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Influences of temperature, fatigue and mixed mode loading on the cohesive properties of adhesive layers
University of Skövde, School of Engineering Science. University of Skövde, The Virtual Systems Research Centre. Chalmers University of Technology. (Maskinteknik)ORCID iD: 0000-0003-0309-3073
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns some aspects that have influence on the strength of adhesive layers. The strength is determined by the stress deformation-relation of the layer. This relation is also referred to as cohesive law. The aspects having influence on the cohesive laws that are studied in this work are temperature, fatigue, multi-axial fatigue and mixed mode loading.

For each aspect, a model is developed that can be used to describe the influence of the aspects on the cohesive laws numerically, e.g. by using the finite element method. These models are shown to give good agreement with the experimental results when performing simulations that aims at reproducing the experiments. For the aspect of temperature, a FE-model is suggested that can be used to simulate the mechanical behaviour in pure mode loadings at any temperature within the evaluated temperature span. Also, a damage law for modelling high cycle fatigue in a bonded structure in multi-axial loading is presented. Lastly, a new experimental set-up is presented for evaluating strength of adhesives during mixed mode loading. The set-up enables loading with a constant mode-mix ratio and by the experimental results, a potential model for describing the mechanical behaviour of the evaluated adhesive is presented.

Place, publisher, year, edition, pages
Göteborg: Chalmers Publication Library , 2015. , 33 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola, ISSN 0346-718X ; 3866
Keyword [en]
adhesive layer, cohesive law, fatigue, finite element analysis, fracture energy, mixed mode, multi-axial fatigue, potential model, temperature
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:his:diva-10972ISBN: 978-91-7597-185-8 OAI: oai:DiVA.org:his-10972DiVA: diva2:814792
Public defence
2015-06-08, 10:00 (English)
Opponent
Available from: 2015-05-29 Created: 2015-05-28 Last updated: 2016-01-12Bibliographically approved
List of papers
1. Fatigue damage of adhesive layers: experiments and models
Open this publication in new window or tab >>Fatigue damage of adhesive layers: experiments and models
2014 (English)In: Procedia Materials Science, ISSN 2211-8128, Vol. 3, 829-834 p.Article in journal (Refereed) Published
Abstract [en]

Mode I fatigue crack growth at load levels close to the threshold is studied with the aim of improving the understanding of the fatigue properties. We also aim at identifying a suitable damage evolution law for large-scale simulation of built-up structures. A fatigue test rig is designed where up to six specimens are tested simultaneously. Each specimen is evaluated separately indicating the specimen-to-specimen variation in fatigue properties. A rubber-based and a PUR-based adhesive are tested. The two adhesives represent adhesives with very different material properties; the rubber adhesive is a stiff structural adhesive and the PUR adhesive is a soft modular adhesive. The experiments are first evaluated using a traditional Paris’ law approach. Inspired by an existing damage evolution law, a modified damage evolution law is developed based on only three parameters. The law is implemented as a user material in Abaqus and the parameters are identified. The results from simulations show a very good ability to reproduce the experimental data. With this model of fatigue damage, a zone of damage evolves at the crack tip. The extension of this zone depends on the stiffness of the adherends; stiffer adherends leads to a larger damage zone. This means that the rate of crack growth depends on the stiffness of the adherends. Thus, not only the state at the crack tip governs the rate of crack growth. This is in contrast to the results of a model based on Paris’ law where only the state at the crack tip, through the energy release rate, governs the rate of crack growth. This indicates that the threshold value of the energy release rate may depend on the stiffness of the adherends.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Applied Mechanics
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-9603 (URN)10.1016/j.mspro.2014.06.135 (DOI)
Conference
20th European Conference on Fracture (ECF20)
Projects
ULFS
Funder
Knowledge Foundation
Available from: 2014-06-27 Created: 2014-06-27 Last updated: 2016-04-27Bibliographically approved
2. Temperature dependence of cohesive laws for an epoxy adhesive in Mode I and Mode II loading
Open this publication in new window or tab >>Temperature dependence of cohesive laws for an epoxy adhesive in Mode I and Mode II loading
2013 (English)In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 183, no 2, 203-221 p.Article in journal (Refereed) Published
Abstract [en]

The influence of the temperature on the cohesive laws for an epoxy adhesive is studied in the glassy region, i.e. below the glass transition temperature. Cohesive laws are derived in both Mode I and Mode II under quasi-static loading conditions in the temperature range C. Three parameters of the cohesive laws are studied in detail: the elastic stiffness, the peak stress and the fracture energy. Methods for determining the elastic stiffness in Mode I and Mode II are derived and evaluated. Simplified bi-linear cohesive laws to be used at any temperature within the studied temperature range are derived for each loading mode. All parameters of the cohesive laws are measured experimentally using only two types of specimens. The adhesive has a nominal layer thickness of 0.3 mm and the crack tip opening displacement is measured over the adhesive thickness. The derived cohesive laws thus represent the entire adhesive layer as having the present layer thickness. It is shown that all parameters, except the Mode I fracture energy, decrease with an increasing temperature in both loading modes. The Mode I fracture energy is shown to be independent of the temperature within the evaluated temperature span. At C the Mode II fracture energy is decreased to about 2/3 of the fracture energy at C. The experimental results are verified by finite element analyses.

Place, publisher, year, edition, pages
Springer Netherlands, 2013
Keyword
Cohesive laws, Epoxy adhesive, Fracture energy, Peak stress, Temperature, Regression analyses, Shear modulus, Young's modulus
National Category
Vehicle Engineering
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-8728 (URN)10.1007/s10704-013-9887-3 (DOI)000326695000006 ()2-s2.0-84888367534 (Scopus ID)
Available from: 2014-01-07 Created: 2014-01-07 Last updated: 2015-05-29Bibliographically approved

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