| 1. |
- Ottosen, Niels Saabye, et al.
(författare)
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Discontinuous bifurcations in a nonassociated Mohr material
- 1991
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Ingår i: Mechanics of Materials. - 0167-6636. ; 12:3-4, s. 255-265
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Tidskriftsartikel (refereegranskat)abstract
- Discontinuous bifurcations of an elastic-plastic material obeying Mohr's yield criterion and a nonassociated flow rule and subjected to general three-dimensional loading are investigated. The first possibility for bifurcation is identified and expressed in terms of the critical hardening modulus and the corresponding orientation of the slip planes. In the case of perfect plasticity the Mohr and Roscoe solutions for the orientation of the slip planes are derived. The corresponding strain rate fields are determined and it is shown that the Roscoe strain rate field differs significantly from the other fields. Moreover, the stress rate field is continuous across the singular surface for the Roscoe solution.
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| 2. |
- Aidanpää, Jan-Olov, et al.
(författare)
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One-dimensional model for the transition from periodic to chaotic motions in granular shear flows
- 1993
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 16:1-2, s. 153-161
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Tidskriftsartikel (refereegranskat)abstract
- A simple one-dimensional mechanical model to simulate some aspects of the dynamics of granular flow is suggested. The model consists of a visco-elastic packet bouncing between two oscillating walls. The motion of the walls is prescribed to be harmonic. The amplitude and frequency of the wall motion are related to the concentration and shear rate, respectively. The dynamics of the system is studied for various parameter combinations and it is shown that periodic as well as chaotic motions are possible for different parameters and initial conditions. Results are presented in the form of time histories, power spectral densities, phase diagrams, Poincare plots and bifurcation diagrams. This simple one-dimensional model presents many features that are analogous to those observed in the two-dimensional simple shear flow of disks.
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| 3. |
- Li, Chunlin, et al.
(författare)
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Deformation of brittle rocks under compression - with particular reference to microcracks
- 1993
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 15:3, s. 223-239
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Tidskriftsartikel (refereegranskat)abstract
- A constitutive model for brittle rocks has been developed based on the analysis of microcracks. The macroscopic deformation of a rock is decomposed into three components: response of the rock matrix, closure of open cracks and deformation due to the fracture of microcracks. The main contribution of this approach is the prediction of macroscopic deformation induced by microcracking. The basic model units are sliding cracks. Wing cracks are initiated at tips of sliding cracks and propagated in the major loading direction. The relationships between the compressive stress, the length of the growing crack and deformation due to the fracture of cracks are established. A deformation solution to an elliptic crack is employed to describe the closure effect of an open crack under compression. The total deformation caused by the closure and fracture of cracks is obtained by the sum of the components of individual cracks. In this model, the nonlinear behavior of deformation results either from the closure of open cracks at low stress levels, or from the fracture of microcracks at high stress levels. Hysteresis is captured under cyclic loading. Comparisons of the model simulations with experimental data are presented and show good agreement in the prefailure stage.
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| 4. |
- Sørensen, Bent F., et al.
(författare)
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Effects of nonuniformity of fiber distribution on thermally-induced residual stresses and cracking in ceramic matrix composites
- 1993
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 16:4, s. 351-363
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional finite element analysis is conducted to estimate stresses induced by thermal cooldown in unidirectionally fiber-reinforced ceramic matrix composites. Various configurations of nonuniform fiber distributions are considered. Both cases of thermal expansion mismatch between isotropic, linearly thermoelastic fibers and matrix are studied. Significant effects of nonuniformity of fiber distributions on the local stress states are found. The initiation of various possible cracking modes is discussed in the light of these results
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| 5. |
- Talreja, Ramesh
(författare)
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Continuum modelling of damage in ceramic matrix composites
- 1991
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 12:2, s. 165-180
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Tidskriftsartikel (refereegranskat)abstract
- A continuum model for determining mechanical response of ceramic matrix composites with damage is presented. The mechanisms of damage considered are those observed in unidirectionally fiber-reinforced ceramic matrix composites, viz. matrix cracking, fiber/matrix interfacial slip and fiber/matrix debonding. Four basic configurations of distributed damage at the microscopic level are treated: matrix cracks only, matrix cracks in conjunction with interfacial slip, debonds only and matrix cracks in conjunction with debonds. The elementary damage entities, i.e. cracks, debonds and slipped surfaces, are represented by second-order tensors which are regarded as internal variables. Using a thermodynamics based formulation of constitutive relationships with internal variables, the stress-strain-damage relationships are derived. Specific expressions are given for changes in the engineering elastic moduli in terms of the densities of damage entities for sparsely distributed damage
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