Nicolas Carrere

Characterization and modelling of the viscous behaviour of adhesives using the modified Arcan device

The non-linear behaviour of an epoxy adhesive has been studied thanks to the use of a modified Arcan test device. Multilevel creep tests have been performed in order to characterize the time-dependent behaviour. A visco-elastic model has been chosen to describe the behaviour of the adhesive. This model is based on the decomposition of the visco-elastic strain into elementary viscous mechanisms. The non-linear behaviour of the visco-elasticity is taken into account thanks to a non-linear function which depends on the stress. A specific identification procedure based on a single test has been proposed. Finally, the model has been validated using tests that have not been used for the identification. The model proposed in this paper enables the time-dependent non-linear behaviour of adhesives to be reproduced in a correct manner.

Investigating the fracture behavior of adhesively bonded metallic joints using the Arcan fixture

In the present study, the fracture behavior of a crash optimized adhesive was examined by means of the Arcan fixture. The specimens were prepared using aluminum substrates and two pre-cracks (one per each extremity of the joint) were created. The section of the substrates has been specially designed to stabilize crack propagation. The thickness of the adhesive layer was fixed at 0.5 mm. The tests were performed in the mixed mode I/II plane and under compression/shear load, at a speed of 0.5 mm/min. To avoid measuring the crack length during the experiments, an alternative methodology to calculate the fracture toughness is proposed. The results are in good accordance with previously published data on the same adhesive using “classical” TDCB (Tapered Double Cantilever Beam) and MMB (Mixed Mode Bending) tests. The influence of compression/shear loading on the fracture properties of the joint is also discussed.

Analysis of the Influence of Geometric Parameters on the Stress Distributions in Adhesively Bonded Scarf Joints Using 2D Models Under Elastic Assumption

The scarf joint is a usual experimental assembly employed to analyze the mechanical behavior of an adhesive. In fact, using a unique type of bonded assembly with a classic tensile testing machine, various tensile-shear loadings of the adhesive can be applied by changing the value of the scarf angle. In this paper, accurate numerical analyses of the stress distributions within the adhesive in scarf joints under elastic assumption using 2D models are developed. Numerical results underline the influence of the adhesive thickness and mainly the influence of the scarf angle on the edge effects, and confirm the presence of an optimal scarf angle associated with very low stress concentrations. Moreover, the use of a suited elastic limit for the adhesive, defined from the two stress invariants, hydrostatic stress and von Mises equivalent stress, allows the more stressed parts of the adhesive with respect to the scarf angle to be defined. These results also underline the possible influences of the edge effects on the experimental results, i.e., possible crack initiations close to the free edges of the adhesive for some scarf angles. Finally, it is shown that a little modification of the free edges of the adhesive (a so-called “cleaning”) can strongly reduce the influences of the edge effects and thus can improve the experimental results for a wide range of scarf angles.

Modelling of the damage development in carbon/epoxy laminates subjected to combined seawater ageing and mechanical loading

In this study, a damage model that accounts for the effect of seawater ageing is proposed. The model is based on a failure criterion that takes into account the effect of the ply thickness, while the kinetics of the damage development are based on a Finite Fracture Mechanics approach. The stiffness degradation is identified by a multiscale approach. The parameters of the model are physically based which facilitates the identification and the coupling with the ageing. These and their evolution as a function of the time of immersion in seawater have been identified for a carbon/epoxy composite. The changes in crack density as a function of the applied load for three ageing times are quite well predicted by the model. The model explains why the damage threshold is strongly influenced by the ageing while the kinetics of the crack propagation remain quasi-constant.

Cracking and Durability of Composites in a Marine Environment

New renewable marine energy sources are increasingly being pursued as alternatives since they represent an important political and economic challenge for countries. Among these new energy sources, marine tidal turbines are growing considerably. Manufacturers used thick composite material to design most of the tidal turbine blades. To ensure the lifetime of the latter, it is necessary to develop damage models that take into account sea water, and analyse its effects on composite materials.