity, Arena innovative technology and business, organizes multi-science undergraduate studies. An important part of this education is to cooperate in so-called greenhouse projects. Here, students from various study years and majors, meets researchers/teachers from different subject fields, and actors from different companies and development firms. The over-all aim of the projects is to stimulate entrepreneurship and starting of new robust companies. DOC comprises an attempt to solve management problem identified in connection to the above activities.The activities have been investigated through participating observations. Individual events have been worked upon and weaved together into a cohesive and anonymous scenario that is told by giving voices to a variety of the participating actors. In the theoretically oriented chapter of the thesis, events are problematised from the scenario through analytical and pragmatic reflections. With help of these reflections, the DOC model is successively built up.

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  • 34.
    Angantyr, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Rotordynamic optimization of large turbo systems using genetic algorithms2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In engineering design, nature has often been the source of inspiration. It is easy to point out solutions in nature that are optimal in some sense. One example is the roughness of the surface of a shark's skin. This is designed by nature to minimize the resistance when the shark swims in the water. Another example is the shape of an egg shell. This is an optimal load carrying structure which often is found in engineering design applications. An even more fascinating question is how nature has found these optimal solutions? The answer to this question is evolution. Instead of just analyzing and copying optimal structures invented by nature it seems reasonable to mimic the process how nature has came up with these solutions. Research on how these ideas can be interpreted and used in engineering design started in the early seventies and has now become a large field known as Evolutionary Algorithms (EAs). During the past decade these methods have emerged as potent tools for engineering design optimization. Some of these methods are especially suited for problems which involve multiple objectives such as almost all real engineering design problems. Just until recently, these methods have seldom been used in the area of rotordynamical design. This thesis deals with the question how these methods can be adapted and applied in order to improve the design and design process of large rotor-bearing system. A hypothesis for this work is that EAs are suitable to use in the late design process of these systems. The aim of this work is to evaluate this hypothesis by studying real applications found in industry. This thesis comprises an introductory part and five appended papers. The introductory part is divided into four different chapters. In the second chapter the concept of engineering design optimization is introduced. In the third chapter Genetic Algorithms (GAs) is presented. Finally, the analysis and design of rotor-bearing systems are introduced and discussed. The purpose with the introductory part is to introduce and prepare the reader to the concepts presented in the papers. The introductory part may serve as a start point for newcomers interested in these areas. The appended papers deal with different rotor-bearing system optimization problems and how these can be formulated and solved with GAs. Paper A introduces a constraint handling technique based on concepts found in multiobjective GAs. In Paper B the multiobjective optimization of a generator is presented and discussed. In Paper C and Paper D the constraint handling technique introduced in Paper A is used for two different rotor- bearing system where the actual bearing geometry parameters are used as design variables in the optimizations. In Paper E the feasibility of site balancing rewinded turbo generators is investigated by the use of a multiobjective GA.

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  • 35.
    Angantyr, Anders
    et al.
    ALSTOM Power Sweden AB.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Constrained optimization of gas turbine tilting pad bearing designs2006In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 128, no 4, p. 873-878Article in journal (Refereed)
    Abstract [en]

    This paper presents the constrained optimization of the tilting pad bearing design on a gas turbine rotor system. A real coded genetic algorithm with a robust constraint handling technique is used as the optimization method. The objective is to develop a formulation of the optimization problem for the late bearing design of a complex rotor-bearing system. Furthermore, the usefulness of the search method is evaluated on a difficult problem. The effects considered are power loss and limiting temperatures in the bearings as well as the dynamics at the system level, i.e., stability and unbalance responses. The design variables are the bearing widths and radial clearances. A nominal design is the basis for comparison of the optimal solution found. An initial numerical experiment shows that finding a solution that fulfills all the constraints for the system design is likely impossible. Still, the optimization shows the possibility of finding a solution resulting in a reduced power loss while not violating any of the constraints more than the nominal design. Furthermore, the result also shows that the used search method and constraint handling technique works on this difficult problem.

  • 36.
    Anthony, Niklas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Suhonen, Heikki
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Laboratory experiments with a laser-based attachment mechanism for small bodiesIn: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030Article in journal (Refereed)
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  • 37.
    Anthony, Niklas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Suhonen, Heikki
    Department of Physics, University of Helsinki, P.O. Box 64, 00014, Finland.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, P.O. Box 64, 00014, Finland.
    Laboratory experiments with a laser-based attachment mechanism for spacecraft at small bodies2021In: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 189, p. 391-397Article in journal (Refereed)
    Abstract [en]

    We present the results of two sets of experiments that investigate laser-based metal-to-rock attachment techniques. Asteroids and comets have low surface gravity which pose a challenge to landers with moving parts. Such parts can generate torques and forces which may tip the lander over or launch it into deep space. Thus, if a lander on a small body is to have moving parts, the spacecraft must be equipped with an anchoring mechanism. To this end, we sought to use a laser to melt and bind a piece of metal mimicking a part of a spacecraft to a rock mimicking the surface of a typical asteroid. In the first set of experiments, extra material was not fed in during the processing. The second set were performed using a standard wire feeder used in laser welding, which added metal to the experiment during processing. During the first experiments, we discovered that a traditional weld, where two melt pools mix and solidify to form a strong bond, was not possible—the melt pools would not mix, and when they did, the resulting weld was extremely brittle. The second set of experiments resulted in a physico-mechanical bond, where a hole was drilled with a laser, and a wire was melted and fed into the hole. These latter experiments were successful in forming bonds as strong as 115 N. Such an attachment mechanism can also be used to maneuver small boulders on asteroid surfaces, to redirect small, monolithic asteroids, or in space-debris removal.

  • 38.
    Anthony, Niklas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Suhonen, Heikki
    Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Laser-induced spallation of minerals common on asteroids2021In: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 182, p. 325-331Article in journal (Refereed)
    Abstract [en]

    The ability to deflect dangerous small bodies in the Solar System or redirect profitable ones is a necessary and worthwhile challenge. One well-studied method to accomplish this is laser ablation, where solid surface material sublimates, and the escaping gas creates a momentum exchange. Alternatively, laser-induced spallation and sputtering could be a more efficient means of deflection, yet little research has studied these processes in detail. We used a 15-kW Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine (minerals commonly found on asteroids) to induce spallation. We observed the process with a high-speed camera and illumination laser, and used X-ray micro-tomography to measure the size of the holes produced by the laser to determine material removal efficiency. We found that pyroxene will spallate at power densities between 1.5 and 6.0 kW cm−2, serpentine will also spallate at 13.7 kW cm−2, but olivine does not spallate at 1.5 kW cm−2 and higher power densities melt the sample. Laser-induced spallation of pyroxene and serpentine can be two- to three-times more energy efficient (volume removed per unit of absorbed energy) than laser-induced spattering, and over 40x more efficient than laser ablation.

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  • 39.
    Anthony, Niklas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Suhonen, Heikki
    Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Penttilä, Antti
    Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Laser processing of minerals common on asteroids2021In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 135, article id 106724Article in journal (Refereed)
    Abstract [en]

    Asteroid mining and redirection are two trends that both can utilize lasers, one to drill and cut, the other to ablate and move. Yet little is known about what happens when a laser is used to process the types of materials we typically expect to find on most asteroids. To shed light on laser processing of asteroid material, we used a 300-W, pulsed Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine, and studied the process with a high-speed camera and illumination laser at 10 000 frames per second. We also measure the sizes of the resulting holes using X-ray micro-tomography to find the pulse parameters which remove the largest amount of material using the least amount of energy. We find that at these power densities, all three minerals will melt and chaotically throw off spatter. Short, low-power pulses can efficiently produce thin, deep holes, and long, high-power pulses are more energy efficient at removing the most amount of material.

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  • 40.
    Arvidsson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Hjelm, Karin
    Southern Swedish Forest Research Centre, SLU, P.O. Box 190, Lomma. SE-234 22, Sweden.
    Lideskog, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Digital precision planning tool for autonomous forest regeneration of mixed tree species2023Conference paper (Refereed)
  • 41. Arwidson, Claes
    et al.
    Bernspång, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Verification of numerical forming simulation in high strength steels2004In: Proceedings of the Conference Innovations in metal forming, 2004Conference paper (Refereed)
  • 42.
    Asplund, Christer
    et al.
    Luleå University of Technology.
    Karlsson, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    MacPherson strut wheel suspension dynamics1989Report (Other academic)
  • 43.
    Atiyah, H.
    et al.
    College of Engineering, Al-Muthanna University, Samawah, Iraq.
    Hussein, R. D.
    College of Engineering, Al-Muthanna University, Samawah, Iraq.
    Rashid, M. M.
    College of Engineering, Al-Muthanna University, Samawah, Iraq.
    Powell, J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Faculty of Engineering, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
    Voisey, K. T.
    Faculty of Engineering, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
    Thermal Degradation and Ablation Energy of Poly (Methyl Methacrylate)2023In: 2nd Muthanna International Conference on Engineering Science and Technolog / [ed] Tariq Al-Mansoori; Ali Al-Rifaie; Haider Kamil Shanbara; Furat Yasir Al-Jaberi; Othman Hameed; Alaa Al-Hussainy; Dakhil Riyadh, American Institute of Physics (AIP), 2023, article id 080002Conference paper (Refereed)
  • 44.
    Atiyah, H.
    et al.
    Faculty of Engineering, The University of Nottingham.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Petring, D.
    Fraunhofer Institute for Laser Technology ILT.
    Stoyanov, S.
    Fraunhofer Institute for Laser Technology ILT.
    Voisey, T.
    Faculty of Engineering, The University of Nottingham.
    Fiber laser cutting: The use of carbon-filled acrylic as a qualitative and quantitative analysis tool2018In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, article id 032009Article in journal (Refereed)
    Abstract [en]

    The use of carbon-filled black acrylic (CFBA) as a quantitative and qualitative analytical tool for fiber laser cutting is investigated. In the qualitative work, CFBA targets placed below the laser cutting zone when cutting stainless steel showed a distinctive “leaf” shaped evaporation crater which can provide information about the nature of the reflections taking place in the cut zone. Quantitative measurements have revealed a specific evaporation energy of 3.4 J/mm3 for CFBA. However, this figure is only applicable when considering intense beams when the CFBA target is stationary with respect to the laser beam.

  • 45.
    Backe, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    An Integrated Development Approach for Monitoring and Simulation to Predict Functional Product Availability2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    For nearly two decades, business models such as Functional Products have been in focus within research and of interest in the manufacturing industry. Functional product offers consist of hardware, software, service -support systems and management of operation which, when developed in an integrated manner, together provide the customer with an agreed-upon function with a specified level of availability. Compared to product-oriented sales, this type of business model can provide added value to customers, usually through an increase in the service content. Due to the total care commitment, offering Functional Products requires management of reliability and maintainability in order to meet the availability requirement of the function provided. The development of the Functional Product must include holistic analysis and prediction of the functional product availability performance to reduce technical and economic risks and ensure that the function is delivered according to contract. The research performed in this thesis presents an integrated development approach for monitoring and simulation to predict functional product availability. It is shown how the constituents of a functional product can be modelled in an integrated manner in order to simulate and predict functional product availability. A part of this modelling strategy is demonstrated through a simulation case example to show that is possible through this approach to evaluate the availability of different functional product designs. To support the development of the monitoring capability needed for availability simulations it is shown how it is possible to develop fault detection and diagnosis methods for fault detection systems based on data stream management systems. It is also shown how data stream forecasting can be used to predict failures due to faults occurring at short notice. Different fault detection methods have been developed, tested and evaluated on real industrial applications to verify applicability as queries on data streams, managed by data stream management systems. The results from these tests have been evaluated for their predictive performance and detection accuracy. Finally, methodological and technological approaches to monitoring and analysis in functional product development and similar business models to functional products are reviewed. The results showed that few research contributions address the information perspective in functional product development and similar business models holistically. The integrated development approach presented is a pragmatic approach to functional product development which is based on the merged research results of the papers included and knowledge domain presented.

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  • 46.
    Backe, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The need of condition monitoring to support simulations when predicting system availability of Functional Products2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Today, competition among product manufacturers has increased and many facebeing copied and thus losing their uniqueness. To differentiate on the market,new businesses, which extend the manufacturer’s responsibility throughsupporting and guaranteeing product performance, thus offering more value-creating activities, have received increasing interest.The concepts of Functional Products or Total Offers have emerged through the realization that it is tougher to compete with hardware products only. The Functional Products concept combines the development of hardware, software, services and management of operation, thereby integrating value-adding activities into complete offers. Offering a Functional Product is usually a lifecycle commitment (long-term business-to-business agreement) between the function provider and customer. In this type of business, agreed-upon availability is of importance, especially since the availability of a function can directly influence customers’ productivity. The provider and customer need to predict and evaluate the availability of the function, both in early phases of the product development process and continuously during operation throughout the contracted time. In this thesis, in paper A, a model for predicting and monitoring industrial system availability has been proposed to enable the provider of Functional Products to continuously evaluate, through simulation, the offer in terms of availability performance. The model integrates hardware, support system and monitoring system components and through this approach it is possible to utilize operational data in simulations for continuous prediction of availability during operation. Further, the results of paper B presented in this thesis may extend and improve the model proposed in paper A, if implemented. The results of paper B describe the addition of data stream forecasting to the data stream management fault detection system and have showed improved prediction capabilities. The approach to evaluate the availability in paper A may also be extended and improved through the results presented and demonstrated in paper C. In paper C, a software tool to predict system availability has been developed and demonstrated with data from a real industrial system. The results from the simulation demonstrated, together with the addition of the partitioned multi-objective risk method in paper C, provided an indication of what level of availability may be guaranteed for the product; thus, the approach may be used to compare the availability performance of different designs.

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  • 47.
    Backe, Björn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kyösti, Petter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The transition from component-based industry toward Functional Products: implications for the demands on the monitoring and information systemIn: International Journal of Product Development, ISSN 1477-9056, E-ISSN 1741-8178Article in journal (Refereed)
  • 48.
    Bang, Han-Sur
    et al.
    Chosun University, Department of Welding & Joining Science Engineering.
    Bang, HeeSeon
    Department of Welding and Joining Science Engineering, Chosun University.
    Hong, J.H.
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Jeon, Geunhong
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Kim, G.S.
    Department of Welding and Joining Science Engineering, Graduate School, Chosun University.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Effect of Tungsten-Inert-Gas Preheating on Mechanical and Microstructural Properties of Friction Stir Welded Dissimilar Al Alloy and Mild Steel2016In: Strength of Materials, ISSN 0039-2316, E-ISSN 1573-9325, Vol. 48, no 1, p. 152-159Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to clarify the effect of tungsten-inert-gas (TIG) welding preheating on the mechanical properties of Al6061-T6 and SS400 welded joints by friction stir welding (FSW). FSW joints with and without TIG welding preheating are characterized and compared in terms of their mechanical and microstructural properties. The results show that the TIG assisted hybrid FSW welded joints (TIG-HFSW) provide an enhanced joint strength. The transversal tensile strength of the TIG-HFSW joints exhibited approximately 104% of the Al6061-T6 base metal tensile strength and was higher than that of the FSW joints. Microstructural investigations also reveal that in the HAZ and TMAZ of TIG-HFSW joints, the grains of Al6061-T6 are smaller than those of the FSW welds

  • 49.
    Belelli, F.
    et al.
    Department of Mechanical Engineering, Politecnico di Milano, Via G. La Masa 1, 20156, Milan, Italy.
    Casati, R.
    Department of Mechanical Engineering, Politecnico di Milano, Via G. La Masa 1, 20156, Milan, Italy.
    Vedani, M.
    Department of Mechanical Engineering, Politecnico di Milano, Via G. La Masa 1, 20156, Milan, Italy.
    Volpp, Jörg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Design and Characterization of Al–Mg–Si–Zr Alloys with Improved Laser Powder Bed Fusion Processability2022In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 53, no 1, p. 331-343Article in journal (Refereed)
    Abstract [en]

    A key-factor for the industrial implementation of beam-based additive manufacturing technologies is the development of novel Al alloys characterized by enhanced hot-tearing resistance. Indeed, most of the standard Al alloys are susceptible to solidification cracking and can hardly be used to produce structural parts by laser-based additive manufacturing processes. In this study, we investigate the strategies to design high-strength Al alloys for Laser Powder Bed Fusion. The addition of Zr to the chemical composition of an Al–Mg–Si alloy (EN AW 6182) was carried out by following two different routes to promote the formation of equiaxed grains which are able to suppress hot cracking and enhance processability of the material. The first route is based on mechanical mixing of ZrH2 particles and gas-atomized Al alloy powder and on the in-situ reaction of the hydride to form Al3Zr nucleants. The second route relies on the use of pre-alloyed gas-atomized powders that feature Zr among the alloy elements. The specimens produced using pre-alloyed powder showed the best mechanical performance. After direct aging from the as-built condition, the alloy showed yield strength and ultimate tensile strength of 354 and 363 MPa, respectively, and elongation at fracture of 9.0 pct. The achieved properties are comparable to those of wrought 6182 alloy processed by conventional routes.

  • 50.
    Benti, Gudeta
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nonlinear dynamic analysis of vertical rotors with tilting pad journal bearings2021Licentiate thesis, comprehensive summary (Other academic)
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