Adhecom 89, 2nd International Congress on Adhesion and Adhesives

Adhecom 89, 2nd International Congress on Adhesion and Adhesives Bordeaux, France, 2 0 - 2 3 March 1989 Following the success of the 1st International Week on Bonding and Joining Technologies held in Bordeaux. in April 1986, a second meeting, Adhecom 89, was organised by the French Adhesion Society comprising 37 papers divided into six sections, a poster session and an exhibition. The following reports provide two impressions of this major meeting in thefield of adhesives. Adhecom 89 was the second major international adhesion and adhesives conference organised by the French Adhesion Society (SFAA). The event was held in Bordeaux and ran in parallel with the 'Composites" meeting of the European Committee of Composite Materials. The Palais des Congres was a fitting venue for the combined conference programme and the associated exhibitions of adhesives and composite materials. Adhecom was attended by 350 delegates although the international representation was surprisingly small for an event of this scale, perhaps due to the conflict of dates with the annual City University Conference in the UK. The Adhecom programme was structured around the primary themes of surfaces and interfaces, products, techniques of application, design and characterisation of joints, and durability. The contributions consisted of 10 plenary presentations, 27 full papers and 34 poster presentations. With such a large number of papers it is not possible to review all the contributions but this personal overview of the collected sessions may serve both as a critical commentary of the event and a reflection of the status of adhesives and adhesion research in Europe. The general themes of the sessions in the conference are broadly accepted as the key areas of interest in adhesion and adhesives. The range of topics also provides a measure of the multi-disciplinary nature of the subject. In his opening address on "Adhesion and adhesives - - the role of basic research" Dr Bikales (National Science Foundation, Washington, USA) identified this multi-disciplinarity as an obstacle to progress. He also argued that the empirical approach to adhesion problems and adhesives research will give diminishing returns in the future. Progress in practical adhesion and adhesives will depend crucially on advances in basic sciences and on cooperation of scientists from various disciplines. These remarks were to provide an accurate prediction of the conference proceedings: perhaps most emphatically observed during the first main theme on surfaces and interfaces session. Professor Briggs (ICI, UK) set the scene for this session with a plenary contribution on recent advances in surface analysis techniques with particular reference to adhesion studies and described developments of xPs imaging and microanalvsis capabilities down to 30/2m. The seven technical papers of the session addressed problems of surface characterization, surface

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modification (including plasma treatment of polymers) and the influence of substrate on the curing of the adhesive. The nine poster papers also dealt with similar topics, a major source of papers being the University of Mulhouse, reflecting the presence and influence of Dr Schultz's team in the area of adhesion science. The theme of the second session was concerned with products and included eight papers covering new developments in adhesives and primers. Three of these contributions related to reactive hot melt adhesives: several systems based variously on EVA, epoxypolyurethanes and polyurethane chemistry, were described. The rapid handling time which can be achieved with reactive hot melts was cited as an attractive property in high volume assembly and was likely to find application in the automotive industry. Four of the poster papers also described research with reactive hot melt materials and these systems featured prominently among the new products on display in the associated exhibition. The plenary contributions for the session described problems both in the formulation and industrial application of adhesives, and in a highly analytical paper. Professor Delhalle (Notre D a m e University, Belgium) demonstrated a computer modelling technique to predict reactivity and properties of chemical species based on quantum chemistry. The use of this system was proposed for the design of deposited organic films/ primers. At a more pragmatic level, a primer development which provides high adhesion to polypropylene with cyanoacrylate, was described by Dr Melody (Loctite, Ireland). The "applications' theme of the conference was introduced by Dr Cuntz (Aerospatiale, France) who highlighted some of the problems and achievements of adhesive bonding technology in the aerospace industry. Commenting on the importance of making the right decisions in the choice of materials and processes in such a complex field, Dr Cuntz observed that expert systems would play a major role in increasing confidence in the future. The contrast of the aerospace industry with automotive bonding technology was shown in a paper on applications of adhesives in the production of the Peugeot 405 car. This contribution included a discussion on the use of induction heating to provide a rapid cure of epoxy adhesives. In another "automotive application" paper from Renault, the importance of viscosity control on automatic

dispensing equipment was discussed. The three poster papers in this session referred to novel rapid-curing methods including microwave and UV irradiation for high speed, high volume applications. Professor Adams (University of Bristol, UK) introduced the session on joint design and characterization with a plenary paper on modelling, design and evaluation of structural bonded joints. The presentation provided a critical assessment of the various theories and techniques used in analysing lap joints. Four full technical papers and 12 poster presentations were included under this theme. The importance of adhesive characterization was emphasized by M. Jeandrau (CETIM, France) who compared properties of various adhesives obtained from different test methods. A paper from Aerospatiale demonstrated the use of expert systems in the study and sizing of bonded joints in space structures. A second plenary contribution in the session on design and characterization of joints was presented by Professor Gent (University of Akron, USA). His paper on "Failure mechanisms in model composites" described experiments which demonstrated internal cracking and cavity formation adjacent to inclusions in a rubber matrix: for weakly bonded systems, disbond occurred at the rubber/inclusion interface in agreement with fracture energy principles. Fracture mechanics also featured in a presentation by J. Cognard (Asulab, Switzerland) who discussed a development of the wedge test, called the chip test, which allows the extension of cleavage tests to plastics and brittle materials. Several of the poster papers discussed developments of experimental test methods and modelling techniques to provide theoretical prediction of joint behaviour. The thick adherend shear test (TAST) was used by a number of different groups to obtain adhesive properties. The Althof system for TAST tests is now adopted as a D I N standard and a similar arrangement is being developed for a French standard. With the exception of the plenary papers all the contributions in this session were from French establishments, demonstrating a considerable commitment of their national effort to the area of adhesive technology. The final conference session was on the theme of durability, and surprisingly was supported by the fewest papers: only two full technical papers were given together with two plenary presentations. No poster contributions were offered. In his plenary address Dr Brockmann (FIM, Bremen, FRG) highlighted the problems of predicting long-term behaviour of bonded joints from accelerated ageing tests. Although he acknowledged that the aerospace industry had established good life predictability of bonds in aluminium alloy, steel presented much more of a problem as failure was likely to be corrosion driyen. It was not possible to correlate performance with oxide structure as in the case of aluminium. Fatigue strength evaluation of bonded joints featured in a paper from a group of French

establishments which was presented by M. Halioui (IRSID, France). Of several methods used to measure the evolution of fatigue damage, ultrasonic testing was preferred. Crack initiation and propagation were studied and the beneficial effects of fillets on fatigue life were demonstrated. The second paper discussed adhesion primers and the microstructural changes induced by ageing when the primers were used with different aluminium alloy pretreatments. Before the c l o s e o f the conference a group of four "unclassified' papers were presented. These included reference to ceramic-metal interfaces, bonding of refractory, composites operating at 1400°C, adhesives for corneal grafts and international standardization of adhesives. The final plenary presentation was given by Professor Wightman (Virginia Polytechnic, USA). His closing address on surface chemistry aspects of the durability, of adhesive bonded joints, discussed the application of various anal~ical techniques in evaluating the effects of pretreatments on bonds in titanium and aluminium alloys, it appropriately linked the first theme of the conference, on surfaces, to the closing session on durability, and provided an opportunity to reappraise the introductory, observation by Dr Bikales on the need for advances in basic science to support the further development of adhesive bonding technology. Undoubtedly much has been achieved through a greater understanding of adhesion science in the study of bond behaviour and degradation mechanisms. Similarly mathematical modelling of stress characteristics in joints has given a much more anal~ical approach to the design of bonded structures. Adhecom 89 provided an excellent forum for the presentation of recent research and developments in adhesion and analysis of bonded joints: clearly the many French research establishments represented at the conference are making a major contribution to these fields. However, it might be observed that there is a widening gap in the transfer of this science into application technology. Perhaps there is still room for empiricism to provide a more specific focus for basic science research. In terms of organisation and structure, the conference generated some interesting observations. The simultaneous translations were, on the whole, well presented and the relative ease of communication could be gauged from the lively multi-lingual discussion at the end of each session. The provision of conference assembly time for the poster presenters was a good idea although three minutes per person was too short, even for a brief synopsis. Indeed the rationale behind the selection of full papers and poster papers seemed somewhat arbitrary. Perhaps parallel sessions for one of the conference days may have provided more opportunity for inclusion of additional full papers. And why were the plenary presentations not supported by full papers in the conference proceedings? One of the valuable spin-offs of conference events is the opportunity for informal exchanges and

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discussions outside the conference hall. The Adhecom 89 programme offered ample facilities for these meetings, particularly with the adjacent exhibition areas. The exhibition itself also provided an excellent supplement to the conference and demonstrated some of the emerging technology and applications from the diverse research programmes. Reactive hot-melts have already been referred to: other developments which mirrored the conference message were various computer programmes for joint analysis and design, with related data bases. Two software packages which had been developed through joint European projects were demonstrated, and these expert systems should make an important contribution to technology transfer in the future. In conclusion the Adhecom 89 event was an excellent meeting with a wide-ranging technical programme. It is hoped that m a n y of the papers may become available in English and accessible to a wider readership. A Beevers Oxford Polytechnic, UK

With 360 attendees and 75 papers the second Adhecom meeting was a great success of which the organiser may be proud. At the opening, the conference was addressed by French former Prime Minister J. C h a b a n Delmas. The programme included an adequate balance of fundamental and applied research, products and applications. It was organised around six major themes covering most facets of adhesion science: Surfaces and Interfaces: Products: Applications: Conception and Characterisation of Assemblies: Durability: and Free Themes: with each section being introduced by a plenary lecture. All papers were simultaneously translated from or into English. In the introductory' plenary lecture the role of basic research and the necessity, for coordination with applied research was reinforced by N.M. Bikales (National Science Foundation, USA). Bas!,; r¢~eurch covered work done on the dynamic of spreading of liquids over contaminated surfaces (P. Caries et al., College de France), the direct measurement of adhesion forces (J. Loubet, INSALyon). the effect of glass composition on adherence (A. Arribart. St-Gobain), the influence of substrates on epoxy curing (V. Pechereaux, Renault) and the relation existing between the resistivity of a joint and its adherence (L. Lavielle, Mulhouse). As far as Products were concerned the most striking development was that of reactive hot melts which have now reached the market (Atochem, Ciba. Emhart. Henkel, SNPE, Teroson).

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In the field of applications the problems faced by the aeronautical industry in bonding Al-plated aluminium alloys were clearly exposed by J.M. Cuntz (Arrospatiale) while T. Stutzmann discussed the use of adhesive in the construction of the Peugeot 405. R. Adams presented with much elegance the difficulties that mechanics has to model a real adhesive joint and the consequences of the necessary simplifications with are made to calculate the joint properties (J.P. Jeandreau, Cetim): (J.P. Maigret, Arrospatiale). Many processes for improving plastic adherence were described in the poster session. Durability, studies were introduced by W. Brockmann (FIAM. Bremen) who questionned the currently used evaluation methods and recommended how improvements might be made. J.P. Wightman (Virginia Polytechnic Institute, USA) showed the ageing of titanium-polymer interphase and I. Berbegier (Uni-Lyon) that of aluminium anodized layers with and without primers from which I wondered whether the anodization process does any good when bonding metals. The result of the studies of a model composite failure were presented by A.N. Gent (University, of Akron, USA) who showed how the fracture mechanics approach - - supposing that the delamination initiate at interracial defects - - described the initiation of the fibre delamination. Few test methods were analysed or presented and as is usual at adhesion meetings, polymer chemistry was almost absent except for the theoretical presentation by J. Delhalle (Bruxelles). We will repeat our criticism of many of the presentations from people in industry: Why do you stay so general in your presentation and hide technical details given in your patents which are, with present computerized information, available to all? For your listeners it is a waste of time and somewhat irritating. Specific aspects of adhesion gathered in the Free Themes section always stimulate the imagination. Papers included: structural bonding of carbon composites or ceramics withstanding 1400°C (L. Heraud. SEP) or the use of fibrin sealants for treatment of corneal ulcers (L. Gauthier, Bordeaux) or a composite trailer without a frame jointed by glueing (M. Verrier, Lamberet). Outside the conference room, an exhibition with 40 exhibitors presented the commercial counterparts of this research and the nearby congress of the European Composite Association stressed the c o m m o n interests between the adhesive and composites field. The next Adhecom meeting will be held in 1992, probably in Mulhouse, and one may guess that it will have a still wider attendance. J. Cognard Asulab S,~ Switzerland