| 1. |
- Holzapfel, Gerhard A., et al.
(author)
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A structural model for the viscoelastic behavior of arterial walls : Continuum formulation and finite element analysis
- 2002
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In: European journal of mechanics. A, Solids. - 0997-7538 .- 1873-7285. ; 21:3, s. 441-463
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Journal article (peer-reviewed)abstract
- In this paper we present a two-layer structural model suitable for predicting reliably the passive (unstimulated) time-dependent three-dimensional stress and deformation states of healthy young arterial walls under various loading conditions. It extends to the viscoelastic regime a recently developed constitutive framework for the elastic strain response of arterial walls (see Holzapfel et al. (2001)). The structural model is formulated within the framework of nonlinear continuum mechanics and is well-suited for a finite element implementation. It has the special merit that it is based partly on histological information, thus allowing the material parameters to be associated with the constituents of each mechanically-relevant arterial layer. As one essential ingredient from the histological information the constitutive model requires details of the directional organization of collagen fibers as commonly observed under a microscope. We postulate a fully automatic technique for identifying the orientations of cellular nuclei, these coinciding with the preferred orientations in the tissue. The biological material is assumed to behave incompressibly so that the constitutive function is decomposed locally into volumetric and isochoric parts. This separation turns out to be advantageous in avoiding numerical complications within the finite element analysis of incompressible materials. For the description of the viscoelastic behavior of arterial walls we employ the concept of internal variables. The proposed viscoelastic model admits hysteresis loops that are known to be relatively insensitive to strain rate, an essential mechanical feature of arteries of the muscular type. To enforce incompressibility without numerical difficulties, the finite element treatment adopted is based on a three-field Hu-Washizu variational approach in conjunction with an augmented Lagrangian optimization technique. Two numerical examples are used to demonstrate the reliability and efficiency of the proposed structural model for arterial wall mechanics as a basis for large scale numerical simulations.
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| 2. |
- Ireman, Peter, et al.
(author)
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Finite element algorithms for thermoelastic wear problems
- 2002
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In: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 21:3, s. 423-440
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Journal article (peer-reviewed)abstract
- In the present paper three algorithms are applied to a finite element model of two thermoelastic bodies in frictional wearing contact. All three algorithms utilize a modification of a Newton method for B-differentiable equations as non-linear equation solver. In the first algorithm the fully-coupled system of thermomechanical equations is solved directly using the modified method, while in the other two algorithms the equation system is decoupled in one mechanical part and another thermal part which are solved using an iterative strategy of Gauss-Seidel type. The two iterative algorithms differ in which order the parts are solved. The numerical performance of the algorithms are investigated for two two-dimensional examples. Based on these numerical results, the behaviour of the model is also discussed. It is found that the iterative approach where the thermal subproblem is solved first is slightly more efficient for both examples. Furthermore, it is shown numerically how the predicted wear gap is influenced by the bulk properties of the contacting bodies, in particular how it is influenced by thermal dilatation. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
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| 3. |
- Ouis, D
(author)
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Effect of Structural Defects on the Strength and Damping Properties of a Solid Material
- 2003
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In: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 22:1, s. 47-54
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Journal article (peer-reviewed)abstract
- In material sciences solid materials are known to be more or lessdispersive, i.e., the Modulus of Elasticity, MOE, and the loss factor are frequency dependent. Furthermore, these two parameters are not totally independent of each other as their frequency variations exhibit some interrelationship. Early studies have revealed that the elasticity and damping properties of wood, unlike many of other solid materials, start to show some frequency dependence already at a few KHz and that these variations depend among others on the species, the drying process, and the size of the specimen. In the present study the variations of the MOE and the loss factor are studied in terms of the number of defects in a wooden element. To this end an increasing number of holes is drilled in a wooden beam, and the major resonance frequencies for the longitudinal mode of vibration are localised on the frequency response curve permitting the determination of the MOE and . The loss factor is evaluated by means of a room acoustical technique using the concept of reverberation time. A refined procedure permits to evaluate in an efficient manner the reverberation time from a single measurement of the impulse response. This latter is also shown to be easily assessed through the use of a cross-correlation operation between the response signal of the system and the input signal to it, this latter being taken as a random broadband noise. As an application, these concepts are used for the study of a wooden beam, and the results obtained for the longitudinal mode of vibration are presented and discussed. It is found that the MOE and values are dependent on the number of defects present in the test sample, and that for an increasing number of these defects the MOE's value decreases steadily whereas the loss factor increases, although to a lesser degree. Some possible explanations of the phenomena underlying such behaviour are addressed and discussed.
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| 4. |
- Simonsson, Kjell, 1964-, et al.
(author)
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A framework for multiplicative associative isotropic elasto-plasticity, that preserves the structure of the infinitesimal theory
- 2002
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In: European journal of mechanics. A, Solids. - 0997-7538 .- 1873-7285. ; 21:2, s. 191-198
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Journal article (other academic/artistic)abstract
- A framework for multiplicative associative isotropic elasto-plasticity that preserves the structure of the infinitesimal theory is presented. Underpinning the work is a kinematical treatment of multiplicative plasticity based on two generic times. To exemplify, the case of one scalar hardening variable is considered in detail. The so obtained relations may be recast in a form identical to relations found in the literature. ⌐ 2002 ╔ditions scientifiques et mΘdicales Elsevier SAS. All rights reserved.
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| 5. |
- Abiri, Olufunminiyi, et al.
(author)
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Non-local damage models in manufacturing simulations
- 2015
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In: European journal of mechanics. A, Solids. - : Elsevier BV. - 0997-7538 .- 1873-7285. ; 49, s. 548-560
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Journal article (peer-reviewed)abstract
- Localisation of deformation is a problem in several manufacturing processes. Machining is an exception where it is a wanted feature. However, it is always a problem in finite element modelling of these processes due to mesh sensitivity of the computed results. The remedy is to incorporate a length scale into the numerical formulations in order to achieve convergent solutions. Different simplifications in the implementation of a non-local damage model are evaluated with respect to temporal and spatial discretisation to show the effect of different approximations on accuracy and convergence.
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| 6. |
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| 7. |
- Areitioaurtena, Maialen, et al.
(author)
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Numerical and experimental investigation of residual stresses during the induction hardening of 42CrMo4 steel
- 2022
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In: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 96
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Journal article (peer-reviewed)abstract
- The usage of induction hardening in the industry has increased in the last years due to its efficiency and repeatability. Induction hardening produces a hard martensitic layer on the specimen surface, which is accompanied by the generation of compressive residual stresses in the hardened case and tensile stresses in the untreated core. Residual stresses generated by induction hardening greatly impact on fatigue performance, as they act as crack growth retardants. In this work, a multiphysical coupled finite element model is developed to simulate induction hardening and compute the final residual stress state of the specimens along the microstructural transformations and hardness evolution. The impact of the transformation induced plasticity strain in the stress-state of the specimen during the process is also studied. The experimental validation shows that considering the transformation induced plasticity in induction hardening simulations improves the residual stress predictions, concluding that this effect should be included to achieve good residual stress predictions, especially in the subsurface region.
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| 8. |
- Cedergren, Joakim, et al.
(author)
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Numerical modelling of P/M steel bars subjected to fatigue loading using an extended Gurson model
- 2004
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In: European Journal of Mechanics. A, Solids. - : Elsevier BV. - 1873-7285 .- 0997-7538. ; 23:6, s. 899-908
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Journal article (peer-reviewed)abstract
- The possibility of modelling experiments conducted on P/M steel bars subjected to strain controlled fatigue loading is investigated. The constitutive relation is an extended Gurson model, using a viscoplastic formulation with plasticity driven damage accumulation supplemented by kinematic as we'll as isotropic hardening. The total damage is modelled as the sum of void growth and void nucleation. Plasticity driven heat accumulation under adiabatic conditions is furthermore included in the model. The damage accumulation was monitored after choosing a kinematically hardening material model. Also rate effects were investigated. It was shown that by assuming the reference viscoplastic strain rate to be constant, increases in damage accumulation and temperature per load cycle with decreasing loading frequency is obtained. This unrealistic behaviour was shown to be eliminated by choosing the reference viscoplastic strain rate a function of the first invariant of the rate of deformation tensor.
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| 9. |
- Cialdea, A., et al.
(author)
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Criterion for the functional dissipativity of the Lam & eacute; operator
- 2023
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In: European journal of mechanics. A, Solids. - : ELSEVIER. - 0997-7538 .- 1873-7285. ; 100
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Journal article (peer-reviewed)abstract
- After introducing the concept of functional dissipativity of the Dirichlet problem in a domain Ω⊂RN for systems of partial differential operators of the form ∂h(Ahk(x)∂k) (Ahk(x) being m×m matrices with complex valued L∞ entries), we find necessary and sufficient conditions for the functional dissipativity of the two-dimensional Lamé system. As an application of our theory we provide two regularity results for the displacement vector in the N-dimensional equilibrium problem, when the body is fixed along its boundary.
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| 10. |
- Croné, Philip, et al.
(author)
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Strain gradient plasticity modelling of cyclic loading in dispersion hardened materials
- 2022
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In: European journal of mechanics. A, Solids. - : Elsevier BV. - 0997-7538 .- 1873-7285. ; 96
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Journal article (peer-reviewed)abstract
- An analytical model, based on an isotropic strain gradient plasticity theory, describing work hardening during cyclic straining in a metal reinforced by a dispersion of non shearable particles is presented. The yield criterion is expressed in terms of isotropic and kinematic hardening contributions and the model is validated against full field finite element (FE) solutions on a 2D axi-symmetric unit cell model. Excellent agreement between analytical and FE results is obtained. The theory presented includes mixed energetic/dissipative contributions from higher order stresses in both bulk and at particle/matrix interfaces. In particular, the influence of a quadratic interface free energy that transitions into a linear form at some threshold value of plastic strain is investigated. It is shown that such an energy is capable of capturing the experimentally observed phenomenon of inflections in the reverse stress-strain curve. It is argued, based on the well known phenomenon where particles are shielded by Orowan dislocation loops during reverse strain, that an energetic interface contribution could be physically relevant for low plastic strains.
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