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Meso-Mechanical Modeling and Analysis of Adhesive Layers
Högskolan i Skövde, Institutionen för teknik och samhälle.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is concerned with the modeling, simulation and analysis of adhesive layers. By use of an in situ scanning electron microscopy study it is found that the adhesive studied in the present thesis has a very complex structure with two different compounds, a mineral and an epoxy/thermoplastic blend. A representative volume element (RVE) model is developed to study the behavior of the adhesive layer at the meso-level. It is a continuum model where interface finite elements are implemented at the boundaries of the continuum elements in order to enable crack initiation and propagation of micro cracks. On a structural level, two deformation modes, modes I and II, dominate the behavior of thin adhesive layers. With the RVE it is possible reproduce experimental stress-deformation relations from both modes. However, in a real structure, mixed mode loading usually occur. A range of mode mixes is studied, using the RVE, from an un-loaded state until fracture of the layer. The results indicate that the behavior of the interface elements dominate for mode mixes close to mode I and plasticity in the continuum elements dominates for mode II dominated mode mixes. Furthermore, effects of large root curvatures of the adherends is analyzed numerically by simulating plastically deforming double cantilever beam specimens using the finite element model. The developed RVE is implemented in the models to simulate the behavior of the adhesive layer. By this methodology, virtual experiments can be analyzed with extreme detail. It is shown that in-plane straining of the adhesive layer significantly influences the strength of adhesive joints at large plastic strain of the adherends. There is a never ending need in industries to minimize computational time. To this end, an interphase finite element for structural analyses is developed. The element considers in-plane straining of the adhesive layer due to large curvatures of surrounding substrates.

Place, publisher, year, edition, pages
Göteborg: Chalmers tekniska högskola , 2007. , 13 p.
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:hj:diva-24122ISBN: 978-91-7291-998-3 (print)OAI: oai:DiVA.org:hj-24122DiVA: diva2:726100
Public defence
2007-10-04, Hörsalsvägen 2b, Göteborg, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2015-02-05 Created: 2014-06-17 Last updated: 2015-02-05Bibliographically approved
List of papers
1. Influence of root curvature on the fracture energy of adhesive layers
Open this publication in new window or tab >>Influence of root curvature on the fracture energy of adhesive layers
2009 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 76, no 13, 2025-2038 p.Article in journal (Refereed) Published
Abstract [en]

Previously performed experiments to study the mode I behavior of an adhesive layer revealed an apparent increase in the fracture toughness when the adherends deformed plastically. Attempts to simulate the experiments are made; both with elastically and plastically deforming adherends. Thus, effects of the size of the process zone and the deformation of the adherends are revealed. The adhesive layer is modeled using finite elements with different approaches; cohesive elements and representative volume elements. The adherends are modeled with solid elements. With a long process zone, all models give good results as compared to the experiments. However, only the model with representative volume elements gives good agreement for large root curvatures and correspondingly short process zones. The results are interpreted by analyzing the deformation and mechanisms of crack propagation in the representative volume elements. It is shown that with large root curvature of the adherends, the in-plane stretching of the adhesive layer gives a substantial contribution to the fracture energy. A simple formula is derived and shown to give an accurate prediction of the effects of the root curvature. This result indicates the limits of conventional cohesive zone modeling of an adhesive layer of finite thickness.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
Double cantilever beam; Representative volume element; Process zone; Adhesive; Fracture energy
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:hj:diva-24120 (URN)10.1016/j.engfracmech.2009.05.010 (DOI)
Available from: 2014-06-17 Created: 2014-06-17 Last updated: 2015-11-13
2. An adhesive interphase element for structural analyses
Open this publication in new window or tab >>An adhesive interphase element for structural analyses
2008 (English)In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 76, no 4, 482-500 p.Article in journal (Refereed) Published
Abstract [en]

A special purpose finite element is developed for structural simulations of complex adhesively bonded structures. In the interphase element, the adhesive is explicitly regarded as a material phase between two substrates. The element considers large rotations. Furthermore, it considers in-plane straining of the adhesive due to large curvatures of the bonded shells. This feature appears especially important when considering bonding of thin plastically deforming metallic shell structures. Simulations are made on specimens where the adherends deform both elastically and plastically. The results are in good agreement with previously performed experiments. 

Place, publisher, year, edition, pages
John Wiley & Sons, 2008
Keyword
adhesive bonding;FEM;element formulation;fracture
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:hj:diva-24119 (URN)10.1002/nme.2333 (DOI)
Available from: 2014-06-17 Created: 2014-06-17 Last updated: 2015-11-13
3. Modeling and parameter calibration of an adhesive layer at the meso level
Open this publication in new window or tab >>Modeling and parameter calibration of an adhesive layer at the meso level
2008 (English)In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 40, no 1, 48-65 p.Article in journal (Refereed) Published
Abstract [en]

A mesomechanical finite element model of a thin adhesive layer is developed. The model is calibrated to previously performed experiments. In these, the adhesive layer is loaded in monotonically increasing peel or shear. An in situ SEM study is also performed and used to guide the modeling and calibration. The purpose of the mesomechanical finite element model is to facilitate the development of constitutive laws for adhesive layers. The modeling is based on Xu and Needleman’s method where all continuum finite elements are surrounded by interface elements that allow for the development of micro cracks. Thus, this enables the modeling of the entire process of degradation and fracture of the adhesive layer. A genetic algorithm is developed for the calibration. The simulations show good agreement with the experiments.

Place, publisher, year, edition, pages
Elsevier, 2008
Keyword
RVE; CZM; Interface; Crack propagation
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:hj:diva-24115 (URN)10.1016/j.mechmat.2007.06.004 (DOI)
Available from: 2014-06-17 Created: 2014-06-17 Last updated: 2015-11-13
4. Mixed mode modeling of a thin adhesive layer using a meso-mechanical model
Open this publication in new window or tab >>Mixed mode modeling of a thin adhesive layer using a meso-mechanical model
2008 (English)In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 40, no 8, 665-672 p.Article in journal (Refereed) Published
Abstract [en]

A representative volume element is modeled using the finite element method. It is used to analyze mixed mode behavior of a thin adhesive layer. Two sources of dissipation is modeled; plasticity and decohesion. Macroscopic traction–separation laws are extracted from the simulations. The results indicate that a boundary of mode mix exists between a region where major plastic dissipation is present and a region where it is not. Without major plastic dissipation, the fracture energy is low and essentially governed by the cohesive properties. This is the case in peel dominated loading cases. In shear dominated loading cases plastic dissipation gives a substantial contribution to the fracture energy. The results show that pure shear loading gives the largest fracture energy.

Place, publisher, year, edition, pages
Elsevier, 2008
Keyword
Mixed mode; Cohesive laws; Fracture energy; Traction–separation laws; Representative volume element; Adhesive
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:hj:diva-24118 (URN)10.1016/j.mechmat.2008.02.006 (DOI)
Available from: 2014-06-17 Created: 2014-06-17 Last updated: 2015-11-13

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