| 1. |
- Abali, Bilen Emek, et al.
(författare)
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Additive manufacturing introduced substructure and computational determination of metamaterials parameters by means of the asymptotic homogenization
- 2021
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Science and Business Media LLC. - 0935-1175 .- 1432-0959. ; 33:4, s. 993-1009
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 2. |
- Agnelli, Filippo, et al.
(författare)
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Design and testing of 3D-printed micro-architectured polymer materials exhibiting a negative Poisson’s ratio
- 2020
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer-Verlag New York. - 0935-1175 .- 1432-0959. ; 32:2, s. 433-449
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Tidskriftsartikel (refereegranskat)abstract
- This work proposes the complete design cycle for several auxetic materials where the cycle consists of three steps (i) the design of the micro-architecture, (ii) the manufacturing of the material and (iii) the testing of the material. We use topology optimization via a level-set method and asymptotic homogenization to obtain periodic micro-architectured materials with a prescribed effective elasticity tensor and Poisson’s ratio. The space of admissible micro-architectural shapes that carries orthotropic material symmetry allows to attain shapes with an effective Poisson’s ratio below −1−1. Moreover, the specimens were manufactured using a commercial stereolithography Ember printer and are mechanically tested. The observed displacement and strain fields during tensile testing obtained by digital image correlation match the predictions from the finite element simulations and demonstrate the efficiency of the design cycle.
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| 3. |
- Argatov, Ivan, et al.
(författare)
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Analysis of the minimal model for the enthalpy relaxation and recovery in glass transition : application to constant-rate differential scanning calorimetry
- 2021
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer. - 0935-1175 .- 1432-0959. ; 33, s. 107-123
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Tidskriftsartikel (refereegranskat)abstract
- The so-called minimal model is formulated for describing the enthalpy relaxation and recovery in glass transition. The model is based on the Arrhenius law for the enthalpy relaxation, which uses two-dimensional parameters, namely the activation energy and the so-called pre-factor (relaxation time at relatively high temperature). A numerically effective exact analytical solution is obtained for the case of constant-rate differential scanning calorimetry. The developed model is analyzed according to the logic of the model itself without introducing additional simplifying assumptions of thermodynamic nature. For typical range of the model parameters, the resulting differential equation contains a large parameter, which offers an opportunity for the application of asymptotic and approximate techniques. A number of simple approximations have been provided for some thermodynamic quantities of interest.
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| 4. |
- Argatov, Ivan, et al.
(författare)
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How to define the storage and loss moduli for a rheologically nonlinear material?
- 2017
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer. - 0935-1175 .- 1432-0959. ; 29:6, s. 1375-1387
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Tidskriftsartikel (refereegranskat)abstract
- A large amplitude oscillatory shear (LAOS) is considered in the strain-controlled regime, and the interrelation between the Fourier transform and the stress decomposition approaches is established. Several definitions of the generalized storage and loss moduli are examined in a unified conceptual scheme based on the Lissajous–Bowditch plots. An illustrative example of evaluating the generalized moduli from a LAOS flow is given.
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| 5. |
- dell'Isola, Francesco, et al.
(författare)
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Advances in pantographic structures : design, manufacturing, models, experiments and image analyses
- 2019
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer. - 0935-1175 .- 1432-0959. ; 31:4, s. 1231-1282
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Tidskriftsartikel (refereegranskat)abstract
- In the last decade, the exotic properties of pantographic metamaterials have been investigated and different mathematical models (both discrete or continuous) have been introduced. In a previous publication, a large part of the already existing literature about pantographic metamaterials has been presented. In this paper, we give some details about the next generation of research in this field. We present an organic scheme of the whole process of design, fabrication, experiments, models and image analyses.
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| 6. |
- Jänicke, Ralf, 1980, et al.
(författare)
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Two-scale modelling of micromorphic continua
- 2009
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Science and Business Media LLC. - 0935-1175 .- 1432-0959. ; 21:4, s. 297-315
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Tidskriftsartikel (refereegranskat)abstract
- According to their peculiar mechanical properties, the description of cellular materials is of high interest. Modelling aspects to be considered are, e.g. pronounced size depending boundary layer effects as well as a deformation-driven evolution of anisotropy or porosity. In the present contribution, we pay special attention to the description of size-dependent microtopological effects on the one hand. On the other hand, we focus on the relevance of extended continuum theories describing the local deformation state of microstructured materials. We, therefore, introduce a homogenization scheme for two-scale problems replacing a heterogeneous Cauchy continuum on the microscale by a homogeneous effective micromorphic continuum on the macroscale. The transitions between both scales are obtained by appropriate projection and homogenization rules which have to be derived, on the one hand, by kinematic assumptions, i.e. the minimization of the macroscopic displacement field, and, on the other hand, by energetic considerations, i.e. the evaluation of an extended Hill–Mandel condition.
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| 7. |
- Kari, Leif
(författare)
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Dynamic stiffness of chemically and physically ageing rubber vibration isolators in the audible frequency range : Part 2-waveguide solution
- 2017
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Ingår i: Continuum Mechanics and Thermodynamics. - : SPRINGER. - 0935-1175 .- 1432-0959. ; 29:5, s. 1047-1059
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic stiffness of a chemically and physically ageing rubber vibration isolator in the audible frequency range is modelled as a function of ageing temperature, ageing time, actual temperature, time, frequency and isolator dimension. In particular, the dynamic stiffness for an axially symmetric, homogeneously aged rubber vibration isolator is derived by waveguides where the eigenmodes given by the dispersion relation for an infinite cylinder satisfying traction free radial surface boundary condition are matched to satisfy the displacement boundary conditions at the lateral surface ends of the finite rubber cylinder. The constitutive equations are derived in a companion paper (Part 1). The dynamic stiffness is calculated over the whole audible frequency range 20-20,000 Hz at several physical ageing times for a temperature history starting at thermodynamic equilibrium at +25 degrees C and exposed by a sudden temperature step down to -60 degrees C and at several chemical ageing times at temperature +25 degrees C with simultaneous molecular network scission and reformation. The dynamic stiffness results are displaying a strong frequency dependence at a short physical ageing time, showing stiffness magnitude peaks and troughs, and a strong physical ageing time dependence, showing a large stiffness magnitude increase with the increased physical ageing time, while the peaks and troughs are smoothed out. Likewise, stiffness magnitude peaks and troughs are frequency-shifted with increased chemical ageing time. The developed model is possible to apply for dynamic stiffness prediction of rubber vibration isolator over a broad audible frequency range under realistic environmental condition of chemical ageing, mainly attributed to oxygen exposure from outside and of physical ageing, primarily perceived at low-temperature steps.
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| 8. |
- Kari, Leif
(författare)
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Dynamic stiffness of chemically and physically ageing rubber vibration isolators in the audible frequency range
- 2017
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Ingår i: Continuum Mechanics and Thermodynamics. - : SPRINGER. - 0935-1175 .- 1432-0959. ; 29:5, s. 1027-1046
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Tidskriftsartikel (refereegranskat)abstract
- The constitutive equations of chemically and physically ageing rubber in the audible frequency range are modelled as a function of ageing temperature, ageing time, actual temperature, time and frequency. The constitutive equations are derived by assuming nearly incompressible material with elastic spherical response and viscoelastic deviatoric response, using Mittag-Leffler relaxation function of fractional derivative type, the main advantage being the minimum material parameters needed to successfully fit experimental data over a broad frequency range. The material is furthermore assumed essentially entropic and thermo-mechanically simple while using a modified William-Landel-Ferry shift function to take into account temperature dependence and physical ageing, with fractional free volume evolution modelled by a nonlinear, fractional differential equation with relaxation time identical to that of the stress response and related to the fractional free volume by Doolittle equation. Physical ageing is a reversible ageing process, including trapping and freeing of polymer chain ends, polymer chain reorganizations and free volume changes. In contrast, chemical ageing is an irreversible process, mainly attributed to oxygen reaction with polymer network either damaging the network by scission or reformation of new polymer links. The chemical ageing is modelled by inner variables that are determined by inner fractional evolution equations. Finally, the model parameters are fitted to measurements results of natural rubber over a broad audible frequency range, and various parameter studies are performed including comparison with results obtained by ordinary, non-fractional ageing evolution differential equations.
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| 9. |
- Kari, Leif
(författare)
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Effective visco-elastic models of tough, doubly cross-linked, single-network polyvinyl alcohol (PVA) hydrogels : Additively separable fractional derivative-based models for chemical and physical cross-links
- 2020
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer. - 0935-1175 .- 1432-0959.
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Tidskriftsartikel (refereegranskat)abstract
- An effective fractional derivative-based visco-elastic model of tough, doubly cross-linked, single-network polyvinyl alcohol (PVA) hydrogels, embodying both chemical and physical cross-links, is developed using a Mittag–Leffler relaxation function of order 1/2 while applying only three material parameters that are physically quantifiable, namely frequency for maximum loss modulus, equilibrium elastic modulus and relaxation intensity. The resulting 3-parameter shear modulus model is possible to additively split into chemical and physical parts; the split being the study focus. Physical explanations of the visco-elastic low-, mid- and high-frequency range properties, and their transitions between the frequency ranges, are given mainly in terms of the permanent chemical cross-links and the distinct adhesion–deadhesion processes of the transient physical cross-links. The latter are running from an associated Rouse mode low-frequency behaviour through a maximum adhesion–deadhesion dissipation and to an elastic, fully active cross-link high-frequency behaviour, while the former are displaying essentially an elastic, fully active cross-link behaviour throughout the frequency range. The developed model covers the full frequency range while matching measurements results remarkably well. Furthermore, the model is refined into a 4-parameter model by additively including an Abel relaxation function of order 1/2 to take into account the superimposed Rouse-type behaviour found in the measurements of the chemical cross-links in addition to their dominating elastic response, with the fourth parameter being a chemical Rouse stress intensity factor. The simple, effective visco-elastic models are suitable in predicting the mechanical properties of tough, doubly cross-linked, single-network PVA hydrogels with application potentials in tissue and noise abatement engineering.
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| 10. |
- Laudato, Marco, et al.
(författare)
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Analysis of the contact critical pressure of collapsible tubes for biomedical applications
- 2023
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Nature. - 0935-1175 .- 1432-0959. ; 36:1, s. 217-228
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Tidskriftsartikel (refereegranskat)abstract
- The onset of self-excited oscillations in airways and blood vessels is a common phenomenon in the human body, connected to both normal and pathological conditions. A recent experimental investigation has shown that the onset of self-excited oscillations happens for values of the intramural pressure close to the contact critical pressure. The goal of this work is to analyse the dependence of the contact critical pressure on the vessel’s geometric parameters. The methodology is based on the implementation of an experimentally validated computational model of a collapsible tube. The results confirm the correlation between the contact critical pressure and the onset of self-excited oscillations in collapsible tubes. Moreover, a set of general equations to compute the contact critical pressure and the corresponding areas of collapsible tubes with arbitrary geometries has been derived.
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| 11. |
- Lidström, Per
(författare)
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On the volume average of energy and net power
- 2011
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Science and Business Media LLC. - 1432-0959 .- 0935-1175. ; 23:4, s. 275-304
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an analysis of volume average relations in connection with internal energy, net power and the balance of energy in continuum mechanics. The role of the so-called Hill and Hill-Mandel conditions in connection with the averaged energy balance equation has been elucidated. The significance of volume averages of stress moments for the calculation of the average net power is demonstrated.
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| 12. |
- Liu, Yiming, et al.
(författare)
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Plate capacitor problem as a benchmark case for verifying the finite element implementation
- 2023
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Nature. - 0935-1175 .- 1432-0959. ; 35:1, s. 245-265
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Tidskriftsartikel (refereegranskat)abstract
- In this work, parallel plate capacitors are numerically simulated by solving weak forms within the framework of the finite element method. Two different domains are studied. We study the infinite parallel plate capacitor problem and verify the implementation by deriving analytical solutions with a single layer and multiple layers between two plates. Furthermore, we study the finite parallel plate capacitor problem and verify it by Love’s potential equation and Xiang’s capacitance equation. Moreover, the fringing effect is considered and extended to problems with multiple dielectric layers, such a solution is not possible by means of the existing analytical solutions. Besides, we realize the possibility of choosing different boundary conditions (electric potential boundary conditions and charge density boundary conditions) by changing the weak form. Finally, a transient solution that includes dielectric loss and calculates the quality factor of a capacitor is presented, which may be used in capacitor design. Convergence and consistency of results are demonstrated by comparing the results between analytical and numerical solutions and also the results from different boundary conditions.
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| 13. |
- Molavitabrizi, Danial, et al.
(författare)
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Second-order homogenization of 3-D lattice materials towards strain gradient media : numerical modelling and experimental verification
- 2023
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Nature. - 0935-1175 .- 1432-0959.
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Tidskriftsartikel (refereegranskat)abstract
- The literature in the field of higher-order homogenization is mainly focused on 2-D models aimed at composite materials, while it lacks a comprehensive model targeting 3-D lattice materials (with void being the inclusion) with complex cell topologies. For that, acomputational homogenization scheme based on Mindlin (type II) strain gradient elasticity theory is developed here. The model is based on variational formulation with periodic boundary conditions, implemented in the open-source software FreeFEM to fully characterize the effective classical elastic, coupling, and gradient elastic matrices in lattice materials. Rigorous mathematical derivations based on equilibrium equations and Hill-Mandel lemma are provided, resulting in the introduction of macroscopic body forces and modifications in gradient elasticity tensors which eliminate the spurious gradient effects in the homogeneousmaterial. The obtained homogenized classical and strain gradient elasticity matrices are positive definite, leading to a positive macroscopic strain energy density value—an importantcriterion that sometimes is overlooked. The model is employed to study the size effects in 2-D square and 3-D cubic lattice materials. For the case of 3-D cubic material, the model is verified using full-field simulations, isogeometric analysis, and experimental three-point bending tests.The results of computational homogenization scheme implemented through isogeometric simulations show a good agreement with full-field simulations and mechanical tests. The developed model is generic and can be used to derive the effective second-grade continuum forany 3-D architectured material with arbitrary geometry. However, the identification of the proper type of generalized continua for the mechanical analysis of different cell architectures is yet an open question.
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| 14. |
- Mousavi, Mahmoud, 1983-
(författare)
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Singularity-free defect mechanics for polar media
- 2019
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer. - 0935-1175 .- 1432-0959. ; 31, s. 1883-1909
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Tidskriftsartikel (refereegranskat)abstract
- We present singularity-free solution for cracks within polar media in which material points possess both position and orientation. The plane strain problem is addressed in this study for which the generalized continua including micropolar, nonlocal micropolar, and gradient micropolar elasticity theories are employed. For the first time, the variationally consistent boundary conditions are derived for gradient micropolar elasticity. Moreover, having reviewed the solution to line defects including glide edge dislocation and wedge disclination from the literature, the fields of a climb edge dislocation within micropolar, nonlocal micropolar and gradient micropolar elasticity are derived. This completes the collection of line defects needed for an inplane strain analysis. Afterward, as the main contribution, using both types of line defects (i.e., dislocation being displacement discontinuity and disclination being rotational discontinuity), the well-established dislocation-based fracture mechanics is systematically generalized to the dislocation- and disclination-based fracture mechanics of polar media for which we have three translations together with three rotations as degrees of freedom. Due to the application of the line defects, incompatible elasticity is employed throughout the paper. Cracks under three possible loadings including stress and couple stress components are analyzed, and the corresponding line defect densities and stress and couple stress fields are reported. The singular fields are obtained once using the micropolar elasticity, while nonlocal micropolar, and gradient micropolar elasticity theories give rise to singularity-free fracture mechanics.
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| 15. |
- Rotoli, G., et al.
(författare)
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Resonant phase dynamics in 0-π Sine–Gordon facets
- 2015
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Science and Business Media LLC. - 0935-1175 .- 1432-0959. ; 27:4-5, s. 639-658
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Tidskriftsartikel (refereegranskat)abstract
- A locally phase-shifted Sine–Gordon model well accounts for the phenomenology of unconventional Josephson junctions. The phase dynamics shows resonant modes similar to Fiske modes that appear both in the presence and in the absence of the external magnetic field in standard junctions. In the latter case, they are also in competition with zero field propagation of Sine–Gordon solitons, i.e., fluxons, which give rise to the so-called zero field steps in the current–voltage (I–V) of the junction. We numerically study the I–V characteristics and the resonances magnetic field patterns for some different faceting configurations, in various dissipative regimes, as a function of temperature. The simulated dynamics of the phase is analyzed for lower-order resonances. We give evidence of a nontrivial dynamics due to the interaction of propagating fluxons with localized semifluxons. Numerical results are compared with experimental outcomes obtained on high-quality high-Tc grain boundary YBCO junctions.
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| 16. |
- Sisman, Altug, et al.
(författare)
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Quantum Size Effects on Classical Thermosize Effects
- 2012
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Ingår i: Continuum Mechanics and Thermodynamics. - 0935-1175 .- 1432-0959. ; 24, s. 339-346
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Tidskriftsartikel (refereegranskat)abstract
- Thermosize effects have been proposed in literature by considering the quantum size effects (QSE)induced by the wave character of particles. These effects appear only if nano and macro domains are connectedto each other when they are under a temperature gradient. QSE are noticeable in nano domain while they arealmost negligible in macro domain. This difference causes thermosize effects, which may be called quantumthermosize effects (QTSE) because of their pure quantum origin. On the other hand, also classical thermosizeeffects (CTSE) appear as a result of different transport regimes in nano and macro domains, and they can benoticeable even if QTSE are negligible. As long as the mean free path (l) is much greater than the mean deBroglie wave length of particles (λ), which is almost the case in practice λ/l < 1, the principal effects areCTSE. QSE cause only small corrections on CTSE when the scale is down to nanoscale. On the other hand, in literature, QTSE and CTSE have been examined individually although it is not possible to observe QTSE alone in practice except for the extreme case of λ/l >> 1. Furthermore, the constant pressure assumption andthe Knudsen law have been used during the derivations of QTSE and CTSE, respectively, although the properassumption at nanoscale is the modified Knudsen law, which considers QSE. In this study, QSE on CTSE areconsidered and the modified Knudsen law is derived and used to obtain the more realistic results for thermosizecoefficients. The results can be used for a possible experimental verification of thermosize effects as well asto design some new devices based on these effects.
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| 17. |
- Vazic, Bozo, et al.
(författare)
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Generalized thermo-mechanical framework for heterogeneous materials through asymptotic homogenization
- 2023
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Nature. - 0935-1175 .- 1432-0959. ; 35, s. 159-181
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental understanding of the interaction between microstructure and underlying physical mechanisms is essential, especially for developing more accurate multi-physics models for heterogeneous materials. Effects of microstructure on the material response at the macroscale are modeled by using the generalized thermomechanics. In this study, strain gradient theory is employed as a higher-order theory on the macroscale with thermodynamics modeled as a first-order theory on the microscale. Hence, energy depends only on the temperature such that we circumvent an extension of Fourier’s law and analyze the “simplest” thermo-mechanical model in strain gradient elasticity. Developing multiphysics models for heterogeneous materials is indeed a challenge and even this “simplest” model in generalized thermomechanics creates dozens of parameters to be determined. We develop a thermo-mechanical framework, in which microstructure is modeled as a periodic structure and through asymptotic homogenization approach, higher-order parameters at macroscopic scale are calculated. To illustrate the importance of higher-order parameters in overall thermo-mechanical response of a heterogeneous materials, finite element method (FEM) is employed with the aid of open-source codes (FEniCS). Verification example of a bulk system and several case studies of porous structures demonstrate how such numerical framework can be beneficial in the design of materials with tailored microstructures.
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| 18. |
- Tafoya Martinez, Daniel, 1981, et al.
(författare)
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Submillimeter H2O masers in water-fountain nebulae
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 562, s. 4-
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Tidskriftsartikel (refereegranskat)abstract
- We report the first detection of submillimeter water maser emission toward water-fountain nebulae, which are post-AGB stars that exhibit high-velocity water masers. Using APEX we found emission in the ortho-H2O (10(29) -> 9(36)) transition at 321.226 GHz toward three sources: IRAS 15445-5449, :IRAS 18043-2116, and IRAS 18286-0959. Similar to the 22 GHz masers, the submillimeter water masers are expanding with higher velocity than do 011 masers, suggesting that these masers also originate in fast bipolar outflows. In IRAS 18043-2116 and IRAS 18286-0959, which figure among the sources with the fastest water masers, the velocity range of the 321 GHz masers coincides with the range of the 22 GHz masers, indicating that they probably coexist. Toward IRAS 15445-5449, the submillimeter masers appear in a different velocity range, indicating that they trace different regions. The intensity of the submillimeter masers is comparable to the 22 GHz masers, implying that the kinetic temperature of the region where the masers originate should be T-k > 1000 K. We propose that the passage of two shocks through the same gas can create the conditions for explaining the strong high-velocity 321 GHz masers coexisting with the 22 GHz masers in the same region.
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| 19. |
- Edlund, Maria, 1972, et al.
(författare)
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Quantitatively measured tremor in hand-arm vibration-exposed workers
- 2015
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Ingår i: International Archives of Occupational and Environmental Health. - : Springer Science and Business Media LLC. - 0340-0131 .- 1432-1246. ; 88:3, s. 305-310
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to investigate the possible increase in hand tremor in relation to hand-arm vibration (HAV) exposure in a cohort of exposed and unexposed workers. Participants were 178 male workers with or without exposure to HAV. The study is cross-sectional regarding the outcome of tremor and has a longitudinal design with respect to exposure. The dose of HAV exposure was collected via questionnaires and measurements at several follow-ups. The CATSYS Tremor Pen(A (R)) was used for measuring postural tremor. Multiple linear regression methods were used to analyze associations between different tremor variables and HAV exposure, along with predictor variables with biological relevance. There were no statistically significant associations between the different tremor variables and cumulative HAV or current exposure. Age was a statistically significant predictor of variation in tremor outcomes for three of the four tremor variables, whereas nicotine use was a statistically significant predictor of either left or right hand or both hands for all four tremor variables. In the present study, there was no evidence of an exposure-response association between HAV exposure and measured postural tremor. Increase in age and nicotine use appeared to be the strongest predictors of tremor.
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| 20. |
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