| 1. |
- Ouchterlony, Finn
(författare)
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Symmetric cracking of a wedge by concentrated loads
- 1977
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Ingår i: International Journal of Engineering Science. - 0020-7225 .- 1879-2197. ; 15:2, s. 109-116
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Tidskriftsartikel (refereegranskat)abstract
- This paper contains an analysis of the plane infinite elastic wedge with a symmetric crack at the end. The edges of the wedge are either free or normally constrained. The wedge is loaded by a pair of unbalanced concentrated line loads at the ends which are symmetric with respect to the crack. Exact expressions for the stress intensity factors as functions of the wedge angle and the force direction are derived for both cases. When transformed, the results compare favorably with known star crack results. The symmetric cracking of a wedge of brittle isotropic material is finally discussed.
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| 2. |
- Petersson, Joakim
(författare)
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On continuity of the design-to-state mappings for trusses with variable topology
- 2001
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Ingår i: International Journal of Engineering Science. - 0020-7225 .- 1879-2197. ; 39:10, s. 1119-1141
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the continuity of the mappings which, for a given set of cross-sectional areas of a truss, gives the bar forces and nodal displacements present in equilibrium. We allow the areas to approach and attain zero values, and hence analyse continuity of the state mappings even as the topology is altered. The main results are then applied to optimal design, primarily the stress-constrained minimum weight problem, to illustrate how they can be used to establish existence of solutions and validity of "e-perturbations" that are common in computational topology optimization. © 2001 Elsevier Science Ltd.
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| 3. |
- Abelen, Aisha, et al.
(författare)
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Modelling of rate-dependent inelasticity and damage in semi-crystalline polymers using an Eulerian framework
- 2023
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Ingår i: International Journal of Engineering Science. - : Elsevier. - 0020-7225 .- 1879-2197. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- The present paper concerns the mechanical response of semi-crystalline polymers during cyclic loading, and it includes both modelling and experimental testing. The model is Eulerian in the sense that it is independent of measures of total deformation and plastic/inelastic deformations. It is able to account for such essential phenomena as strain-rate dependence, work hardening, and damage. The model was applied to uniaxial tension tests performed on high-density polyethylene (HDPE), which is a semi-crystalline polymer widely used in the industry. Two types of tests were conducted: monotonic tests, and loading-unloading tests. The model was able to reproduce the experimental results very well. The proposed model was also implemented as a UMAT in Abaqus, including an analytic tangent. The UMAT was used for simulating two 3D geometries. The implementation seems to be robust, and no convergence problems were observed.
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| 4. |
- Alberdi-Muniain, Ane, et al.
(författare)
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Modelling energy flow through magneto-sensitive vibration isolators
- 2013
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225 .- 1879-2197. ; 65, s. 22-39
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Tidskriftsartikel (refereegranskat)abstract
- A highly nonlinear model of the energy flow in a magneto-sensitive (MS) vibration isolation system is developed where it is possible to investigate the influences of MS rubber material parameters; magnetic field strength; MS isolator dimension and position; excitation force magnitude, position and frequency; engine mass, inertia and dimension and, finally, foundation inertance. The MS vibration isolation system consists of an engine modelled by a solid mass, excited by a vertical force and mounted upon four MS isolators being connected to a relatively stiff foundation characterised by its driving-point and transfer inertances at and between the connection points. The energy flow into the foundation is the most appropriate indicator of the effectiveness of a real vibration isolation system while considering both foundation velocity and force. The MS isolator model applied is a nonlinear MS rubber model including frequency, dynamic amplitude and magnetic field dependence. The energy flow model results are compared to those of measurements, showing good agreement. Finally, parameter studies are carried out. The developed energy flow model provides a basis for designing MS vibration isolation systems to meet specific requirements.
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| 5. |
- Almqvist, Andreas, et al.
(författare)
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New concepts of homogenization applied in rough surface hydrodynamic lubrication
- 2007
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225 .- 1879-2197. ; 45:1, s. 139-154
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Tidskriftsartikel (refereegranskat)abstract
- This work introduces a new concept of homogenization that enables efficient analysis of the effects of surface roughness representations obtained by measurements in applications modeled by the Reynolds equation. Examples of such applications are trust- and journal-bearings. The numerical analysis of these types of applications requires an extremely dense computational mesh in order to resolve the surface roughness, suggesting some type of averaging. One such method is homogenization, which has been applied to Reynolds type equations with success recently. This approach is similar to the technique proposed by Patir and Cheng, who introduced flow factors determining the hydrodynamic action due to surface roughness. The difference is, however, that the present technique has a rigorous mathematical support. Moreover, the recipe to compute the averaged coefficients is simple without any ambiguities. Using either the technique proposed by Patir and Cheng or homogenization, the coefficients determining the averaged Reynolds equation are obtained by solving differential equations on a local scale. Unfortunately, this is detrimental when investigating the effects induced by real, measured, surface roughness, even though these local problems may be solved in parallel. The present work presents a solution by applying the technique based on bounds. This technique transforms the stationary Reynolds equation into two computationally feasible forms, one for the upper bound and one for the lower bound, where the flow factors are obtained by straightforward integration. Together with the preciseness of these bounds, the bounds approach becomes an eminent tool suitable for investigating the effect of real, measured, surface roughness on hydrodynamic performance.
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| 6. |
- Almqvist, Andreas, et al.
(författare)
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New insights on lubrication theory for compressible fluids
- 2019
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Ingår i: International Journal of Engineering Science. - : Elsevier. - 0020-7225 .- 1879-2197. ; 145
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Tidskriftsartikel (refereegranskat)abstract
- The fact that the film is thin is in lubrication theory utilised to simplify the full Navier–Stokes system of equations. For incompressible and iso-viscous fluids, it turns out that the inertial terms are small enough to be neglected. However, for a compressible fluid, we show that the influence of inertia depends on the (constitutive) density-pressure relationship and may not always be neglected. We consider a class of iso-viscous fluids obeying a power-law type of compressibility, which in particular includes both incompressible fluids and ideal gases. We show by scaling and asymptotic analysis, that the degree of compressibility determines whether the terms governing inertia may or may not be neglected. For instance, for an ideal gas, the inertial terms remain regardless of the film height-to-length ratio. However, by means of a specific modified Reynolds number that we define we show that the magnitudes of the inertial terms rarely are large enough to be influential. In addition, we consider fluids obeying the well-known Dowson and Higginson density-pressure relationship and show that the inertial terms can be neglected, which allows for obtaining a Reynolds type of equation. Finally, some numerical examples are presented in order to illustrate our theoretical results.
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| 7. |
- Almqvist, Andreas, et al.
(författare)
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Variational bounds applied to unstationary hydrodynamic lubrication
- 2008
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225 .- 1879-2197. ; 46:9, s. 891-906
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Tidskriftsartikel (refereegranskat)abstract
- This paper is devoted to the effects of surface roughness in hydrodynamic lubrication. The numerical analysis of such problems requires a very fine mesh to resolve the surface roughness, hence it is often necessary to do some type of averaging. Previously, homogenization (a rigorous form of averaging) has been successfully applied to Reynolds type differential equations. More recently, the idea of finding upper and lower bounds on the effective behavior, obtained by homogenization, was applied for the first time in tribology. In these pioneering works, it has been assumed that only one surface is rough. In this paper we develop these results to include the unstationary case where both surfaces may be rough. More precisely, we first use multiple-scale expansion to obtain a homogenization result for a class of variational problems including the variational formulation associated with the unstationary Reynolds equation. Thereafter, we derive lower and upper bounds corresponding to the homogenized (averaged) variational problem. The bounds reduce the numerical analysis, in that one only needs to solve two smooth problems, i.e. no local scale has to be considered. Finally, we present several examples, where it is shown that the bounds can be used to estimate the effects of surface roughness with very high accuracy.
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| 8. |
- Barbagallo, Mathias, et al.
(författare)
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A self-adjoint variational principle for anisotropic viscoelastic Biot’s equations
- 2013
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225 .- 1879-2197. ; 63, s. 71-83
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Tidskriftsartikel (refereegranskat)abstract
- A variational principle for anisotropic viscoelastic Biot’s equations of motion is presented. It is based upon an extended Hamilton’s principle, also valid for dissipative systems. Using this principle, a functional analogous to the Lagrangian is defined, starting from Biot’s variational formulation based on frame and fluid displacements. Then, a mixed displacement–pressure formulation is presented, which reduces the number of variables of response from six to four. The corresponding functional analogous to the Lagrangian is derived making full use of variational calculus. The derived functionals are self-adjoint and stationary for true motion.
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| 9. |
- Bustamante, R., et al.
(författare)
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Methods to compute 3D residual stress distributions in hyperelastic tubes with application to arterial walls
- 2010
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Ingår i: International Journal of Engineering Science. - : Elsevier BV. - 0020-7225 .- 1879-2197. ; 48:11, s. 1066-1082
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the problem of modeling three-dimensional residual stress distributions in hyperelastic tubes is addressed. First, the problem of a radially opened straight and bent tube, where the opening angle depends on the axial position, is explored with the semi-inverse method. As a result a rather complicated system of nonlinear partial differential equations is achieved which is difficult to solve. Second, a different approximate method considers the tube as a composition of two, three, four or more rings in the axial direction. Also here the opening angle of the tube depends on the axial position. Some numerical solutions for the stress components in the radial, circumferential and axial directions are analyzed in more detail. Third, the tube wall is divided into a number of radial layers, with different mechanical properties, and an approximate method to treat that problems is presented. It is emphasized that the proposed approach can also be used to compute 3D residual stress distributions in arterial walls. A final conclusion points to possible future research directions.
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| 10. |
- Karimi, Pouyan, et al.
(författare)
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RVE problem : mathematical aspects and related stochastic mechanics
- 2020
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Ingår i: International Journal of Engineering Science. - : Elsevier. - 0020-7225 .- 1879-2197. ; 146
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Tidskriftsartikel (refereegranskat)abstract
- The paper examines (i) formulation of field problems of mechanics accounting for a random material microstructure and (ii) solution of associated boundary value problems. The adopted approach involves upscaling of constitutive properties according to the Hill--Mandel condition, as the only method yielding hierarchies of scale-dependent bounds and their statistics for a wide range of (non)linear elastic and inelastic, coupled-field, and even electromagnetic problems requiring (a) weakly homogeneous random fields and (b) corresponding variational principles. The upscaling leads to statistically homogeneous and isotropic mesoscale tensor random fields (TRFs) of constitutive\ properties, whose realizations are, in general, everywhere anisotropic. A summary of most general admissible correlation tensors for TRFs of ranks 1, \dots, 4 is given. A method of solving boundary value problems based on the TRF input is discussed in terms of torsion of a randomly structured rod. Given that many random materials encountered in nature (e.g., in biological and geological structures) are fractal and possess long-range correlations, we also outline a method for simulating such materials, accompanied by an application to wave propagation.
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