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  • 1.
    Aspenberg, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Larsson, Rikard
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    An evaluation of the statistics of steel material model parameters2012In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 6, p. 1288-1297Article in journal (Refereed)
    Abstract [en]

    In robustness studies, variations of material properties are often represented by simple assumptions, such as scaling of stress-strain relations, often due to lack of knowledge or deeper understanding of the material physics and the material model applied. By performing material characterisation tests on several batches of a DP600 steel and fitting a phenomenological material model to each batch, this paper studies the dispersion of material model parameters, as well as correlations between both experimental and model parameters. It is concluded that some of the charcterisation tests may be omitted in the future, due to correlations found between parameters. The results may also be applied in a robustness study by inversely using the retrieved statistics to generate reasonable new sets of material model parameters. The methodology presented may be adopted for any other type of material characterisation process.

  • 2.
    Björklund, Oscar
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Govik, Alexander
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Prediction of fracture in a dual-phase steel subjected to non-linear straining2014In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 11, p. 2748-2758Article in journal (Refereed)
    Abstract [en]

    In this work, selected fracture criteria are applied to predict the fracture of dualphase steel subjected to non-linear strain paths. Furthermore, the effects of manufacturing history are studied. Four fracture criteria were calibrated in three tests using standard specimens. The fracture criteria were first validated in the circular Nakajima test. A second validation test case was included in order to validate fracture prediction for non-linear strain paths. In this test a sheet metal component was manufactured and subsequently stretched until it fractured. All fracture criteria included in this study predict fracture during the Nakajima test with reasonable accuracy. In the second validation test however, the different fracture criteria show considerable diversity in accumulated damage during manufacturing which caused substantial scatter of the fracture prediction in the subsequent stretching. This shows that manufacturing history influences the prediction of fracture.

  • 3.
    Björklund, Oscar
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Larsson, Rikard
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Failure of high strength steel sheets: Experiments and modelling2013In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 7, p. 1103-1117Article in journal (Refereed)
    Abstract [en]

    Failure in sheet metal structures of ductile material is usually caused by one of, or a combination of, ductile fracture, shear fracture or localised instability. In this paper the failure of the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M is explored. The constitutive model used in this study includes plastic anisotropy and mixed isotropic-kinematic hardening. For modelling of the ductile and shear fracture the models presented by Cockroft–Latham and Bressan–Williams have been used. The instability phenomenon is described by the constitutive law and the finite element (FE) models. For calibration of the failure models and validation of the results, an extensive experimental series has been conducted including shear tests, plane strain tests and Nakajima tests. The geometries of the Nakajima tests have been chosen so that the first quadrant of the forming limit diagram (FLD) were covered. The results are presented both in an FLD and using prediction of force–displacement response of the Nakajima test employing element erosion during the FE simulations. The classical approach for failure prediction is to compare the principal plastic strains obtained from FE simulations with experimental determined forming limit curves (FLCs). It is well known that the experimental FLC requires proportional strains to be useful. In this work failure criteria, both of the instability and fracture, are proposed which can be used also for non-proportional strain paths.

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  • 4.
    Björklund, Oscar
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Failure characteristics of a dual-phase steel sheet2014In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, p. 1190-1204Article in journal (Refereed)
    Abstract [en]

    Failure in ductile sheet metal structures is usually caused by one, or a combination of, ductile tensile fractures, ductile shear fractures or localised instability. In this paper the failure characteristics of the high strength steel Docol 600DP are explored. The study includes both experimental and numerical sections. In the experimental sections, the fracture surface of the sheet subjected to Nakajima tests is studied under the microscope with the aim of finding which failure mechanism causes the fracture. In the numerical sections, finite element (FE) simulations have been conducted using solid elements. From these simulations, local stresses and strains have been extracted and analysed with the aim of identifying the fracture dependency of the stress triaxiality and Lode parameter.

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  • 5.
    Govik, Alexander
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moshfegh, Ramin
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology. Outokumpu Stainless AB, Avesta, Sweden.
    Finite element simulation of the manufacturing process chain of a sheet metal assembly2012In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 7, p. 1453-1462Article in journal (Refereed)
    Abstract [en]

    An increasing number of components in automotive structures are today made from advanced high strength steel (AHSS). Since AHSS demonstrates more severe springback behaviour than ordinary mild steels, it requires more efforts to meet the design specification of the stamped parts. Consequently, the physical fine tuning of the die design and the stamping process can be time consuming. The trial-and-error development process may be shortened by replacing most of the physical try-outs with finite element (FE) simulations of the forming process, including the springback behaviour. Still it can be hard to identify when a stamped part will lead to an acceptable assembly with respect to the geometry and the residual stress state. In part since the assembling process itself will distort the components. To resolve this matter it is here proposed to extend the FE-simulation of the stamping process, to also include the first level sub-assembly stage. In this study a methodology of sequentially simulating each step in the manufacturing process of an assembly is proposed. Each step of the proposed methodology is described, and a validation of the prediction capabilities is performed by comparing with a physically manufactured assembly. The assembly is composed of three sheet metal components made from DP600 steel which are joined by spot welding. The components are designed to exhibit severe springback behaviour in order to put both the forming and subsequent assembling simulations to the test. The work presented here demonstrates that by using virtual prototyping it is possible to predict the final shape of an assembled structure.

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  • 6.
    Gustafsson, E.
    et al.
    Combitech AB, P.O. Box 15042, 580 15 Linköping.
    Hofwing, Magnus
    Department of Mechanical Engineering Jönköping University P.O. Box 1026, 551 11 Jönköping.
    Strömberg, N.
    Department of Mechanical Engineering Jönköping University P.O. Box 1026, 551 11 Jönköping.
    Residual stresses in a stress lattice: experiments and finite element simulations2009In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 209, no 9, p. 4320-4328Article in journal (Refereed)
    Abstract [en]

    In this work, residual stresses in a stress lattice are studied. The residual stresses are both measured and simulated. The stress lattice is casted of low alloyed grey cast iron. In fact, nine similar lattices are casted and measured. The geometry of the lattice consists of three sections in parallel. The diameter of the two outer sections are thinner than the section in the middle. When the stress lattice cools down, this difference in geometry yields that the outer sections start to solidify and contract before the section in the middle. Finally, an equilibrium state, with tensile stresses in the middle and compressive stresses in the outer sections, is reached. The thermo-mechanical simulation of the experiments is performed by using Abaqus. The thermo-mechanical solidification is assumed to be uncoupled. First a thermal analysis, where the lattice is cooled down to room temperature, is performed. Latent heat is included in the analysis by letting the fraction of solid be a linear function of the temperature in the mushy zone. After the thermal analysis a quasi-static mechanical analysis is performed where the temperature history is considered to be the external force. A rate-independent J2-plasticity model with isotropic hardening is considered, where the material data depend on the temperature. Tensile tests are performed at room temperature, 200 °C, 400 °C, 600 ° C and 800 ° C in order to evaluate the Young’s modulus, the yield strength and the hardening accurate. In addition, the thermal expansion coefficient is evaluated for temperatures between room temperature and 1000 °C. The state of residual stresses is measured by cutting the midsection or the outer section. The corresponding elastic spring-back reveals the state of residual stresses. The measured stresses are compared to the numerical simulations. The simulations show good agreement with the results from the experiments.

  • 7.
    Jansson, Mikael
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    On process parameter estimation for the tube hydroforming process2007In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 190, no 1-3, p. 1-11Article in journal (Refereed)
    Abstract [en]

    Tube hydroforming is a forming process where an inner pressure combined with axial feeding deforms the tube to the shape of a die cavity. One of the main concerns when designing such a process is to avoid burst pressure, i.e. the process state where the hardening of the material is unable to resist the increase in inner pressure and wall thickness reduction. The success of a hydroforming process strongly depends on the choice of process parameters, i.e. the combination of material feeding and inner pressure. Especially in hydroforming processes, where the free forming phase is substantial, the process is proved to be very sensitive to the inner pressure. By transforming the problem into a deformation controlled rather than a force controlled process, the results from the process parameter estimation become more reliable but on the other hand less intuitive. In this context, three distinct parameter estimation procedures are suggested. Firstly, a self feeding based procedure is proposed with the intention of being a fast method to be used as a first estimate of suitable process parameters. Secondly, an iterative optimization problem set up is presented. Thirdly, and finally, an adaptive simulation procedure based on process response approximations is proposed, which only requires a limited number of simulation runs.

  • 8.
    Jansson, Mikael
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    On strain localisation in tube hydroforming of aluminium extrusions2008In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 195, no 1-3, p. 3-14Article in journal (Refereed)
    Abstract [en]

    One important issue when simulating tube hydroforming is to predict bursting, i.e. when the increase in cavity pressure cannot be compensated by hardening of the tube material. Traditionally, this is made by a forming limit diagram (FLD), where the limit strains determine whether a material point is experiencing necking or failure. However, the experimental FLD depends on the strain path, and the methods which are used to determine the FLD are adapted to conventional deep drawing which, depending on the process characteristics, could make it unsuitable for tube hydroforming applications. In this work, analytical and numerical forming limit predictions are studied from a hydroforming point of view. These predictions are then applied to free bulge cases, and a case with extensive feeding in a die where the results from the latter case is compared to experiments. Further, the influence from extrusion welds and a circumferential thickness distribution on the forming limit is also evaluated.

  • 9.
    Jansson, Mikael
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    The use of biaxial test data in the validation of constitutive descriptions for tube hydroforming applications2007In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 184, no 1-3, p. 69-76Article in journal (Refereed)
    Abstract [en]

    When considering finite element simulations of aluminium tube hydroforming, the user is facing several challenges. Firstly, extruded aluminium is anisotropic in yield stress and plastic flow. Secondly, the hydroforming process introduces new issues concerning friction and process control. This imposes a demand for accurate constitutive models as well as for hydroforming process related testing methods. The present study focuses on how biaxial tests can be used to calibrate and validate a constitutive model. It is also shown that by using inverse modelling, additional information can be obtained through these types of tests, such as, e.g. the frictional behaviour for different lubrication conditions.

  • 10.
    Jansson, Mikael
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Tube hydroforming of aluminium extrusions using a conical die and extensive feeding2008In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 198, no 1-3, p. 14-21Article in journal (Refereed)
    Abstract [en]

    Tube hydroforming is gaining increasing interest from the metal forming industry. Complicated parts with a high level of structural component integration, e.g. engine cradles, subframes and exhaust systems, can be manufactured at a low cost with excellent repeatability. By using finite element (FE) simulations, there is a possibility to reduce the cost of expensive prototypes and reduce the trial and error design process to a minimum. However, when simulating a hydroforming process, the knowledge and computational methods used in conventional metal forming simulations are not always applicable. This concerns, e.g. the material modelling and validation. In this work, the influence of constitutive modelling on the results from a hydroforming process with extensive feeding is studied. In addition, interrupted tests have been used in order to validate the prediction of radial deformation and wall thickness throughout the complete process.

  • 11.
    Jansson, Tomas
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Andersson, A.
    Volvo Car Corporation, Body Components, Olofström, Sweden and the Division of Production and Materials Engineering, Lund University, Sweden.
    Nilsson, Larsgunnar
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimization of draw-in for an automotive sheet metal part: an evaluation using surrogate models and response surfaces2005In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 159, no 3, p. 426-434Article in journal (Refereed)
    Abstract [en]

    In the present paper, an optimization of the draw-in of an automotive sheet metal part has been carried out using response surface methodology (RSM) and space mapping technique. The optimization adjusts the draw bead restraining force in the model such that the draw-in in the FE-model corresponds to the draw-in in the physical process. The conclusion of this study is that space mapping is a very effective and accurate method to use when calibrating the draw-in of a sheet metal process. In order to establish draw bead geometry from the draw bead restraining force a 2D-model was utilized. The draw bead geometry found showed good agreement with the physical draw bead geometry.

  • 12.
    Jansson, Tomas
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Lars
    Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
    Moshfegh, Ramin
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Reliability analysis of a sheet metal forming process using Monte Carlo analysis and metamodels2008In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 202, no 1-3, p. 255-268Article in journal (Refereed)
    Abstract [en]

    The aim of the present paper is to evaluate the use of linear and quadratic approximating response surfaces as metamodels in a reliability assessment of a sheet metal forming process using the Monte Carlo simulation technique. Monte Carlo simulation was used to determine the probability for springback and thickness variation in a sheet metal part. The conclusions of this study is that Monte Carlo analysis can be used to identify the most important variables and to estimate the range of the studied responses. Linear metamodels can be used to identify the important variables and to give an estimate of the probabilistic response. But quadratic surfaces are required for a more accurate analysis.

  • 13.
    Jansson, Tomas
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimizing sheet metal forming processes: using a design hierarchy and response surface methodology2006In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 178, no 1-3, p. 218-233Article in journal (Refereed)
    Abstract [en]

    In the present paper optimization has been used to evaluate alternative sheet metal forming processes. Six process set-ups were first defined in a hierarchy of designs and optimization was then used to evaluate each forming process of these designs. The challenge in designing the forming process was to avoid failure in the material and at the same time reach an acceptable through thickness strain. The conclusions of this study is that there may exist a different process that can give an improved product for the desired geometry. This process might be impossible for the optimization algorithm to reach due to either a poor starting point or a not so wise process set-up.

  • 14.
    Jensen, M.R.
    et al.
    Department of Production, Aalborg Univ., Rm. 4.103, F., Aalborg, Denmark.
    Olovsson, L.
    Danckert, J.
    Department of Production, Aalborg University, DK-9220, Aalborg, Denmark.
    Numerical model for the oil pressure distribution in the hydromechanical deep drawing process2000In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 103, no 1, p. 74-79Article in journal (Refereed)
    Abstract [en]

    This paper presents an attempt to simulate the hydromechanical deep drawing process using the finite element method (FEM). The basic idea is to compute the counter pressure and the fluid film pressure by solving a finite difference approximation of Reynold's equation. The concept is implemented as a contact algorithm in Exhale2D, an explicit finite element code for two-dimensional analyses. The numerical results illustrate a rather good agreement with experimental data.

  • 15.
    Larsson, Rikard
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Björklund, Oscar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    A study of high strength steels undergoing non-linear strain paths—Experiments and modelling2011In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, no 1, p. 121-131Article in journal (Refereed)
    Abstract [en]

    This paper presents an evaluation of the constitutive behaviour, including plastic anisotropy and mixed isotropic-kinematic hardening of two high strength steels, Docol 600DP and Docol 1200M, during strain path changes. A series of tensile and shear tests was performed on both virgin and pre-strained materials. The initial anisotropy and work hardening parameters were obtained from tensile tests, shear tests and a bulge test of the virgin material, whereas the kinematic hardening parameters were identified by comparing numerical predictions to experimental results related to the pre-strained materials. Numerical predictions using the obtained parameters agree well with the experimental results, both in the case of proportional, and under non-proportional strain paths.

  • 16.
    Larsson, Rikard
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    On the modelling of strain ageing in a metastable austenitic stainless steel2012In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 1, p. 46-58Article in journal (Refereed)
    Abstract [en]

    The plastic hardening of metastable austenitic stainless steel is partly governed by martensitic transformation, the occurrence of serrated plastic flow, and plastic strain ageing phenomena. In this paper an elasto-viscoplastic material model with isotropic distortional plastic hardening is developed. The model accounts for static and dynamic strain ageing as well as the martensitic transformation. An experimental programme has been conducted in order to fit the model parameters to an austenitic stainless steel within the EN 1.4310 standard. The identification of the dynamic strain ageing was based on so called jump tests, where a sudden strain rate increase was shown to result in an instantaneous positive strain rate sensitivity followed by negative steady state strain rate sensitivity. Furthermore, the static strain ageing was identified by unloading tensile test specimens at specified plastic strains and then reloading these specimens after different periods of time. The observed material behaviour in the test situations can be predicted by the developed model. Lastly, the model was validated by predicting the force-displacement relation of the material in a shear test: the prediction agrees well with experimental results.

  • 17.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Finite element analysis and simulation of powder materials, metallurgical processes and products - A bibliography (1985-2000)2003In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 133, no 3, p. 378-397Other (Other academic)
    Abstract [en]

    This bibliography contains references to papers, conference proceedings and theses/dissertations dealing with powder materials, powder metallurgical processes and products simulated by the finite element methods that were published in 1985-2000, 460 references are listed.

  • 18.
    Mangalaraja, R.V.
    et al.
    University of Concepción.
    Mouzon, J.
    Luleå University of Technology.
    Hedström, P.
    Luleå University of Technology.
    Kero, I.
    Luleå University of Technology.
    Ramam, K.V.S.
    University of Concepción.
    Camurri, Carlos P.
    University of Concepción.
    Odén, Magnus
    Luleå University of Technology.
    Combustion synthesis of Y2O3 and Yb-Y2O3 Part I. Nanopowders and their characterization2008In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 208, no 1-3, p. 415-422Article in journal (Refereed)
    Abstract [en]

     Nanosized yttrium oxide and ytterbium doped yttrium oxide powders were prepared by ceramic combustion techniques such as flash combustion, citrate gel decomposition and glycine combustion using urea, citric acid and glycine respectively as fuels. As synthesized precursors and calcined powders were characterized for their structural, particle size and morphology, and the optimization of calcination process by differential scanning calorimetry and thermal gravimetry. The thermal analyses together with XRD results demonstrate the effectiveness of the combustion process for the synthesis of pure phase nanocrystalline powders. Nanocrystalline pure yttria powders were obtained by the calcination of as-prepared precursors at 1100 ◦C for 4h.

  • 19.
    Yadroitsev, I.
    et al.
    Université de Lyon, Ecole Nationale d'Ingénieurs de Saint-Etienne (ENISE), Saint-Etienne, France.
    Krakhmalev, Pavel
    Dept of Mechanical ang Materials Engineering, Karlstad University.
    Yadroitsava, I.
    Université de Lyon, Ecole Nationale d'Ingénieurs de Saint-Etienne (ENISE), Saint-Etienne, France.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Smurov, I.
    Université de Lyon, Ecole Nationale d'Ingénieurs de Saint-Etienne (ENISE), Saint-Etienne, France.
    Energy Input Effect on Morphology and Microstructure of Selective Laser Melting Single Track from Metallic Powder2013In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 4, p. 606-613Article in journal (Refereed)
    Abstract [en]

    Process parameters of selective laser melting affect the response of a powder–substrate system and, therefore, the geometry and microstructure of the manufactured parts. The experiments were carried out at fixed values of laser power (50 W), spot diameter (70 μm) and powder layer thickness (80 μm). In this research, influence of the energy input parameters (80–900 °C preheating temperature and 0.08–0.28 m/s laser scanning speed) on microstructure and geometry of single tracks fabricated of stainless steel grade 316L powder was analysed. Both factors were found statistically significant with regard to their influence on the remelted depth and the primary cell spacing in the colonies observed in the tracks cross-sections. More specifically, the contact angle and track height were controlled by the preheating temperature, and track width and contact zone characteristics were governed by the laser scanning speed. Because of the threshold behaviour of these two factors, values starting with 700 °C and 0.24 m/s were found not optimal and causing instability and balling effect. Conclusions regarding the selection of process parameters for the formation of tracks with the desired geometry and microstructure were formulated based on statistical analysis of the experimental data.

  • 20.
    Zhou, Nian
    et al.
    Dept of Materials Science, Dalarna University, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Pettersson, Rachel
    Jernkontoret, Stockholm.
    Surface Integrity of 2304 Duplex Stainless Steel After Different Grinding Operations2016In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, no 229, p. 294-304Article in journal (Refereed)
    Abstract [en]

    Surface integrity has significant effect on service performance of a component. In this study, the evolution of the surface and sub-surface changes induced by grinding duplex stainless steel (DSS) 2304 was studied with regard to the residual stress, the microstructure, surface roughness and surface defects. The results provide insights into the effect of abrasive grit size, grinding force and lubrication on the surface integrity. The abrasive grit size was found to have the largest influence. Surface defects, a highly deformed surface layer and the generation of tensile residual stresses along the grinding direction have been found to be the main types of damage induced by the grinding operation. Residual stresses induced by mechanical effects dominate over thermal effects in this study. The results obtained can be used to understand the contribution of surface condition and residual stress on failure of duplex stainless steels in service by fatigue or stress corrosion cracking.

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