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  • 1.
    An, Wei
    KTH, Superseded Departments, Materials Processing.
    Electronic speckle pattern interferometry applied to shape and deformation measurement2000Licentiate thesis, comprehensive summary (Other scientific)
  • 2.
    Bayard, Ove
    KTH, Superseded Departments, Production Engineering. KTH, Superseded Departments, Materials Processing.
    Investigation of the verification techniques for modelling turning processes2000Licentiate thesis, monograph (Other scientific)
  • 3.
    Bejhem, Mats
    KTH, Superseded Departments, Materials Processing.
    Integrerat system för bearbetningsstyrning1998Licentiate thesis, monograph (Other scientific)
  • 4.
    Dahlström, Johan
    KTH, Superseded Departments, Materials Processing.
    On the solidification of Al alloys during microgravity1999Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Thermal analyses have been performed on Al, Al-Cu alloys,Al-Sn alloys, Pb, Sn, Pb-Sn alloys and Al-based amorphousalloys were also investigated. The cooling rates varied fromless than a Kelvin per minute to more than 10,000 Kelvin persecond. Solidification was made under normal gravity and undermicrogravity conditions. In the last case parabolic flight wereused to reduce the gravity.

    All the samples, except the Al-based alloys containing Ysolidified by forming dendrite crystals. It was found that thedendrite structure was coarser in the samples that solidifiedunder microgravity conditions compared to referenceexperiments. For pure metals and Al-Cu alloys the latent heatof solidification is decreasing with increasing cooling, whilefor Al-Sn alloys the latent heat was independent of the coolingrate. It was also found that in the samples immediately heatedafter solidification the melting temperature were below thealloy liquidus temperature.

    The experimental results were explained by the possibilityof excess vacancies formed at the solidification front. Anexcess of vacancies would decrease the melting temperature andthe latent heat for Al, Pb or Sn. A thermodynamic analysis wasperformed to explain the result and to find if excess vacanciesare depending on the alloy system.

    Key-words: Thermal analyses, solidification, rapid cooling,microgravity, parabolic flight, latent heat, undercooling,melting, dendrite, dendrite arm spacing, Al, Al-Cu, Al-Sn,Pb-Sn, amorphous metals, vacancy

  • 5.
    Elfsberg, Jessica
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Fredriksson, Hasse
    KTH, Superseded Departments, Materials Processing.
    Oscillation Mark Formation on Continuously Cast Stainless Steel and Carbon Steel Slabs2003Report (Other academic)
  • 6.
    Eriksson, Jan I.
    KTH, Superseded Departments, Materials Processing.
    Studies of new stainless steels and products with application of new welding processes1998Licentiate thesis, comprehensive summary (Other scientific)
  • 7.
    Ervasti, Esa
    et al.
    KTH, Superseded Departments, Materials Processing.
    Ståhlberg, Ulf
    KTH, Superseded Departments, Materials Processing.
    A new closed-die forging concept for the manufacturing of crown wheels1999In: Advanced Technology of Plasticity 1999: Proceedings of the 6th International Conference on Technology of Plasticity Nuremberg, September 19 - 24, 1999, Vol. III / [ed] M. Geiger, 1999, p. 1663-1668Conference paper (Refereed)
  • 8.
    Ervasti, Esa
    et al.
    KTH, Superseded Departments, Materials Processing.
    Ståhlberg, Ulf
    KTH, Superseded Departments, Materials Processing.
    Behaviour of longitudinal surface cracks in the hot rolling of steel slabs1999In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 94, no 2-3, p. 141-150Article in journal (Refereed)
    Abstract [en]

    The behaviour of a longitudinal V-shaped crack, on the surface of a continuously cast steel slab, is studied during hot rolling. The analysis is carried out by means of the commercial FE-code LS-DYNA3D. Process parameters obtained from industry are used as a reference. The slab of initial width 1000 mm and thickness 220 mm is rolled down to 30 mm. It is assumed that the material can be treated as rigid-perfectly plastic and that the cracks do not propagate. The latter assumption is in agreement with industrial observations for a steel grade similar to that analysed here. The aim of the study is to investigate the possibility of controlling the plastic deformation so that the cracks disappear or so that their deteriorating effects are minimised. The analysis is focused upon the influence of friction, roll radius and rolling schedule on the change in the shape of a crack of initial depth 20 mm and a crack angle of 6 degrees. The reliability of the simulations is checked by pilot-plant experiments using aluminium as the model material for steel.

    The results indicate that it is not possible to prevent the bottom side surfaces of the crack from coming into contact, especially not for small reductions/pass and small roll radii. The influence of friction was found to be marginal. Contact between the crack surfaces is found already at the beginning of the rolling, as the V-shaped crack is being changed to Y-shape. Considering the upper part of the crack, this remained open during the majority of the schedules studied. However for heavy reduction/pass and a large roll radius, this part of the crack is closed also, but not before the final passes. If the bottom side surfaces of the crack are in complete contact, they are prevented from further oxidisation. It is assumed that for such conditions the deteriorating influence of the bottom part of the defect decreases during subsequent rolling. During the elongation of the workpiece, the oxide flake of the Y-crack bottom is broken into splinters with oxide free material in between, making the creation of a high performance weld possible. Provided that this supposition is correct, the best results should be obtained for Light reductions/pass at the beginning of the rolling, resulting in an early closure of the crack bottom, followed by heavy reductions/pass enabling also the closure and oxide splintering of the upper part of the folded crack.

  • 9.
    Ervasti, Esa
    et al.
    KTH, Superseded Departments, Materials Processing.
    Ståhlberg, Ulf
    KTH, Superseded Departments, Materials Processing.
    Transversal cracks and their behaviour in the hot rolling of steel slabs2000In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 101, no 1-3, p. 312-321Article in journal (Refereed)
    Abstract [en]

    The behaviour of transversal cracks in reverse rolling of steel slabs is analysed. For this purpose a commercial FE-program, LS-Dyna3D has been utilised. Process parameters from an industrial rolling mill have been used as a reference. One basic assumption is that the cracks do nor propagate for the steel considered. This is in agreement with observations in industry. Furthermore the material is treated as elastic-plastic. The aim of the study is to investigate the possibility of controlling the plastic deformation so that the cracks disappear at the same time as their boundary surfaces are prevented from getting into contact with each other. If they should get into contract, a defect in the form of an oxide flake should be created. The optimum situations are assumed to be found when the depth of the crack decreases more rapidly than the height of the slab at the same time as the crack width increases. For such rolling conditions it should be possible to find the crack bottom on the workpiece surface without any trace let by the original crack.

    During rolling two phenomena are present, counteracting each other. At the entrance to the roll gap, the crack widens, which is regarded as beneficial. The explanation to the phenomenon is that when the front edge of the crack gets into contact with the roil it is dragged towards the gap at the same time as its velocity is rapidly changed from horizontal to become parallel to the tangential velocity of the roll. If this phenomenon did not occur, the risk for the creation of a permanent oxide Rake should be big. During the passage of the gap the widened crack angle is decreased. The decrease of the angle is explained by the high hydrostatic pressure that is associated with the roll/workpiece contact surface. At the exit the angle is slightly increased once again which might be explained by the fact that the back edge of the crack is still in contact with the roll and its movement is retarded because of friction. Thus the final result depends on which of the two phenomena, widening or contraction that has been dominating.

    The analysis shows that light reductions/pass, small roll radius and high friction are preferred. A deep crack of V-shape is easily transformed to Y-shape. This means that a remaining defect should be formed at the bottom of the crack. Reverse rolling is found to be beneficial because this way of rolling implies that the crack does nor tilt so easily which should result in the formation of an oxide flake.

  • 10.
    Gunnarsson, Lars
    KTH, Superseded Departments, Materials Processing.
    Process control in sheet metal forming focused upon friction1998Licentiate thesis, comprehensive summary (Other scientific)
  • 11.
    Hallström, Jonas
    KTH, Superseded Departments, Materials Processing.
    Wear and friction in counterblow hammer forging: a practical example1999Licentiate thesis, comprehensive summary (Other scientific)
  • 12.
    Hedegård, Joakim
    KTH, Superseded Departments, Materials Processing.
    Moderna svetsprocesser - produktivitet kontra mekaniska egenskaper av Joakim Hedegård1997Licentiate thesis, comprehensive summary (Other scientific)
  • 13.
    Hellström, Erik
    KTH, Superseded Departments, Materials Processing.
    In process evaluation of external centerless grinding roundness using acoustic emission1999Licentiate thesis, monograph (Other scientific)
  • 14.
    Iravani, Ebrahim
    KTH, Superseded Departments, Materials Processing.
    Part quality control as a tool for rapid resetting1999Licentiate thesis, monograph (Other scientific)
  • 15.
    Lundberg, Sven-Erik
    KTH, Superseded Departments, Materials Processing.
    The theory and practice of roll pass design1999Doctoral thesis, comprehensive summary (Other scientific)
  • 16.
    Magnusson, Lena
    KTH, Superseded Departments, Materials Processing.
    On the nucleation and solidification of silicon and refractory materials2001Licentiate thesis, comprehensive summary (Other scientific)
  • 17.
    Magnusson, Lena
    et al.
    KTH, Superseded Departments, Materials Processing.
    El-Benawy, Talaat
    KTH, Superseded Departments, Materials Processing.
    Fredriksson, Hasse
    KTH, Superseded Departments, Materials Processing.
    Solidification processing of si, an experimental study on the variation of latent heat (and lattice defects) with the cooling rate2001Report (Other (popular science, discussion, etc.))
  • 18.
    Mahmoudi, Jafar
    KTH, Superseded Departments, Materials Processing.
    Modelling of solidification processing andcontinuous strip casting for copper-base alloys2000Doctoral thesis, comprehensive summary (Other scientific)
  • 19.
    Nilsson, Bengt
    KTH, Superseded Departments, Materials Processing.
    Interferometric 3D-shape and deformation measurements using ultra short pulses1999Licentiate thesis, comprehensive summary (Other scientific)
  • 20.
    Sivesson, Patrik
    KTH, Superseded Departments, Materials Processing.
    On the control of centreline segregation in continous casting1997Doctoral thesis, comprehensive summary (Other scientific)
  • 21.
    Skogberg, Tero
    KTH, Superseded Departments, Materials Processing.
    Jet engine manufacturing engineering: machining of metal matrix composites (MMCs)1998Licentiate thesis, monograph (Other scientific)
  • 22.
    Svendsen, Lena
    KTH, Superseded Departments, Materials Processing.
    On the processing of aluminium-C/TiC/TiB2 composites1998Doctoral thesis, comprehensive summary (Other scientific)
  • 23.
    Söderholm, Mattias
    KTH, Superseded Departments, Materials Processing.
    Use of Barkhausen noise for grinding quality control2000Licentiate thesis, monograph (Other scientific)
  • 24.
    Sörqvist, Lars
    KTH, Superseded Departments, Materials Processing.
    Poor quality costing1998Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis presents an effective model for measuring the cost of poor quality. It consists of two models, developed during the research project, assessments and the construction of measurement systems. By tradition, most companies prefer to design systems of their own for measuring their poor quality costs, but experience shows that this is difficult and time consuming, and, none the less, there is always the risk of failure. With this experience as a base, the model for a measurement system, put forward in the thesis, has been constructed and it should, consequently, have a better chance of success. The author would, however, like to point out that these measurement systems can only be used to measure a limited number of selected costs and should therefore only be applied when the company has matured some in its quality activities.

    Assessments, on the other hand, are simpler to perform, produce quick results, and, as shown in case studies, tend to be very successful. On account of that, the thesis highly recommends that assessments should be used as main means, particularly when the intention is to influence attitudes and behaviors, or to give priority to the most costly problems. The bulk of the research work has for this reason been focused on the development and test of a methodology for assessments, as past experiences and researches into these fields are very limited.

    Case studies show that the method developed for assessments has functioned quite well in the companies using it. Poor quality costs, studied in the area 9-16% of the business turnover, have been registered. This is far from the total poor quality costs of these businesses, but it is a considerably higher part than previously measured. The time spent on these assessments has been moderate, and the members of the assessment groups and the co-workers tended to respond in favor. The management groups, in the companies in question, have all taken an considerable interest in the studies and, consequently, in the results.

     

     

  • 25. Vinet, Bernhard
    et al.
    Magnusson, Lena
    KTH, Superseded Departments, Materials Processing.
    Fredriksson, Hasse
    KTH, Superseded Departments, Materials Processing.
    Desré, Pierre J.
    Correlation between surface and interface energies in transition metals with respect to crystal nucleation; other common undercooled elementsIn: Journal of Non-Equilibrium Thermodynamics, ISSN 0340-0204, E-ISSN 1437-4358Article in journal (Refereed)
  • 26.
    Wessén, Magnus
    KTH, Superseded Departments, Materials Processing.
    On the mechanisms of structure formation in nodular cast iron1997Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The mechanisms of structure formation in nodular cast ironhave been examined by experiments and by physical modelling. Byincorporation of models for nucleation and growth for allrelevant phases into a heat flow calculation. it is possible topredict the as-cast structure by computer simulation. Mainly,this work has focused on the eutectoid transformation and onnucleation of graphite during solidification.

    From experimental observations it was concluded that a purediffusion model was not sufficient to describe thetransformation rate of austenite into ferrite and graphite aspreviously proposed in the literature. By introducing aninterfacial mass transfer resistance at the graphit/ferriteinterface, to control the incorporation rate of carbon atoms onthe graphite nodules, it is possible to reproduce the ferritegrowth experimentally observed by numerical simulation.

    Silicon, copper and manganese are three alloying elementswhich are frequently used in nodular cast iron. Silicon isknown to increase the ferrite content while copper andmanganese have the opposite effect, thus promoting pearliteformation. The mechanisms responsible for the different actionof these elements have been studied by thermal analysis ofcooling curves in plate castinags (4 to 50 mm) at differentalloying levels(1.7<%Si<4.9,0.03<%Cu<0.88.0.16<%Mn<0.99).The tendency for copper to decrease the section sizesensitivity can be explained by the new theories.

    The effectiveness of inoculants used in nodular cast iron isto a large extent dependent on the Mg-treatment and the meltpreparation. In a detailed examination of two inoculants it wasfound that the nodule counts obtained were linearlyproportional to the maximum eutectic supercooling.

    The models have been implemented as a subroutine into afinite difference (FDM) program in order to be able to relateheat flow calculations and structure evolution in complex threedimensional castings.

    Key words: Nodular cast iron, ductie iron, SG ironferrite, modelling, eutecroid transformation, silicon, copper,manganese, thermal analysisis, interface control, pearlite,diffusion control, casting simulation.

  • 27.
    Åberg, Jonas
    et al.
    KTH, Superseded Departments, Materials Processing.
    Widell, Björn
    KTH, Superseded Departments, Casting of Metals.
    Uniaxial material damping measurements using a fiber optic lattice: a discussion of its performance envelope2004In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 44, no 1, p. 33-36Article in journal (Refereed)
    Abstract [en]

    Damping is the internal transfer of kinetic energy to other forms of energy. Today, most methods use either bending or torsional vibration to measure damping. This means that the strain field in the specimen is nonhomogeneous. If the damping of the tested material is linear, strain-independent, the values acquired with these traditional methods will be equal to the intrinsic material damping of the material. If, however, the damping is strain-dependent, nonlinear, the measured value will be an average of the damping of the specimen, and not equal to its intrinsic material damping. To address this problem, a method is required to experimentally determine the damping in uniaxial tension in order to produce the same strain level in all parts of the test specimen and hence obtain a measurement of the intrinsic material damping. Using such a method, it is possible to view the material damping as the phase angle between the stress and the strain in a harmonic oscillation. In this paper, a method is suggested for measuring this phase shift in uniaxial tension to determine the material damping properties. It uses a tensile test machine, an optical fiber Bragg grating technique and a lock-in amplifier. Measurements with the phase shift technique have been suggested previously, but its performance envelope has been overestimated. In this paper, the performance envelope is discussed and restricted. It is shown that the envelope depends on the specimen length, loss factor and test frequency. An optical strain measurement method is also believed to help avoid many electrical measurement problems seen with the originally proposed method.

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