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Mechanical Behaviour of Adhesive Layers - Experimental Methods, Cohesive Laws, and Fracture Mechanics

Anders Biel (Institutionen för tillämpad mekanik)
Göteborg : Chalmers University of Technology, 2008. ISBN: 978-91-7385-135-0.- 142 s.

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.

Nyckelord: experimental method, adhesive layer, cohesive law, fracture, fracture energy, energy release rate, peel, shear

Denna post skapades 2008-05-21. Senast ändrad 2013-09-25.
CPL Pubid: 71102


Institutioner (Chalmers)

Institutionen för tillämpad mekanik (1900-2017)


Övrig teknisk mekanik

Chalmers infrastruktur


Datum: 2008-06-10
Tid: 13:00
Lokal: HA2
Opponent: Docent Kristofer Gamstedt

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