R. Créac’hcadec

Numerical study of the local behaviour of adhesive bonds under dynamic loading

Nowadays, adhesively bonded structures are widely used in the transport sector for the development of lightweight vehicles. In order to guarantee passenger safety, it is thus necessary to understand the behaviour of such assemblies under dynamic and combined loadings. This paper presents a numerical study of the local behaviour of adhesively bonded assemblies under dynamic loading. In the first part, the ASTM D950-03 block impact test is studied. This device does not enable a homogeneous loading of the adhesive and causes stress concentrations. On the basis of existing quasi-static works, strategies are then implemented at a local scale. By combining a specific substrate geometry and by limiting the stiffness gradient between the substrates and the adhesive, results show that it is possible to obtain a qualitatively acceptable stress fields in the adhesive for mechanical characterization under dynamic loadings. The Arcan TCS device mentioned below uses such solutions to characterize the mechanical behaviour of bonded joints subjected to combined quasi-static loadings. In this study, the question of its extensibility to dynamic loadings by the use of an impactor guided into a drop tower is investigated. A dedicated finite element model is built under the plane stress assumption. The stress distributions in the adhesive are analysed through time and space for several loading conditions. The stress versus time signals are then compared with the results coming from modal analysis in order to highlight the vibration behaviour of the device, directly linked to the configuration.

A Prediction Method of the Behavior of Adhesively Bonded Structures under Cyclic Shear Loading Based on a Characterization of the Viscous Aspects of the Adhesive in an Assembly

The capabilities of structural bonding are more and more used. Estimating the abilities of an adhesive to endure repetitive loadings and to keep stable its mechanical properties along service life is an essential point to analyze in order to conduct fatigue assessments. The aim of this study is to develop a predictive tool for describing the fatigue behavior of an adhesive in an assembly under cyclic loadings. The approach developed analyzes the influence of viscosity on the mechanical behavior of an adhesive in an assembly based on monotonic and creep test results. Thanks to the evaluation of viscous phenomena, it is possible to predict the cyclic response of the adhesive. The experimental approach uses a unique bonded joint designed to limit the stress concentrations and with a maximum stress state in the center of the adhesive. In this paper, following the strategy developed under monotonic loading, experimental results under cyclic loading are presented for different types of loading using several load ratios and amplitudes. These results underline that the evolution of viscous deformations depends on the loading type. Under shear loading and for a ductile structural adhesive, the experimental results are well described using a viscoelastic–viscoplastic constitutive model with nonlinear viscous parameters. This model makes it possible to analyze the influence of different parameters on the mechanical response of bonded joints under cyclic shear loadings.

A new method to measure the adhesion capability of the metallic surface under shear loading using a modified Arcan test

ABSTRACT The single lap shear test is considered by carmakers as a standard test to control the adhesion of a bonded assembly. In some special cases, when thin steel surfaces are bonded to a structural toughened epoxy-based adhesive, interfacial failure could occur using this mechanical test. Understanding the contribution of the steel surface on the failure mechanisms using the single lap shear test is complex: heterogeneous distribution of stresses, contributions of edge effects, plasticity of the sheet metal, and stiffness of the specimen. It is very difficult to determine failure criteria using the single lap shear test for the interfaces. This work proposes a new method to measure the adhesion capability of the metallic surface under a well-controlled loading. The method is based on the modified Arcan test in shear loading which is adjusted to steel plates. Three different types of surfaces were characterised experimentally and numerically with different adhesion behaviours regarding their failure patterns. The new modified Arcan test is a suitable test to identify the properties of the interfaces in the bonded assemblies using strain and energy criteria.