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Percussive rotary drilling is recognized as the most efficient method for hard rock drilling. Despite clear advantages over conventional rotary methods, there are still some uncertainties associated with percussive drilling. For geothermal applications, drilling accounts for a large portion of the total cost. Specifically, the wear of drill bits when drilling in hard rock is a predominant cost factor and drilling parameters are often based on the experience of the field operator. Within the framework of the H2020 project GEOFIT, numerical simulations of percussive drilling are performed in order to evaluate the rock drilling process and gain insight about the trade-off between wear and Rate of Penetration (ROP). In the simulations, the rock material was represented by the Bonded Discrete Element Method (BDEM), the drill bit by the Finite Element Method (FEM), the drilling fluid by the Particle Finite Element Method (PFEM) and the abrasive wear on the surface of the drill bit was represented by Archard’s wear law. The drilling simulations were conducted for two rock materials; a sedimentary rock material corresponding to what was found when drilling at the GEOFIT pilot site in Aran Islands, Ireland, and a harder reference rock similar to granite. The results show that, at a drill bit impact force of 10 kN, the ROP in the sedimentary rock was 6.3 times faster than for granite. When increasing the impact force to 40 and 50 kN, however, the ROP for the sedimentary rock is only 1.9 and 1.6 times faster, respectively. Furthermore, the wear rate decreased with increased impact force when drilling in the granite rock. For the sedimentary rock, however, the loading resulting in the best trade-off between abrasive wear and ROP was the second highest loading of 40 kN, which suggests that an increase in impact energy may increase the rate of penetration but may not be economically motivated. Raw datais available for download here.

For the reduction of the environmental footprint of Heavy-Duty vehicles (HDV), lighter chassis components can be considered. A lighter HDV chassis gives the opportunity of lower fuel consump-tion, increased payloads, and savings of material resources. One way of achieving this, is to reduce thicknesses of components in combination of using higher strength steels. For the aim of forming UHSS into complex geometries the need to characterize thick sheet metal at elevated temperatures arises. This work aims at expanding earlier research of characterization of thinner sheet metal and create a testing methodology for tensile tests of 7 mm thick steel sheets at elevated temperatures. An experimental methodology for evaluating high strength steel under warm conditions have been de-veloped and demonstrated. A Digital Image Correlation system is used to extract strain fields for all three testing temperatures. This together with an automatized induction system pre-defined temperature cycles are applied. When the desired Hollomon-Jaffe constant is obtained the tensile test is executed. The methodology shows promising results with good repeatability of stress-strain curves. The methodology shows good stability and are promising for future development and investigations of high strength steels under warm forming conditions., This research has been funded by the Research Fund for Coal and Steel, Project: WarmLight, Grant Agreement: 800649.

The automotive industry is currently adapting to a new reality, where anthropogenic emissions need to decrease significantly. To meet present and future demands of vehicle design, press harden-ing techniques to produce complex geometries with high strength and ductility as well as good precision are of great interest. New generations of hot forming steels enable both further weight reductions by using thinner sheets as well as better crash performance due to its ability to improve the structural integrity of the body-in-white. To promote the use of these new steel grades, it is important to study their performance using well-instrumented lab scale test of full-scale compo-nents. Since these tests are often time consuming and expensive, calibrating constitutive models with tensile specimens and using finite element analysis is a more cost-effective alternative. How-ever, these calibrated models should be validated against full-scale experiments to verify their effectiveness in predicting the material behaviour in complex crash environments. In this paper, a high-speed 3D digital image correlation experiment is performed on a crash box under axial com-pression. The material is a hot forming steel grade with a specified tensile strength of 1000 MPa. The axial crash tests are modelled based on a visco-plastic model calibrated by high-speed tensile tests. The computed results in terms of force response and obtained deformations agree well with the corresponding measurements.

Numerical modelling of the fracture of heterogeneous brittle materials is of interest for several industries, such as rock excavation and comminution applications. A numerical model of brittle materials needs to be able to capture the unpredictable results, e.g. with regards to measured strength and fracture pattern, as observed experimentally. In a previous work [1], the Bonded Discrete Element Method [2] was combined with statistical methods in order to generate heterogeneous rock bodies. Grains of random sizes and shapes, consisting of multiple bonded discrete elements, were generated in the body and the micromechanical parameters of these grains were governed by the Weibull distribution [3]. In this work, this modelling approach was used to evaluate the fracture behaviour of experiments commonly found within the field of rock mechanics - the unconfined and confined axial compression test, Brazilian disc test and the three point bend test. For each test, a large set of numerical samples were generated and simulated. The fracture behaviour, e.g. initiation, propagation and coalescence of cracks, were investigated for different levels of heterogeneity and grain cement strengths. The results show that a variety of different fracture modes can be obtained with this modelling approach. Further, the results suggests that the statistical methods employed in this work improves the versatility of the Bonded Discrete Element Method for rock modelling. ISBN för värdpublikation: 978-84-123222-8-6

Failure in industrial processes is often related to wear and can cause significant problems. It is estimated that approximately 1–4% of the gross national product for an industrialized nation is related to abrasive wear. This work aims to numerically predict development of wear for full-scale mining applications in harsh sub-arctic conditions. The purpose is to increase the understanding of wear development in industrial processes and optimize service life and minimize costs related to wear. In the present paper, a granular material model consisting of the discrete element method (DEM) and rigid finite element particles is utilized to study wear in full-scale mining applications where granular materials and steel structures are present. A wear model with the basis in Finnie’s wear model is developed to calculate wear from combined abrasive sliding and impact wear. Novel in situ full-scale experiments are presented for calibration of the wear model. A simulation model of the rope shovel loading process is set up where the bucket filling process is simulated several times, and the wear is calculated with the calibrated wear model. From the full-scale validation, it is shown that the simulated wear is in excellent agreement when compared to the experiments, both regarding wear locations and magnitudes. After validation, the model is utilized to study if wear can be minimized by making small changes to the bucket. One major conclusion from the work is that the presented wear simulator is a suitable tool that can be used for product development and optimization of the loading process. Validerad;2021;Nivå 2;2021-06-16 (alebob);Finansiär: KIC RawMaterials (17152)

Modeling of wet stirred media mill processes is challenging since it requires the simultaneous modeling of the complex multiphysics in the interactions between grinding media, the moving internal agitator elements, and the grinding fluid. In the present study, a multiphysics model of an HIG5 pilot vertical stirred media mill with a nominal power of 7.5 kW is developed. The model is based on a particle-based coupled solver approach, where the grinding fluid is modeled with the particle finite element method (PFEM), the grinding media are modeled with the discrete element method (DEM), and the mill structure is modeled with the finite element method (FEM). The interactions between the different constituents are treated by loose (or weak) two-way couplings between the PFEM, DEM, and FEM models. Both water and a mineral slurry are used as grinding fluids, and they are modeled as Newtonian and non-Newtonian fluids, respectively. In the present work, a novel approach for transferring forces between grinding fluid and grinding media based on the Reynolds number is implemented. This force transfer is realized by specifying the drag coefficient as a function of the Reynolds number. The stirred media mill model is used to predict the mill power consumption, dynamics of both grinding fluid and grinding media, interparticle contacts of the grinding media, and the wear development on the mill structure. The numerical results obtained within the present study show good agreement with experimental measurements. Validerad;2021;Nivå 2;2021-02-09 (alebob);Finansiär: KIC RawMaterials (17152)

Numerical modelling of the fracture of heterogeneous brittle materials is of interest for several industries,such as rock excavation and comminution applications. A numerical model of brittle materials needs tobe able to capture the unpredictable results, e.g. with regards to measured strength and fracture pattern,as observed experimentally. In this study a new approach, based on the Parallel Bond Model (PBM) [1] and theWeibull distribution, for modelling brittle heterogeneous materials in 3D is proposed and appliedto the Brazilian Disc Test (BDT) [2]. The PBM is used to generate irregular grains with varying bondstrengths and stiffnesses. For the grain generation, a parent particle is chosen at random in the rockbody and a randomized ellipsoid is generated around the particle. The mean grain bond stiffnesses andstrengths are associated with the grain and all particles within the ellipsoid surface are bonded togetherwithin +/- 10 % of these mean values. Further, the bond parameters of the cement between a grain andits neighbours is scaled based on the mean grain properties. An example of a generated sample is shownin Figure 1 a). In order to evaluate the model, a series of simulations of the BDT were conducted.The effects of the Weibull heterogeneity index and cement strengths on the predicted tensile strengthand crack pattern were evaluated. Specifically, the initiation, propagation, coalescence and branching ofcracks were examined in detail. Apart from demonstrating challenges with the BDT, the results also showthat the proposed model is able to capture key phenomena related to brittle heterogeneous materials, suchas unpredictable fracture pattern and a large variation in tensile strength, see Figure 1 b-c). Horizon 2020 (grant no. 792210) GEOFIT

Machining of metals is an essential operation in the manufacturing industry. Chip formation in metal cutting is associated with large plastic strains, large deformations, high strain rates and high temperatures, mainly located in the primary and in the secondary shear zones. During the last decades, there has been significant progress in numerical methods and constitutive modeling for machining operations. In this work, the Particle Finite Element Method (PFEM) together with a dislocation density (DD) constitutive model are introduced to simulate the machining of Ti-6Al-4V. The work includes a study of two constitutive models for the titanium material, the physically based plasticity DD model and the phenomenology based Johnson&ndash, Cook model. Both constitutive models were implemented into an in-house PFEM software and setup to simulate deformation behaviour of titanium Ti6Al4V during an orthogonal cutting process. Validation show that numerical and experimental results are in agreement for different cutting speeds and feeds. The dislocation density model, although it needs more thorough calibration, shows an excellent match with the results. This paper shows that the combination of PFEM together with a dislocation density constitutive model is an excellent candidate for future numerical simulations of mechanical cutting.

Harshwork

Harshwork

Electron beam melting (EBM) is emerging as a promising manufacturing process where metallic components are manufactured from three-dimensional (3D) computer aided design models by melting layers onto layers. There are several advantages with this manufacturing process such as near net shaping, reduced lead times and the possibility to decrease weight by topology optimization, aspects that are of interest for the aerospace industry. In this work two alloys, Ti-6Al-4V and Alloy 718, widely used within the aerospace industry were investigated with X-ray microtomography (XMT), to characterize defects such as lack of fusion (LOF) and inclusions. It was furthermore possible to view the macrostructure with XMT, which was compared to macrostructure images obtained by light optical microscopy (LOM). XMT proved to be a useful tool for defect characterization and both LOF and un-melted powder could be found in the two investigated samples. In the EBM built Ti-6Al-4V sample high density inclusions, believed to be composed of tungsten, were found. One of the high-density inclusions was found to be hollow, which indicate that the inclusion stems from the powder manufacturing process and not related with the EBM process. By performing defect analyses with the XMT software it was also possible to quantify the amount of LOF and un-melted powder in vol%. From the XMT-data meshes were produced so that finite element method (FEM) simulations could be performed. From these FEM simulations the significant impact of defects on the material properties was evident, as the defects led to high stress concentrations. It could moreover, with FEM, be shown that the as-built surface roughness of EBM material is of importance as high surface roughness led to increased stress concentrations.

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.

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. During transportation and handling of iron ore pellets they are exposed to different loads, resulting in degradation of the strength and in some cases fragmentation. The aim of this work is to increase the knowledge of how to design the handling systems for iron ore pellets to decrease the amount of fractured materials in the flows. A numerical finite element model for iron ore pellets fracture probability analysis is presented with a stress based fracture criterion. The model is used to simulate different flows of iron ore pellets hitting guide plates and to predict the proportion of fractured iron ore pellets in the flow. The amount of fractured iron ore pellets are predicted at different flow velocities, showing good agreement with experimental measurements.

In this work a Lagrangian nite element approach for simulation of metalforming is presented, based on the so-called Particle Finite Element Method (PFEM). Thegoverning equations for the deformable bodies are discretized with the FEM via a mixedformulation using simplicial elements with equal linear interpolation for displacements,pressure and temperature. The use of PFEM for modeling of metal forming processesincludes the use of a remeshing process, -shape concepts for detecting domain boundaries,contact mechanics laws and material constitutive models. The merits of the formulationare demonstrated in the solution of 2D thermally coupled metal forming processes usingthe particle nite element method. The method shows good results and is a promisingmethod for future simulations of thermally/coupled forming processes.

Godkänd; 2014; 20140813 (parj)

Godkänd; 2014; 20140813 (parj)

Godkänd; 2014; 20140813 (parj)

Godkänd; 2014; 20140813 (parj)

Transportation and storage are important parts in the process chain for producers of iron ore pellets. Knowledge and optimization of these processes are very important for further efficiency progress and increased product quality. The existence of a numerical simulation tool with accurate material characteristics will significantly increase the possibility to predict critical forces in developing new and existing transportation and storing systems and thereby decrease the amount of damaged, fractured or crushed pellets (fines). In this work modelling and simulation of iron ore pellets are carried out at different length scales. An elastic plastic granular continuum flow model for iron ore pellets using smoothed particle (SP) method is presented [1]. The model is used to model iron ore pellets silo flow. A finite element (FE) model of single iron ore pellets is also worked out with statistical data for an elastic plastic constitutive model with a fracture criterion [2]. The model is used to simulate loading and fracture on single iron ore pellets and is validated with a two point load test. In order to find the relation between the behaviour of iron ore pellets at different length scales, e.g. compare the stresses in a silo to the critical stress inside a single iron ore pellet, modelling of iron ore pellets on an intermediate length scale is established. A multi particle finite element model (MPFEM) consisting of individual discretized models of the iron ore pellets is here presented [3]. An instrumented confined compression tests is developed for measuring the global response on a limited amount of iron ore pellets [4]. The experiment is used to validate the MPFEM model in terms of the amount of broken pellets. Godkänd; 2013; 20131003 (gusgus)

Godkänd; 2013; 20130521 (ysko)

Few studies have been conducted to investigate the strain rate behavior of metal powders. To achieve better understanding of the strain rate dependency of metal powders, it's necessary to conduct dynamic experiments and numerical simulations e.g. using finite element method. High strain rate experiments of iron powder material have been conducted using the split Hopkinson pressure bar method [1]. The dynamic testing is performed using a modified split Hopkinson pressure bar (Kolsky bar). 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. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite and 0.6% Kenolube. This process is modeled and simulated by using finite element method. In order to model the impact process a constitutive relation describing the powder behavior taking into account the strain-rate and density variations are proposed [2]. The stress and strain history in the specimen during impact is validated against the experimental measurements. To capture the global response caused by cracking during impact, a failure criterion is implemented. In conclusion, the proposed material model captures the increase in yield stress due to higher strain rates and the decrease in stress due to cracking. Godkänd; 2013; 20131003 (gusgus)

In the field of powder metallurgy, high velocity compaction (HVC) is a production technique with capacity to improve the mechanical properties of powder metallurgy parts because high density of powder metallurgy parts can be achieved in less than 0.5 s [1, 2]. In order to extend the usage of the HVC method, detailed knowledge of the HVC process is important. To facilitate development of production processes, numerical simulations can be utilized. A common numerical method for powder compaction is the finite element method (FEM). To conduct on FEM simulation precisely, constitutive data of HVC specimens at high strain-rate are required [3, 4]. In this study, the dynamic compressive properties of cylindrical specimens made by HVC were measured using a Spit Hopkinson Pressure Bar (Kolsky bar). The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite (uf-4) and 0.6% Kenolube. During dynamic compression, the failure behavior of specimens was also observed using a high speed video camera. The experimental results, such as failure stress, Young’s modulus and failure behavior, of dynamic compressive tests were compared with those of static compressive tests. Among specimens made by HVC and Conventional Compaction (CC), the effects of specimen density, 6.9, 7.2 and 7.4 g/cm3, on the compressive properties and failure behavior were also examined. For each density, the difference in the failure behavior between HVC-pressed specimens and conventional pressed specimens was observed, whereas stress-strain curves of HVC-pressed specimens were the same as conventional pressed specimens. Moreover, the effects of specimen size on failure behavior and stress-strain curves of specimens were examined. Godkänd; 2013; 20131003 (gusgus)

Godkänd; 2012; 20121030 (andbra)

Godkänd; 2011; 20110816 (ysko)

Physically realistic methods are a necessity to close the gap between reality and numerical result in modelling of tumbling mills. A problem is that tumbling mills often operate in a metastable state because of the difficulty to balance the rate of replenishment of large ore particles from the feed with the consumption in the charge. Understanding of the charge motion within the mill is of significance in mill optimisation. Both the breakage of ore particles and the wear of liners/ball media are closely linked to the charge motion. In this work, a ball charge and its interaction with the mill structure is modelled with the smoothed particle hydrodynamic (SPH) method. The mesh free formulation and the adaptive nature of the SPH method result in a method that handles extremely large deformations and thereby suits modelling of grinding charges and pulp liquids. The flexible rubber lifter and the lining are modelled with the finite element method (FEM). A hyper-elastic model governs the elastic behaviour of the rubber. The comminution process is complex and to include all phenomena that occur in a single numerical model is today not possible. Therefore, modelling the physical interaction between charge, mill structure and pulp liquid is the major goal in this work. The SPH-FEM model can predict responses of the mill structure e.g. stress and strain. All parts of the mill system will affect its response and the model gives the opportunity to study the influence of the mill structure and e.g. pressure and shear stresses in the charge. This computational model also makes it possible to predict, the contact forces for varying mill dimensions, liner combinations and pulp densities. By comparing numerical results with experimental measurement from grinding in a pilot mill equipped with an instrumented rubber lifter a validation is done. The deflection profile of the lifters obtained from SPH-FEM simulation shows a reasonably good correspondence to pilot mill measurements as measured by an embedded strain gauge sensor. This model gives information on the grinding process in tumbling mills and better correlation with experimental measurements. Godkänd; 2011; 20111110 (ysko)

Godkänd; 2011; 20110915 (patjon)

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. Godkänd; 2011; 20110916 (gusgus)