| 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. |
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| 8. |
- Biel, Anders, 1977-, et al.
(författare)
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Adhesive Tapes; Cohesive Laws for a Soft Layer
- 2014
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Ingår i: Procedia Materials Science. - Amsterdam : Elsevier. - 2211-8128. ; 3, s. 1389-1393
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Tidskriftsartikel (refereegranskat)abstract
- For adhesive tapes, the strain before fracture often exceeds 500%. Although the maximum stresses are quite modest the high strains to fracture result in impressive fracture energy. Due to hydrostatic stress the fracture process often starts by nucleation of microscopic cracks inside the layer. The final crack path is usually close to one of the adherends.Repeated experiments are performed both with DCB-specimens and butt-joints. The used adhesive tape is an acrylic foam tape with a thickness of 1.1 mm and a width of 19 mm. The geometry of the specimen is adapted to the properties of the soft layer. For the DCB-specimen this implies that the length of the specimen is about 1 m. The evaluated cohesive laws from the DCB- specimens give a fracture energy of 2 kN/m and a maximum stress about 0.5 MPa. For the butt-joints, the evaluated cohesive law corresponds well to the results from the DCB-experiments. However, the strain to fracture is slightly smaller. The stress in these specimens is distributed over a larger area and a nucleated crack rapidly crosses the load bearing area and fails the joint prematurely. For both kinds of experiments the evaluated cohesive laws show a small linear part. After this part there is an almost linear strain-hardening phase until fracture.
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| 9. |
- Carlberger, Thomas, et al.
(författare)
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Explicit FE-formulation of interphase elements for adhesive joints
- 2008
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Ingår i: International Journal for Computational Methods in Engineering Science and Mechanics. - : Taylor & Francis. - 1550-2287 .- 1550-2295. ; 9:5, s. 288-299
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Tidskriftsartikel (refereegranskat)abstract
- The potential of adhesive bonding to improve the crashworthiness of cars is attracting the automotive industry. Large-scale simulations are time consuming when using the very small finite elements needed to model adhesive joints using conventional techniques. In the present work, a 2D-interphase element formulation is developed and implemented in an explicit FE-code. A simplified joint serves as a test example to compare the interphase element with a straightforward continuum approach. A comparison shows the time-saving potential of the present formulation as compared to the conventional approach. Moreover, the interphase element formulation shows fast convergence and computer efficiency.
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| 10. |
- Islam, Md Shafiqul, 1984-, et al.
(författare)
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Peeling of metal foil from a compliant substrate
- 2021
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Ingår i: The journal of adhesion. - : Taylor & Francis. - 0021-8464 .- 1563-518X .- 1545-5823. ; 97:7, s. 672-703
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Tidskriftsartikel (refereegranskat)abstract
- Large displacement peel was studied for cases where a compliant substrate leads to a large value of the root rotation. An existing simplified beam model to calculate the peel fracture energy was modified to allow for a kinematic hardening beam model of the foil. The steady-state peel force and the root rotation were used as input data to the resulting analytical beam model. Test results from the literature were analysed. A more elaborate finite element model was also studied, using cohesive elements for the interface layer between the foil and the substrate. The cohesive zone parameters used were the fracture energy, the cohesive strength and a shape parameter. An optimization scheme for the cohesive zone parameters was developed and optimized against experimental steady-state peel force and root rotation. The optimization scheme was effective to characterize the cohesive parameters. The method yields similar values of fracture energy for the two peel angles, with the one for being slightly higher than for . The difference in fracture energies for different peel angles suggests that the fracture energy can be mode dependent.
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