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  • 1.
    Aare, Magnus
    et al.
    KTH, Superseded Departments (pre-2005), Aeronautical and Vehicle Engineering.
    Kleiven, Svein
    KTH, Superseded Departments (pre-2005), Aeronautical and Vehicle Engineering.
    Halldin, Peter
    KTH, Superseded Departments (pre-2005), Aeronautical and Vehicle Engineering.
    Injury tolerances for oblique impact helmet testing2004In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 9, no 1, p. 15-23Article in journal (Refereed)
    Abstract [en]

    The most frequently sustained severe injuries in motorcycle crashes are injuries to the head, and many of these are caused by rotational force. Rotational force is most commonly the result of oblique impacts to the head. Good testing methods for evaluating the effects of such impacts are currently lacking. There is also a need for improving our understanding of the effects of oblique impacts on the human head. Helmet standards currently in use today do not measure rotational effects in test dummy heads. However rotational force to the head results in large shear strains arising in the brain, which has been proposed as a cause of traumatic brain injuries like diffuse axonal injuries (DAI). This paper investigates a number of well-defined impacts, simulated using a detailed finite element (FE) model of the human head, an FE model of the Hybrid III dummy head and an FE model of a helmet. The same simulations were performed on both the FE human head model and the FE Hybrid III head model, both fitted with helmets. Simulations on both these heads were performed to describe the relationship between load levels in the FE Hybrid III head model and strains in the brain tissue in the FE human head model. In this study, the change in rotational velocity and the head injury criterion (HIC) value were chosen as appropriate measurements. It was concluded that both rotational and translational effects are important when predicting the strain levels in the human brain.

  • 2.
    Abali, B. Emek
    Technische Universität Berlin.
    Damage Formulation in Generalized Mechanics Based on a Variational Formulation2021In: Proceedings of the International scientific symposium on problems of the mechanics of deformable bodies: dedicated to the 110th anniversary from the birthday of A. A. ILYUSHIN / [ed] Brovko, G. L., Georgievskii, D. V. & Molodtsov, I. N., Moscow: Moscow State University Press, 2021, p. 350-357Conference paper (Refereed)
    Abstract [en]

    Damage mechanics is often modeled by using adhoc or phenomenological methodologies, which is useful but challenging to generalize. Especially inapplications with several length scales, a homogenization procedure leads to ametamaterial to be modeled by the generalized mechanics. We aim for a unifiedtheory of generalized damage mechanics by following a variation purelyalformulation.

  • 3.
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    An Introduction to Piezoelectric and Thermoelectric Materials2022In: Handbook of Energy Materials / [ed] Ram Gupta, Singapore: Springer, 2022, p. 1-18Chapter in book (Refereed)
    Abstract [en]

    Materials may demonstrate electromagnetism and thermomechanics coupling. Although we benefit from this coupling in our modern lives, comprehending this coupling is challenging. We intuitively understand that temperature increase causes an expansion in polymers and alloys. Typical example is a plastic water bottle left in the sun, the expansion is visible by naked eyes. Yet it is more abstract to consider that an electric field may create a deformation or even a temperature change. Electromagnetic fields are more abstract since our senses fail to be sensitive to these physical quantities. There are indeed materials with so-called piezoelectric and pyroelectric properties and we use them for sensors and actuators. More confusingly, there is a thermoelectric effect relating electric current and heat flux. In order to set the ideas correctly, we explain these phenomena and introduce to the abstract world of electromagnetism and thermomechanics coupling. Furthermore, we provide an inside look to realize how different types of thermal and electric coupling phenomena work and how to model such materials adequately.

  • 4.
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Asymptotic homogenization and parameter determination in metamaterials2021Conference paper (Other academic)
  • 5.
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Energy based methods applied in mechanics by using the extended Noether's formalism2023In: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 103, no 12Article in journal (Refereed)
    Abstract [en]

    Physical systems are modeled by field equations; these are coupled, partial differential equations in space and time. Field equations are often given by balance equations and constitutive equations, where the former are axiomatically given and the latter are thermodynamically derived. This approach is useful in thermomechanics and electromagnetism, yet challenges arise once we apply it in damage mechanics for generalized continua. For deriving governing equations, an alternative method is based on a variational framework known as the extended Noether's formalism. Its formal introduction relies on mathematical concepts limiting its use in applied mechanics as a field theory. In this work, we demonstrate the power of extended Noether's formalism by using tensor algebra and usual continuum mechanics nomenclature. We demonstrate derivation of field equations in damage mechanics for generalized continua, specifically in the case of strain gradient elasticity.

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  • 6.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Aldakheel, Fadi
    Zohdi, Tarek I.
    Multiphysics Computation of Thermomechanical Fatigue in Electronics Under Electrical Loading2022In: Current Trends and Open Problems in Computational Mechanics / [ed] Fadi Aldakheel, Blaž Hudobivnik, Meisam Soleimani, Henning Wessels, Christian Weißenfels, Michele Marino, Cham: Springer Nature, 2022, p. 1-14Chapter in book (Refereed)
  • 7.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics. Institute of Mechanics, MS 2, Technische Universität Berlin, Einsteinufer 5, 10587, Berlin, Germany.
    Barchiesi, Emilio
    Additive manufacturing introduced substructure and computational determination of metamaterials parameters by means of the asymptotic homogenization2021In: Continuum Mechanics and Thermodynamics, ISSN 0935-1175, E-ISSN 1432-0959, Vol. 33, no 4, p. 993-1009Article in journal (Refereed)
    Abstract [en]

    Metamaterials exhibit materials response deviation from conventional elasticity. This phenomenon is captured by the generalized elasticity as a result of extending the theory at the expense of introducing additional parameters. These parameters are linked to internal length scales. Describing on a macroscopic level, a material possessing a substructure at a microscopic length scale calls for introducing additional constitutive parameters. Therefore, in principle, an asymptotic homogenization is feasible to determine these parameters given an accurate knowledge on the substructure. Especially in additive manufacturing, known under the infill ratio, topology optimization introduces a substructure leading to higher-order terms in mechanical response. Hence, weight reduction creates a metamaterial with an accurately known substructure. Herein, we develop a computational scheme using both scales for numerically identifying metamaterials parameters. As a specific example, we apply it on a honeycomb substructure and discuss the infill ratio. Such a computational approach is applicable to a wide class substructures and makes use of open-source codes; we make it publicly available for a transparent scientific exchange.

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  • 8.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics. Institute of Mechanics Technische Universität Berlin Einsteinufer 5 Berlin 10967 Germany.
    Klunker, Andre
    Institute of Mechanics Technische Universität Berlin Einsteinufer 5 Berlin 10967 Germany.
    Barchiesi, Emilio
    International Research Center on Mathematics and Mechanics of Complex Systems Università degli Studi dell'Aquila Via Giovanni Gronchi 18 ‐ Zona industriale di Pile L'Aquila 67100 Italy.
    Placidi, Luca
    Engineering Faculty International Telematic University Uninettuno Corso Vittorio Emanuele II Rome 39 00186 Italy.
    A novel phase‐field approach to brittle damage mechanics of gradient metamaterials combining action formalism and history variable2021In: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 101, no 9, article id e202000289Article in journal (Refereed)
    Abstract [en]

    Metamaterials response is generally modeled by generalized continuum based theories. Their inherent substructure leads to a necessity for higher-order theories, and especially in damage mechanics, such a generalization is difficult to acquire. We exploit the action formalism in order to obtain the governing equations in generalized damage mechanics for metamaterials. Additionally, by using auxilliary variables, the variational formulation is endowed with the first rate of damage variable that is missing in standard approaches. The presented action formalism with auxilliary variables leads directly to the weak form. We implement a finite element method based approach by using open-source computing platform called FEniCS and solve this weak in order to obtain the deformation and damage numerically. Metamaterials simulations are demonstrated for simple geometries in mixed mode (I and II) as well as in mode III.

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  • 9.
    Abali, Bilen Emek
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Vazic, Bozo
    Univ Utah, Dept Mech Engn, Salt Lake City, UT USA..
    Newell, Pania
    Univ Utah, Dept Mech Engn, Salt Lake City, UT USA..
    Influence of microstructure on size effect for metamaterials applied in composite structures2022In: Mechanics research communications, ISSN 0093-6413, E-ISSN 1873-3972, Vol. 122, article id 103877Article in journal (Refereed)
    Abstract [en]

    Microstructure related deviation from elastic response is known as "size-effect."Metamaterials - for example modeled by strain gradient elasticity - capture this effect adequately by means of additional parameters to be determined. We employ a methodology based on asymptotic homogenization in order to obtain metamaterials parameters and then present the influence of these additional parameters by using simulations. By means of the finite element method, we solve metamaterials deformation modeled by the strain gradient elasticity. The implementation is established by open-source packages (FEniCS) for a realistic, composite structure with round and oval inclusions.

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  • 10.
    Abbasi, Saeed
    Sharif university of Technology, Iran.
    A feasibilty study to establish freight cars overhaul center (Master thesis), Sharif university of technology2005Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
  • 11. Abbasi, Saeed
    Implementing theory of constraint in choosing six sigma project2008Conference paper (Refereed)
  • 12.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Non-exhaust Nano particle emission in Rail traffic2010Conference paper (Refereed)
  • 13.
    Abbasi, Saeed
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Moslemi, Kianoush
    A new approach for optimization of heating system in tank wagons2003Conference paper (Refereed)
  • 14.
    Abbasi, Saeed
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Larsson, Christina
    Bombardier Transportation Sweden AB, Västerås, Sweden.
    Jansson, Anders
    Stockholm University, Applied Environmental Science, Stockholm, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    A field test study of airborne wear particles from a running regional train2012In: IMechE, Part F: Journal of Rail and Rapid Transit, ISSN 0954-4097, Vol. 226, no 1, p. 95-109Article in journal (Refereed)
    Abstract [en]

    Inhalable airborne particles have inverse health affect. In railways, mechanical brakes, the wheel–rail contact, current collectors, ballast, sleepers, and masonry structures yield particulate matter. Field tests examined a Swedish track using a train instrumented with particle measurement devices, brake pad temperature sensors, and speed and brake sensors. The main objective of this field test was to study the characteristics of particles generated from disc brakes on a running train with an on-board measuring set-up.

    Two airborne particle sampling points were designated, one near a pad–rotor disc brake contact and a second under the frame, not near a mechanical brake or the wheel–rail contact; the numbers and size distributions of the particles detected were registered and evaluated under various conditions (e.g. activating/deactivating electrical brakes or negotiating curves). During braking, three speed/temperature-dependent particle peaks were identified in the fine region, representing particles 280 nm, 350 nm, and 600 nm in diameter. In the coarse region, a peak was discerned for particles 3–6 μm in diameter. Effects of brake pad temperature on particle size distribution were also investigated. Results indicate that the 280 nm peak increased with increasing temperature, and that electrical braking significantly reduced airborne particle numbers. FESEM images captured particles sizing down to 50 nm. The ICP-MS results indicated that Fe, Cu, Zn, Al, Ca, and Mg were the main elements constituting the particles.

     

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  • 15.
    Abbasi, Saeed
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. Department of Mechanical engineering, Golpayegan University of Technology.
    Teimourimanesh, Shahab
    Chalmers.
    Vernersson, Tore
    Chalmers.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Lunden, Roger
    Chalmers.
    Temperature and Thermoelastic Instability at Tread Braking Using Cast Iron Friction Material2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 314, no 1–2, p. 171-180Article in journal (Refereed)
    Abstract [en]

    Braking events in railway traffic often induce high frictional heating and thermoelastic instability (TEI) at the interfacing surfaces. In the present paper, two approaches are adopted to analyse the thermomechanical interaction in a pin-on-disc experimental study of railway braking materials. In a first part, the thermal problem is studied to find the heat partitioning between pin and disc motivated by the fact that wear mechanisms can be explained with a better understanding of the prevailing thermal conditions. The numerical model is calibrated using the experimental results. In a second part, the frictionally induced thermoelastic instabilities at the pin-disc contact are studied using a numerical method and comparing them with the phenomena observed in the experiments. The effects of temperature on material properties and on material wear are considered. It is found from the thermal analysis that the pin temperature and the heat flux to the pin increase with increasing disc temperatures up to a transition stage. This agrees with the behaviour found in the experiments. Furthermore, the thermoelastic analysis displays calculated pressure and the temperature distributions at the contact interface that are in agreement with the hot spot behaviour observed in the experiments.

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  • 16.
    Abbasi, Saeed
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Teimourimanesh, Shahab
    Chalmers.
    Vernersson, Tore
    Chalmers.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Lunden, Roger
    Chalmers.
    Temperature and thermo-elastic instability of tread braking friction materials2012Conference paper (Refereed)
  • 17.
    Abbaszadeh Shahri, Abbas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Larsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Johansson, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Updated relations for the uniaxial compressive strength of marlstones based on P-wave velocity and point load index test2016In: INNOVATIVE INFRASTRUCTURE SOLUTIONS, ISSN 2364-4176, Vol. 1, no 1, article id UNSP 17Article in journal (Refereed)
    Abstract [en]

    Although there are many proposed relations for different rock types to predict the uniaxial compressive strength (UCS) as a function of P-wave velocity (V-P) and point load index (Is), only a few of them are focused on marlstones. However, these studies have limitations in applicability since they are mainly based on local studies. In this paper, an attempt is therefore made to present updated relations for two previous proposed correlations for marlstones in Iran. The modification process is executed through multivariate regression analysis techniques using a provided comprehensive database for marlstones in Iran, including UCS, V-P and Is from publications and validated relevant sources comprising 119 datasets. The accuracy, appropriateness and applicability of the obtained modifications were tested by means of different statistical criteria and graph analyses. The conducted comparison between updated and previous proposed relations highlighted better applicability in the prediction of UCS using the updated correlations introduced in this study. However, the derived updated predictive models are dependent on rock types and test conditions, as they are in this study.

  • 18.
    Abdeljaber, O.
    et al.
    Qatar University, Doha, Qatar.
    Younis, Adel
    Qatar University, Doha, Qatar.
    Avci, O.
    Qatar University, Doha, Qatar.
    Catbas, N.
    University of Central Florida, FL, United States.
    Gul, M.
    University of Central Florida, FL, United States.
    Celik, O.
    University of Central Florida, FL, United States.
    Zhang, H.
    University of Alberta, Edmonton, AB, Canada.
    Dynamic Testing of a Laboratory Stadium Structure2016In: Proceedings of the Joint Geotechnical and Structural Engineering Congress 2016, 2016, p. 1719-1728Conference paper (Refereed)
    Abstract [en]

    Studies with large physical models are a vital link between the theoretical work and field applications provided that these models are designed to represent real structures where various types and levels of uncertainties can be incorporated. While comprehensive analytical and laboratory joint studies are ongoing at Qatar University, University of Central Florida and University of Alberta, this paper presents the initial findings of dynamic testing at Qatar University. A laboratory stadium structure (grandstand simulator) has been constructed at Qatar University. Capable of housing thirty spectators, Qatar University grandstand simulator is arguably the largest laboratory stadium in the world. The structure is designed in a way that several different structural configurations can be tested in laboratory conditions to enable researchers to test newly developed damage detection algorithms. The study presented in this paper covers the finite element modeling and modal testing of the test structure. © ASCE.

  • 19.
    Abdul-Rahman, William
    et al.
    Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Andersson, Viktor
    Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Conceptual design and development of an off-road cargo trailer for bicycles2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report presents the conceptual development of an off-road cargo trailer designed for usage in conjunction with bicycles when camping. The objective of the study is to address the limitations of existing cargo trailers and thereafter create a trailer that efficiently can navigate off-road terrains while carrying various types of cargo. The research includes collecting data regarding user behaviours and desired functions an optimal trailer should obtain and was translated into user requirements. The result demonstrates the successful development of an off-road cargo trailer on a conceptual level that offers innovative solutions and improved load-carrying capacity in comparison to the available market, while considering factors such as weight, manoeuvrability, and ease of use. This research contributes to the field by presenting data, which can be used in development and a comprehensive solution that expands the possibilities for bicycle-based cargo transportation in off-road environments. Future work can include further refinements to optimise the trailer’s performance and address additional user requirements based on the data presented.

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  • 20.
    Abebe, Abay Damte
    et al.
    Halmstad University, School of Business, Engineering and Science.
    He, Qikang
    Halmstad University, School of Business, Engineering and Science.
    Foam Behavior Analysis Based On A Force Measurement System2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Abstract

    In the world where every sector of industrial manufacturing is being converted toautomated systems, surface finishing processes like sanding and polishing seem to lag.This phenomenon is not surprising as these processes are complex to optimize. Therehave been projects going on with the support of European Commission to findsolutions under SYMPLEXITY (Symbiotic Human-Robot Solutions for ComplexSurface Finishing Operations). One of the projects in under this include poliMATIC(Automated Polishing for the European Tooling Industry). Halmstad University isinvolved in doing projects.

    This project took a portion of this study in aim to understand a foam material’s behavior used for sanding tool at the tip of a robotic arm. This is studied using a forcemeasurement system developed at Halmstad University. The project has two sectionsand starts with one; Understanding the force measurement system and upgrading innecessary ways. Two; studying how the foam material compressive hardness propertyis affected when the material is fit with sandpaper for sanding operation using theforce measurement system. The study finally revealed how the combination of thefoam with sandpaper affects the robustness of the material, and significantlyimproved the output of the system with by reducing the noise level with 40%.

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  • 21.
    Abed, Kason
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    FEM-analys av torkapparat2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 22.
    Abelen, Aisha
    et al.
    Eindhoven Univ Technol, Netherlands.
    Kroon, Martin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Modelling of rate-dependent inelasticity and damage in semi-crystalline polymers using an Eulerian framework2023In: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197, Vol. 193, article id 103945Article in journal (Refereed)
    Abstract [en]

    The present paper concerns the mechanical response of semi-crystalline polymers during cyclic loading, and it includes both modelling and experimental testing. The model is Eulerian in the sense that it is independent of measures of total deformation and plastic/inelastic deformations. It is able to account for such essential phenomena as strain-rate dependence, work hardening, and damage. The model was applied to uniaxial tension tests performed on high-density polyethylene (HDPE), which is a semi-crystalline polymer widely used in the industry. Two types of tests were conducted: monotonic tests, and loading-unloading tests. The model was able to reproduce the experimental results very well. The proposed model was also implemented as a UMAT in Abaqus, including an analytic tangent. The UMAT was used for simulating two 3D geometries. The implementation seems to be robust, and no convergence problems were observed.

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  • 23.
    Abiri, Olufunminiyi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. National Mathematical Centre, Gwagwalada, Abuja, Nigeria.
    Svoboda, Ales
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Wedberg, Dan
    AB Sandvik Coromant, Sandviken, Sweden.
    Controlling Thermal Softening Using Non-Local Temperature Field in Modelling2016In: Journal of Machining and Forming Technologies, ISSN 1947-4369, Vol. 8, no 1-2, p. 13-28Article in journal (Refereed)
    Abstract [en]

    One of the aims of this work is to show that thermal softening due to the reduced flow strength of a material with increasing temperature may cause chip serrations to form during machining. The other purpose, the main focus of the paper, is to demonstrate that a non-local temperature field can be used to control these serrations. The non-local temperature is a weighted average of the temperature field in the region surrounding an integration point. Its size is determined by a length scale. This length scale may be based on the physics of the process but is taken here as a regularization parameter.

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  • 24.
    Abiri, Olufunminiyi
    et al.
    Institute of Intelligent Systems, University of Johannesburg.
    Wedberg, Dan
    AB Sandvik Coromant.
    Svoboda, Ales
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Non-Local Modelling of Strain Softening in Machining Simulations2017In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 225, article id 012053Article in journal (Refereed)
    Abstract [en]

    Non-local damage model for strain softening in a machining simulation is presented in this paper. The coupled damage-plasticity model consists of a physically based dislocation density model and a damage model driven by plastic straining in combination with the stress state. The predicted chip serration is highly consistent with the measurement results. 

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  • 25.
    Abrahamsen, Alexandra
    University West, Department of Engineering Science.
    Data Science for In-process Chatter Classification2022Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Milling is one of the most crucial processes in machining. Every industry demands a stable milling process for a smoother finish and material cost reduction. Chatter is a vibrating phenomenon which affects the workpiece's quality, its dimensional accuracy, and tool life. It is required to classify the chatter phenomenon to devise an effective chatter prevention strategy.

    Several classification strategies are being used, including frequency and time-related strategies. Since the chattering phenomenon is a frequency-based phenomenon so a frequency-based feature set can be of vital importance. However, frequency-based strategies have a problem of noise. The noise problem can be addressed by combining frequency and time-domain methods.

    Thus, a hybrid approach based on the frequency and time-based feature set is developed and used in conjunction with k-means-based unsupervised learning to come up with a practical but reliable classifier. The proposed classifier algorithm offers good performance, clearly distinguishing between chatter and stable conditions.

    Based on the chatter classification in this work, it is possible to identify thresholds for chattering detection. It is essential to mention that the thresholds obtained from this work will only be useful for the machine and tool used in the experiments and will not be of use for other machines and need more investigation. 

  • 26.
    Abrahamsen, Rune
    et al.
    Moelven Limtre, Norway.
    Bjertnæs, Magne A.
    Sweco, Norway.
    Bouillot, Jacques
    Eiffage, France.
    Brank, Boštjan
    University of Ljubljana, Slovenia.
    Crocetti, Roberto
    Moelven SE, Sweden.
    Flamand, Olivier
    CSTB, France.
    Garains, Fabien
    Arbonis, France.
    Gavrić, Igor
    InnoRenew, Slovenia.
    Hahusseau, Ludwig
    Eiffage, France.
    Jalil, Alan
    CSTB, France.
    Johansson, Marie
    RISE, Sweden.
    Johansson, Thomas
    Moelven, Sweden.
    Ao, Wai Kei
    Uni Exeter, UK.
    Kurent, Blaž
    University of Ljubljana, Slovenia.
    Landel, Pierre
    Linnaeus University, Faculty of Technology, Department of Building Technology. Rise, Sweden.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Malo, Kjell
    NTNU, Norway.
    Manthey, Manuel
    CSTB, France.
    Nåvik, Petter
    Sweco, Norway.
    Pavic, Alex
    Uni Exeter, UK.
    Perez, Fernando
    Smith&Wallwork, Switzerland.
    Rönnquist, Anders
    NTNU, Norway.
    Šušteršič, Iztok
    InnoRenew, Slovenia.
    Tulebekova, Saule
    NTNU, Norway.
    Dynamic response of tall timber buildings under service load: results from the dynattb research program2023In: World Conference on Timber Engineering 2023 (WCTE 2023): Timber for a Livable Future, 19-22 june, 2023,Oslo, Norway / [ed] Nyrud, A. Q. and Malo, K. A. et al., Curran Associates, Inc., 2023, p. 2907-2914Conference paper (Refereed)
    Abstract [en]

    Wind-induced dynamic excitation is a governing design action determining size and shape of modern Tall Timber Buildings (TTBs). The wind actions generate dynamic loading, causing discomfort or annoyance for occupants due to the perceived horizontal sway, i.e. vibration serviceability problem. Although some TTBs have been instrumented and measured to estimate their key dynamic properties (eigenfrequencies, mode shapes and damping), no systematic evaluation of dynamic performance pertinent to wind loading had been performed for the new and evolving construction technologies used in TTBs. The DynaTTB project, funded by the ForestValue research program, mixed on site measurements on existing buildings excited by mass inertia shakers (forced vibration) and/or the wind loads (ambient vibration), for identification of the structural system, with laboratory identification of building elements mechanical features, coupled with numerical modelling of timber structures. The goal is to identify and quantify the causes of vibration energy dissipation in modern TTBs and provide key elements to finite element models. This paper presents an overview of the results of the project and the proposed Guidelines for design of TTBs in relation to their dynamic properties.

  • 27.
    Abu-Ragheef, Basil
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Polymer Aging Mechanics: An investigation on a Thermoset Polymer used in the Exterior Structure of a Heavy-duty Vehicle2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The use of plastic materials in the design of vehicle components is primarily driven by the need for vehicle weight and cost reduction. Additionally, these materials give design engineers freedom in creating appealing exterior designs. However, creating self-carrying exterior structures with polymers must fulfill long-term strength, creep and fatigue life requirements. Thus, the polymer polyDicyclopentadiene (pDCPD) has been chosen for this purpose. Its aging mechanics need to be understood by the design engineers to make the right decisions. This thesis has carried out mechanical tests such as uniaxial tensile testing, fatigue, and creep testing. Digital image correlation (DIC) system has been used to capture strain data from tensile tests. In the final analysis, DIC measurements proved more accurate than extensometer data retrieved from the testing machine. The rise in temperature has been captured using thermal imaging. Several degradation processes have been explored including physical aging, thermo-oxidation, photo-oxidation, chemical- and bio- degradations. Test results showed significant changes in mechanical properties after 17 years of aging. Additionally, severe thermal degradation has been observed in one of the tested panels of pDCPD. Temperature can rise to significant levels during cyclic loading at high stresses, which could have an impact on physical aging effects. Viscoelastic behavior has been explored and changes in dynamic and creep properties have been observed. The investigation also reviled that different defects caused by flawed manufacturing also can affect the material severely as one case has proved in this research.

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  • 28. Achani, D.
    et al.
    Eriksson, Magnus
    SINTEF Materials and chemistry, Applied mechanics and corrosion, Trondheim, Norway.
    Hopperstad, O.S.
    Lademo, O.-G.
    Modelling of local necking and fracture in aluminium alloys2007In: Materials processing and design : modeling, simulation and applications ; NUMIFORM '07: proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes, Porto, Portugal, 17 - 21 June 2007 / [ed] J.M.A. Cesar de Sa; Abel D. Santos, American Institute of Physics (AIP), 2007, p. 111-116Conference paper (Refereed)
  • 29.
    Adelholt, Martin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hydra Coupler: Snabbkoppling till protessystem2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Många amputerade upplever att deras protessystem inte är lika anpassningsbara som de hoppats på. Dagens protes­system är utformade med låsta komponenter vilket begrän­sar användarens möjlighet att anpassa systemen till specifika ändamål. Därför påbörjades ett projekt med målet att under­söka om det finns möjlighet att skapa en snabbkoppling till protessystem genom att framställa ett konstruktionsförslag av ett lösningsalternativ. I starten av projektet påbörjades en problemformulering för att undersöka om problemen uppvisade några beroenden eller påverkade andra poster inom det framställda flödesschemat. Efter genomförd problemformulering påbörjades förstudierna för att samla in relevant information till genomförandet av projektet, där förstudien genomfördes med hjälp av en konkurrensanalys, funktionsanalys och enkätundersökning. Efter att förstudien var avklarad påbörjades en designprocess för att framställa ett konstruktionsförslag av ett lösningsförslag. Under designprocessens start formulerades en kravspecifikation så att konstruktionsförslaget hade något att förhålla sig till, och sedan påbörjades modelleringen av ett konstruktionsförslag med hjälp av Solidworks. En prototyp framställdes i plast med hjälp av en 3D- printer för att kontrollera passform av ingående komponenter och slutligen så undersöktes konstruktionsförslagets hållfasthet i Solidworks med hjälp av hållfasthetssimuleringar. Genomförandet av projektet har resulterat i en framställning av konstruktionsmaterial, prototyp, konstruktionsritningar till ett konstruktionsförslag av en snabbkoppling till protessystem. Konstruktionsförslaget kallat Hydra Coupler förser protesanvändare med möjligheten att enkelt byta proteskomponenter efter ändamål utan behov av externa verktyg, och Hydra Coupler kan även inneslutas av kosmetik utan att förlora funktionalitet.

  • 30.
    Adelholt, Martin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Production preparations of Hydra Coupler: Preparations, Planning, Calculations2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 31.
    Adelholt, martin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Production preparations of Hydra Coupler: Preparations, Planning, Calculations2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 32. Adolfsson, E
    et al.
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Matrix crack closure effects on the thermoelastic properties of [(0/90/+q/-q)s]M composite laminates1994Conference paper (Refereed)
  • 33.
    Adolfsson, Matilda
    Halmstad University, School of Business, Engineering and Science.
    Vibrationer och engesvängningar i Alfdex separator2019Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose of this thesis is to create a greater understanding of what happens inAlfdex’s separator in terms of natural frequencies, also called resonances. Try in asystematic way to find out where the problem is and produce a possible solutionto the problem. To achieve this smoothly, vibration measurements were made onthree different models with two variants, a total of six different variants. Themeasurements made with an electric shaker were set to run a sweep of 2-500Hz,which means that it increases the frequency from 20-500Hz with a constantacceleration of 2G. The measurement was first made on these six variants and, onthe basis of the results, it has been possible to compare with the modificationsmade.As the first modification, the disks in the separator were glued together to see ifthey made any difference from the previous result. As the next test spacers wereprinted out of the 3D-printer, that would replace the existing springs in theseparator, to aww what happens if we do not have any springs. There was also atest where the top of the separator the so-called house, was cut into a larger holeso as to see how the disks hold a constant amplitude relative to each other, whichmeans that the disks are not exposed to any natural frequencies. The springs werefilmed to see how they act and move, where it is clear that there are naturalfrequencies in the springs.Based on these tests, it can be concluded that the disk in question are not aproblem. The problem instead has its foundation in the springs that carry the diskstack throughout the separator, resonances in these give a great influence in theentire contents of the separator.

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  • 34. Adolfsson, Vilhelm
    et al.
    Goldberg, Max
    Jawerth, Björna
    Lennerstad, Håkan
    Localized Galerkin Estimates for Boundary Integral Equations on Lipschitz Domanis1992In: SIAM Journal on Mathematical Analysis, Vol. 5, no 23, p. 751-764Article in journal (Refereed)
    Abstract [en]

    The Galerkin method is studied for solving the boundary integral equations associated with the Laplace operator on nonsmooth domains. Convergence is established with a condition on the meshsize, which involves the local curvature on certain approximating domains. Error estimates are also proved, and the results are generalized to systems of equations.

  • 35.
    af Klinteberg, Ludvig
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Sorgentone, Chiara
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Tornberg, Anna-Karin
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Quadrature error estimates for layer potentials evaluated near curved surfaces in three dimensions2022In: Computers and Mathematics with Applications, ISSN 0898-1221, E-ISSN 1873-7668, Vol. 111, p. 1-19Article in journal (Refereed)
    Abstract [en]

    The quadrature error associated with a regular quadrature rule for evaluation of a layer potential increases rapidly when the evaluation point approaches the surface and the integral becomes nearly singular. Error estimates are needed to determine when the accuracy is insufficient and a more costly special quadrature method should be utilized.& nbsp;The final result of this paper are such quadrature error estimates for the composite Gauss-Legendre rule and the global trapezoidal rule, when applied to evaluate layer potentials defined over smooth curved surfaces in R-3. The estimates have no unknown coefficients and can be efficiently evaluated given the discretization of the surface, invoking a local one-dimensional root-finding procedure. They are derived starting with integrals over curves, using complex analysis involving contour integrals, residue calculus and branch cuts. By complexifying the parameter plane, the theory can be used to derive estimates also for curves in R3. These results are then used in the derivation of the estimates for integrals over surfaces. In this procedure, we also obtain error estimates for layer potentials evaluated over curves in R2. Such estimates combined with a local root-finding procedure for their evaluation were earlier derived for the composite Gauss-Legendre rule for layer potentials written in complex form [4]. This is here extended to provide quadrature error estimates for both complex and real formulations of layer potentials, both for the Gauss-Legendre and the trapezoidal rule.& nbsp;Numerical examples are given to illustrate the performance of the quadrature error estimates. The estimates for integration over curves are in many cases remarkably precise, and the estimates for curved surfaces in R-3 are also sufficiently precise, with sufficiently low computational cost, to be practically useful.

  • 36.
    af Klinteberg, Ludvig
    et al.
    KTH, Sweden.
    Sorgentone, Chiara
    KTH, Sweden.
    Tornberg, Anna-Karin
    KTH, Sweden.
    Quadrature error estimates for layer potentials evaluated near curved surfaces in three dimensions2022In: Computers and Mathematics with Applications, ISSN 0898-1221, E-ISSN 1873-7668, Vol. 111, p. 1-19Article in journal (Refereed)
    Abstract [en]

    The quadrature error associated with a regular quadrature rule for evaluation of a layer potential increases rapidly when the evaluation point approaches the surface and the integral becomes nearly singular. Error estimates are needed to determine when the accuracy is insufficient and a more costly special quadrature method should be utilized.& nbsp;The final result of this paper are such quadrature error estimates for the composite Gauss-Legendre rule and the global trapezoidal rule, when applied to evaluate layer potentials defined over smooth curved surfaces in R-3. The estimates have no unknown coefficients and can be efficiently evaluated given the discretization of the surface, invoking a local one-dimensional root-finding procedure. They are derived starting with integrals over curves, using complex analysis involving contour integrals, residue calculus and branch cuts. By complexifying the parameter plane, the theory can be used to derive estimates also for curves in R3. These results are then used in the derivation of the estimates for integrals over surfaces. In this procedure, we also obtain error estimates for layer potentials evaluated over curves in R2. Such estimates combined with a local root-finding procedure for their evaluation were earlier derived for the composite Gauss-Legendre rule for layer potentials written in complex form [4]. This is here extended to provide quadrature error estimates for both complex and real formulations of layer potentials, both for the Gauss-Legendre and the trapezoidal rule.& nbsp;Numerical examples are given to illustrate the performance of the quadrature error estimates. The estimates for integration over curves are in many cases remarkably precise, and the estimates for curved surfaces in R-3 are also sufficiently precise, with sufficiently low computational cost, to be practically useful.

  • 37.
    Afshar, R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Stjärnesund, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering.
    Gamstedt, E. K.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering.
    Girlanda, O.
    Hitachi Energy Res Sweden, Västerås, Sweden.
    Sahlen, F.
    ABB Corp Res, Västerås, Sweden.
    Tjahjanto, D.
    NKT HV Cables Abtechnol Consulting, Västerås, Sweden.
    A micro-CT investigation of densification in pressboard due to compression2023In: Strain, ISSN 0039-2103, E-ISSN 1475-1305, Vol. 59, no 4, article id 12442Article in journal (Refereed)
    Abstract [en]

    As a non-destructive inspection method, micro-computed tomography has been employed for determining local properties of a cellulose-based product, specifically pressboard. Furthermore, by utilizing the determined properties in a detailed numerical model, by means of a finite element analysis, we demonstrate a continuum anisotropic viscoelastic-viscoplastic model. Through such a combination of non-invasive experiments with accurate computations in mechanics, we attain a better understanding of materials and its structural integrity at a pre-production stage increasing the success of the first prototype. In detail, this combination of micro-computed tomography and finite element analysis improves accuracy in predicting materials response by taking into account the local material variations. Specifically, we have performed indentation tests and scanned the internal structure of the specimen for analysing the densification patterns within the material. Subsequently, we have used a developed material model for predicting the response of material to indentation. We have computed the indentation test itself by simulating the mechanical response of high-density cellulose-based materials. In the end, we have observed that pressboard, having initially a heterogeneous density distribution through the thickness, shows a shift in the densification to the more porous part after indentation. The densification maps of the simulated results are presented by comparing with the experimental results. A reasonable agreement is observed between the experimental and the simulated densifications patterns, which suggests that the proposed methodology can be used to predict densification also for other fibre-based materials during manufacturing or in service loading.

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  • 38.
    Afshar, Reza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Ahlgren, Anders
    Vasa museum.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Characterization of mechanical properties of Vasa oak and their application in a full-scale numerical model for support assessment2019Conference paper (Other academic)
    Abstract [en]

    The 17th century Vasa shipwreck is a well-known object of cultural heritage. According to geodetic measurements inside and outside of the ship as well as on the support structure, the ship is sinking onto its cradle. The analysis of measurements showed the ship undergoes continued deformation with increasing strain. Previous research projects on the Vasa ship have largely been focused on the chemical degradation of the Vasa oak, which concerns the waterlogged polyethylene glycol (PEG) impregnated oak wood. The main goal was to provide understanding of the degradation mechanisms and possible remedies to mitigate the chemical decay. In this paper, a review is presented of previous research in term of characterization of mechanical properties, and effects of PEG and moisture on the mechanical behaviour of the Vasa oak. In addition, a full-scale finite-element model of the Vasa ship has been developed to assess its current and future structural behaviour, as well as a tool to design an improved support structure. The mechanical properties, defined in the model in terms of orthotropic elastic engineering constants, have been determined in previous work. Moreover, creep properties of the archaeological wood material have been and are being characterized, so that the model can be extended by extrapolation to predict future deformation. Geodetic measurements have been used for validation of the static model. The approach undertaken in this project could hopefully be useful in design strategies of improved support for other aging and deforming wood structures in cultural heritage.

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  • 39.
    Afshar, Reza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Alavyoon, Navid
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ahlgren, Anders
    Swedish National Maritime Museums, the Vasa Museum.
    van Dijk, Nico P.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Vorobyev, Alexey
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    A full-scale finite-element model of the Vasa ship2017In: Proceedings of ECCOMAS Thematic Conference CompWood 2017: Computational Methods in Wood Mechanics, 2017Conference paper (Refereed)
    Abstract [en]

    A full-scale model of the 17th century Vasa shipwreck has been developed to assess its current and future structural stability as well as design an improved support structure. A wireframe model, consisting of only lines, points and curves to describe the geometry of the ship, has been provided by the Vasa museum. It has been developed based on geodetic measurements using a total station. From this wireframe model, a three-dimensional (3D) model comprising solid bodies for solid-like parts (i.e. hull and keel), surfaces for the shell-like components (deck planks) and lines for beam-like constituents (deck beams) has been developed in Creo Parametric 3D software. This geometric model has been imported in finite-element software, Ansys, for further development of the stiffeners (knees, riders, stanchions, masts, etc.), adjustment of the correct location of deck beams and, finally, structural analyses of the entire ship (Figure 1). The procedure for selection of the different types of elements in the finite-element (FE) model, the definition of orthotropic material properties for the timber structure and preliminary results are discussed in this paper. Experiences drawn from this engineering project may also be useful in development of finite element models for structural assessment of other complex wooden structures in cultural heritage.

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  • 40.
    Afshar, Reza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Jeanne, Simon
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Effects of 3-D Printing Infill Density Parameter on the Mechanical Properties of PLA Polymer2023In: Sixty Shades of Generalized Continua: Dedicated to the 60th Birthday of Prof. Victor A. Eremeyev / [ed] Holm Altenbach; Arkadi Berezovski; Francesco dell'Isola; Alexey Porubov, Cham: Springer, 2023, p. 1-12Chapter in book (Refereed)
    Abstract [en]

    This study presents some results on the mechanical behavior of polylactide (PLA) material, produced using the fused deposition modeling (FDM) additive manufacturing technique. We investigate the effect of infill density on the mechanical properties of PLA specimens. We used tensile specimens, prepared according to ISO 527-2 standard, and tested them by a universal testing machine with analysis by means of digital image correlation (DIC) method. The results in terms of UTS and nominal strain at break of PLA material are presented. They demonstrate a significant impact of infill density on material behavior of PLA specimens, as expected. Yet the effect is nonlinear that is indeed valuable to understand. As infill density increases, from 10% to 100%, the nominal strain at break decreases from about 2.1% to 1.2%, respectively. In other words, the material becomes more ductile by decreasing the infill density of PLA material, which is possible to justify with an effect of the microstructure created by the infill density. There is a transition of this observed behavior, from being more ductile to more brittle, by increasing the infill density of the PLA specimens.

  • 41.
    Afshar, Reza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Jeanne, Simon
    Abali, Bilen Emek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Mechanics.
    Nonlinear Material Modeling for Mechanical Characterization of 3-D Printed PLA Polymer With Different Infill Densities2023In: Applied Composite Materials, ISSN 0929-189X, E-ISSN 1573-4897, Vol. 30, no 3, p. 987-1001Article in journal (Refereed)
    Abstract [en]

    In additive manufacturing, also called 3-D printing, one of widely used materials is polylactide thermoplastic polymer (PLA) by means of the fused deposition modeling. For weight reduction purposes, infill density is an often used feature in slicing for 3-D printing. We aim at investigating the effect of infill density on the mechanical properties of structures. Therefore, we demonstrate how to prepare tensile specimens and test them by a universal testing machine. Results are collected by a so-called digital image correlation method. As infill density increases, from 10% to 100%, the nominal strain at break decreases from about 2.1% to 1.2%, respectively. In other words, the material becomes more ductile by decreasing the infill density of PLA material, which is possible to justify with an effect of the microstructure created by the infill density. Furthermore, we discuss a possible material model fitting all the presented results and report that a hyperelastic material model is needed for the PLA. We utilize Neo-Hookean, Mooney–Rivlin, and Yeoh models, all for different infill densities. All three models show a fairly good agreement to the experimental data. Neo-Hookean model has an advantage of only one parameter, which increases monotonously with infill density.

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  • 42.
    Afzal, Mohammad
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Numerical modelling and analysis of friction contact for turbine blades2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    High cycle fatigue failure of turbine and compressor blades due to resonance in the operating frequency range is one of the main problems in the design of gas turbine engines. To suppress excessive vibrations in the blades and prevent high cycle fatigue, dry friction dampers are used by the engine manufacturers. However, due to the nonlinear nature of friction contact, analysis of such systems becomes complicated.

    This work focuses on the numerical modelling of friction contact and a 3D friction contact model is developed. To reduce the computation time in the Newton-iteration steps, a method to compute the Jacobian matrix in parallel to the contact forces is proposed. The developed numerical scheme is successfully applied on turbine blades with shroud contact having an arbitrary 3D relative displacement. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of the cyclic symmetry boundary condition for a periodic structure.

    The developed 3D coupled numerical contact model is compared with a 3D contact model having uncoupled tangential motion and drawback of the uncoupled contact model is discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different harmonic indices (nodal diameters) of the bladed disk are systematically presented. Moreover, due to the quasi-analytical computation of the Jacobian matrix, the developed scheme is proved to be effective in solving the equations of motion and significant reduction in time is achieved without loss of accuracy.

     

     

     

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    Thesis
  • 43.
    Afzal, Mohammad
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH.
    On efficient and adaptive modelling of friction damping in bladed disks2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work focuses on efficient modelling and adaptive control of friction damping in bladed disks. To efficiently simulate the friction contact, a full-3D time-discrete contact model is reformulated and an analytical expression for the Jacobian matrix is derived that reduces the computation time drastically with respect to the classical finite difference method. The developed numerical solver is applied on bladed disks with shroud contact and the advantage of full-3D contact model compared to a quasi-3D contact model is presented. The developed numerical solver is also applied on bladed disks with strip damper and multiple friction contacts and obtained results are discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different nodal diameters of the bladed disk are systematically presented. The main parameters that influence the effectiveness of friction damping in bladed disks are engine excitation order,  contact stiffnesses,  friction coefficient, relative motion at the friction interface and the normal contact load. Due to variation in these parameters during operation, the obtained friction damping in practice may differ from the optimum value. Therefore, to control the normal load adaptively that will lead to an optimum damping in the system despite these variations, use of magnetostrictive actuator is proposed. The magnetostrictive material that develops an internal strain under the influence of an external magnetic field is employed to increase and decrease the normal contact load. A linearized model of the magnetostrictive actuator is used to characterize the magnetoelastic behavior of the actuator.  A nonlinear static contact analysis of the bladed disk reveals that a change of normal load more than 700 N can be achieved using a reasonable size of the actuator. This will give a very good control on friction damping once applied in practice.

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  • 44.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Arteaga, Ines Lopez
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Netherlands.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Numerical analysis of multiple friction contacts in bladed disks2018In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 137, p. 224-237Article in journal (Refereed)
    Abstract [en]

    The damping potential of multiple friction contacts in a bladed disk is investigated. Friction contacts at tip shrouds and strip dampers are considered. It is shown that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single kind of friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations. A highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.

  • 45.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Adaptive control of normal load at the friction interface of bladed disks using giant magnetostrictive material2020In: Journal of Intelligent Materials Systems and Structures, ISSN 1045-389X, E-ISSN 1530-8138, Vol. 31, no 8, p. 1111-1125Article in journal (Refereed)
    Abstract [en]

    A novel application of magnetostrictive actuators in underplatform dampers of bladed disks is proposed for adaptive control of the normal load at the friction interface to achieve the desired friction damping in the structure. Friction damping in a bladed disk depends on operating parameters, such as rotational speed, engine excitation order, nodal diameter normal contact load, and contact interface parameters, such as contact stiffness and friction coefficient. The operating parameters have a fixed value, whereas the contact interface parameters vary in an unpredictable way at an operating point. However, the ability to vary some of these parameters such as the normal contact load in a controlled manner is desirable to attain an optimum damping in the bladed disk at different operating conditions. Under the influence of an external magnetic field, magnetostrictive materials develop an internal strain that can be exploited to vary the normal contact load at the friction interface, which makes them a potentially good candidate for this application. A commercially available magnetostrictive alloy, Terfenol-D is considered in this analysis that is capable of providing magnetostrain up to 2 × 10-3 under prestress and a blocked force over 1500 N. A linearized model of the magnetostrictive material, which is accurate enough for a direct current application, is employed to compute the output force of the actuator. A nonlinear finite element contact analysis is performed to compute the normal contact load between the blade platform and the underplatform damper as a result of magnetostrictive actuation. The nonlinear contact analysis is performed for different actuator mounting configurations and the obtained results are discussed. The proposed solution is potentially applicable to adaptively control vibratory stresses in bladed disks and consequently to reduce failure due to high-cycle fatigue. Finally, the practical challenges in employing magnetostrictive actuators in underplatform dampers are discussed.

  • 46.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics. kth.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics. Eindhoven University of Technology, the Netherlands.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    A formulation of the Jacobian matrixfor 3D numerical friction contact model applied to turbine blade shroud contactIn: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Article in journal (Other academic)
    Abstract [en]

    An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modelling that eciently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for thecalculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3Drelative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite dierence method, with many points at the contact interface. Therefore,it also significantly reduces the overall computation time for the solution of the equations of motion,since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite dierence approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for aperiodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.

  • 47.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    An analytical calculation of the Jacobian matrix for 3D friction contact model applied to turbine blade shroud contact2016In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 177, p. 204-217Article in journal (Refereed)
    Abstract [en]

    An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modeling that efficiently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for the calculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3D relative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite difference method, with many points at the contact interface. Therefore, it also significantly reduces the overall computation time for the solution of the equations of motion, since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite difference approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for a periodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.

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  • 48.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez-Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Adaptive control of normal load at the friction interface of bladed disks using giant magnetostrictive materialIn: Journal of Vibration and Control, ISSN 1077-5463, E-ISSN 1741-2986Article in journal (Other academic)
    Abstract [en]

    A novel application of magnetostrictive actuators in underplatform dampers of bladed disks is proposed for adaptive control of the normal load at the friction interface in order to achieve the desired friction damping in the structure. Friction damping in a bladed disk depends on many parameters such as rotational speed, engine excitation order, nodal diameter, contact stiffness, friction coefficient and normal contact load. However, all these parameters have a fixed value at an operating point. On the other hand, the ability to vary some of these parameters such as the normal contact load is desirable in order to obtain an optimum damping in the bladed disk at different operating conditions. Under the influence of an external magnetic field, magnetostrictive materials develop an internal strain that can be exploited to vary the normal contact load at the friction interface, which makes them a potentially good candidate for this application. A commercially available magnetostrictive alloy, Terfenol-D is considered in this analysis that is capable of providing magnetostrain up to 0.002 under prestress and a blocked force over 1500 N. A linearized model of the magnetostrictive material, which is accurate enough for a DC application, is employed to compute the output displacement and the blocked force of the actuator. A nonlinear finite element contact analysis is performed to compute the normal contact load between the blade platform and the underplatform damper as a result of magnetostrictive actuation. The contact analysis is performed for different mounting configurations of the actuator and the obtained results are discussed. The proposed solution is potentially applicable to adaptively control vibratory stresses in bladed disks and consequently to reduce failure due to high-cycle fatigue. Finally, the practical challenges in employing magnetostrictive actuators in underplatform dampers are discussed.

  • 49.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez-Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Numerical analysis of multiple friction contacts in bladed disksIn: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162Article in journal (Other academic)
    Abstract [en]

    The damping potential of multiple friction contacts in a bladed disk, tip shroud and strip damper is investigated, showing that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations and a highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the approximate steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.

  • 50.
    Aghaali, Habib
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Exhaust Heat Utilisation and Losses in Internal Combustion Engines with Focus on the Gas Exchange System2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Exhaust gas energy recovery should be considered in improving fuel economy of internal combustion engines. A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocharger and turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the efficiency and mass flow of the turbine(s) as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity. The exhaust gas pressure is the principal parameter which is required for the turbine energy recovery, but higher exhaust back-pressures on the engines create higher pumping losses. This is in addition to the heat losses in the turbochargers what makes any measurement and simulation of the engines more complex.

    This thesis consists of two major parts. First of all, the importance of heat losses in turbochargers has been shown theoretically and experimentally with the aim of including heat transfer of the turbochargers in engine simulations. Secondly, different concepts have been examined to extract exhaust heat energy including turbocompounding and divided exhaust period (DEP) with the aim of improved exhaust heat utilisation and reduced pumping losses.

    In the study of heat transfer in turbochargers, the turbocharged engine simulation was improved by including heat transfer of the turbocharger in the simulation. Next, the heat transfer modelling of the turbochargers was improved by introducing a new method for convection heat transfer calculation with the support of on-engine turbocharger measurements under different heat transfer conditions. Then, two different turbocharger performance maps were assessed concerning the heat transfer conditions in the engine simulation. Finally, the temperatures of turbocharger’s surfaces were predicted according to the measurements under different heat transfer conditions and their effects are studied on the turbocharger performance. The present study shows that the heat transfer in the turbochargers is very crucial to take into account in the engine simulations, especially in transient operations.

    In the study of exhaust heat utilisation, important parameters concerning turbine and gas exchange system that can influence the waste heat recovery were discussed. In addition to exhaust back-pressure, turbine speed and turbine efficiency, the role of the air-fuel equivalence ratio was demonstrated in details, because lower air-fuel equivalence ratio in a Diesel engine can provide higher exhaust gas temperature. The results of this study indicate that turbocompound engine efficiency is relatively insensitive to the air-fuel equivalence ratio.

    To decrease the influence of the increased exhaust back-pressure of a turbocompound engine, a new architecture was developed by combining the turbocompound engine with DEP. The aim of this study was to utilise the earlier phase (blowdown) of the exhaust stroke in the turbine(s) and let the later phase (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow was divided between two different exhaust manifolds with different valve timing.

    According to this study, this combination improves the fuel consumption in low engine speeds and deteriorates it at high engine speeds. This is mainly due to long duration of choked flow in the exhaust valves because this approach is using only one of the two exhaust valves on each cylinder at a time.

    Therefore, the effects of enlarged effective flow areas of the exhaust valves were studied. Two methods were used to enlarge the effective flow area i.e. increasing the diameters of the blowdown and scavenging valves by 4 mm; and modifying the valve lift curves of the exhaust valves to fast opening and closing. Both methods improved BSFC in the same order even though they were different in nature. Fast opening and closing of the exhaust valves required shorter blowdown duration and longer scavenging duration. The modified lift curves provided less pumping losses, less available energy into the turbine and larger amplitude of the pulsating flow through the turbine.

    In order for defining a set of important parameters that should be examined in experimental studies, a sensitivity analysis was performed on the turbocompound DEP engine in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency.

    Finally, to overcome the restriction in the effective flow areas of the exhaust valves, DEP was implemented externally on the exhaust manifold instead of engine exhaust valves, which is called externally DEP (ExDEP). This innovative engine architecture, which benefits from supercharging, turbocharging and turbocompounding, has a great fuel-saving potential in almost all load points up to 4%.

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