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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 99
Edited by: B.H.V. Topping
Paper 142

Analysis of Stress Concentrations in Adhesively-Bonded Assemblies subject to Thermo-Mechanical Loads: Application to the Characterisation of the Adhesive Behaviour

J.Y. Cognard1, C. Badulescu1, N. Carrère1, R. Créac'hcadec1 and P. Védrine2

1Laboratoire Brestois de Mécanique et des Systèmes, ENSTA Bretagne/Université de Brest/ENIB/UEB, France
2CEA Saclay, DSM/Irfu/SACM, Gif sur Yvette, France

Full Bibliographic Reference for this paper
, "Analysis of Stress Concentrations in Adhesively-Bonded Assemblies subject to Thermo-Mechanical Loads: Application to the Characterisation of the Adhesive Behaviour", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 142, 2012. doi:10.4203/ccp.99.142
Keywords: adhesively-bonded joint, stress concentration, thermo-mechanical loads, finite element analysis, joint design.

Bonded assemblies are increasingly used in the design of mechanical structures because of the major advantages of this technique, i.e. the weight reduction and the facility to join different material and especially composites. But bonded assemblies are often characterized by large stress concentrations at the ends of the overlap length which are mainly associated with a high ratio of the mechanical properties between the adhesive and the adherents (mainly the Young's modulus), the low thickness of the adhesive in the assembly and the mechanical load. Moreover, the use of bonded assemblies at different temperatures can lead to an increase in the stress concentrations associated with the thermal stresses. Thus, specific studies are required because the mechanical behaviour of the adhesive and the stress concentrations in bounded assemblies can depend on the service temperature, especially in the case of high-tech applications under high or low temperatures. The Young's modulus and the so-called elastic limit of an adhesive strongly depend on the service temperature. Moreover, the coefficients of thermal expansion for the adherents and the adhesive are generally different, thus a change of service temperature leads to a pre-load of the adhesive which can also be associated with stress concentrations. Therefore such properties have to be taken into account in the joint design. The objective of the paper is first to characterize the influence of thermo-mechanical loads on the stress state in a bonded assembly for the elastic assumption by taking into account that the mechanical properties of the adhesive are temperature dependent. Such thermo-mechanical loads can lead to a complex history path in the von Mises equivalent stress - hydrostatic stress plane which is often used to describe the temperature dependent elastic limit of an adhesive. Starting from two-dimensional numerical simulations, the influence of the service temperature on the stress concentrations is analysed in order to define the requirements of the bonded specimens for reliable experimental tests. Some experimental results, for a temperature range between 20°C and -60°C using a modified Arcan device designed to strongly limit stress concentrations, are presented in order to validate the proposed numerical studies. Moreover, the proposed experimental strategy can be interesting to study the temperature-dependent visco-plastic behaviour of an adhesive in an assembly under various thermo-mechanical loads.

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