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Effects of constitutive parameters on the accuracy of measured fracture energy using the DCB-specimen
University of Skövde, School of Technology and Society.
University of Skövde, School of Technology and Society.
2008 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, no 10, 2968-2983 p.Article in journal (Refereed) Published
Abstract [en]

Several methods exist to estimate the fracture energy for adhesive joints using the double cantilever beam specimen and linear elastic fracture mechanics. Since the mechanical properties of all adhesives are non-linear, errors are generated. By use of an exact solution experiments are simulated. These are evaluated with eight different methods. The influence of the constitutive parameters is systematically studied. This influence is small for most methods. The error due to the choice of evaluation method is considerably larger. One of the commonly used methods gives accurate results; the error is less than 3%. However, most methods yield substantial errors.

Place, publisher, year, edition, pages
Elsevier, 2008. Vol. 75, no 10, 2968-2983 p.
Keyword [en]
Test standards, DCB-specimen, Toughness testing, Fracture energy, Adhesive
National Category
Materials Engineering
Research subject
Technology
Identifiers
URN: urn:nbn:se:his:diva-2806DOI: 10.1016/j.engfracmech.2008.01.002ISI: 000256014600009Scopus ID: 2-s2.0-40849083441OAI: oai:DiVA.org:his-2806DiVA: diva2:201016
Available from: 2009-03-02 Created: 2009-03-02 Last updated: 2013-04-15Bibliographically approved
In thesis
1. Mechanical behaviour of adhesive layers: experimental methods, cohesive laws, and fracture mechanics
Open this publication in new window or tab >>Mechanical behaviour of adhesive layers: experimental methods, cohesive laws, and fracture mechanics
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Adhesive joining is today viewed as one of the key technologies to achieve decreased emissions in the automobile industry. To decrease weight, optimal material selection often results in different materials for different parts. This leads to the necessity to join mixed material. Here, the use of adhesives is the most promising joining technology. For a rational design process, good models for strength analysis of adhesively joined structures are essential. With cohesive modelling, fracture of the adhesive layer is modelled with a stress-deformation law. This law - often denoted a cohesive law - gives the traction exerted on the adherends due to the deformation of the adhesive layer. This thesis is concerned with experimental methods to measure cohesive properties of engineering adhesives and standardized methods to measure the fracture energy of adhesives. A new method to measure cohesive laws is developed. With this method, the cohesive law of an epoxy adhesive is measured in shear. In peel loading, with elastically deforming adherends, the cohesive law is shown to be independent of the geometry of the specimen. If the adherends deform plastically the fracture energy increases. Experiments are performed in order to determine the temperature dependence of the cohesive layer for an epoxy adhesive. It is shown that the peak stress is strongly dependent on the temperature while the fracture energy shows only small temperature dependence. Experiments are also performed to study the influence of strain rate in peel and shear loading. The experiments show that the peak stress increases with an increasing strain rate and that the fracture energy increase in peel loading and decreases in shear with increasing strain rate. A new method to experimentally determine the relation between damage and plasticity in the adhesive during the fracture process is developed. For the present adhesive, it is shown that only minor plasticity occurs during the fracture process in peel loading. For peel, several commonly used methods to evaluate the fracture energy using the double cantilever beam specimen are critically studied. For some methods the error in evaluated fracture energy is larger than 40 %. It is shown that the evaluated fracture energy is more dependent on the choice of method than on the cohesive properties of the adhesive layer.

Place, publisher, year, edition, pages
Chalmers tekniska högskola, 2008. 16 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola, ISSN 0346-718X ; 2816
Keyword
experimental method, adhesive layer, cohesive law, fracture, fracture energy, energy release rate, peel, shear
National Category
Materials Engineering
Research subject
Technology
Identifiers
urn:nbn:se:his:diva-2941 (URN)978-91-7385-135-0 (ISBN)
Public defence
2008-10-06, 13:00 (English)
Opponent
Available from: 2009-04-03 Created: 2009-04-03 Last updated: 2013-04-16Bibliographically approved

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