Endre søk
Begrens søket
57585960 2951 - 2963 of 2963
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 2951.
    Östberg, Martin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Dynamic stiffness of hollowed cylindrical rubber vibrationisolators: The wave-guide solutionArtikkel i tidsskrift (Annet vitenskapelig)
  • 2952.
    Östberg, Martin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Transverse, tilting and cross-coupling stiffness of cylindrical rubber isolators in the audible frequency range-The wave-guide solution2011Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 330, nr 13, s. 3222-3244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Audio-frequency wave-guide models for antisymmetric dynamic stiffness of arbitrary long elastomer cylinders are presented. The locally non-mixed boundary conditions at the lateral and radial surfaces are simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in cylinders satisfying the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied by mode matching. The elastomer is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid embodying a Mittag-Leffler relaxation kernel, the main advantage being the minimum parameter number required to successfully model the material properties over a broad frequency band. The stiffness is found to depend strongly on frequency: displaying resonances and anti-resonances. The method is compared with and verified against finite element models. In addition, comparison to thin beam theories, i.e. Euler and Timoschenko theory and a simple shear model, is presented, illustrating the limitations of these models.

  • 2953.
    Österlind, Tomas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Nicolescu, Cornel-Mihai
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Maskin- och processteknologi.
    Analysis of stationary displacement patterns in rotating machinery subject to local harmonic excitation2017Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 389, s. 224-235Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Rotor vibration and stationary displacement patterns observed in rotating machineries subject to local harmonic excitation are analysed for improved understanding and dynamic characterization. The analysis stresses the importance of coordinate transformation between rotating and stationary frame of reference for accurate results and estimation of dynamic properties. A generic method which can be used for various rotor applications such as machine tool spindle and turbo machinery vibration is presented. The phenomenon shares similarities with stationary waves in rotating disks though focuses on vibration in shafts. The paper further proposes a graphical tool, the displacement map, which can be used for selection of stable rotational speed for rotating machinery. The results are validated through simulation of dynamic response of a milling cutter, which is a typical example of a variable speed rotor operating under different load conditions.

  • 2954. Österlöf, R.
    et al.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Temperature dependency of a viscoplastic constitutive model for rubber with reinforcing fillers2015Inngår i: Constitutive Models for Rubber IX - Proceedings of the 9th European Conference on Constitutive Models for Rubbers, ECCMR, CRC Press/Balkema , 2015, s. 149-156Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A material model is presented that captures the amplitude and frequency dependency of rubber with reinforcing fillers at temperatures between 23 to 85°C. It is a modification of the authors previous work and the basic principle is a smooth elastoplastic element in series with a viscoelastic network, implemented in the time domain. The rheological equivalence is based on the observation in literature that the frequency dependency of filled rubber is stronger for smaller strain amplitudes than for large amplitudes. Finally, the assumption that rubber with reinforcing fillers is thermo-rheologically simple is not always true for higher filler concentrations, resulting in discontinuous master curves for the temperature- frequency dependency. There as on for this discontinuity is that the amplitude dependency is temperature dependent. Therefore, material characterizations evaluated at a low strain amplitude could lead to erroneous results when a higher strain amplitude is of interest. Instead, it is suggested that a material model is fitted to a wide range of experimental data in order to enable realistic calculations of an actual component under operational conditions. To test the constitutive model, a double shear test specimen of natural rubber with 50 phr of carbon black filler is subjected to sinusoidal strains. The amplitudes are varied between 0.2 and 50% shear strain for frequencies between 0.5 and 20 Hz at 23, 60 and 85°C. The derived model needs only 5 material parameters to be fitted to experimental data and captures the storage and loss modulus for the entire range of strain amplitudes and frequencies, as well as non-sinusoidal loading conditions. Moreover, with the proposed modelling technique, it is expected that frequencies well above the available experimental data can be simulated. This is important, since the purpose of every model should be to make predictions outside of the range of available experimental data.

  • 2955.
    Österlöf, Richard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    A finite strain viscoplastic constitutive model for filled rubber2015Inngår i: 22nd International Congress on Sound and Vibration, ICSV 2015, International Institute of Acoustics and Vibrations , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A phenomenological material model for carbon black filled natural rubber based on the multiplicative split of the deformation gradient is implemented for finite strains in three dimensions. This is a generalising of the authors previous work, where the uniaxial rheological equivalent is a smooth friction element in series with a generalized Maxwell chain. The aim of the paper is to demonstrate the advantage of this viscoplastic modelling approach. With only 5 material parameters, the storage and loss modulus is calculated for strain amplitudes between 0.2-50% strain and 0.5-20 Hz, with very encouraging results. These are reasonable ranges of interest when designing the reliability of load bearing components, such as vibration isolators for drivelines in the automotive industry. The Fletcher-Gent effect is well captured, where the strain rate dependency on the storage modulus is higher at smaller strain amplitudes. In addition, the storage and loss modulus are similar to measurements in literature, both in value and shape over the entire range of amplitudes and frequencies. It should be emphasized that capturing both the storage and loss modulus of a material is essential for a material model's capability to describe more complex loading situations than sinusoidal loading. A future implication of the developed model is that it enables realistic simulation of vibration isolators early in the design process whereby extensive physical testing can be reduced, saving both time and money.

  • 2956.
    Österlöf, Rickard
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Modelling of the Fletcher-Gent effect and obtaining hyperelastic parameters for filled elastomers2014Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The strain amplitude dependency , i.e. the Fletcher-Gent effect and Payne effect, and the strain rate dependency of rubber with reinforcing fillers is modelled using a modified boundary surface model and implemented uniaxially. In this thesis, a split of strain instead of stress is utilized, and the storage and loss modulus are captured over two decades of both strain amplitudes and frequencies. In addition, experimental results from bimodal excitation are replicated well, even though material parameters were obtained solely from harmonic excitation. These results are encouraging since the superposition principle is not valid for filled rubber, and real-life operational conditions in general contain several harmonics. This means that formulating constitutive equations in the frequency domain is a cumbersome task, and therefore the derived model is implemented in the time domain. Filled rubber is used irreplaceable in several engineering solutions, such as tires, bushings, vibrations isolators, seals and tread belts, to name just a few. In certain applications, it is sufficient to model the elastic properties of a component during finite strains. However, Hooke’s law is inadequate for this task. Instead, hyperelastic material models are used. Finally, the thesis presents a methodology for obtaining the required material parameters utilizing experiments in pure shear, uniaxial tension and the inflation of a rubber membrane. It is argued that the unloading curve rather than the loading curve is more suitable for obtaining these parameters, even at very low strain rates.

  • 2957.
    Österlöf, Rickard
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Scania.
    Modelling the viscoplastic properties of carbon black filled rubber: A finite strain material model suitable for Finite Element Analysis2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    An increased environmental awareness, legal demands and the large part of total costs attributable to fuel cost are all incentives for the automotive industry to reduce fuel consumption. The optimal driveline to enable this reduction depends on the operational conditions and the available infrastructure. Moreover, special care is needed when developing the driveline isolators, since the demands on noise, vibration and harshness (NVH) are the same regardless of driveline. To this end, computer aided calculations can be used in order to evaluate a large number of configurations. However, these calculations are only, at best, as good as the material models employed. In the foreseeable future, rubber with reinforcing fillers will be used in vibration isolators in order to obtain the desired properties of these components. However, the stiffness and damping of rubber with reinforcing fillers are highly non-linear functions, and the available material models in commercial software and in the literature are often insufficient. Therefore, a finite strain viscoplastic material model is derived in the time domain and implemented as a user defined material model in Abaqus Explicit. The model captures the strain amplitude and frequency dependency of the storage and loss modulus for a carbon black filled natural rubber. The model is accurate over a wide range of shear strain amplitudes and frequencies, 0.2-50 % and 0.5-20 Hz, respectively, using only 5 material parameters. In addition, the model correctly captures the response from bimodal excitations. The implementation in Abaqus Explicit enables component characteristics to be evaluated early in the development phase, with material parameters derived from simple test specimens. The improved accuracy of simulations of these components can aid engineers develop more optimized solutions faster than with conventional methods.

  • 2958.
    Österlöf, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Scania CV AB, Sweden.
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). Scania CV AB, Sweden.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A finite strain viscoplastic constitutive model for rubber with reinforcing fillers2016Inngår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 87, s. 1-14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A three dimensional viscoplastic constitutive model for finite strains in a co-rotational explicit scheme is developed and implemented using finite elements that captures the amplitude dependency, commonly referred to as the Fletcher-Gent effect, and frequency dependency of rubber with reinforcing fillers. The multiplicative split of the deformation gradient is utilized and the plastic flow rule stems from an extension to finite strains of a boundary surface model with a vanishing elastic region. The storage and loss modulus for a 50 phr carbon black filled natural rubber are captured over a large range of strain amplitudes, 0.2-50% shear strain, and frequencies, 0.2-20 Hz. In addition, bimodal excitation is replicated accurately, even though this measurement data is not included when obtaining material parameters. This capability is essential when non-sinusoidal loading conditions are to be replicated. By separating the material and geometrical influence on the properties of a component, the design engineers have the capability to evaluate more concepts early in the design phase. This also reduces the need of complex prototypes for physical testing, thereby saving both time and money.

  • 2959.
    Österlöf, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Scania.
    Wentzel, Henrik
    Scania.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    A finite strain viscoplastic constitutive model for rubberwith reinforcing fillersManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    A three dimensional viscoplastic constitutive model for finite strains in aco-rotational explicit scheme is developed and implemented using finite elementsthat captures the amplitude dependency, commonly referred to as theFletcher-Gent effect, and frequency dependency of rubber with reinforcingfillers. The multiplicative split of the deformation gradient is utilized andthe plastic flow rule stems from an extension to finite strains of a boundarysurface model with a vanishing elastic region. The storage and loss modulusfor a 50 phr carbon black filled natural rubber are captured over a largerange of strain amplitudes, 0.2 − 50% shear strain, and frequencies, 0.2 − 20Hz. In addition, bimodal excitation is replicated accurately, even though thismeasurement data is not included when obtaining material parameters. Thiscapability is essential when non-sinusoidal loading conditions are to be replicated.By separating the material and geometrical influence on the propertiesof a component, the design engineers have the capability to evaluate more concepts early in the design phase. This also reduces the need of complexprototypes for physical testing, thereby saving both time and money.

  • 2960.
    Österlöf, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden .
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    An efficient method for obtaining the hyperelastic properties of filled elastomers in finite strain applications2015Inngår i: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 41, s. 44-54Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An efficient methodology for obtaining hyperelastic material parameters for filled elastomers utilizing unloading curves in uniaxial tension, pure shear and the inflation of a rubber membrane is presented. Experimental results from biaxial extension are crucial when fitting hyperelastic material parameters, and the bubble inflation technique is an excellent method of obtaining this data when specialized test equipment is unavailable. Moreover, filled elastomers have considerable hysteresis, and the hysteresis grows with increasing strain amplitudes. Therefore, the loading curve is in general comprised of both elastic and inelastic contributions, even at very low strain rates. Consequently, it is deemed more accurate to use experimental data from the unloading curve to describe the elastic behavior of the material. The presented methodology enables obtainment of parameters related to both the first and second strain invariant, which is required for a good fit between measurement and simulation results. Finally, it is essential that a chosen material model is accurate in all deformation modes when designing components subjected to a complex, multi-axial load history. An accurate material model enables more concepts and geometries of a component to be studied before a physical prototype is available.

  • 2961.
    Österlöf, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Scania.
    Wentzel, Henrik
    Scania.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Temperature dependency of a viscoplastic materialmodel derived for rubber with reinforcing fillersManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The temperature dependency of a finite strain time domain viscoplastic materialmodel for filled rubber is studied over the ranges 0.2-50% shear strain,0.8-17.9 Hz and 0 to 85 C. The storage and loss modulus of a 54 phr carbonblack filled natural rubber are accurately captured by the model at eachtemperature, thereby supporting the notion that a viscoelastic network inseries with a plastic element is suitable material model for rubber with reinforcingfillers. The variation of the moduli as a function of temperatureis non-linear, with a stronger dependency at lower temperatures. Therefore,a set of measurements are representative in a broader temperature range athigher compared to lower temperatures. Highly filled rubber are not thermorheologicalsimple materials, and an elevated temperature influences the stiffnessand dissipation differently at low and high strain amplitudes. Therefore,relying merely on low strain amplitude measurements can led to erroneousconclusions, when strain amplitudes in operational conditions are moderate to large. The presented modelling technique enables an accurate evaluationbetween compounds, early in the development phase of new components inindustrial applications.

  • 2962.
    Österlöf, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. Scania, Södertälje, Sweden .
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Diercks, N.
    Wollscheid, D.
    Constitutive modelling of the amplitude and frequency dependency of filled elastomers utilizing a modified Boundary Surface Model2014Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, nr 19-20, s. 3431-3438Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A phenomenological uniaxial model is derived for implementation in the time domain, which captures the amplitude and frequency dependency of filled elastomers. Motivated by the experimental observation that the frequency dependency is stronger for smaller strain amplitudes than for large ones, a novel material model is presented. It utilizes a split of deformation between a generalized Maxwell chain in series with a bounding surface plasticity model with a vanishing elastic region. Many attempts to capture the behaviour of filled elastomers are found in the literature, which often utilize an additive split between an elastic and a history dependent element, in parallel. Even though some models capture the storage and loss modulus during sinusoidal excitations, they often fail to do so for more complex load histories. Simulations with the derived model are compared to measurements in simple shear on a compound of carbon black filled natural rubber used in driveline isolators in the heavy truck industry. The storage and loss modulus from simulations agree very well with measurements, using only 7 material parameters to capture 2 decades of strain (0.5-50% shear strain) and frequency (0.2-20 Hz). More importantly, with material parameters extracted from the measured storage and loss modulus, measurements of a dual sine excitation are well replicated. This enables realistic operating conditions to be simulated early in the development process, before an actual prototype is available for testing, since the loads in real life operating conditions frequently are a combination of many harmonics.

  • 2963.
    Östlund, Stefan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Andersson, Evert
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Järnvägsteknik.
    Kottenhoff, Karl
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Trafik och logistik.
    Efficient Passenger Trains for the Future1999Inngår i: Proceedings of the WCRR99, 1999Konferansepaper (Fagfellevurdert)
57585960 2951 - 2963 of 2963
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf