| 1. |
- Gustafsson, Gustaf, et al.
(författare)
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Characterization modelling and validation of a two-point loaded iron ore pellet
- 2013
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Ingår i: Powder Technology. - Elsevier S.A.. - 0032-5910. ; 235
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Tidskriftsartikel (övrigt vetenskapligt)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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| 2. |
- Gustafsson, Gustaf, et al.
(författare)
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Comparison of smoothed particle method and particle finite element method in applied granular flow problems
- 2009
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Ingår i: Particle-Based Methods : Fundamentals and Applications. - Barcelona : International Center for Numerical Methods in Engineering. - 978-84-96736-82-5 ; 204-207
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Annan publikation (populärvet., debatt m.m.)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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| 3. |
- Gustafsson, Gustaf, et al.
(författare)
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Determination of bulk properties and fracture data for iron ore pellets using instrumented confined compression experiments
- 2013
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Ingår i: Powder Technology. - Elsevier S.A.. - 0032-5910. ; 241
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Tidskriftsartikel (övrigt vetenskapligt)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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| 4. |
- Gustafsson, Gustaf, et al.
(författare)
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Experimental characterization of constitutive data of iron ore pellets
- 2009
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Ingår i: Powder Technology. - Elsevier S.A.. - 0032-5910. ; 194:1-2
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Tidskriftsartikel (övrigt vetenskapligt)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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| 5. |
- Gustafsson, Gustaf, et al.
(författare)
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Modelling and simulation of high velocity loaded iron powder
- 2012
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Ingår i: Powder Metallurgy World Congress & Exhibition.
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Konferensbidrag (övrigt vetenskapligt)abstract
- High velocity compaction is a production technique with capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts. The dynamic testing is performed using a modified split Hopkinson pressure bar (SHPB). 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 an input bar creating elastic wave propagation. This process is modelled and simulated by using finite element method. The stress and strain history in the specimen during impact are compared with the evaluated experimental values from the strain measured on the input and output bars. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite and 0.6% Kenolube. In order to model the impact process a constitutive relation describing the powder behaviour taking into account the strain-rate and density variations are proposed. In conclusion, the proposed material model captures the increase in yield stress due to higher strain rates.
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| 6. |
- Gustafsson, Gustaf, et al.
(författare)
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Multi-particle finite element modelling of the compression of iron ore pellets with statistically distributed geometric and material data
- 2013
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Ingår i: Powder Technology. - Elsevier S.A.. - 0032-5910. ; 239
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- The multi-particle finite element method (MPFEM) is used to simulate confined compression of iron ore pellets. The confined compression test consists of a cylindrical steel tube and two compressive platens. The iron ore pellets are confined by the tools and compressed. In the MPFEM model of the test, the iron ore pellets are represented by 1680 finite element (FE) discretised particles (7-16 mm). The size, shape and material properties of the pellets are statistically distributed. The contacts are modelled using the penalty stiffness method and Coulomb friction. The compression is simulated in two steps. In the first step, the iron ore pellet models are sparsely placed in the computational model of the steel tube and a gravity-driven simulation is conducted to make the pellets arrange themselves randomly. In a second step, the compression is simulated by a prescribed motion of the upper compressive platen. From the MPFEM simulation, the stresses inside the individual pellet models are evaluated, and the fracture probability of the iron ore pellets is derived and compared with experimental data. In addition, data on the global axial and radial stresses and axial displacement are presented and compared with experimental confined compression test data. The MPFEM model can reproduce the fracture ratio of iron ore pellets in uniaxial confined compression and is a feasible method for virtual fracture experiments of iron ore pellets.
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| 7. |
- Gustafsson, Gustaf, et al.
(författare)
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Simulation of metal powder die filling processes using smoothed particle hydrodynamics method
- 2007
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Ingår i: Proceedings : PM in Toulouse - at the forefront of european technology; 15 - 17 October 2007, Pierre Baudis Congress Centre, Toulouse, France. - Shrewsbury : European powder metallurgy association. - 978-1-899072-31-6 ; 3 : Powder pressing : sintering ; full density & alternative consolidation ; modelling ; secondary & finishing operations
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Annan publikation (populärvet., debatt m.m.)abstract
- The die filling is an important stage in the manufacturing process of powder metallurgical components as proceeding stages are influenced by the powder distribution achieved by the filling process. Numerical simulation is a powerful tool in process development and can be used to increase the knowledge about the filling behaviour. In this work smoothed particle hydrodynamics (SPH) method is used to simulate shoe filling of metal powder into simple and stepped dies. An elastic-plastic material model is used as constitutive model where the material parameters are estimated using results from filling rate experiments and loose powder shear tests. The powder flow behaviour and packing density is simulated and compared with experimental results. The results indicate that SPH simulations can capture major observed features of powder die filling.
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| 8. |
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| 9. |
- Gustafsson, Gustaf, et al.
(författare)
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Simulation of stresses in iron ore pellets for confined compression-tests using the multi particle finite element method
- 2011
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Ingår i: Svenska mekanikdagar 2011.
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Konferensbidrag (övrigt vetenskapligt)abstract
- Numerical simulation of the compaction of granular materials is an area of active research. One approach is to use deformable discrete elements of the individual particles using a 2D finite element (FE) mesh, see e.g. [1] and [2]. In this work, the axial compression of iron ore pellets inside a steel cylinder is studied and the individual particles are discretized with a coarse FE mesh in 3D. One possibility of this model is to study the stresses and strains inside the granular particles. Experiment and simulation of iron ore pellets in a confined compression test are done. The experiment consists of an upper and lower piston of thick circular steel plates surrounded by a 2 mm steel cylinder containing the iron ore pellets. The total mass of the iron ore pellets is 46.0kg. During a test, an axial load is applied on the lower piston to a certain level and then unloaded. Measured data are the force and displacement of the lower piston. In addition, strain gauges are measuring the circumferential strain in the middle of the steel membrane. Experimental compression tests between two plates of 18 randomly chosen iron ore pellets were done in order to characterize the load displacement behaviour of the individual pellets. FE models of the experimental tested pellets were carried out and simulated. Each pellet was discretized with an eight-node FE mesh. An elasto-plastic material model with linear hardening is used. The Young’s modulus, the plastic hardening modulus, and the yield stress of the material model were found by inverse modelling. Different material parameters were tested systematically in the FE model and compared with the experimental results until the same load displacement curve was obtained. A multi particle finite element model (MPFEM) was used to simulate the confined compression test. The iron ore pellets are represented in a quarter-model of the real experimental setup by 4756 discretized particles (7-16 mm) with a normal distribution measured from size distribution in the experiment. The contacts are modelled with the penalty stiffness method. The pistons are considered rigid in the simulation and the steel cylinder is modelled with thin elastic shell elements. The compression is simulated in two steps. In the first step, the iron ore pellets models are randomly sparse placed the cylinder and a gravity driven simulation is carried out where the pellets are arranged in the cylinder. In the second step, the compression is simulated by a prescribed displacement of the upper piston. Compared data from the experiment and simulation are; fill density, force-displacement curve and circumferential strain. A relation between the global stress state from the loading of the piston and the maximum stresses inside the individual iron ore pellets was carried out from the simulation. References [1] A.T. Procopio, A. Zavaliangos. “Simulation of multi-axial compaction of granular media from loose to high relative densities”, Journal of the Mechanics and Physics of Solids, 53 pp. 1523-1551, 2005. [2] D.T. Gethin, R.S. Ransing, R.W. Lewis, M. Dutko, A.J.L. Crook, “Numerical comparison of a deformable discrete element model and an equivalent continuum analysis for the compaction of ductile porous material”, Computers and Structures, 79 pp. 1287-1294, 2001.
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