Bouchra Hassoune-Rhabbour

Development of an Adhesion Test for Characterizing the Interface Fiber/Polymer Matrix

There are several models on the relationship structures and properties of the composite fiber / matrix interface [1]. Including literature proposes the development of micromechanical tests suitable for assessing the shear strength of the interface fiber / polymer matrix. The first test which allowed to characterize the fiber / matrix interface is the pull-out test developed by Broutman [2]. It consists in extracting the fiber from the matrix that can be in block form, gout or disk of resin. To reduce the variation in results due to the geometries used, it was agreed to use a drop of resin with small dimensions. The test is to characterize the fiber / matrix interface of natural thermosetting or thermoplastic by determining the shear stress.

Graft Interpenetrating Continuous Epoxy-Polysiloxane Polymeric Network

The objective is to design a joint, suitable for use from low to high temperature by combination of two adhesives along the overlap length in single lap joint. This mixed modulus concept is called Multi-module Bond line (MMBL). At high temperatures, a brittle adhesive (high modulus) in the middle of the joint retains the strength and transfers the entire load. At low temperatures, a ductile adhesive at the ends of the joint is the load-bearing adhesive. The first part of this work deals with the formulation of adhesives with differend stiffnesses to be used in the MMBL concept. Starting from a DGEBA resin/DETDA hardener system, different contents of amine terminated polysiloxane modifiers are added to the original mixture. A phase-separated structure is observed via scanning electron microscopy. The thermal, mechanical and dynamic viscoelastic properties of polysiloxane modified epoxy networks are studied. The second part of this paper will present the infinite element study of the assembly with two formulated adhesives in order to verify if they respect the MMBL concept.

In Situ Determination of Glass Transition Temperatures of Epoxy Adhesives in Structural Ceramic Assemblies

A method is described for measuring the glass transition temperature (Tg) of epoxy joints bonding ceramic (SiC) substrates. This method is based on the strain measure of a single-lap joint subjected to a temperature variation. The resulting displacement (d) is observed as a function of the temperature (T) by means of a contact strain gauge extensometer. Thus Tg value can be determined using (d-T) curves recorded. The influence of joint parameters (joint thickness and overlap length) and of other parameters such as the applied load and the surface state of substrates were studied for a structural epoxy adhesive showing different thermomechanical behaviours. The results show that it is possible, with appropriate experimental conditions, to measure Tg with this method and to find Tg values similar to those found by classical techniques such as the static thermomechanical analysis (TMA) and the differential scanning calorimetry (DSC). This method shows similarities with TMA, but it has the advantage to allow the thermomechanical analysis of adhesives without destructive sampling of joints.

Study of DGEBA and Novolac Adhesives Hydrothermal Ageing for a Ceramic/ Steel Substrates Bonding Assembly

The industrial application (not described for confidential reasons) needs the assembly of a ceramic piece and a steel one. This PhD research work aims to provide a reliable industrial bonding between ceramic and steel substrate using structural adhesive. This industrial joint shall withstand a wide range of temperature with pretty brutal thermal changes and also severe humidity conditions. As prerequisite to this bonding assembly qualification, the purpose of this work is the study of the durability, in a hot-wet environment. Depending on the formulations, we observe different behaviours in term of weight uptake, morphological, thermomechanical and chemical modifications of the epoxy network.

Study of DGEBA and Novolac Adhesive Solutions between Ceramic and Steel Substrates

The industrial application (under a confidential clause) concerns a ceramic/steel assembly. This PhD research is concerned with providing a reliable industrial bonding between ceramic and steel using structural adhesive. This industrial joint shall withstand a wide range of temperatures with brutal thermal changes. This paper focuses on the adhesive formulation. Indeed, we needed to compromise the adhesive flexibility: soft enough to resist the thermal stresses and compensate the coefficient of thermal expansion mismatch between the two substrates. We find this good compromise with DGEBA and Novolac epoxy based adhesive separated or blended. The influence of the different formulation parameters on the initial properties was studied by chemical, rheological and thermal tests on adhesive samples. Depending on those formulations, we observed different behaviours in term of glass transition temperature, cross-linking time and flexibility.