| 1. |
- Alfredsson, K. Svante, et al.
(författare)
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Flexural analysis of discontinuous tile core sandwich structure
- 2012
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Ingår i: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 94:5, s. 1524-1532
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Tidskriftsartikel (refereegranskat)abstract
- Three-point flexure loading of sandwich beams with a core consisting of discrete ceramic tiles (DTSS) is considered. The tile gaps may be bonded or unbonded (open gaps). The analysis utilizes a layer-wise beam theory approach. The general formulation for the displacements and stresses in the face sheets, face/core adhesive layer, and core is derived. Solutions for stresses and displacements of the beam constituents are obtained from finite element formulation based on analytical solution of the face sheet/tile unit cell. The approach is verified by comparison to stress results obtained from ordinary finite element analysis where each layer is modeled discretely. Effects of load introduction and support conditions on the effective flexural stiffness are examined. It is demonstrated that the face sheets experience substantial stress concentrations at the tile joint locations, especially if the gaps are unfilled. Analysis of beam compliance reveals sensitivity to details of load introduction and support conditions, especially when the span length becomes comparable to the tile length.
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| 2. |
- Alfredsson, K. Svante
(författare)
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On the determination of constitutive properties of adhesive layers loaded in shear - an inverse solution
- 2003
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Ingår i: International Journal of Fracture. - : Springer. - 0376-9429 .- 1573-2673. ; 123:1-2, s. 49-62
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Tidskriftsartikel (refereegranskat)abstract
- A method to determine constitutive properties of thin adhesive layers loaded in shear is presented. The test specimen consists of two adherends joined by the adhesive layer. By loading the specimen antisymmetrically with respect to the adhesive layer a state of pure shear is ensured. To avoid instability the test specimen is designed to give a non-uniform stress distribution in the adhesive layer. This is achieved by using a long specimen loaded at one side. The method is based on an exact inverse solution which is derived utilizing the balance of the energetic forces of the applied loads and of the adhesive at the start of the adhesive layer. The method is intended for determination of both hardening and softening behaviour of adhesives but is confined to monotonic loading
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| 3. |
- Alfredsson, K. Svante
(författare)
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On the instantaneous energy release rate of the end-notch flexure adhesive joint specimen
- 2004
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683. ; 41:16-17, s. 4787-1807
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Tidskriftsartikel (refereegranskat)abstract
- The energy release rate of the ENF adhesive joint specimen is derived. The resulting formula accounts for the presence of an adhesive layer with a possibly non-linear constitutive relation. The actual form of the constitutive relation need not to be known a priori. It is shown that measurements of both the applied load and the adhesive deformation at the crack tip are needed to determine the instantaneous value of the energy release rate. Experimental results show that the influence of the deformation of the adhesive layer can be substantial. The stability of the ENF-specimen is studied and a method to estimate the critical value of the crack length, accounting for the flexibility of the adhesive layer, is presented. In the analysis, the adherends are modelled as elastically deforming Euler–Bernoulli beams and the intermediate adhesive layer is modelled as a material surface transmitting shear stress between the adherends.
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| 4. |
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| 5. |
- Alfredsson, K. Svante, et al.
(författare)
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Stability of beam-like fracture mechanics specimens
- 2012
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 89, s. 98-113
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Tidskriftsartikel (refereegranskat)abstract
- Test specimens used to determine the interlaminar strength of composites as well as the strength of adhesive layers are known to occasionally suffer from instability. Thus, even though the experiments are performed under controlled load-point displacement, the experiments are terminated prematurely by unstable crack propagation. Often there exists a critical crack length which must be exceeded in order to obtain stable crack propagation. In this paper, a general method to assess the stability of beam-like fracture mechanics specimens is developed. Both systems subjected to a single load and the more general situation with several independent loads are treated. A simple formula is derived for the critical crack length for one-parameter loading. The only parameter necessary as input is the compliance of the un-cracked specimen. For the case of non-proportional loading, stability is determined by studying the eigenvalues of a symmetric matrix. Other findings quantified in the paper are the effect of orthotropy, the influence of a flexible interphase layer and the influence of the compliance of the loading device.
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| 6. |
- Alfredsson, K. Svante, et al.
(författare)
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Stress analysis of axially and thermally loaded discontinuous tile core sandwich with and without adhesive filled core gaps
- 2011
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Ingår i: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 93:7, s. 1621-1630
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Tidskriftsartikel (refereegranskat)abstract
- An analytical study is performed to investigate the stress states in an axially and thermally loaded sandwich structure with a discontinuous ceramic tile core. General and simplified models are developed to determine stresses in the constituents of the sandwich structure with and without adhesive in the gaps between adjacent tiles. A general model that allows local bending of the face sheet and a simplified model which assumes uniform through-thickness stress distribution in the face sheets are developed. It is shown that the normal stress in the face sheet decreases when the gap is filled by adhesive, although the tile stress increases. The analytical model shows that normal and shear stresses at the face/core interface can be reduced by filling the gaps between tiles. Filled gaps also elevate the axial stiffness of the structure. Model results are verified by comparison to a previously developed analytical model and finite element analysis. (C) 2011 Elsevier Ltd. All rights reserved.
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| 7. |
- Alfredsson, Svante, et al.
(författare)
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A closed-form solution to statically indeterminate adhesive joint problems — exemplified on ELS-specimens
- 2008
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Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier. - 0143-7496 .- 1879-0127. ; 28:7, s. 350-361
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Tidskriftsartikel (refereegranskat)abstract
- A beam/adhesive-layer model is developed. For this model a closed-form solution method applicable to arbitrary boundary conditions is presented. This enables the solution of a large number of practical problems which may be statically indeterminate. The stress state in the adhesive layer and the adherends of the beam/adhesive-layer model is also scrutinized. The method is exemplified in an analysis of the end-loaded split (ELS) specimen, commonly used to determine fracture energies of adhesive layers. The effect of the flexibility of the adhesive layer on the energy release rate and the critical crack length for stable crack growth is examined. Both symmetric and unsymmetric ELS-specimens are studied.
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| 8. |
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| 9. |
- Alfredsson, Svante
(författare)
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Constitutive Behaviour and Fracture of Adhesive Layers : Inverse Methods and Energetic Balance
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the automobile industry, current demands on reduced emissions with maintained or even increased crash worthiness, forces the industry to seek weight-reducing designs. The possibility to use lightweight materials is obviously attractive. At joints, these lightweight materials have to be connected to high-strength or low-cost materials. In this context adhesive joining can provide a flexible solution. The method adds little weight to the structure, it allows for material combinations that are not possible to weld, and it provides increased stiffness to the structure as compared to the conventional spot-welding procedure. Moreover, electrolytic isolation of the multi-material joints is achieved. In this thesis, experimental methods are developed to determine the complete stress-deformation relation for an adhesive layer loaded in shear. Generally, the stress distribution is non-uniform in the test geometries used. Evaluation of experiments is performed using an inverse method. The idea is to measure the energy release rate as a function of the crack tip deformation. The stress-deformation relation is obtained by a subsequent differentiation. The method is shown to be capable of capturing the complete stress-deformation relation under stable loading conditions. A method to accurately determine the energy release rate is needed for the inverse method to be successful. A closed form expression for the energy release rate of the end-notch flexure adhesive joint specimen (ENF) is derived in this thesis. An approximate formula containing measurable quantities is also given. It is shown that both the applied load and the crack tip deformation are needed to determine the instantaneous value of the energy release rate of the ENF-specimen. Experimental results show that the influence of the crack tip deformation can be substantial. An alternative specimen is also analysed theoretically. An initial theoretical study on mixed mode fracture of adhesive layers is also given in this thesis. A detailed comparison is made of the mode-mixity obtained using two different, frequently used mechanical models; the beam/adhesive layer model, and the continuum model, i.e. a model neglecting the presence of the adhesive layer. It is tempting to assume that the two methods would produce similar results for the case of a thin adhesive layer. However, this is only the case for geometries which are materially and geometrically symmetric with respect to the adhesive layer. For asymmetric joints, on the other hand, the two models are found to predict fundamentally different values of the mode-mixity. Moreover, the mode-mixity of the beam/adhesive layer model is found to depend highly on the relative stiffness of the adherends and the adhesive layer. This dependency is found to be quantified through two parameters.
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| 10. |
- Alfredsson, Svante, et al.
(författare)
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Continuum damage mechanics revised
- 2004
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683. ; 41:15, s. 4025-4045
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Tidskriftsartikel (refereegranskat)abstract
- A framework is derived for developing constitutive laws for engineering materials. The framework is based on physically motivated assumptions on the mechanical and thermal behaviour of plastically deformed and damaged materials. These assumptions are the starting point in a derivation of the relevant thermodynamic quantities. The procedure reveals important cross-dependencies that have to be considered while developing constitutive equations. A major result of this study is that both deterioration (increase of damage) and healing (decrease of damage) can be modelled in an integrated manner using the same constitutive law. For greater clarity the description is limited to small strain and isotropic behaviour
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