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| 2. |
- Al-Mashikhi, S.O., et al.
(författare)
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An explanation of ‘striation free' cutting of mild steel by fibre laser
- 2009
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Ingår i: Lasers in manufacturing 2009. - Stuttgart : AT-Fachverlag.
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Konferensbidrag (refereegranskat)abstract
- 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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| 3. |
- Alam, Md. Minhaj, et al.
(författare)
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Fatigue behaviour study of laser hybrid welded eccentric fillet joints : Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints
- 2009
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Ingår i: 12th NOLAMP proceeding 2009. - Kgs. Lyngby : ATV-SEMAPP.
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Konferensbidrag (refereegranskat)abstract
- 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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| 4. |
- Alam, Md. Minhaj, et al.
(författare)
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Fatigue behaviour study of laser hybrid welded eccentric fillet joints : Part I
- 2009
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Ingår i: 12th NOLAMP proceeding 2009. - Kgs. Lyngby : ATV-SEMAPP.
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Konferensbidrag (refereegranskat)abstract
- 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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| 5. |
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| 6. |
- Alam, Minhaj M, et al.
(författare)
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The Effects of Surface Topography and Lack of Fusion on The Fatigue Strength of Laser Hybrid Welds
- 2009
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Ingår i: Congress proceedings. - : Laser Institute of America. ; , s. 38-46
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Konferensbidrag (refereegranskat)abstract
- The geometrical aspects of laser hybrid welds (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 micro-topography (i.e. the surface ripples) can be more important than the macrogeometry of the weld surface or 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 micro-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 Finite element analysis (FEA) for the complex joint geometry and a 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 micro-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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| 7. |
- Alam, Md. Minhaj, et al.
(författare)
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The effects of surface topography and lack of fusion on the fatigue strength of laser hybrid welds
- 2009
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Ingår i: Congress proceedings. - Orlando, Fla : Laser institute of America. - 9780912035598 ; , s. 38-46
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Konferensbidrag (refereegranskat)abstract
- 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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| 8. |
- Amer, Eynas, et al.
(författare)
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Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling
- 2009
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 255:21, s. 8917-8925
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Bergström, David, et al.
(författare)
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A ray-tracing analysis of the absorption of light by smooth and rough metal surfaces
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:11, s. 113504-1
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Tidskriftsartikel (refereegranskat)abstract
- Ray tracing has been employed to investigate the absorption of light by smooth and random rough metal surfaces. For normally incident light the absorptance of the surface increases with surface roughness. However, for light incident at a tangent to the surface the absorptance-surface roughness relationship is more complex. For example, in certain cases the absorptance can rise, fall, and rise again as the surface roughness increases. In this paper this complex absorptance-roughness relationship is defined and explained. The wavelengths of the light chosen for this study correspond to the primary and secondary output wavelengths of Nd:YAG lasers.
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| 10. |
- Bergström, David, et al.
(författare)
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Absorptance of Non-Ferrous Alloys to Nd:YLF and Nd:YAG Laser Light at Room Temperature
- 2007
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 46:8, s. 1290-1301
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of absorptance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the absorptance data presently available considers only polished pure metals rather than the commercially available (unpolished, oxidised) alloys which are actually being processed in manufacturing. This paper presents the results of absorptance measurements carried out at room temperature on as-received engineering grade non-ferrous metals (Al, Cu and Zn alloys). The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053nm and 527nm � which means that the results are also valid for Nd:YAG radiation at 1064nm and 532nm). The absorptance results obtained differ considerably from existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified. For all 22 cases studied the absorptance was higher than for ideal pure, polished metals. For all Al- and Cu-samples the absorptance was higher for the green than it was for the infrared wavelength, while for all Zn-coatings this trend was reversed. No clear correlation between absorptance and surface roughness was found at low roughness values (Sa 0.15 � 0.60) but one, rougher set of samples (Sa 2.34), indicated a roughness-absorptance correlation at higher roughness levels.
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