| 31. |
- 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
|
|
| 32. |
- Jonsén, Pär, et al.
(författare)
-
Modelling the non-linear elastic behaviour and fracture of metal powder compacts
- 2015
-
Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 284, s. 496-503
-
Tidskriftsartikel (refereegranskat)abstract
- In the powder metallurgy (PM) pressing process the mechanical properties of the green body are highly dependent on the material density. During the ejection stage of the pressing process the elastic behaviour is important especially for the crack formation in the powder compact. Experiments show a non-linear and also stress dependent elastic behaviour of green bodies. In this study diametral compression tests have been used to study elastic deformation during crack formation in a tensile fracture process of metal powder discs compacts. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite (uf-4) and 0.6% Kenolube. Tensile strength is used as a failure condition and limits the stress in the fracture interface. To control the tensile fracture, a cohesive zone model is used. The softening rate of the fracture model is obtained from the corresponding rate of the dissipated energy. The deformation of the powder material is modelled with an elastic-plastic cap model where an easy-to-use model for non-linearity in the elastic state due to stress is presented. The model is implemented in a finite element code and tested in simulation of a diametral compression testing. Results from simulations correlates well with experimental results and demonstrates the importance of including the non-linear elastic effect of the powder compacts. Results also show the necessity to accurate model the elasticity in the tooling to correct capture force-displacement response and fracturing processes.
|
|
| 33. |
- Kuroyanagi, Yuki, et al.
(författare)
-
Effects of aspect ratio and specimen size on uniaxial failure stress of iron green bodies at high strain rates
- 2015
-
Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 94
-
Tidskriftsartikel (refereegranskat)abstract
- Powder metallurgy is used for the production of a number of mechanical parts and is an essential production method. These are great advantages such as product cost effectiveness and product uniqueness. In general, however parts created by powder metallurgy have low strength because of low density. In order to increase strength as well as density, new techniques such as high-velocity-compaction (HVC) was developed and further investigation has been conducted on improvement of techniques and optimum condition using computer simulation. In this study, the effects of aspect ratio and specimen size of iron green bodies on failure strength of uniaxial compression and failure behavior were examined using a split Hopkinson pressure Bar. The diameters of specimens were 12.5 mm and 25 mm the aspect ratios (thickness/diameter) were 0.8 and 1.2.
|
|
| 34. |
- Larsson, Simon, et al.
(författare)
-
DEM-CFD Simulation of the Effect of Air on Powder Flow During Die Filling
- 2018
-
Ingår i: ABSTRACTS. - : IACM. ; , s. 1695-1695
-
Konferensbidrag (refereegranskat)abstract
- In the field of powder metallurgy (PM), complex components with complicated shapes can be manufactured. One important step in the PM process is the powder pressing process, where powder is consolidated during a forming operation into a desired shape, normally by applying pressure. During powder pressing, the mechanical properties of powder materials change dramatically. PM manufacturers tend to produce components with shapes of increasing complexity, requiring improved pressing equipment and methods. The most crucial aspect is to control the powder flow during die filling and the final powder density distribution after the filling stage, which has been shown to affect the strength of the final component significantly [1].To investigate the non-homogeneity of the density of PM components, experimental studies combined with numerical simulations of the die filling stage are exploited.This work covers the numerical modelling and simulation of die filling. The discrete element method (DEM) [2] was used to model the powder, and computational fluid dynamics (CFD) to model the air. To study the effect of air on powder flow, the DEM was coupled to the CFD using a two-way coupling approach. Experimental measurements with digital speckle photography (DSP) from a previous study [3] were used for comparison with the numerical simulations.The comparison of the DSP measurements and the numerical simulations showed similar macroscopic flow characteristics. Thus, the adequacy of the proposed DEM-CFD model has been demonstrated in a metal powder die filling operation. The DEM-CFD method has been shown to be an effective method for the numerical simulation of the interaction between powder and air. References[1] Zenger, D. & Cai, H. (1997). Handbook of the Common Cracks in Green P/M Compacts. Metal Powder Industries Federation, MPIF. Worcester, USA.[2] Cundall, P. A., & Strack, O. D. (1979). A discrete numerical model for granular assemblies. geotechnique, 29(1), 47-65.[3] Larsson, S., Gustafsson, G., Jonsén, P. & Häggblad, H.-Å. (2016). Study of Powder Filling Using Experimental and Numerical Methods. In: World PM2016 Congress & Exhibition, Hamburg, October 9-13, 2016.
|
|
| 35. |
|
|
| 36. |
- Larsson, Simon, et al.
(författare)
-
Experimental and numerical study of potassium chloride flow using smoothed particle hydrodynamics
- 2018
-
Ingår i: Minerals Engineering. - : Elsevier. - 0892-6875 .- 1872-9444. ; 116, s. 88-100
-
Tidskriftsartikel (refereegranskat)abstract
- Materials in granular form are widely used in industry and in the society as a whole. Granular materials can have various behaviours and properties. An accurate prediction of their flow behaviour is important to avoid handling and transportation issues. In this study, the flow behaviour of dry potassium chloride (KCl) in granular form was investigated experimentally and simulated numerically. The aim was to develop numerical tools to predict the flow of KCl in transportation and handling systems and granular material flow in various industrial applications. Two experimental setups were used to quantify the flow of KCl. In the first setup, the collapse of an axisymmetric granular column was investigated. In the second setup, digital image correlation was used to obtain velocity field measurements of KCl during the discharge of a flat-bottomed silo. The two experiments were represented numerically using two-dimensional computational domains. The smoothed particle hydrodynamics method was used for the simulations, and a pressure-dependent, elastic-plastic constitutive model was used to describe the granular materials. The numerical results were compared to the experimental observations, and an adequate qualitative and quantitative agreement was found for the granular column collapse and the silo discharge. Overall, the simulated flow patterns showed adequate agreement with the experimental results obtained in this study and with the observations reported in the literature. The experimental measurements, in combination with the numerical simulations, presented in this study adds to the knowledge of granular material flow prediction. The results of this study highlights the potential of numerical simulation as a powerful tool to increase the knowledge of granular material handling operations.
|
|
| 37. |
- Larsson, Simon, et al.
(författare)
-
Experimental methodology for study of granular material flow using digital speckle photography
- 2016
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 155, s. 524-536
-
Tidskriftsartikel (refereegranskat)abstract
- Granular material flow occurs in many industrial applications, and the characteristics of such flow is challenging to measure. Therefore, an experimental method that captures the flow behavior at different loading situations is desired.In this work, experimental measurements of granular material flow with digital speckle photography (DSP) are carried out. The granular flow process is recorded with a high-speed camera; the image series are then analyzed using the DSP method. This approach enables field data such as displacement, velocity, and strain fields to be visualized during the granular material flow process. Three different scenarios were studied: free surface flow in a fill shoe, flow without a free surface in a fill shoe, and the rearrangement of material in a cavity. The results showed that it is possible to obtain field data of the motion of particles for all three scenarios with the DSP technique. The presented experimental methodology can be used to capture complex flow behavior of granular material.
|
|
| 38. |
- Larsson, Simon, et al.
(författare)
-
Modelling and characterisation of the high-rate behaviour of rock material
- 2018
-
Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X.
-
Konferensbidrag (refereegranskat)abstract
- For future reliable numerical simulations of impact wear on steel structures caused by rock material, knowledge about the dynamic mechanical properties of rock material is required. This paper describes the experimental and numerical work to investigate the dynamic mechanical properties of diabase (dolerite), a subvolcanic rock material. In this study, diabase from southern Sweden was used. The impact compressive strength of diabase with a density of 2.63 g/cm3 was examined by using the split-Hopkinson pressure bar (Kolsky bar) method. Cylindrical specimens were used, with a diameter of 8.9 mm and a length of 14 mm. To characterise the rock material, uniaxial compression tests were performed, at high strain rates (150 s-1). Using an inverse modelling approach, material parameters for an elastic constitutive model, with a stress-based fracture criterion were determined. The constitutive model was used in a finite element simulation of a high strain rate uniaxial compression test. Results obtained from the numerical model were in line with the experimental results.
|
|
| 39. |
- Larsson, Simon, et al.
(författare)
-
Modelling of interaction between multi-phase fluid and mill structure in a tumbling mill
- 2015
-
Konferensbidrag (refereegranskat)abstract
- Free surfaces in fluid structure interaction (FSI) with multiple fluids are difficult to numerically predict. Hydro and wind power turbines and lubrication of mechanical components are examples of engineering applications where FSI can be important to consider. This work investigates the possibility to use a node (particle) based finite element method coupled to a standard finite elementmethod (FEM) to simulate a tumbling mill partly filled with a pulp fluid and the FSI between solid mill casing and pulp fluid. Modelling of wet milling is a complex multi-physics problem; wet milling is often used in the mining industry. For better understanding of the tumbling mill process numericalmethods can be used, and the process has previously been modelled with a combination of other numerical methods, [1]. The tumbling mill has four equally spaced lifters and measures Ø300 x 450 mm, see Fig. 1. A mixture of magnetite and water was filled to 30 % of the total volume of the mill. In this work, the mixture was considered as one homogeneous fluid with a density of 2500 kg/m3 and with a dynamic viscosity of 267 mPa∙s. Air in the tumbling mill was considered as a second fluid phase. In this work the mixing of air into the pulp fluid and its impact on the dynamics of the pulp phase is investigated.Experimentally measured driving torque from the laboratory tumbling mill was compared with numerically predicted torque from the multi-phase fluid simulations. It was clear that the node (particle) based finite element method, using multiple fluid phases and coupled to the FEM solver, was capable of predicting torque from FSI. It was also concluded that the interface between fluids with large differences in viscosity and density could be modelled.The interface tracking between air and magnetite pulp and the mixture of air into the magnetite pulp phase in the form of bubbles is shown in Fig. 2. From the experiments it was concluded that the pulp fluid had a tendency of sticking to the mill structure, this was also predicted by the multi-phase model as can be seen in Fig. 2.
|
|
| 40. |
- Larsson, Simon, et al.
(författare)
-
Numerical simulation and validation of powder filling using particle based methods
- 2017
-
Ingår i: PARTICLES 2017.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Powder pressing is a complicated process as the mechanical behaviour of the powder material changes with increasing density. Manufacturers tend to produce components with shapes of increasing complexity requiring improved pressing equipment and methods. Mechanical properties of powder materials changes dramatically from the beginning to the end of the compaction phase. Previous investigations have shown that powder transfer and large powder flow during filling affects the strength of the final component significantly. Combined experimental and numerical studies can improve the understanding of the impact the filling stage has on the final component, e.g. to explain the non-homogeneity of the density of powder pressed parts.This work covers numerical modelling and simulation of powder filling using two different approaches, the discrete element method (DEM) [1,2] which is a micro mechanical based method and the particle finite element method (PFEM) [3] which is a continuum based method. Experimental measurements with digital speckle photography (DSP) [4] from a previous study [5] are used to validate the numerical simulations. The numerical results are compared in terms of agreement with the experimental results, such as velocity- and strain field data. The numerical simulations are further compared in terms of computational efficiency.The comparison of DSP measurements and simulations gives similar flow characteristics. In conclusion, experimental measurements with DSP together with numerical simulation are powerful tools to increase the knowledge of powder filling and also to improve the numerical model prediction. Improved numerical models will facilitate future product development processes and decrease the lead time.
|
|
