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  • 1.
    Abolhasani, Hasanali
    et al.
    Department of Materials and Polymer Engineering, Faculty of Engineering, Hakim Sabzevari University, Sabzevar 9617976487, Iran.
    Farzi, Gholamali
    Department of Materials and Polymer Engineering, Faculty of Engineering, Hakim Sabzevari University, Sabzevar 9617976487, Iran.
    Davoodi, Ali
    Materials and Metallurgical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad 917751111, Iran.
    Vakili-Azghandi, Mojtaba
    Department of Materials Engineering, Faculty of Engineering, University of Gonabad, Gonabad, 96919-57678, Iran.
    Das, Oisik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Neisiany, Rasoul Esmaeely
    Department of Materials and Polymer Engineering, Faculty of Engineering, Hakim Sabzevari University, Sabzevar 9617976487, Iran.
    Development of self-healable acrylic water-based environmental-friendly coating as an alternative to chromates coatings2023Ingår i: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 176, artikel-id 107402Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, different coating systems, including solvent-based epoxy and water-based acrylic resins, were evaluated for their potential as an alternative to chromate coatings in order to avoid Cr(VI) toxic hazards. The resins were used as either pigment-free coatings or were formulated with 20-wt% zinc/aluminum pigments. The coatings were subsequently applied on galvanized ST12 steel plates and their corrosion resistance was investigated by electrochemical impedance spectroscopy (EIS) evaluations. The effect of the binder and pigment type on the impact resistance of two different polymeric coatings was also evaluated. The results of impact tests revealed completely peeled film from the substrate for epoxy coatings. However, under the same experimental conditions, very few small cracks were created in water-based acrylic coatings for both pigmented and pigment-free cases. In addition, some other parameters such as drying time and coating cost were taken into account to select a good alternative to chromate coatings. The results of this work can facilitate the introduction of an inexpensive environmentally friendly acrylic coating as a promising self-healing alternative to chromate coating.

  • 2.
    Abrahamsson, Lena
    et al.
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Arbetsvetenskap.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Johansson, Jan
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Arbetsvetenskap.
    Rask, Kjell
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Arbetsvetenskap.
    Fältholm, Ylva
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Arbetsvetenskap.
    Kumar, Uday
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Bergquist, Bjarne
    Projekt: LUPO - globala länkar2010Övrigt (Övrig (populärvetenskap, debatt, mm))
  • 3.
    Acharya, Sarthak
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Sattar, Shahid
    Department of Physics & Electrical Engineering, Linnæus University, 39231 Kalmar, Sweden.
    Chouhan, Shailesh Singh
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Delsing, Jerker
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Detailed Characterization of a Fully-Additive Covalent Bonded PCB Manufacturing Process (SBU-CBM Method)2022Ingår i: Processes, ISSN 2227-9717, Vol. 10, nr 4, artikel-id 636Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To bridge the technology gap between IC-level and board-level fabrications, a fully additive selective metallization has already been demonstrated in the literature. In this article, the surface characterization of each step involved in the fabrication process is outlined with bulk metallization of the surface. This production technique has used polyurethane as epoxy resin and proprietary grafting chemistry to functionalize the surface with covalent bonds on an FR-4 base substrate. The surface was then metalized using an electroless copper (Cu) bath. This sequential growth of layers on top of each other using an actinic laser beam and palladium (Pd) ions to deposit Cu is analyzed. State-of-the-art material characterization techniques were employed to investigate process mechanism at the interfaces. Density functional theory calculations were performed to validate the experimental evidence of covalent bonding of the layers. This manufacturing approach is capable of adding metallic layers in a selective manner to the printed circuit boards at considerably lower temperatures. A complete analysis of the process using bulk deposition of the materials is illustrated in this work.

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  • 4.
    Akselsen, Odd M.
    et al.
    SINTEF, Trondheim.
    Wiklund, Greger
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Østby, Erling
    SINTEF, Trondheim.
    Sörgjärd, Arve
    Kværner Verdal.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    A first assessment of laser hybrid welding of 420 mpa steel for offshore structure application2013Ingår i: 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, s. 171-182Konferensbidrag (Övrigt vetenskapligt)
    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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  • 5.
    Akselsen, Odd Magne
    et al.
    SINTEF, Trondheim.
    Wiklund, Greger
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Østby, Erling
    SINTEF, Trondheim.
    Sørgjerd, Arve
    Kværner Verdal.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Properties of laser hybrid butt welds of 420 MPa steel2013Ingår i: 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, s. 290-294Konferensbidrag (Refereegranskat)
    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

  • 6.
    Alam, M. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Z.
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, SE-100 44 Stockholm, Sweden.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet.
    Häggblad, Hans-Åke
    Luleå tekniska universitet.
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 265, nr 6, s. 1936-1945Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Alam, Md. Minhaj
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    A study of the fatigue behaviour of laser and hybrid laser welds2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    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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  • 8.
    Alam, Md. Minhaj
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Laser welding and cladding: the effects of defects on fatigue behaviour2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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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  • 9.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Z
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, Stockholm.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint2011Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, nr 10, s. 2246-2258Artikel i tidskrift (Refereegranskat)
    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

  • 10.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part I2009Ingår i: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Konferensbidrag (Refereegranskat)
    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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  • 11.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints2009Ingår i: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Konferensbidrag (Refereegranskat)
    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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  • 12.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Geometrical aspects of the fatigue behaviour of laser hybrid fillet welds2009Ingår i: Proceedings of the Fatigue Design Conference, Cetim , 2009Konferensbidrag (Refereegranskat)
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  • 13.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The effects of surface topography and lack of fusion on the fatigue strength of laser hybrid welds2009Ingår i: 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, s. 38-46Konferensbidrag (Refereegranskat)
    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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  • 14.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Analysis of the rapid central melt pool flow in hybrid laser-arc welding2012Ingår i: Physics Procedia, E-ISSN 1875-3892, Vol. 39, s. 853-862Artikel i tidskrift (Refereegranskat)
    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.

  • 15.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    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 deposits2013Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 46, s. 328-337Artikel i tidskrift (Refereegranskat)
    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.

  • 16. Alam, Md. Minhaj
    et al.
    Karlsson, Jan
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Generalising fatigue stress analysis of different laser weld geometries2011Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, nr 4, s. 1814-1823Artikel i tidskrift (Refereegranskat)
    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.

  • 17.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    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 components2013Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 25, nr 3Artikel i tidskrift (Refereegranskat)
    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.

  • 18.
    Al-Gburi, Majid
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Nilsson, Martin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Reducing Thermal Crack Risks Caused by Restraint in Young Concrete - A Case Study on Walls of Water Tanks2022Ingår i: Nordic Concrete Research, ISSN 0800-6377, Vol. 66, nr 1, s. 41-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Concrete cracks in structures such as water tanks and nuclear power stations cause anxiety to owners, contractors and engineers. These cracks may significantly increase the structure’s permeability and thus increase leakage, reduce durability, and eventually lead to loss of structural functionality. Therefore it is important to minimize their occurrence and size. To identify effective ways of minimizing cracking in young concrete segments, a parametric study was conducted using the finite element method (FEM). Parameters considered include casting sequence, joint position, wall height, and cooling. The study examined continuous and jumped casting approaches to the casting of a cylindrical reinforced concrete tank for a sewage-treatment plant, with and without the application of the ‘kicker’ technique in which the lower part of the wall is cast with the slab. The main cause of cracking is thermal change and restraint imposed by adjacent older structures, and the FEM predictions agree well with experimental observations. Continuous casting is most effective at minimizing cracking because it creates only two contact edges between newly cast and existing structures producing the lowest level of restraint. The kicker technique is shown to be very effective for reducing restraint and consider rephasing.

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  • 19.
    Al-Mashikhi, S.O.
    et al.
    University of Notttingham.
    Powell, John
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    University of Notttingham.
    An explanation of ‘striation free' cutting of mild steel by fibre laser2009Ingår i: 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 , 2009Konferensbidrag (Refereegranskat)
    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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  • 20.
    Al-Mashikhi, S.O
    et al.
    Salalah College of Technology, Engineering Department, Salalah, Oman and Faculty of Engineering, University of Nottingham.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Voisey, K.T.
    Faculty of Engineering, University of Nottingham.
    Heat affected zones and oxidation marks in fiber laser–oxygen cutting of mild steel2011Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 23, nr 4Artikel i tidskrift (Refereegranskat)
    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.

  • 21.
    Al-Ramahi, Nawres Jabar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Comprehensive numerical analysis of stress state in adhesive layer of joint including thermal residual stress and material non-linearity2021Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The main objective of this work is to improve understanding of the stress state in the adhesive layer of bonded joints and identify key parameters which govern performance of adhesive joints. This information is crucial for the prediction of the failure initiation and propagation with the further estimation of the durability and strength of adhesively bonded structures.

    A systematic numerical analysis of stress state in the adhesive layer of a single-lap and double- lap joint under various loading conditions (thermal and mechanical loading) and an alternative methodology to predict the direction for crack propagation within adhesive layer are presented in this thesis.  To identification of the most important parameters of joints is done based on the assessment of the peel and shear stress distributions in the adhesive layer. The thermal residual stresses arising after assembling of joints at elevated temperature are accounted for in the analysis.

    Initially, accurate, realistic 3D finite element model with novel boundary conditions (displacement coupling) was developed and validated. The employed boundary conditions allow to eliminate the edge effect and simulate the behavior of an infinite plate of composite laminate with off-axis layers (monoclinic materials). It is also possible to decouple the edge effects induced by the finite specimen width from the interaction with ends of the joint overlap region. Due to these advanced setting it is possible to eliminate influence of some of the parameters as well as to reduce geometry of the model without losing precision. Thus, the model is optimized with respect to the number of elements as well as element size distribution and does not require excessive computational power to obtain accurate stress distributions even near to the possible sites with stress perturbations (e.g. corners, cracks, etc). Additionally to the geometrical parameters, various material models have been employed in simulations of adhesive joints. A linear and non-linear material models (adherend and adhesive) was used for the single-lap joint, while a linear material behavior was considered for double-lap joint. The geometrical non-linearity was also included in the analysis whenever required. To make results more general and applicable to a wide range of different joints the normalized (with respect to the thickness of adhesive layer) dimensions of joints were used. 

    Depending on the analyzed type of joint (single- or double- lap), combination of similar and dissimilar (hybrid) materials for adherends are considered: a) metal-metal; b) composite-composite; c) composite-metal. In case of the composite adherend (carbon and/or glass fibers) different laminate lay-ups were selected: uni-directional ([08]T and [908]T) and quasi-isotropic ([0/45/90/-45]S and [90/45/0/-45]S). 

    In general, discussion and conclusions concerning the importance of various joint parameters are based on the magnitude of the peel and shear stress concentration at the ends of the overlap. In order to identify general trends with respect to the influence of mechanical properties of adherends the master curves for shear and peel stresses are constructed and analyzed. 

    To simulate effect of the residual thermal stresses on the behavior of joints different methods for assembly of joints were considered (using dedicated adhesive or employing co-curing method). The results of this investigation lead to the conclusions that the one of the most important factors affecting the simulation results is the sequences of application of thermo-mechanical loading for different assembly methods. It is shown that simple superposition of thermal and mechanical stresses (most common approach) in the adhesive layer works properly only for linear material but it gives inaccurate results if non-linear material is considered. The thesis demonstrates the appropriate way to combine thermal and mechanical loads to obtain correct stress distributions for any material (linear and non-linear). The analysis of the influence of residual thermal stresses has shown that the peel and shear stress concentration at the ends of overlap joint and the shear stress within the over-lap region are reduced due to thermal effect. In case of composite adherend the co-curing assembly method is more favorable (in terms of reducing stress concentrations) than using adhesive for joining the materials.

    Finally, the simulation of the crack propagation within the adhesive layer for the bi-material (steel and composite) DCB sample with thick adhesive layer was carried out. The alternative to traditional fracture mechanics approach is proposed for the prediction of the crack path in the adhesive layer: a maximum hoop stress criterion. The hoop stress on the perimeters of a relatively large circle around the crack tip is evaluated to predict the direction of the crack extension with respect to the existing crack. The fracture mechanics is used to validate this approach and it is proved that if the Mode I is dominant for the crack propagation the hoop stress criterion be successfully used to predict crack path in the adhesive layer. This methodology is much more effective (in terms of required time and resources) than energy release based criterion or even X-FEM.

    The main result of this thesis is a tool to obtain accurate stress distributions in the adhesive layer of joints. This tool provided better understanding of the behavior of adhesive joints and allowed to develop new approach for prediction of crack propagation in the adhesive layer. This is definitely a development in the design of stronger, more durable adhesive joints for lighter structural components.   

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  • 22.
    Al-Ramahi, Nawres
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Institute of Technology / Baghdad, Middle Technical University, Baghdad, Iraq.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Swerea SICOMP AB, Piteå, Sweden.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Investigation of end and edge effects on results of numerical simulation of single lap adhesive joint with non-linear materials2018Ingår i: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 87, s. 191-204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents systematic numerical study of stresses in the adhesive of a single-lap joint with the objective to improve understanding of the main material and geometrical parameters determining performance of adhesive joints. For this purpose a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates), are employed. The model accounts for non-linearity of materials (adherend and adhesive) as well as geometrical non-linearity. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint allowing to separate edge effect from end effects is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criterion. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters on peel and shear stress distributions in the adhesive layer is examined carefully and mechanical parameters governing the stress concentrations in the joint have been identified, this dependence can be described by simple but accurate fitting function. The effect of the used material model (linear vs non-linear) on results is also demonstrated.

  • 23.
    Amer, Eynas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Sjödahl, Mikael
    Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling2009Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, nr 21, s. 8917-8925Artikel i tidskrift (Refereegranskat)
    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.

  • 24.
    Amer, Eynas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    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 interferometry2010Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, nr 14, s. 4633-4641Artikel i tidskrift (Refereegranskat)
    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.

  • 25.
    Andersson, Anders
    et al.
    Luleå tekniska universitet.
    Engström, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Wiklund, Greger
    Påsvetsning, upplegering och ytomsmältning (glasering) med högeffektlaser1983Rapport (Övrigt vetenskapligt)
  • 26.
    Andersson, Carl
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Modeling the Evolution of Grain Texture during Solidification of Laser-Based Powder Bed Fusion Manufactured Alloy 625 Using a Cellular Automata Finite Element Model2023Ingår i: Metals, E-ISSN 2075-4701, Vol. 13, nr 11, artikel-id 1846Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The grain texture of the as-printed material evolves during the laser-based powder bed fusion (PBF-LB) process. The resulting mechanical properties are dependent on the obtained grain texture and the properties vary depending on the chosen process parameters such as scan velocity and laser power. A coupled 2D Cellular Automata and Finite Element model (2D CA-FE) is developed to predict the evolution of the grain texture during solidification of the nickel-based superalloy 625 produced by PBF-LB. The FE model predicts the temperature history of the build, and the CA model makes predictions of nucleation and grain growth based on the temperature history. The 2D CA-FE model captures the solidification behavior observed in PBF-LB such as competitive grain growth plus equiaxed and columnar grain growth. Three different nucleation densities for heterogeneous nucleation were studied, 1 × 1011, 3 × 1011, and 5 × 1011. It was found that the nucleation density 3 × 1011 gave the best result compared to existing EBSD data in the literature. With the selected nucleation density, the aspect ratio and grain size distribution of the simulated grain texture also agrees well with the observed textures from EBSD in the literature.

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  • 27.
    Andersson, Roger
    Luleå tekniska universitet.
    Deformation characteristics of stainless steels2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis describes the results of a theoretical and experimental investigation into the deformation characteristics of stainless steels. The title of the chapters is as follows; A new type of forming limit diagram for use with meta-stable stainless steels. A new equation to describe the microstructural transformation of meta- stable austenitic stainless steels during plastic deformation. FEM-simulation of the forming and impact behaviour of stainless steel automobile components. The development of high strain rate equations for stainless steels. The metallurgy and mechanical properties of laser welds between stainless and carbon steels.

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  • 28.
    Andersson, Roger
    Luleå tekniska universitet.
    Effects of composition and the production process on formability of austenitic stainless steels1999Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Formability of austenitic stainless steels is strongly influenced by the chemical composition, the internal texture and the deformation conditions. The purpose of this study is to determine how small variations in chemical composition and minor variations in the production process are influencing the formability of type 304 and 316 austenitic stainless steels. In this study, the formability of ten sub-grades of type 316 austenitic stainless steel and four sub-grades of type 304 austenitic stainless steel were investigated. These investigations are expected to have significant impact for both stainless steel producers and users. If the influence of the chemistry on the formability and the influence of different paths in the cold-rolling plant on the anisotropy are better understood, then manufacturers will be able to design processes which optimise the limiting strains.

  • 29.
    Andersson, Roger
    et al.
    Luleå tekniska universitet.
    Magnusson, Claes
    Schedin, Erik
    Luleå tekniska universitet.
    Using stainless steel for energy absorbing components in automobiles2001Ingår i: Innovations in processing and manufacturing of sheet materials: proceedings / the Second Global Symposium on Innovations in Materials Processing and Manufacturing: Sheet Materials, held at the 2001 TMS annual meeting, February 11 - 15, 2001, New Orleans, Louisiana / [ed] Mahmoud Y. Demeri, Warrendale, Pa: Minerals, Metals & Materials Society, 2001, s. 97-110Konferensbidrag (Refereegranskat)
    Abstract [en]

    To increase the crash performance in automobiles it is necessary to use new techniques and materials. To produce energy absorbing components the material should have high yield strength, high elongation to fracture and strong work hardening. The total work a component absorbs during impact is the area under the stress-strain curve for unit material volume. This has lead to an interest in high strength stainless steels as crash safety components in automobiles due to their excellent material properties. The material performance of different stainless grades has been evaluated through intrinsic and simulative tests. A stainless steel bumper beam has been optimised for a VOLVO car and comparisons have been made with the present application. Simulations have been done and verified by experiments.

  • 30.
    Andersson, Roger
    et al.
    Luleå tekniska universitet.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    Fem-simulation of forming and subsequently impact behaviour of a stainless steel component2005Ingår i: Proceedings of the 8th ESAFORM Conference on Material Forming / [ed] Dorel Banabic, Bucharest: The Romanian Academy Publishing House , 2005, Vol. 1, s. 265-268Konferensbidrag (Refereegranskat)
  • 31. Andersson, Roger
    et al.
    Schedin, Erik
    Magnusson, Claes
    Ocklund, J.
    Persson, A.
    Stainless steel components in automotive vehicles2004Ingår i: Stainless Steel World, ISSN 1383-7184, Vol. 16, nr 1, s. 34-37Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Components linked to crash safety in automotive vehicles are required to transmit or absorb energy. The energy absorbing capability of a given component depends on a combination of geometry, material properties and loading conditions. Increased crash performance can be obtained by using materials with higher yield strength and relatively high elongation to fracture. These demands have led to increasing interest in the use of high strength stainless steels due to their relatively high elongation to fracture and good formability. To increase knowledge of the formability and forming behaviour of these materials, several components from current and prototype vehicles have been made using high strength stainless steels at Volvo Cars Body Components, Olofstrom, Sweden. These were subsequently analysed in close collaboration with the Division of Manufacturing Systems Engineering at Lulea University of Technology, Sweden.

  • 32.
    Andersson, Roger
    et al.
    Luleå tekniska universitet.
    Schedin, Erik
    AvestaPolarit Inc..
    Magnusson, Claes
    Ocklund, Jonny
    Volvo Car Corporation.
    Persson, Arne
    Volvo Car Corporation.
    The applicability of stainless steels for crash absorbing components2002Ingår i: ACOM : Avesta Sheffield corrosion management and application engineering, ISSN 1101-0681, Vol. 3-4, s. 7-12Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    To increase crash performance in automotive vehicles it is necessary to use new techniques and materials. Components linked to crash safety should transmit or absorb energy. The energy absorbing capability of a specific component is a combination of geometry and material properties. For these components the chosen material should have high yield strength and relatively high elongation to fracture. These demands have led to increasing interest in the use of high strength stainless steels. The relative performance of three high strength carbon steels and two high strength stainless steel grades was evaluated through intrinsic and simulative tests. The rear bumper for a Volvo Car model in current production was manufactured using the five sheets tested to verify formability and behaviour under load. The bumpers were clamped in a rig that allowed quasi-static impact tests to be made. The energy absorbing capabilities were evaluated by measuring force versus displacement during the impact test.

  • 33.
    Andersson, Roger
    et al.
    Luleå tekniska universitet.
    Syk, M.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Magnusson, Claes
    Formability behaviour of meta-stable stainless steels2005Ingår i: Proceedings of the 8th ESAFORM Conference on Material Forming / [ed] Dorel Banabic, Bucharest: The Romanian Academy Publishing House , 2005, Vol. 1, s. 359-362Konferensbidrag (Refereegranskat)
  • 34.
    Anthony, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Suhonen, Heikki
    Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Wanhainen, Christina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Granvik, Mikael
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Laser-induced spallation of minerals common on asteroids2021Ingår i: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 182, s. 325-331Artikel i tidskrift (Refereegranskat)
    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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  • 35.
    Anthony, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Frostevarg, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Suhonen, Heikki
    Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Wanhainen, Christina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Penttilä, Antti
    Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Granvik, Mikael
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland.
    Laser processing of minerals common on asteroids2021Ingår i: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 135, artikel-id 106724Artikel i tidskrift (Refereegranskat)
    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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  • 36.
    Arwidson, Claes
    Luleå tekniska universitet.
    Numerical simulation of sheet metal forming for high strength steels2005Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    New demands for passenger safety, vehicle performance and fuel economy have led to an increase in the use of advanced high strength steel. An increase in strength decreases the formability of the material and increases the spring back behaviour. Recently the development of high strength steel has rapidly advanced, requiring verification of earlier material models suitable for describing the plasticity behaviour in sheet metal forming. The aim of the here conducted numerical simulations is to verify the deep drawing process and the shape of the final component of a simple hat profile geometry for studying spring-back of high strength steels. Four advanced high strength steels were selected for detailed investigation, namely the dual phase steels DP600 and DP750, the triple phase steel TRIP700 and the stainless steel HYTENS800. The plastic properties of these steels have been assessed through intrinsic and simulative tests, leading to verification and comparison at different levels. The hat profile serves as a simple test geometry for deep drawing due to elimination of the lateral dimension in first order. The corresponding simpler plasticity behaviour in space facilitates systematic analysis Experiments and simulations were carried out, leading to comparison of the resulting draw in, strain, thinning, final shape and spring-back. The verification and analysis concerns the friction coefficient, two software codes, Finite Element properties and the two material models Hill48 and Hill90. The simulation provides a good qualitative coincidence with experimental results, which enables to develop a process theory and to study the individual mechanisms involved. The friction coefficient, varied from 0 to 0.1, shows very low sensitivity on the process. The simulation underestimates the spring-back by 8-12° at the flange edge. Among the four materials studied basically the stainless steel HYTENS800 shows the largest deviations during comparison. In general the results partially reveal distinct quantitative discrepancies, in particular in the critical bending regions, demanding for improved material models and better knowledge of the boundary conditions.

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  • 37. Arwidson, Claes
    et al.
    Bernspång, Lars
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Verification of numerical forming simulation in high strength steels2004Ingår i: Proceedings of the Conference Innovations in metal forming, 2004Konferensbidrag (Refereegranskat)
  • 38.
    Asnafi, Nader
    Luleå tekniska universitet.
    Aluminiumplåts formbarhet1990Licentiatavhandling, monografi (Övrigt vetenskapligt)
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  • 39.
    Asnafi, Nader
    Luleå tekniska universitet.
    Formbarhet under dragpressning, sträckpressning och bockning samt egenskaper efter formning av aluminiumplåt1988Rapport (Övrigt vetenskapligt)
  • 40.
    Asnafi, Nader
    Luleå tekniska universitet.
    Mechanics of sheet metal forming: strength, stiffness, dent resistance, and springback of double-curved autobody panels : fracture and wringling in stretch and shrink flanging by fluid forming1997Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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  • 41.
    Asnafi, Nader
    Luleå tekniska universitet.
    Återfjädring vid bockning längs krökta linjer1987Rapport (Övrigt vetenskapligt)
  • 42.
    Asnafi, Nader
    et al.
    Luleå tekniska universitet.
    Magnusson, Claes
    On formability of sheet aluminium1990Ingår i: Sheet metals in forming processes: 16th biennial congress IDDRG, open sessions, Borlänge, June 11 - 13, 1990 ; congress proceedings, reports, posters, Borlänge: Materials Center, HTM , 1990, s. 81-91Konferensbidrag (Refereegranskat)
    Abstract [en]

    Sheet metal behaves differently for different stress and strain ratios. For instance, the material tolerates less deformation at plane strain compared with uniaxial tension. Hill's yield criteria can be used to describe sheet material's deformation behavior. Hill's original yield criterion for plane stress, assuming that there is no planar anisotropy is given. The equation shows better agreement with experimental results when r > 1 (steel 4010), while there is no agreement with experimental results when r < 1 (Al-5052). Hill proposed, therefore, a new yield criterion, which is given. The value of a can be determined by comparing the experimental work-hardening characteristics for uniaxial tension and balanced biaxial tension; 1 < = a < = 2. For soft Al, having an average r-value of 0.723, the value of a has been found to be 1.8. The parameter a has its greatest effect at balanced biaxial tension. Graphs

  • 43.
    Atiyah, H.
    et al.
    Faculty of Engineering, The University of Nottingham.
    Powell, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    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 tool2018Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, artikel-id 032009Artikel i tidskrift (Refereegranskat)
    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.

  • 44.
    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 tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Effect of Tungsten-Inert-Gas Preheating on Mechanical and Microstructural Properties of Friction Stir Welded Dissimilar Al Alloy and Mild Steel2016Ingår i: Strength of Materials, ISSN 0039-2316, E-ISSN 1573-9325, Vol. 48, nr 1, s. 152-159Artikel i tidskrift (Refereegranskat)
    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

  • 45.
    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 tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Design and Characterization of Al–Mg–Si–Zr Alloys with Improved Laser Powder Bed Fusion Processability2022Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 53, nr 1, s. 331-343Artikel i tidskrift (Refereegranskat)
    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.

  • 46.
    Bemani, M.
    et al.
    Eurecat, Centre Tecnològic de Catalunya, Metal Digital Manufacturing JRU, 08242 Manresa, Spain; CIEFMA – Department of Materials Science and Engineering, EEBE, Universitat Politècnica de Catalunya, Barcelona-Tech, 08019 Barcelona, Spain; Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne 3000, Australia.
    Parareda, S.
    Eurecat, Centre Tecnològic de Catalunya, Metal Digital Manufacturing JRU, 08242 Manresa, Spain.
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära. Eurecat, Centre Tecnològic de Catalunya, Metal Digital Manufacturing JRU, 08242 Manresa, Spain.
    Mateo, A.
    CIEFMA – Department of Materials Science and Engineering, EEBE, Universitat Politècnica de Catalunya, Barcelona-Tech, 08019 Barcelona, Spain.
    Das, R.
    Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne 3000, Australia.
    Molotnikov, A.
    Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne 3000, Australia.
    Rapid fatigue evaluation of additive manufactured specimens: Application to stainless steel AISI 316L obtained by laser metal powder bed fusion2024Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 184, artikel-id 108279Artikel i tidskrift (Refereegranskat)
  • 47.
    Benito Olmos, Víctor
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik. Vivere.
    Insight into cosmetology, emulsions and product development in a Fast-moving consumer good company through the scaling up of a salicylic acid cleanser2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Fast-moving consumer goods (FMCG) companies are being an innovative way to develop successful products in the market. This project focuses on the development of a salicylic acid cleanser using the development procedure implemented by a FMCG company, Vivere. Insights into cosmetology, material types, emulsion concepts, key parameters and important steps in the development of a cosmetic product are described in the report. 

    Such fabricated product did undergo different tests to assure the quality and stability of the product during long period of times, showing great stability, especially in good storage conditions for more than 120 days. 

    Furthermore, a scale-up test was made using two different homogenisers machines, JF-A 4000 and PMC-3000. The results were astounding, JF-A 4000 product samples showed great results with similar behaviour and quality to the laboratory sample, meanwhile, PMC-300 product samples showed a 3,04-fold higher viscosity than the laboratory sample and showed low homogenisation. Therefore, only JF-A 4000 homogeniser will be used for the future productions of the material. 

    Finally, an economic analysis was executed, concluding that the estimated number of units that should be sold before the project becomes profitable is 2190 units. 

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  • 48.
    Berglund, Göran
    Luleå tekniska universitet.
    Presshärdning av borstål: utveckling av presshärdningstekniken till verkstadsmässighet1984Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 49.
    Bergström, David
    Luleå tekniska universitet.
    The absorptance of metallic alloys to Nd:YAG and Nd:YLF laser light2005Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In Laser Material Processing of metals, an understanding of the fundamental absorption mechanisms plays a vital role in determining the optimum processing parameters and conditions. The absorptance, which is the fraction of the incident laser light which is absorbed, depends on a number of different parameters. These include laser parameters such as intensity, wavelength, polarisation and angle of incidence and material properties such as composition, temperature, surface roughness, oxide layers and contamination. The vast theoretical and experimental knowledge of the absorptance of pure elements with smooth, contamination-free surfaces contrasts with the relatively sparse information on the engineering materials found in real processing applications. In this thesis a thorough investigation of the absorption mechanisms in engineering grade materials has been started. The Licentiate thesis consists of 5 papers. Paper 1 is a short review of some of the most important mathematical models used in describing the interaction between laser light and a metal. Paper 2 is a review of a few experimental methods of measuring the absorptance of an opaque solid such as a metal. Papers 3 and 4 are experimental investigations of the absorptance of some of the most frequently found metallic alloys used in Laser Material Processing today. Paper 5 is a co-authored paper on the cleaning of copper artefacts with the use of second harmonic generated Nd:YAG laser light.

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  • 50.
    Bergström, David
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    The absorption of laser light by rough metal surfaces2008Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In Laser Material Processing of metals, an understanding of the fundamental absorption mechanisms plays a vital role in determining the optimum processing parameters and conditions. The absorptance, which is the fraction of the incident laser light which is absorbed, depends on a number of different parameters. These include laser parameters such as intensity, wavelength, polarisation and angle of incidence and material properties such as composition, temperature, surface roughness, oxide layers and contamination. The vast theoretical and experimental knowledge of the absorptance of pure elements with smooth, contamination-free surfaces contrasts with the relatively sparse information on the engineering materials found in real processing applications. In this thesis a thorough investigation of the absorption mechanisms in engineering grade materials has been conducted, both experimentally and theoretically. Integrating sphere reflectometry has been employed to study the impact of surface conditions on Nd:YAG and Nd:YLF laser absorptance of some of the most common ferrous and non-ferrous metallic alloys found in Laser Material Processing. Mathematical modelling and simulations using ray-tracing methods from scattering theory have been used to analyze the influence of surface topography on light absorption. The Doctoral thesis consists of six papers: Paper 1 is a short review of some of the most important mathematical models used in describing the interaction between laser light and a metal surface. Paper 2 is a review of experimental methods available for measuring the absorptance of an opaque solid such as a metal. Papers 3 and 4 are experimental investigations of the absorptance of some of the most frequently found metallic alloys used in Laser Material Processing today. Paper 5 presents results from 2D ray-tracing simulations of random rough metal surfaces in an attempt to investigate the influence of surface roughness on laser scattering and absorption. Paper 6 is a full 3D ray-tracing investigation of the interaction of laser light with a rough metallic surface, where some comparisons also are made to the previous 2D model.

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