| 1. |
- Holzapfel, Gerhard A., et al.
(författare)
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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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Ingår i: European journal of mechanics. A, Solids. - 0997-7538 .- 1873-7285. ; 21:3, s. 441-463
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Finite element algorithms for thermoelastic wear problems
- 2002
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 21:3, s. 423-440
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Tidskriftsartikel (refereegranskat)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
(författare)
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Effect of Structural Defects on the Strength and Damping Properties of a Solid Material
- 2003
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 22:1, s. 47-54
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: European journal of mechanics. A, Solids. - 0997-7538 .- 1873-7285. ; 21:2, s. 191-198
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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.
(författare)
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Non-local damage models in manufacturing simulations
- 2015
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier BV. - 0997-7538 .- 1873-7285. ; 49, s. 548-560
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Numerical and experimental investigation of residual stresses during the induction hardening of 42CrMo4 steel
- 2022
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 96
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Tidskriftsartikel (refereegranskat)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. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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A direct approach for three-dimensional elasto-static and elasto-dynamic solutions in curvilinear cylindrical coordinates with application to classical cylinder problems
- 2022
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Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 95
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with introducing a unique representation of the three-dimensional Navier's equations of motion in cylindrical coordinate system in an exact simplified form without any approximation, aiming at facilitating solution procedure for different 3-D elasto-static and elasto-dynamic problems in the future. A novel form of the 3-D elasticity equations of motion including the body forces in cylindrical coordinate system is derived in an uncoupled form in terms of the longitudinal (axial) displacement component and the 'r-theta' in-plane anti-symmetric rotation function instead of introducing any additional auxiliary unknown potential function. The other displacement components (i.e., circumferential and radial displacement components) are shown to be obtained from two independent equations in terms of the determined axial displacement and the aforementioned rotation component. The correctness, validity and easy implementation of the introduced elasticity approach for obtaining exact elasticity solutions for various 3-D elasto-static and elasto-dynamic problems are demonstrated through solving a number of known elasticity problems. Three-dimensional static and free vibrations of finitelength solid cylinders as well as thick-walled hollow cylindrical shells are analytically solved. Numerical comparative results and discussion are conducted. Excellent agreement between the obtained results and those reported in the literature is observed in all cases, confirming the validity of the proposed new approach.
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| 9. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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On the complete solution of the three-dimensional solid space problems based on a novel curvilinear elasticity representation
- 2023
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Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 97
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Tidskriftsartikel (refereegranskat)abstract
- A solution scheme is presented for the three-dimensional elasticity theory in the curvilinear cylindrical coordinate, without introducing any new physically dubious potential function. Exact analytical solutions for the essential 3-D solid full- and half-space problems are developed based on the introduced elasticity approach. The Kelvin's classical problem of concentrated force acting in the interior of an infinite solid space, as well as the Boussinesq's half-space problem of concentrated force normal to the free surface of a semi-infinite 3-D solid are treated. Furthermore, the three-dimensional non-axisymmetric problem of semi-infinite solid space under concentrated tangential force on its surface (the so-called Cerruti's problem) is revisited. It is demonstrated that unlike most of the conventional solutions in the literature for the aforementioned problems, the present approach is capable of obtaining the complete solution without needing to combine with other approaches. Evidently, the completeness issue associated with any new method of potentials is not present for the established direct elasticity approach. At the end, an extension of the approach to a nonhomogeneous elastic media is presented and, as an application, the Boussinesq's problem for a nonhomogeneous half-space is solved analytically. The developed representation may serve as an efficient replacement of the original three-dimensional Navier's elasticity equations for solving different 3-D elastic problems in the future.
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| 10. |
- Auth, Kim Louisa, 1995, et al.
(författare)
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A thermodynamic framework for ductile phase-field fracture and gradient-enhanced crystal plasticity
- 2024
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Ingår i: European Journal of Mechanics, A/Solids. - 0997-7538. ; 108
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses ductile fracture of single grains in metals by modeling of the formation and propagation of transgranular cracks. A proposed model integrates gradient-extended hardening, phase-field modeling for fracture, and crystal plasticity. It is presented in a thermodynamical framework in large deformation kinematics and accounts for damage irreversibility. A micromorphic approach for variationally and thermodynamically consistent damage irreversibility is adopted. The main objective of this work is to analyze the capability of the proposed model to describe transgranular crack propagation. Further, the micromorphic approach for damage irreversibility is evaluated in the context of the presented ductile phase-field model. This is done by analyzing the impact of gradient-enhanced hardening considering micro-free and micro-hard boundary conditions, studying the effect of the micromorphic regularization parameter, evaluating the performance of the model in ratcheting loading and testing its capability to predict three-dimensional crack propagation. In order to solve the fully coupled global and local equation systems, a staggered solution scheme that extends to the local level is presented.
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