An experimental method to determine the complete stress versus deformation relation for a thin adhesive layer loaded in shear is presented. The work is based on a classical specimen geometry, i.e. the end-notch flexure specimen (ENF-specimen) and the experiments are evaluated based on an inverse method. By studying the energy balance at the crack tip an expression for the energy release rate is derived. The theory considers the effects of a flexible adhesive layer and is based on beam theory. From the energy release rate the stress-deformation relation is derived using the inverse method.

Quasi-static experiments are performed using a servo-hydraulic testing machine. The deformation process at the crack tip is monitored during the experiments by use of a CCD-camera attached to a microscope. The method requires differentiation of the energy-deformation relation, therefore a Monte-Carlo simulation is performed to investigate how small errors in the data acquisition system affects the final stress-deformation relation. Small errors in the measurement of the force and shear deformation give small effects on the final stress-deformation relation.

Experiments on three different geometries of the specimen are performed. The experiments give consistent results. It is shown that if the process zone in front of the crack tip is large, then the stress-deformation relation does not depend on the dimensions of the adherends. Thus, the constitutive relation can be considered to be a property of the adhesive layer.

2.

Leffler, Karin

et al.

University of Skövde, School of Technology and Society.

Alfredsson, K. Svante

University of Skövde, School of Technology and Society.

Stigh, Ulf

University of Skövde, School of Technology and Society.

Shear behaviour of adhesive layers2007In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 44, no 2, p. 530-545Article in journal (Refereed)

Abstract [en]

An experimental method to determine the complete stress versus deformation relation for a thin adhesive layer loaded in shear is presented. The method is based on a classic specimen geometry; the end-notch flexure specimen. The experiments are evaluated using an inverse method. First, the variation of the energy release rate with respect to the shear deformation at the crack tip is measured during an experiment. Then the traction–deformation relation is derived using an inverse method. The theory is based on the path-independence of the J-integral and considers the effects of a flexible adhesive layer.

Quasi-static experiments on three different specimen geometries are performed using a servo-hydraulic testing machine. The experiments give consistent results. This shows that the traction–deformation relation can be taken as independent of the dimensions of the adherends. Thus, the constitutive relation can be considered as a property of the adhesive layer. The deformation process at the crack tip is also monitored during the experiments by the use of a digital camera attached to a microscope.

An experimental method to determine the complete stress vs. deformation relation for a thin adhesive layer loaded in shear is presented. The experiments are performed by use of a classical specimen geometry, i.e. the end-notch flexure specimen, though the experiments are evaluated based on a novel inverse technique. With this technique, the instantaneous energy release rate is first evaluated by use of a theory for the specimen based on the Euler-Bernoulli beam theory. Effects of a flexible adhesive layer are considered in an approximate way. From the energy release rate, the stress-deformation relation is evaluated using an inverse method. In order for the theory to be valid, the adherends of the specimen are only allowed to deform elastically. Quasi-static experiments are performed using a servo-hydraulic testing machine. In the experiments, the displacement of the loading point is gradually increased to obtain a constant velocity of the shear deformation at the crack tip. Formation of micro-cracks and the propagation of a macro-crack are monitored during the experiments by use of a CCD-camera attached to a microscope. By varying the heights of the adherends, the size of the process zone in front of the crack tip changes from about 200 to 400 times the thickness of the adhesive layer. The results of the experiments give a fracture toughness of 2.5 kJ/m 2 , a critical shear deformation of 0.13 mm, and a maximal strength of 30 MPa independent of the specimen geometry. The experiments show consistent results. The results show that if the process zone is large as compared to the thickness of the adhesive layer, the shear stress – shear deformation relation can be considered as a constitutive property of the adhesive layer.