Yves Baziard

Study of critical failure parameters for an adhesive-bonded single lap joint with ceramic adherends

Abstract The failure behaviour of an adhesive-bonded single lap joint with ceramic (silicon carbide) adherends has been investigated using an experimental crack test in which the conditions are close to those in the ASTM D2293-69 standard test. The critical strain energy release rate (GIIC) and the critical stress intensity factor in shear mode (KIIC) are the propagation criteria used. The ANSYS finite element code has been used to model the experimental work, with good agreement being obtained between experimental and numerical results. Adhesive and cohesive failures of the joints were encountered, with different values of GIIC and KIIC for each type of failure. The GIIC value observed for cohesive failure of the joint is 10 times greater than that calculated for adhesive failure.

STUDY OF BONDED PLASMA-TREATED POLYETHERIMIDE COMPONENTS FOR POWER INTEGRATION: DURABILITY IN A HOT/WET ENVIRONMENT

This work deals with the study of the durability, in a hot/wet environment, of structural adhesively bonded polyetherimide (PEI) assemblies used in power electronics packaging technology. An overall approach is proposed, for which the epoxy joint-PEI substrates assembly on the one hand, and the adhesive system components (substrate surface and bulk adhesive) on the other hand, are studied separately with different analytical techniques. The first part of this work was devoted to the substrate surface state and to its modification using a cold plasma treatment of the PEI surface. Then for chosen parameters (power, duration) contact angle measurements indicated an increased surface tension resulting from surface decontamination (removal of release agent and carbon contaminants) and from the creation of polar species, such as esters or carboxylic acid groups, on the PEI surface (XPS analyses). The second part of this study concerned the bulk adhesive ageing in an ethylene glycol-water solution at 70°C. Mass uptake measurements versus time showed the liquid diffusion in the bulk adhesive associated with a microscopic damage of the epoxy system. An overall plasticizing of the adhesive with a considerable decay of the α-transition temperature of one of the two adhesive epoxy-amine networks (TGDDM-BAPP) was also highlighted using rheometry. However, in these ageing conditions, the adhesive glassy modulus decreases slighty because of the thermomechanical stability of the other epoxy network. In the third part, the asymmetric wedge test showed the beneficial effect of the cold plasma treatment on the epoxy/PEI interface durability in the aggressive medium.

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.