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1.
  • Gustafsson, Gustaf, et al. (författare)
  • Determination of bulk properties and fracture data for iron ore pellets using instrumented confined compression experiments
  • 2013
  • Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 241, s. 19-27
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, an experimental method for measuring the bulk properties and fracture loading relations for iron ore pellets is presented. Knowledge on the bulk behaviour and fracture data for iron ore pellets is of great importance for improving the material transportation systems and to increase the product quality. Trustworthy numerical simulations of iron ore pellets also demand reliable materials data for the models. Here, instrumented confined compression tests are carried out at different load levels. Measurement data of the axial and radial stresses and the axial displacement are recorded for each test. Measurements of fractured iron ore pellets are carried out at different loads giving rise to crushing up to 20% of the total material. From the measured data, the Poisson´s ratio, the bulk modulus and a plastic strain hardening function are determined. In addition, friction measurements of iron ore pellets are carried out at different loads and configurations. In conclusion, the test method developed here is usable for the determination of the bulk properties and fracture characteristics of iron ore pellets.
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2.
  • Gustafsson, Gustaf, et al. (författare)
  • Experimental characterization of constitutive data of iron ore pellets
  • 2009
  • Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 194:1-2, s. 67-74
  • Tidskriftsartikel (refereegranskat)abstract
    • For trustworthy numerical simulations of iron ore pellets flow, knowledge about the mechanical properties of pellets is needed. In this work, an elastic-plastic continuum material model for blast furnace iron ore pellets is worked out from an experimental data. The equipment used is a Norwegian simple shear apparatus, designed for compression and shear test of granular material with a grain size less than 100 mm. It consists of a cylindrical cell filled with pellets surrounded by a rubber membrane and a rigid top and bottom. Two types of tests are performed. One test is pure compression and unloading and the second is shearing at different stress levels. Evaluation of these tests is performed and the elastic-plastic behaviour of iron ore pellets is characterized. Determined constitutive data are two elastic parameters and a yield function. The presented material model captures the major characteristics of the pellets even though it is too simple to completely capture the complex behaviour shown in the experiments.
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3.
  • Jonsén, Pär, et al. (författare)
  • Modelling of physical interactions between pulp, charge and mill structure in tumbling mills
  • 2015
  • Konferensbidrag (refereegranskat)abstract
    • To develop a tumbling mill model that includes the pulp fluid and its simultaneous interactions with both the charge and the mill structure is an interesting challenge. The interactions have previously been modelled for dry grinding with a combination of discrete element method (DEM) or smoothedparticle hydrodynamics (SPH) together with the finite element method (FEM). In such combination the DEM particles or SPH particles represent the grinding balls and FEM is used to model the mill structure. In this work, the previous model is extended to include fluids using SPH. Wet milling with water and a magnetite pulp, for graded and mono-size charges are numerically modelled and validated. The charge behaviour and its interaction with the mill structure are studied. An important part of the model is the coupling between DEM and SPH elements. Sliding and impact along the contacting interfaces are important for the response of the model. In the present work, the contact between the grinding balls and the pulp is realized using a penalty based “nodes to node” contact. The combined SPH-DEM-FEM model presented here can predict responses from the mill structure, as well as the pulp liquid flow and pressure. Validation is conducted by comparing numerical results with experimental measurements from grinding in an instrumented small-scale batch ball millequipped with an accurate torque meter. The simulated charge movement is also compared with high speed video of the charge movement for a number of cases. In conclusion, the SPH-DEM-FEM can predict the charge movement and driving torque with good agreement compared to experimental measurement for a wet tumbling mill process. In addition, the presented methodology is generic and can as well be applied to dry or wet stirred media mills of various configurations
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4.
  • Cante, J., et al. (författare)
  • PFEM-based modeling of industrial granular flows
  • 2014
  • Ingår i: Computational Particle Mechanics. - : Springer Science and Business Media LLC. - 2196-4378 .- 2196-4386. ; 1:1, s. 47-70
  • Tidskriftsartikel (refereegranskat)abstract
    • The potential of numerical methods for the solution and optimization of industrial granular flows problems is widely accepted by the industries of this field, the challenge being to promote effectively their industrial practice. In this paper, we attempt to make an exploratory step in this regard by using a numerical model based on continuous mechanics and on the so-called Particle Finite Element Method (PFEM). This goal is achieved by focusing two specific industrial applications in mining industry and pellet manufacturing: silo discharge and calculation of power draw in tumbling mills. Both examples are representative of variations on the granular material mechanical response—varying from a stagnant configuration to a flow condition. The silo discharge is validated using the experimental data, collected on a full-scale flat bottomed cylindrical silo. The simulation is conducted with the aim of characterizing and understanding the correlation between flow patterns and pressures for concentric discharges. In the second example, the potential of PFEM as a numerical tool to track the positions of the particles inside the drum is analyzed. Pressures and wall pressures distribution are also studied. The power draw is also computed and validated against experiments in which the power is plotted in terms of the rotational speed of the drum.
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5.
  • Gustafsson, Gustaf, et al. (författare)
  • Characterization modelling and validation of a two-point loaded iron ore pellet
  • 2013
  • Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 235, s. 126-135
  • Tidskriftsartikel (refereegranskat)abstract
    • Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different stresses, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental and numerical work to investigate the mechanical properties of blast furnace iron ore pellets. To study the load deformation behaviour and the fracture of iron ore pellets, a number of point load tests are carried out and analysed. Material parameters for an elastic–plastic constitutive model with linear hardening for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. Two finite element models are developed for different purposes. For the material parameter determination, a perfectly spherical model is used. The constitutive model is validated with a finite element model based on a representative optically scanned iron ore pellet. The proposed constitutive model is capturing the force displacement relation for iron ore pellets in a two-point load test. A stress based fracture criterion which takes the triaxiality into account is suggested and calculated as the maximum equivalent effective stress dependent on the three principal stresses at fracture. The results of this study show that the equivalent effective stress in the vicinity of the centre of an irregular model of an iron ore pellet is very close to the results of a model of a perfectly spherical iron ore pellet. The proposed fracture criterion indicates fracture in the representative iron ore pellet model coincident with the location of the crack developed during the test of the optically scanned iron ore pellet.
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6.
  • Gustafsson, Gustaf, et al. (författare)
  • Comparison of smoothed particle method and particle finite element method in applied granular flow problems
  • 2009
  • Ingår i: Particle-Based Methods. - Barcelona : International Center for Numerical Methods in Engineering (CIMNE). - 9788496736825 ; , s. 204-207
  • Konferensbidrag (refereegranskat)abstract
    • Traditionally, discrete element (DE) method and finite element (FE) method are used in numerical simulation of granular flow problems. A drawback with the (DE) method is the limitations in modelling the extreme large number of particles, which normally are in real granular flow problems. With a numerical method based on continuum mechanics modelling like the FE-method, the problems can be solved with less computation particles. However, the limitations of the FE-method have been pointed out to be when extremely large deformation needs to be captured. Granular flow problem motions produce large distortions of the mesh and ruin the convergence of the problem. The purpose of this paper is to compare two alternative continuum based methods, the Particle Finite Element Method (PFEM) and the Smoothed Particle (SP) method, to model two different granular flow problems.
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7.
  • Gustafsson, Gustaf, et al. (författare)
  • Experimental studies and modelling of high-velocity loaded iron-powder compacts
  • 2014
  • Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 268, s. 293-305
  • Tidskriftsartikel (refereegranskat)abstract
    • A production technique with the capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts is high-velocity compaction (HVC). To extend the usage of the HVC method, detailed knowledge of the HVC process is important. To facilitate the development of production processes, numerical simulations can be utilised. In the development of high-precision simulation models, constitutive data of HVC specimens at high strain rates are required. In this study, the dynamic compressive properties of cylindrical specimens made by HVC were measured using a split Hopkinson pressure bar (Kolsky bar) assembly. For this technique, a specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of the input bar and generates elastic-wave propagation.The powder material used for the experiments is a press-ready iron-based premix. Among specimens made by HVC and conventional compaction (CC), the effects of the specimen density and the strain rate on the compressive properties, such as failure stress, Young´s modulus and failure behaviour, are investigated. During dynamic compression, the failure behaviour of the specimens was also recorded using a high-speed video camera. The difference in the mechanical behaviour between HVC-pressed specimens and conventionally pressed specimens are also investigated. The stress–strain curves of HVC-pressed specimens are identical to those of conventionally pressed specimens, but the failure behaviour differs are concluded.A well-established numerical method for forming simulations also conducted for powder compaction is the finite element method (FEM). The impact loading of the powder is modelled and simulated using nonlinear three-dimensional FEM. To model the impact process, a constitutive relation for the powder behaviour is proposed, taking into account the strain rate and density variations. To capture the global response caused by cracking during impact, a damage model is implemented. The numerical results in terms of the stress and strain history in the specimen during impact are compared with the experimental measurements. In conclusion, the proposed material model captures the increase in the yield stress due to the higher strain rates and the decrease in stress due to cracking.
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8.
  • Gustafsson, Gustaf, et al. (författare)
  • Fracture probability modelling of impact-loaded iron ore pellets
  • 2017
  • Ingår i: International Journal of Impact Engineering. - : Elsevier. - 0734-743X .- 1879-3509. ; 102, s. 180-186
  • Tidskriftsartikel (refereegranskat)abstract
    • Blast furnace iron ore pellets are sintered, centimetre-sized ore spheres with a high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In transporting pellets from pelletizing plants to customers, iron ore pellets are exposed to different static and dynamic loading situations, resulting in strength degradation and, in some cases, fragmentation. This can lead to a reduced gas flow in the blast furnace, which causes reduced quality in steel production. Reliable numerical simulations that can predict the ability of the pellets to endure their handling are important tools for optimizing the design of equipment for iron ore handling. This paper describes the experimental and numerical work performed to investigate the impact fracture behaviour of iron ore pellets at different strain rates. A number of split Hopkinson pressure bar tests with different striker velocities are carried out and analysed to investigate the strain rate dependency of the fracture strength of iron ore pellets. Fracture data for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. A stress based, strain-rate dependent fracture model that takes triaxiality into account is suggested. The fracture model is used and validated with impact tests of iron ore pellets. In the validation experiment, iron ore pellets are fired against a steel plate, and the percentage of fractured pellets at different impact velocities are measured. Finite element simulations of the experiment are carried out and the probability of pellets fracturing during impact are calculated and compared with the experimental results. The agreement between the experiments and numerical simulations shows the validity of the model.
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9.
  • Gustafsson, Gustaf, et al. (författare)
  • High-rate behaviour of iron ore pellet
  • 2015
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 94
  • Tidskriftsartikel (refereegranskat)abstract
    • Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different loading situations, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental work to investigate the dynamic mechanical properties of blast furnace iron ore pellets. To study the dynamic fracture of iron ore pellets a number of split Hopkinson pressure bar tests are carried out and analysed
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10.
  • Gustafsson, Gustaf, et al. (författare)
  • Mechanical characterization and modelling of the temperature-dependent impact behaviour of a biocompatible poly(L-lactide)/poly(ε-caprolactone) polymer blend
  • 2015
  • Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161 .- 1878-0180. ; 51, s. 279-290
  • Tidskriftsartikel (refereegranskat)abstract
    • Poly(ε-caprolactone) (PCL) is a ductile, bioabsorbable polymer that has been employed as a blend partner for poly(L-lactic acid) (PLLA). An improvement of the material strength and impact resistance of PLLA/PCL polymer blends compared to pure PLLA has been shown previously. To use numerical simulations in the design process of new components composed of the PLLA/PCL blend, a constitutive model for the material has to be established. In this work, a constitutive model for a PLLA/PCL polymer blend is established from the results of compressive tests at high and low strain rates at three different temperatures, including the body temperature. Finite element simulations of the split Hopkinson pressure bar test using the established constitutive model are carried out under the same condition as the experiments. During the experiments, the changes in the diameter and thickness of the specimens are captured by a high-speed video camera. The accuracy of the numerical model is tested by comparing the simulation results, such as the stress, strain, thickness and diameter histories of the specimens, with those measured in the experiments. The numerical model is also validated against an impact test of non-homogenous strains and strain rates. The results of this study provide a validated numerical model for a PLLA/PCL polymer blend at strain rates of up to 1800 s−1 in the temperature range between 22 °C and 50 °C.
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  • Resultat 1-10 av 38

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