| 1. |
- Adolfsson, Erik, et al.
(författare)
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Matrix crack initiation and progression in composite laminates subjected to bending and extension
- 1999
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 36:21, s. 3131-3169
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Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation of matrix crack initiation and progression in glass/epoxy laminates of different stacking sequences is presented. The laminates have been loaded in extension and bending, and the degree of damage as function of the load has been recorded. The changes in certain elastic properties caused by the damage were also measured, and are compared to results from a previously developed approximate analytic model. An energy release rate resistance curve is adopted in an attempt to describe the initiation and progression of matrix cracks in the laminates. The amount of cracking is also viewed in relation to the strain transverse to the fibres in the ply under consideration, and the ply stresses at the onset of cracking are calculated. The different damage evolution criteria are compared to the experimental results, and their validity and reliability are discussed. By use of the ply strain transverse to the fibres as a critical parameter for damage evolution, the load-deformation curves of the tested laminates are simulated taking damage progression into account.
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| 2. |
- Adolfsson, Erik, et al.
(författare)
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Thermoelastic properties in combined bending and extension of thin composite laminates with transverse matrix cracks
- 1997
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 34:16, s. 2035-2060
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Tidskriftsartikel (refereegranskat)abstract
- Approximate analytic expressions for the thermoelastic properties in combined bending and extension of composite laminates containing transverse matrix cracks are derived. The model covers two-dimensional laminates of arbitrary lay-up sequences. The derived expressions for the compliances and thermal expansion coefficients merely contain ply property data and crack distributions. In order to check the accuracy and reliability of the presented analytic method, some sample cracked geometries were examined by use of the finite element method. A good agreement was found between the numerically and analytically obtained results for all cases under consideration.
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| 3. |
- Klisinski, Marek
(författare)
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On constitutive equations for arbitrary stress-strain control in multi-surface plasticity
- 1998
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 35:20, s. 2655-2678
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Tidskriftsartikel (refereegranskat)abstract
- The structure of incremental constitutive equations in multi-surface plasticity is discussed with respect to different choices of state and control variables. The state and control variables can combine stresses and strains as long as they are decomposed into energy-conjugate parts. A general uniqueness condition is established for non-associated flow rules and any choice of control variables. Furthermore, proper tangent constitutive matrices are given within each loading/unloading region. The theory is demonstrated in a simple example involving Tresca's yield condition
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| 4. |
- Storåkers, Bertil, et al.
(författare)
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Similarity analysis of inelastic contact
- 1997
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 34:24, s. 3061-3083
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of mechanical contact of solids is of interest not only regarding a variety of mechanical assemblies but also on a smatter scale such as roughness properties of surfaces and compaction of powder particles. indentation testing is another prominent problem in the context. To analyse the phenomena involved is inherently difficult at application essentially due to the presence of large strains, nonlinear material behaviour, time dependence and moving contact boundaries. Recently, progress has been made, however, to explicitly solve basic boundary value problems especially due to advances in computational techniques. A substantial ingredient which facilitates solution procedures is self-similarity and it is the present purpose to explore in detail the advantages in a general setting when this feature prevails. A viscoplastic framework is laid down for a wide class of constitutive properties where strain-hardening plasticity, creep and also nonlinear elasticity arise as special cases. It is then shown that when surface shapes and material properties are modelled by homogeneous functions, associated boundary value problems posed may be reduced to stationary ones. As a consequence, within Hertzian kinematics, relations between contact impression and regions become independent of loading and time and the connection to loading characteristics does not usually require a full solution of the problem. In particular it is shown that for general head-shapes it proves efficient to use an approach where an intermediate Aat die solution serves as a basic tool also for hereditary materials. An invariant computational procedure based on the intermediate problem is arrived at and decisive results shown to be found by simple cumulative superposition. Illustrations are given analytically for ellipsoidal contact of Newtonian fluids and by detailed computations for spherical indentation of viscoplastic solids for which also universal hardness formulae an proposed. For several bodies in contact it is shown how general results may be extracted from fundamental solutions for a half-space.
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| 5. |
- Strömberg, Niclas, 1968-
(författare)
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A Newton method for three-dimensional fretting problems
- 1999
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 36:14, s. 2075-2090
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Tidskriftsartikel (refereegranskat)abstract
- The present paper concerns the numerical treatment of fretting problems using a finite element analysis. The governing equations resulting from a formal finite element discretization of an elastic body with a potential contact surface are considered in a quasi-static setting. The constitutive equations of the potential contact surface are Signorini's contact conditions, Coulomb's law of friction and Archard's law of wear. Using a backward Euler time discretization and an approach based on projections, the governing equations are written as an augmented Lagrangian formulation which is implemented and solved using a Newton algorithm for three-dimensional fretting problems of didactic nature. Details concerning the implementation are provided.
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| 6. |
- Strömberg, Niclas, 1968-, et al.
(författare)
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Derivation and analysis of a generalized standard model for contact, friction and wear
- 1996
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 33:13, s. 1817-1836
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Tidskriftsartikel (refereegranskat)abstract
- A model for mechanical contact including friction, wear and heat generation is proposed. By defining an internal state variable for the wear process, a generalized standard model for contact, friction and wear is derived from the principle of virtual power and the fundamental laws of thermodynamics. Within the frame of the generalized standard model some specific constitutive models are presented. For instance, a free energy corresponding to an extension of Signorini's unilateral contact conditions to include the wear process at the interface and having a linear tangential compliance between the relative tangential displacement and the tangential contact traction is suggested. Furthermore, a dual pseudo-potential with a friction and wear limit criterion in agreement with Coulomb's law of friction Archard's law of wear is given. In order to study existence and uniqueness questions, this pair of free energy and dual pseudo-potential is analysed in a one point elastic quasi-static contact problem with two degrees of freedom and thermal effects neglected. The so-called rate problem is solved.
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| 7. |
- Larsson, Per-Lennart, et al.
(författare)
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Analysis of Berkovich indentation
- 1996
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 33:2, s. 221-248
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Tidskriftsartikel (refereegranskat)
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| 8. |
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| 9. |
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| 10. |
- Ottosen, Niels Saabye, et al.
(författare)
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Corners in Plasticity - Koiter's Theory Revisited
- 1996
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 33:25, s. 3697-3721
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Tidskriftsartikel (refereegranskat)abstract
- A general theory for plastic loading at corners is presented that includes Koiter's theory as a special case. This theory is derived within a thermodynamic framework and includes non-associated as well as associated theory. The non-associated theory even allows the number of potential functions to differ from the number of yield functions. The properties of the matrix of plastic moduli as well as of another important matrix are discussed in detail and hardening, perfect and softening plasticity are concisely defined. The existence of limit points is also discussed. The strain driven format turns out to be the most general. Moreover, consistent loading and unloading criteria are established for general non-associated plasticity. An explicit criterion for uniqueness is derived, and finally, some of the general findings are illustrated by means of specific plasticity formulations often encountered in practice.
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