| 1. |
- Chen, S.H., et al.
(författare)
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A crack perpendicular to a bimaterial interface an interface in finite solid
- 2003
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Ingår i: International Journal of Solids and Structures. - : Elsevier, UK. - 0020-7683. ; 40:11, s. 2731-55
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Tidskriftsartikel (refereegranskat)abstract
- The dislocation simulation method is used in this paper to derive the basic equations for a crack perpendicular to the bimaterial interface in a finite solid. The complete solutions to the problem, including the T stress and the stress intensity factors are obtained. The stress field characteristics are investigated in detail. It is found that when the crack is within a weaker material, the stress intensity factor is smaller than that in a homogeneous material and it decreases when the distance between the crack tip and interface decreases. When the crack is within a stiffer material, the stress intensity factor is larger than that in a homogeneous material and it increases when the distance between the crack tip and interface decreases. In both cases, the stress intensity factor will increase when the ratio of the size of a sample to the crack length decreases. A comparison of stress intensity factors between a finite problem and an infinite problem has been given also. The stress distribution ahead of the crack tip, which is near the interface, is shown in details and the T stress effect is considered.
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| 2. |
- Kao-Walter, Sharon, et al.
(författare)
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A study of the relation between mechanical properties and adhesion level in a laminated packaging material
- 2004
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Ingår i: Mechanics of composite materials. - Riga, Latvia : Zinatne. - 0191-5665 .- 1573-8922. ; 40:1, s. 29-36
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of a laminate consisting of aluminum-foil, adhesive, and polymer layers were studied in relation to the adhesion level. A special application for liquid-food packaging materials was considered. In experiments, laminates with and without adhesive layers were tested. Tensile tests were first run for every layer of the laminate, and the data obtained were then used in analyzing the results of tensile tests on the entire laminate, as well as in theoretical and finite-element calculations. Relations between different mechanical properties (such as Young's modulus, the peak stress, and the strain at the peak stress) and the adhesion level were analyzed. It was found that the tensile strength and the strain at the peak stress increased with adhesion level. Only slight differences in Young's modulus were observed at different adhesion levels.
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| 3. |
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| 4. |
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| 5. |
- Kao-Walter, Sharon, et al.
(författare)
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Fracture toughness of a laminated composite
- 2003
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Ingår i: Fracture of Polymers, Composites and Adhesives II. - : Elsevier. - 0080441955 ; , s. 355-364
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The fracture toughness of a polymer-metal laminate composite is obtained by mechanical testing of a specimen containing a pre-crack. The result is compared with a calculated fracture toughness based on the measured fracture toughness of the individual layers. The laminate is a material used for packaging. It consists of a thin aluminium foil and a polymer coating. A centred crack panel test geometry is used. Each of the layers forming the laminate is also tested separately. It is observed that the load carrying capacity increases dramatically. At the strain when peak load is reached for the laminate only aluminium is expected to carry any substantial load because of the low stiffness of the LDPE. However, the strength of the laminate is almost twice the strength of the aluminium foil. The reason seems to be that the aluminium forces the polymer to absorb large quantities of energy at small deformation. The result is compared with the accumulated toughness of all involved layers. A more elaborate model is proposed in the light of non-linear material behaviour and development of a fracture process zone at the crack tip. Possible fracture of the interface between the layers is discussed.
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| 6. |
- Kao-Walter, Sharon
(författare)
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Mechanical and Fracture Properties of Thin Al-foil
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Mechanical and fracture behaviour of thin Aluminium foil (with a thickness of 6-9 mm) was studied. Tensile tests and fracture toughness tests of different material thickness and different specimen size have been performed. Results influence by the size of specimen has been discussed.
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| 7. |
- Kao-Walter, Sharon
(författare)
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On the Fracture of Thin Laminates
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns mechanical and fracture properties of a thin aluminium foil and polymer laminate that is widely used as packaging material. The possibility of controlling the path of the growing crack propagation by adjustment of the adhesion level and the property of the polymer layer is investigated. First, the fracture process of the aluminium foil is investigated experimentally. It is found that fracture occurs at a much lower load than what is suggested by standard handbook fracture toughness. Observations in a scanning electron microscope with a tensile stage show that small-scale stable crack growth occurs before the stress intensity factor reaches its maximum. An examination using an optical profilometric method shows almost no plastic deformation except for in a small necking region at the crack tip. However, accurate predictions of the maximum load are obtained using a strip yield model with a geometric correction. Secondly, the mechanical and fracture properties of the laminate are studied. A theory for the mechanics of the composite material is used to evaluate a series of experiments. Each of the layers forming the laminate is first tested separately. The results are analysed and compared with the test results of the entire laminate with varied adhesion. The results show that tensile strength and strain at peak stress of the laminate, with or without a crack, increase when the adhesion of the adhesive increases. It is also found that a much larger amount of energy is consumed in the laminated material at tension compare with the single layers. Possible explanations for the much higher toughness of the laminate are discussed. Finally, the behaviour of a crack in one of the layers, perpendicular to the bimaterial interface in a finite solid, is studied by formulating a dislocation superposition method. The stress field is investigated in detail and a so-called T stress effect is considered. Furthermore, the crack tip driving forces are computed numerically. The results show that the analytical methods for an asymptotically small crack extension can also be applied for a fairly large amount of crack growth. By comparing the crack tip driving force of the crack deflected into the interface with that of the crack penetrating into the polymer layer, it is shown how the path of the crack can be controlled by selecting a proper adhesion level of the interface for different material combinations of the laminate.
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| 8. |
- Mfoumou, Etienne, et al.
(författare)
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Fracture Toughness Testing of Non Standard Specimens
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The fracture behavior of the main layers used in food packaging material is studied. Investigations include aluminium foil (9μm), paper board (100 μm) and Low Density Polyethylene (27 μm). The plane stress fracture toughness of each layer is derived based on a centered crack panel. Different crack sizes have been tested. A compromise (crack length) was found, at which Strip Yield Model as well as Linear Elastic Fracture Mechanics allow the validation of experimental results. Meanwhile, accurate results are obtained using the Strip Yield Model with a geometric correction. The result is also used to evaluate crack initiation from a notch when all three layers are laminated.
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