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  • 251.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Computer simulation of powder compaction1987Rapport (Övrigt vetenskapligt)
  • 252.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Constitutive modelling of hard metal powder1985Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 253.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Constitutive models for powder materials1991Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 67, nr 2, s. 127-136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Constitutive models to describe the mechanical material behaviour of hardmetal powders are studied. Three classes of constitutive relationships are examined, described as cap plasticity, multisurface plasticity and endochronic plasticity. A representative model of each class is studied in detail, An optimization technique is used to fit the constitutive parameters to empirical test data on multiaxially loaded hardmetal powder specimens. Of all models tested, an endochronic model proposed by Bazant shows the best agreement with the empirical test data. Different phenomena can be simulated with the model by adding certain constitutive functions. It is, however, difficult to fit the model to test data because of the large number of model parameters, most of which have no physical meaning

  • 254.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Explicit versus implicit finite element simulation of metal powder compaction1992Ingår i: Numerical methods in industrial forming processes: proceedings of the 4th International Conference on Numerical Methods in Industrial Forming Processes, Valbonne/France, 14-18 September 1992; NUMIFORM '92 / [ed] J.L. Chenot; R.D. Wood; O.C. Zienkiewicz, Rotterdam: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1992Konferensbidrag (Refereegranskat)
  • 255.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling and simulation of metal powder pressing1993Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The pressing of hard metal components was analysed with numerical methods. The aim was to calculate the density distribution and the springback during unloading. This thesis concentrated on the following parts; constitutive modelling, explicit versus implicit time integration schemes and contact constraint methods. Three constitutive models for the simulation of the mechanical material behaviour of hard metal powder were evaluated. The models were cap plasticity, multisurface plasticity and endochronic plasticity. The compaction of powder specimen was simulated assuming quasi-static conditions. The method of using explicit time integration of the equations of motion was compared with a traditional method employing implicit time integration. The results show that an explicit code is advantageous in terms of development potential, solution time and ease of use. Alternative constraint methods were evaluated when modelling the contact between powder and tool. A contact constraint method with friction based on direct integration of the equations of the contact interface was proposed. Two specific powder metallurgical parts, a highway engineering tip and a plate for testing crack sensibility, were selected for the analyses. The calculated density distributions were qualitatively in good agreement with experimental results. The springback obtained in the numerical simulation of unloading and ejection processes was in good agreement with measured values.

  • 256.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical simulation of ceramic-metal diffusion bonded and brazed joints1993Ingår i: Designing ceramic interfaces II : understanding and tailoring interfaces for coating, composite and joining applications: proceedings of the Second European Colloquium held at Petten on 11 - 13 November 1993 [i.e. 11 - 13 November 1991] / Commission of the European Communities, JRC, Institute for Advanced Materials / [ed] S.D. Peteves, Office for official publications of the European communities , 1993, s. 105-116Konferensbidrag (Refereegranskat)
    Abstract [en]

    finite element method to calculate residual stress fields caused by thermal mismatch in ceramic/metal joints was applied to three problems. These were: an Incoloy 909 cap brazed to a Si3N4 cylinder with Ag-27%Cu filler; diffusion bonding of the same materials with a tungsten interlayer by hot isostatic pressing; and brazing of Al2O3 to Incoloy 909

  • 257.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    On friction models in contact problems1987Rapport (Övrigt vetenskapligt)
  • 258.
    Häggblad, Hans-Åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Berglund, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Formulation of a finite element model for localisation and crack initiation in components of ultra high strength steels2009Ingår i: Hot sheet metal forming of high-performance steel, CHS2: 2nd international conference, June 15-17 2009, Luleå, Sweden. Proceedings / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Parkash, Auerbach: Verlag Wissenschaftliche Scripten , 2009, s. 229-237Konferensbidrag (Refereegranskat)
  • 259.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Doremus, P.
    Bouvard, D.
    An International research programme on the mechanics of metal powder forming1996Ingår i: Advances in powder metallurgy & particulate materials - 1996: proceedings of the 1996 World Congress on Powder Metallurgy & Particulate Materials ..., June 16 - 21, Washington, DC / sponsored by the Metal Powder Industries Federation / [ed] Terry M. Cadle, Princeton, NJ: Metal powder industries federation , 1996, Vol. Vol. 2, s. 179-192Konferensbidrag (Refereegranskat)
    Abstract [en]

    A collaborative research programme, Mechanics of Metal Powder Forming, has been initiated at PM'94 Conference in Paris. It aims at evaluating the procedures and facilities involved in the numerical modelling of the forming of metal powders by hot and cold compaction, in particular through the identification of bench mark problems. This paper gives a general presentation of this programme and focus on the advancement of cold compaction programme. Material investigated was Distaloy AE (Fe-4Ni-1.5Cu-0.5Mo).

  • 260.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Hockauf, Matthias
    Luleå tekniska universitet.
    Eriksson, Mikael
    Swedish Ceramic Institute.
    Berggren, Carina
    Nobel Biocare AB.
    Simulation of high velocity compaction of powder in a rubber mould with characterization of silicone rubber and titanium powder using a modified split Hopkinson set-up2005Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 154, nr 1, s. 33-42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper introduces a method for characterization of silicone rubber and titanium powder in high velocity compaction using the split Hopkinson set-up. The impact test data has been used to estimate parameters in constitutive models for rubber and powder. A finite element study has been performed with different geometrical design of the high velocity compaction of titanium powder against an aluminium mandrel using a rubber mould as pressing medium. One goal of this study is to investigate if and how the manufacturing method can be applied for making dental copings. A conclusion of the experimental work is that it is possible to characterize rubber material and powder material for high velocity compaction of metal powder by the use of a modified split Hopkinson pressure bar set-up. The numerical simulation shows qualitatively good agreement with the experience from practical tests. In conclusion, the work shows the possibility to numerically study the geometric design and to optimize the densification behaviour of a complex high velocity compaction process.

  • 261.
    Häggblad, Hans-Åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Modeling of tensile crack formation in metal powder pressing2010Ingår i: Proceedings of the 13th International Conference on Metal Forming :: September 19 - 22, 2010, Hotel Nikko Toyohashi, Toyohashi, Japan / [ed] K. Mori; M. Pietrzyk; J. Kusiak; J. Majta; P. Hartley; J. Lin, Weinheim: Wiley-VCH Verlagsgesellschaft, 2010, s. 1344-1347Konferensbidrag (Refereegranskat)
  • 262.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gustafsson, Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Golling, Stefan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling And Simulation The Cracking Of Green Metal Powder Body2016Ingår i: Proceedings World PM2016 Congress: International Powder Metallurgy Congress & Exhibition 9-13 October 2016, Hamburg, Germany, European Powder Metallurgy Association , 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    During the ejection stage of the powder metallurgy (PM) pressing process the elastic behaviour is important. Especially, if the in the powder compact is unloaded in a non-beneficially manner crack formation can occur. Experiments show a non-linear and also stress dependent elastic behaviour of green bodies. Calibrated against experimental data, a fracture model controlling the stress versus crack-width relationship is used. The softening rate of the fracture model is obtained from the corresponding rate of the dissipated energy. The model is implemented with a smeared crack approach in a finite element code and tested in simulation of a diametral compression testing. Results from simulations correlates well with experimental results. The smeared crack method combined with a cohesive fracture model is an interesting tool for predicting fracture in powder compacts.

  • 263.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Li, Wen-Bin
    Luleå tekniska universitet.
    A micro mechanical based constitutive model for finite element simulation of hot isostatic pressing of powder1995Ingår i: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 128, nr 1-2, s. 191-198Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hot isostatic pressing (HIP) facilitates new designs and product shaping, for example by direct manufacture of composite products with differing materials in the various parts (compound). The specific material characteristics are thus created at the manufacturing stage (consolidation), and these in themselves often give good possibilities regarding shape, so-called NS (Net Shape)-or NNS (Near Net Shape)-manufacture. The HIP-technique is used economically in the low series production of complex-shaped steel parts. In order to achieve quality products, an integration of material, design and manufacturing technology is necessary, since the function and cost of the final component depends to a large extent on the development of production technology and its integration with design technology. Simulation of the hot isostatic pressing process is required to reduce the need for expensive and time-consuming experimental design. The use of finite element techniques in analyses of the highly non-linear process is preferable, especially for complex-shaped components. In this work, a micro-mechanical based continuum mechanics model for finite element analysis is presented. The model is used in the finite element simulation of hot isostatic pressing of two components. The results from the analyses correspond well with the experimental results.

  • 264.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nilsson, L.
    On the fit of constitutive parameters through optimization1983Ingår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 12, nr 6, s. 282-284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The need for more reliable finite element analyses of materials with complex behaviour has led to the development of new constitutive theories. These theories often have a large number of parameters which must be determined from experiments. A method is described of fitting constitutive parameters through optimization. An application is made to the Prevost multisurface plasticity theory. Good agreement is obtained between theoretical results and experimental data in the case of a multi axially loaded hard metal powder

  • 265.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nilsson, Larsgunnar
    Luleå tekniska universitet.
    Oldenburg, Mats
    Implementation of substructure technique in the finite element program FEMP1986Rapport (Övrigt vetenskapligt)
  • 266.
    Häggblad, Hans-Åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nishida, Masahiro
    Nagoya Institute of Technology.
    Cillia, Mathieu De
    IFMA Clermont-Ferrand.
    Jonsén, Pär
    Oldenburg, Mats
    Strain rate effects on constitutive properties of iron powder2009Ingår i: Euro PM2009, European powder metallurgy association , 2009, Vol. 3, s. 15-20Konferensbidrag (Refereegranskat)
  • 267.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    A model for the influence of lubricants on the pressing behaviour of iron powder1996Ingår i: Modelling in materials science and processing : COST 512: MMSP '96 General Workshop, Davos, Switzerland, 29 September - 2 October 1996 / [ed] Michel Rappaz, Luxembourg: Office for official publications of the European communities , 1996Konferensbidrag (Refereegranskat)
  • 268.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Modelling and simulation of metal powder die pressing with use of explicit time integration1994Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 2, nr 4, s. 893-911Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pressing of hard metal components is analyzed with numerical methods. The analyzed components are selected from produced components for which the density distribution in the material after pressing has been measured. The expected results from the analyses are the density distribution and the springback after unloading and ejection of the components. The highly non-linear quasistatic problem is analyzed with the use of explicit integration of the equations of motion. A contact constraint method based on direct integration of the equations of the contact interface is used in the analyses. The contact and friction algorithms have been developed in earlier work and are further verified by analyses of a test problem that has an analytical solution. The behaviour of the powder is described by a special cap plasticity material model developed for powder applications. In one example the results obtained using the cap model are compared with results obtained with a multisurface plasticity model. The parameters of the constitutive models are fitted to triaxial experimental data through optimization methods. The presented methods are evaluated by comparing the results with experimental data from density measurements where a technique based on gamma ray absorption is used. The density distributions are qualitatively in good agreement with experimental results. The springback obtained in the simulation of unloading and ejection is in good agreement with measured values.

  • 269.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Numerical simulation of powder compaction for two multilevel ferrous parts, including powder characterisation and experimental validation2002Ingår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 45, nr 4, s. 335-344Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper presents a summary of two case studies that were carried out by the scientific team in the Thematic Network PM Modnet. During the life of this project, the compaction of complex multilevel ferrous components was investigated. These formed a vehicle to explore methods to characterise the yield and friction properties of the powder, perform simulation of the compression stage of the forming process, complete experimental trials, and compare experimental and simulated results. Density comparisons were made with results from Archimedes, quantitative metallography, and computerised tomography and force levels were compared with recordings from the pressing trials. The results highlight differences between equipment and experimental techniques used in characterising powders. They also show that hardness, metallographic analysis, and computerised tomography may be used to measure density variations throughout the compact. The prediction of density variation was reasonably consistent when using different simulations, whereas punch force prediction showed good consistency. It was found that predicted and measured density distributions agree within 0·05 to 0·5 g cm-3 and that punch force levels may be predicted within 10 to 30%. The study effectively establishes a benchmark with which to compare and improve future simulations.

  • 270.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Larsson, Hans
    On nonlinear constitutive models: including numerical experiments1983Rapport (Övrigt vetenskapligt)
  • 271. Häggblad, Hans-åke
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Wikman, Bengt
    Bengtsson, S.
    Design and evaluation of die pressing experiments for inverse modelling2000Ingår i: Proceedings of 2000 Powder Metallurgy World Congress : November 12 - 16, 2000, Kyoto International Conference Hall, Japan: organized by Japan Society of Powder and Powder Metallurgy, Japan Powder Metallurgy Association. / [ed] Koji Kosuge; Hiroshi Nagai, Tokyo: Japan Society of Powder and Powder Metallurgy , 2000Konferensbidrag (Refereegranskat)
  • 272.
    Isaksson, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation methods for bumper system development2006Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    n development of bumper systems for the automotive industry, iterative Finite Element (FE) simulations are normally used to find a bumper design that meets the requirements of crash performance. The crash performance of a bumper system is normally verified by results from standardized low speed crash tests based on common crash situations. Consequently, these crash load cases are also used in the FE simulations during the development process. However, lack of data for the car under development implies that simplified models must be used as a representation of the car in the FE simulations. Present simplified models of the car lead to uncertainties of the design even though the bumper system is modelled in a proper manner. The present work focuses on methods of how to represent the car in the FE crash simulations. The work is limited to the standardized crash tests in which the force acts longitudinally along the vehicle. Two different types of modelling perspectives are investigated. With the traditional approach, the aim is to obtain agreement of the results from the FE simulation and the physical test in terms of force from the barrier as a function of the compression of the bumper system. Here, the vehicle is represented by a point mass connected via rigid beam elements to the bumper system. The point mass, which only is allowed to translate longitudinally, is assigned with a reduced mass compared to the physical mass of the car to compensate for energy transformations in the car during the collision. In paper A, it is shown that the required mass reduction is dependent on vehicle and bumper characteristics as well as on the loading conditions. Also, the simple method of mass reduction leads to difficulties in attaining high agreement for time history of force and compression. In contrast to this, the idea with the second modelling technique is to reach a high agreement of the time history of force and compression of the bumper system. This methodology is based on a model structure that consists of mass elements, linear spring and viscous damper elements. It is shown that this model structure can provide high agreement between the FE simulation and the physical crash test in terms of force and compression as functions of time even for different loading conditions without adjusting the model parameters. Within the current thesis, a methodology of identifying parameters in the Mass Spring Damper (MSD) model from physical crash tests is presented. The methodology identifies a set of parameters that minimizes the deviation of the resulting displacements from the crash test and the simulation. This identification methodology is then used in a Design of Experiments (DOE) approach for relating model parameters in the MSD model to general properties of an arbitrary vehicle such as axial stiffness, bending stiffness and mass. For this, a public domain FE simulation model of a Ford Taurus is used. The knowledge gained from this study makes it possible to use the MSD model for representation of a coming car in the FE simulations associated with bumper development.

  • 273. Isaksson, Erik
    et al.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Correlation of vehicle crash model parameters to car properties in low-speed collisions: a design of experiments approach2010Ingår i: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 15, nr 3, s. 241-249Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the current study, a methodology for relating model parameters in a one dimensional Mass Spring Damper (MSD) model to global properties of a car, e.g. axial stiffness, bending stiffness and mass, is presented. It is shown that these three vehicle properties affect the vehicle's crash performance in low-speed collision tests used for industrial verification of bumper system performance. Based on information of the properties for a vehicle under development, parameters in the MSD model can be adjusted to give the correct boundary conditions for a finite element (FE) crash simulation with a candidate bumper design. In the FE simulations, the MSD model is then coupled to the FE mesh of candidate bumper design to find a bumper that meets the crash performance requirements of a car under development. The methodology is based on Design of Experiments (DOE) and FE simulations on a public domain model of a Ford Taurus. The knowledge gained from this study gives a valuable tool to use in design and development of bumper systems for the automotive industry.

  • 274.
    Jansson, Ida
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A monitoring system to estimate the pressure field of a Kaplan runner blade prototype2008Ingår i: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    The technical development of hydraulic machinery has gone towards lighter components and higher power concentration levels. A deregulation of the power market world-wide means that the machines experience more transient loads and are sometimes operated at off-design points. Those facts demand a more precise dynamic analysis at the design level of hydraulic machinery than what was formerly customary. Mechanical engineering needs enhanced tools for this purpose. Prediction models need to be validated against experimental data. There are limited possibilities to perform experimental investigations of hydropower prototypes. Fundamental in an experimental dynamic analysis is to determine the forces acting on the machine. This paper is concerned with a monitoring system to estimate the angular resolved pressure field on the suction- and pressure side of a prototype Kaplan runner blade. By measuring the pressure at different positions on the runner blade, we have a tool to determine the hydraulic load acting on the runner. This is part of an experimental dynamic analysis of the behavior of 10 MW prototype of a low-head Kaplan prototype lodged in an old machine hall inaugurated 1914 situated above the polar circle in Porjus, Sweden.

  • 275.
    Jansson, Ida
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Åkerstedt, Hans O.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The effect of inertia and angular momentum of a fluid annulus on lateral transversal rotor vibrations2012Ingår i: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 28, s. 328-342Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An extensive amount of work exists on experimental and theoretical analysis of unsteady flow phenomena in hydraulic turbines. Still, resonance phenomena and self-excited vibrations of the rotor of hydropower machines are not considered as a major problem during normal operation conditions. Nevertheless, in development and research it is not sufficient to rely on earlier experience. An accurate predictive rotor model is crucial in risk assessment of rotor vibrations of hydraulic generator units. This paper discusses the effects of inertia and the rotational energy of the fluid in the turbine on lateral transversal shaft vibrations of hydraulic generator units. There is a lack of agreement among engineers upon how fluid inertia of the turbine should be included in rotor models. The rotational energy of the fluid has a potential risk of feeding self-excited vibrations. A fluid-rotor model is presented that captures the effect of inertia and angular momentum of a fluid annulus on vibrations of an inner rigid cylinder. The purpose of the model is to gain physical understanding of the phenomena at work and it is not applicable to specific turbines. The linearized equation of motion of the cylinder surrounded by a fluid annulus is solved for by one single complex equation. The constrained cylinder has two degrees of freedom in the plane perpendicular to its axis. By the assumption of irrotational cyclic flow, the fluid motion is described by a complex potential function. The motion of the cylinder is described by three parameters. Two surfaces are defined that splits the parameter space into regions with different qualitative behaviour. One surface defines the limit of stability whereas the other defines a limit when the eigenvalues have opposite signs or are both positive. The response to an external periodic rotating force is visualized by the magnitude of the inverse of the complex dynamic stiffness.

  • 276.
    Jansson, Ida
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Åkerstedt, Hans O.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Fluidinducerade reaktionskrafter för vertikalaxlade vattenkraftturbiner och dess betydelse för axelns laterala egensvängningar2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 97-Konferensbidrag (Övrigt vetenskapligt)
  • 277.
    Jeppsson, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Karlsson, Lennart
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A concurrent engineering system with application to hot isostatic pressing1997Ingår i: Modeling in welding, hot powder forming, and casting, Materials Park, Ohio: ASM International, 1997, s. 117-128Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 278.
    Jeppsson, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A neutral database for preparation of computer controlled coordinate measurements1993Ingår i: Computer integrated manufacturing: proceedings of the 2nd international conference ; 6 - 10 September 1993, Singapore / [Second International Conference on Computer Integrated Manufacturing], Singapore: World Scientific and Engineering Academy and Society, 1993Konferensbidrag (Refereegranskat)
  • 279.
    Jeppsson, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Svoboda, Ales
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Integrated design and verification system for finite element modelling1993Ingår i: Concurrent Engineering - Research and Applications, ISSN 1063-293X, E-ISSN 1531-2003, Vol. 1, nr 4, s. 213-217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a computer-integrated system for design, manufacturing simulation, and inspection using a coordinate measurement machine (CMM). The work is concerned with the problem of predicting the shape of the container for hot isostatic pressing (HIP) and it focuses on the verification of a finite element (FE) simulation model for HIP. The verification is performed by comparing the simulated geometry of a real component produced by HIP. The geometry of the HIP component is measured by a CMM. The whole process from design and manufactunng simulation to inspection and geometry verification is performed within a computer-aided concurrent engineering (CACE) system. The system is built on both commercial and non-commercial software. The communication between a CMM, a geometnc modelling system, and the finite element simulation codes is developed. The manufacturing of a turbine component to net shape geometry using HIP is chosen as a demonstrator example. The benefits of the presented CACE system are time and cost savings as well as higher product quality.

  • 280.
    Jonsson, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    TM-rolling of heavy plate and roll wear2006Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The heavy plate rolling process needs accurate predictions of the process parameters. The plate thickness, flatness and rolling stability are of this direct influenced as well as the productivity. Therefore, careful calculation of the process parameters and pass schedules is necessary. The thesis is concerned with two aspects of controlling rolling; the choice of optimal pass schedules and roll wear. A software has been developed in Paper A to determine optimal pass schedules for thermomechanical rolling in order to obtain a fine microstructure. It includes models of the effect of strain, precipitates, static and dynamic recrystallization and austenite grain size on the final grain size. The predicted grain sizes for four different cases were compared with experimental results. It was also used to study the effect of different delay times during the pass schedule of rolling thermomechanical plate. The results shows that an increase in delay times results in finer ferrite grains are received. The refinement is however small for long delay times. Long delay times also affect the productivity negatively. A method for modeling of the work roll contour in a four high mill is presented in Paper B. The active parameters were found to be the plate length and the variations of the pressure from the plate and the back-up roll on the work roll along the work roll barrel. The method is build up with statistical methods. The bases for the statistics are simulations of different rolling cases and measurements from the production of heavy plates in Oxelösund. The proposed wear contour model was found to be in good agreement with the measurements from the production.

  • 281. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Deformation and stresses in butt-welding of large plates1985Ingår i: Numerical methods in heat transfer: expanded and edited versions of selected papers from an international conference held in Swansea, July 1979 / [ed] R.W. Lewis; K. Morgan, John Wiley & Sons, 1985, Vol. 3, s. 35-57Konferensbidrag (Refereegranskat)
  • 282. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Deformations and stresses in butt-welding of large plates with special reference to the mechanical material properties1985Ingår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 107, nr 4, s. 265-270Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Simulation of automatic butt-welding of large plates was investigated. Two different steels were considered. The plates were tack-welded before the butt-welding. The simulation includes the tack-welding, the butt-welding and the cooling to room temperature. The simulations should lead to an understanding of the mechanics behind the change in gap width in front of the moving arc, which is of importance in automatic welding production. The residual stresses due to the butt-welding were also studied. The magnitude and the distribution of the residual stress are important in design of welded structures.

  • 283. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kan svetsegenspänningar och svetsdeformationer förutsägas?1986Ingår i: Svetsen, ISSN 0039-7091, Vol. 45, nr 5, s. 6-9Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Many difficulties in welding result from the fact that heat input causes uneven heating of the welded object. This article reports on the results of an investigation carried out with the object to find out whether it is possible to predict residual stresses in welding and weld deformations with the aid of new computational methods used in continum mechanics. Butt welding of flat plates was studied in this investigation. Deformations, residual stresses, and gap width variations during the welding process were calculated.

  • 284. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Plate motion and thermal stresses in root-bead butt-welding and one-pass butt-welding of two different steels1984Konferensbidrag (Övrigt vetenskapligt)
  • 285. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Plate motion and thermal stresses in root-bead butt-welding of plates1985Ingår i: Numerical methods in thermal problems: proceedings of the fourth international conference held in Swansea, UK on 15th - 18th July, 1985 / [ed] R.W. Lewis, Swansea: Pineridge Press , 1985, s. 1092-1102Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper root-bead welding of plates of two different sizes was experimentally and theoretically analysed. The material of the plates was a fine-grain steel with yield limit 360 MPa. The finite element method was used for both the thermal analyses and the mechanical analyses. Temperature-dependent material properties and volume changes due to phase transformations were considered. Plane stress conditions were assumed. Good agreement between calculated and measured values were obtained.

  • 286. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Plate motion in butt-welding of tack-welded plates1984Ingår i: Numerical methods for transient and coupled problems: proceedings of an International Conference held in Venice, Italy on July 9th-13th, 1984 / [ed] R. W. Lewis; P. Bettess; E. Hinton; B.A. Schreffler, Swansea: Pineridge Press , 1984, s. 351-359Konferensbidrag (Refereegranskat)
  • 287. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation of tack welding procedures in butt joint welding of plates1985Ingår i: Welding Journal, ISSN 0043-2296, Vol. 64, nr 10, s. 296-301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of tack welding procedure on change in root opening was investigated. This change during the first part of welding depends on the order in which the tack welds are made. It is also affected by the starting position of the welding arc. These effects were studied in seven theoretical analyses - three cases where the tack welding procedures differed and four cases where the temperature fields at the beginning of the butt joint welding differed. The material investigated was a fine-grain steel with a yield stress of 360 MPa (52,200 psi) at room temperature. The filler material was ESAB 1. 2/12. 51 (AWS ER70S-6).

  • 288. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermal stresses and plate motion in butt-welding1983Ingår i: Numerical methods in thermal problems: proceedings of the third international conference, held in Seattle, USA, on 2nd - 5th August, 1983 / [ed] R.W. Lewis, Swansea: Pineridge Press , 1983, s. 270-279Konferensbidrag (Refereegranskat)
  • 289. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermal stresses, plate motion and hot-cracking in butt-welding1983Ingår i: Mechanical behaviour of materials - IV: proceedings of the fourth International conference, Stockholm, Sweden, 15-19 August 1983 / [ed] Janne Carlsson; Nils-Gunnar Ohlson, Oxford: Elsevier, 1983, s. 273-279Konferensbidrag (Refereegranskat)
  • 290. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindén, G.
    The influence of welding deformations on tolerance requirements in automatic butt welding1985Konferensbidrag (Refereegranskat)
  • 291. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental and numerical analysis of damped transient vibration of beam structures1989Ingår i: Proceedings of the International conference on noise and vibration: August 16-18, 1989 at Novetel Orchid Inn Singapore, Singapore: Nanyang Technological Institute , 1989, s. B.53-B.64Konferensbidrag (Refereegranskat)
  • 292.
    Jonsson, Patrick
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Smoothed Particle Hydrodynamic Simulation of Hydraulic Jump using Periodic Open Boundaries2016Ingår i: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 40, nr 19-20, s. 8391-8405Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The natural phenomena hydraulic jump that is commonly used in spillways as an energy dissipater coupled to hydropower applications has been investigated with Smoothed Particle Hydrodynamics. A new approach was applied based on a periodic open boundary condition. The model consisted of a tank, a gate, a stilling basin and periodic open boundaries at each end of the computational domain. The tank provided a hydraulic head and in turn a specific flow through the gate, and a downstream condition in terms of a depth for the jump. The gate elevation had a major impact and was calibrated to ensure a correct and stable flow rate, when compared to experiments. With the proper flow rate, the position of the jump toe was significantly improved. The jump toe oscillated with a frequency in good agreement with experimental findings found in the literature and the oscillation amplitude increased with Froude number. However, for high Froude number cases the position was still too close to the gate but could be improved by including a correction based on the length of the jump. The depths in both the super- and subcritical zones was in good agreement with experiments and previous numerical studies. Furthermore, the Froude number was in-line with the definition of super- and subcritical flows.

  • 293.
    Jonsson, Patrick
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Smoothed particle hydrodynamics modellering av hydrauliska språng2011Konferensbidrag (Övrigt vetenskapligt)
  • 294.
    Jonsson, Patrick
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling Dam Break Evolution over a Wet Bed with Smoothed Particle Hydrodynamics: A Parameter Study2015Ingår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 7, nr 5, s. 248-260Artikel i tidskrift (Refereegranskat)
  • 295.
    Jonsson, Patrick
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Smoothed Particle Hydrodynamics Modeling of a Hydraulic Jump2012Konferensbidrag (Refereegranskat)
  • 296.
    Jonsson, Patrick
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Smoothed particle hydrodynamics modeling of hydraulic jumps2011Ingår i: Particle-based Methods – Fundamentals and Applications / [ed] E. Oñate; D.R.J. Owen, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2011, s. 490-501Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This study focus on Smoothed Particle Hydrodynamics (SPH) modeling of twodimensional hydraulic jumps in horizontal open channel flows. Insights to the complex dynamics of hydraulic jumps in a generalized test case serves as a knowledgebase for real world applications such as spillway channel flows in hydropower systems. In spillways, the strong energy dissipative mechanism associated with hydraulic jumps is a utilized feature to reduce negative effects of erosion to spillway channel banks and in the old river bed. The SPH-method with its mesh-free Lagrangian formulation and adaptive nature results in a method that handles extremely large deformations and numerous publications using the SPH-method for free-surface flow computations can be found in the literature. Hence, the main objectives with this work are to explore the SPH-methods capabilities to accurately capture the main features of a hydraulic jump and to investigate the influence of the number of particles that represent the system. The geometrical setup consists of an inlet which discharges to a horizontal plane with an attached weir close to the outlet. To investigate the influence of the number of particles that represents the system, three initial interparticle distances were studied, coarse, mid and fine. For all cases it is shown that the SPH-method accurately captures the main features of a hydraulic jump such as the transition between supercritical- and subcritical flow and the dynamics of the highly turbulent roller and the air entrapment process. The latter was captured even though a single phase was modeled only. Comparison of theoretically derived values and numerical results show good agreement for the coarse and mid cases. However, the fine case show oscillating tendencies which might be due to inherent numerical instabilities of the SPH-method or it might show a more physically correct solution. Further validation with experimental results is needed to clarify these issues.

  • 297.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Fracture and stress in powder compacts2006Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In the field of powder metallurgy (PM), the production methods are constantly developed and improved to produce components with high precision and strength. Cold uniaxial pressing of powder into a green body is a common process in PM. During uniaxial die powder pressing, the volume enclosed between the die and punches is reduced and the powder consolidates until a final height is obtained or a prescribed compacting pressure is reached. Desired properties of the green body are high strength, uniform density, no defects and narrow dimension tolerances. In the development process of new components finite element (FE) modelling and simulations are useful tools, especially to predict density distributions. Today, it is desired to include prediction of fracture and residual stress of powder compacts. The aim of this work is to increase the knowledge of the pressing process and its effect on green body properties. This includes a better understanding of residual stress development in the green body during pressing and the tensile fracture processes of unsintered powder. Both experimental and numerical investigations have been performed to gain knowledge in these fields. An elasto-plastic Cap model has been developed for powder pressing. To improve modelling of strength in the green state a density dependent failure envelope has been used. The model is implemented as a user material subroutine in a nonlinear finite element program. An inverse method is used to adjust the model behaviour to a water atomised metal powder. The fracture process of powder material is studied experimentally with diametral compression test. The properties of conventional and high velocity compacted (HVC) powder is also studied. Methods to determine the tensile strength and fracture energy in metal powder are presented. The test is virtually reproduced with finite element simulations. The residual stress field of a powder compacted rectangular bar is predicted with 3D and 2D finite element models. The effects of kinematics, friction, compacting pressures and die tapers have also been investigated. Numerical results show that the thickness of the small compressive residual stress region close to the side surface varies between 50 ìm and 600 ìm along the surface. Compacting pressure, "upper punch hold down" and die taper geometry have all a significant influence on the residual stress state while die wall friction has only a small influence. The numerical results are in agreement with results from X-ray and neutron diffraction measurements. The diametral compression test is an established method for measurement of the tensile strength in a brittle material. During the test a load, P, is applied along a diameter inducing compressive stresses. Stresses are tensile perpendicular to the compressed diameter. These tensile stresses act until failure. During fracturing a large crack along the compressive loaded diameter in the centre of the disc is visible. The crack development is studied with both experimental and numerical investigations. The results show that both tensile strength and fracture energy is strongly density dependent. A cohesive material behaviour is observed in the experiments. The central crack is virtually introduced in a finite element model and controlled with a proposed energy based fracture model. A numerical investigation of the tensile fracture process in powder compacts is performed and results are in agreement with experimental results. This work has given a better understanding of residual stress development in powder compacts. Another outcome from this work is a refined experimental method to determine tensile strength and fracture energy of powder material. An energy based fracture model is proposed for numerical simulations of tensile fracture in powder material.

  • 298.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling and simulation of powder pressing with consideration of residual stresses2004Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In powder metallurgy (PM), production methods are constantly developed and improved to produce component with high precision and strength. Cold uniaxial pressing of powder into a green body is a common process in PM. During uniaxial die powder pressing, the enclosed volume between the die and punches is reduced and the powder consolidates until a final height is obtained or a prescribed compacting pressure is reached. Desired properties of the green body are high strength, uniform density, no defects and tight dimension tolerances. For many cases it is beneficial to perform the design changes on the computer. In the development process are finite element (FE) modelling and simulations useful tools. Many of the commercial nonlinear FE codes available today can be used for powder pressing simulations. Some critical features in simulation of the powder pressing process are; material behaviour, large displacement, contact boundary conditions and friction variations. The aim of this work is to numerically capture and understand the development of residual axial stresses in the green body. The used constitutive model is based on a soil mechanical elasto-plastic model by DiMaggio-Sandler. The model has been refined for powder material behaviour. To improve modelling of strength in the green state a new density dependent failure envelope has been used. The model is implemented as a user material subroutine in the non-linear finite element program LS-DYNA. An inverse method is used to adjust the model to a water atomised metal powder from Höganäs AB. The residual stress field of a powder compacted rectangular bar is predicted, three dimensional and two dimensional finite element models are used. The influences of different kinematics, friction, compacting pressures and die tapers have also been investigated. Numerical results show that the thickness of the small compressive stress region close to the side surface varies between 50 to 600 micrometer along the surface. Compacting pressure, upper punch hold down and die taper geometry have all a significant influence on the residual stress state while die wall friction has only a small influence. The numerical results are in agreement with results from X-ray and neutron diffraction measurements.

  • 299.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Tensile fracture in high velocity compacted metal powder2007Ingår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 77-Konferensbidrag (Övrigt vetenskapligt)
  • 300.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Alatalo, Johanna
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Pålsson, Bertil
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Tano, Kent
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Prediction of contact forces between a grinding charge and mill lifters2009Ingår i: 12th European Symposium on Comminution and Classification ESCC 2009, 2009Konferensbidrag (Refereegranskat)
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