| 1. |
- Ireman, Peter, et al.
(författare)
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A model of damage coupled to wear
- 2003
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 40:12, s. 2957-2974
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Tidskriftsartikel (refereegranskat)abstract
- The present paper presents a model of damage coupled to wear. The damage model is based on a continuum model including the gradient of the damage variable. Such a model is non-local in the sense that the evolution of damage is governed by a boundary-value problem instead of a local evolution law. Thereby, the well-known mesh-dependency observed for local damage models is removed. Another feature is that the boundary conditions can be used to introduce couplings between bulk damage and processes at the boundary. In this work such a coupling is suggested between bulk damage and wear at the contact interface. The model is regarded as a first attempt to formulate a continuum damage model for studying crack initiation in fretting fatigue. The model is given within a thermodynamic framework, where it is assured that the principles of thermodynamics are satisfied. Furthermore, two variational formulations of the full initial boundary value problem, serving as starting points for finite element discretization, are presented. Finally, preliminary numerical results for a simple one-dimensional example are presented and discussed. It is qualitatively shown how the evolution of damage may influence the wear behaviour and how damage may be initiated by the wear process. © 2003 Elsevier Science Ltd. All rights reserved.
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| 2. |
- Ireman, Peter, 1974-
(författare)
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Algorithms for gradient damage models based on a semi-smooth Newton method
- 2005
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825 .- 1879-2138. ; 194:6-8, s. 727-741
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Tidskriftsartikel (refereegranskat)abstract
- In this paper two different algorithms are applied to a model of brittle damage including the gradient of the damage variable. Both algorithms are based on a modified Newton method. In the first algorithm the Newton method is applied directly to the whole system of equations, while in the second algorithm, the equilibrium equations and the damage evolution problem are solved uncoupled from each other in a Gauss-Seidel scheme. The algorithms are applied to two different formulations of the problem. In the first formulation the thermodynamic force, work conjugate to the damage variable is kept as an auxiliary variable, while in the second formulation this variable is eliminated. It turns out that the formulation using the extra variable is more robust in the sense that the algorithms converge even for very large load increments. On the other hand, the formulation where the extra variable is eliminated is more efficient for small time steps since a smaller system of equations is solved for each increment. Furthermore, it is found that the direct approach is more efficient than the decoupled approach for this problem.
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| 3. |
- Ireman, Peter, et al.
(författare)
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Algorithms for thermoelastic wear problems
- 2002
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Ingår i: Contact mechanics. - Dordrecht : Kluwer Academic. - 9781402008115 - 1402008112 ; , s. 363-370
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Konferensbidrag (refereegranskat)abstract
- This contribution concerns the numerical treatment of discrete thermoelastic wear problems. Two different approaches, both utilizing a non-smooth Newton method as non-linear equation solver, are outlined and compared. Furthermore, a numerical example shows how the predicted wear gap is influenced by the bulk properties of the contacting bodies.
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| 4. |
- Ireman, Peter, 1974-
(författare)
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Continuum models and numerical methods for fretting
- 2001
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study is concerned with continuum models and numerical methods for wear, frictional heat and damage. Of special interest are so called fretting phenomena. Fretting occurs when two bodies in contact experience small periodic, relative motion which leads to wear and the promoted initiation of fatigue cracks. The work presented here is a part of a general attempt to give this phenomenon a continuum mechanical description suitable for numerical treatment.The study consists of two main contributions concerning (i) the numerical treatment of a thermoelastic wear model and (ii) the formulation of a model of damage coupled to wear, regarded as a first attempt to develop a continuum model in order to study the crack initiation phase in fretting fatigue. The thesis consists of four papers.Paper I concerns the numerical treatment of thermoelastic wear problems. Two different approaches, both utilizing a non-smooth Newton method as non-linear equation solver, are outlined and compared. Furthermore, the behaviour of the thermoelastic wear model is discussed based on the solution of two numerical examples.Paper II is an review of some general observations regarding crack initiation in fretting and a survey of existing models and methods for predicting fretting fatigue failures.Paper III is a literature survey concerning various methods to avoid mesh-dependency in connection with numerical solution of models exhibiting strain-softening with special emphasis on continuum damage mechanics.Paper IV presents a model of damage coupled to wear. The model is based on a continuum damage model including the gradient of the damage variable.
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| 5. |
- 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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| 6. |
- Ireman, Peter, et al.
(författare)
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Gradient theory of damage coupled to frictional contact and wear, and its numerical treatment
- 2009
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Ingår i: CMES - Computer Modeling in Engineering & Sciences. - : Tech Science Press. - 1526-1492 .- 1526-1506. ; 52:2, s. 125-158
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Tidskriftsartikel (refereegranskat)abstract
- In this paper finite element approaches for fretting fatigue are proposed on the basis of a non-local model of continuum damage coupled to friction and wear. The model is formulated in the frame-work of a standard material. In a previous paper this was done in the spirit of Maugin, where an extra entropy flux is introduced in the second law in order to include the gradient of the internal variable in a proper manner. In this paper we follow instead the ideas of Frémond and others, where this extra entropy flux is no longer needed, but instead new non-classical balance laws associated to damage, friction and wear, respectively, are derived from the principle of virtual power. The standard material is then defined as usual by state laws based on free energies and complementary laws based on dissipation potentials. In particular, we pick free energies and dissipation potentials that correspond to a non-local continuum damage model coupled to friction and wear. In addition, the boundary conditions at the contact interface creates a coupling between damage and wear. This is a key feature of our model, which makes it very useful in studies of fretting fatigue. By starting from a variational formulation of the governing equations, two different finite element algorithms are implemented. Both algorithms are based on a Newton method for semi-smooth equations. In the first algorithm the Newton method is applied to the entire system of equations, while in the second algorithm the system of equations is split into two different parts such that an elastic wear problem is solved for fixed damage followed by the solution of the damage evolution problem for the updated displacements and contact forces in an iterative process. The latter algorithm can be viewed as a Gauss-Seidel scheme. The numerical performance of the algorithms is investigated for three twodimensional examples of increasing complexity. Based on the numerical solutions, the behavior of the model is also discussed. For instance, it is shown numerically how the initiation of damage depends on the contact geometry, the coefficient of friction and the evolution of wear.
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| 7. |
- Ireman, Peter Jarl, 1974-
(författare)
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Continuum models and numerical methods for tribological systems
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the formulation of continuum mechanical models and the development of numerical methods for frictional heating, wear and damage in tribological systems.The models are formulated in the spirit of generalized standard materials, i.e. by defining observable and internal state variables and stating the constitutive relations by means of gradients of a free energy and a dissipation potential. Here two extensions of this framework is discussed: (i) the case when the free energy is non-smooth and (ii) when gradients of internal variables are included in the constitutive model. The latter extension is used to formulate a model of damage which is non-local in the sense that the evolution of damage is governed by a boundary-value problem instead of a local evolution law. This way the well-known problem with mesh-dependent solutions is removed. Another feature of the gradient model is that the boundary conditions can be used to include couplings between bulk damage and processes at the boundary. This feature is used to establish a coupling between bulk damage and wear.The governing equations are stated as a variational problem which is discretized and reformulated as a system of semi-smooth equations. The numerical methods are based on a modified Newton method for semi-smooth equations. The Newton method is applied in two different ways, either directly to the whole system of equations or by splitting the system of equations into different parts which are treated in a Gauss-Seidel scheme. In this case the Newton method is used to solve the different parts in each Gauss-Seidel step. This approach is applied to three different problems: (i) thermoelastic wear problems including frictional heating and heat conduction through the contact interface (ii) the gradient damage problem and (iii) the coupled wear and damage problem. For the thermoelastic wear problem it is found that the decoupled approach is slightly more efficient than the the direct application of the Newton method. The numerical solution shows how the wear process is influenced by the change of geometry due to frictional heating. Furthermore, it is shown how fretting can be induced by a prescribed varying boundary temperature. For the plain gradient damage problem the direct application of the Newton method is more efficient. Finally, for the coupled wear and damage problem the two approaches are about equally efficient. Numerical solutions of this problem shows how the initiation of damage depends on contact geometry, friction and wear.
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| 8. |
- Ireman, Peter, et al.
(författare)
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Using the gradients of temperature and internal parameters in Continuum Thermodynamics
- 2004
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Ingår i: Comptes rendus. Mecanique. - : Elsevier BV. - 1631-0721 .- 1873-7234. ; 332:4, s. 249-255
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the possibility of using the gradients of the temperature and of the internal parameters as additional state variables in Continuum Thermodynamics is considered. The expressions of the two principles are discussed and Clausius-Duhem inequality is derived under an appropriate statement of the internal entropy production. Several formulations are proposed and compared to existing results in the literature. To cite this article: P. Ireman, Q.S. Nguyen, C. R. Mecanique 332 (2004). © 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.
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