Community Research and Development Information Service - CORDIS

Methods and data for the design of adhesive joints

A consistent procedure has been developed to design adhesive joints for ship building applications.

At the beginning of a design process lists of requirements for the specific application case have to be worked out by the shipyards. These lists have to be filled out with a specific set of main characteristic features which yield full information about any aspect of the specific joint, if the lists will be carefully worked out. Finally the lists of requirements might provide a complete technical description of the specific application case. With this method the shipyard is provided with a methodology to find a safe approach to a new technology. The list of requirements is the basis of any further work from testing to design, production and manufacturing etc.

According to the requirements of the application cases screening tests have to be defined and to be done in order to select adhesives, adhesive primers and surface preparations. One severe influence to the screening tests and to the enormous amount of tests, which might be necessary, is determined by requirement to bond on painted surfaces.

In parallel to the first working steps in the design process of the joints a test programme has to be worked out to determine necessary data for numerical and analytical design approaches with consideration of possible effects of ageing and fatigue. The types of tests are determined by the requirements of software for finite element analysis on one hand side and by the concept of knockdown and safety factors to be used for the design process of adhesive joints on the other hand side.

This concept needs data about the strength of the adhesive joint before and after ageing, fatigue, temperature or any other influence to determine specific knockdown factors. The data have to be determined for any surface of paint, which should be used. It turned out, for example, that the fatigue behaviour of rigid joints is significantly influenced by the surface, especially if the surface is painted or not.

Besides the data for the work-horse adhesives and selected surfaces which can be obtained from the project partners the main result is an experimental methodology to determine characteristic values and knock-down and safety factors, as well as mechanical data for finite element analysis. The experimental method will be one backbone of the guidelines. For the modelling of joints different approaches have to be used for flexible and for rigid adhesives. For flexible adhesives the "energy approach" with hyperelastic non-linear material law was generalised in order to be able to optimise any local joint geometry. The hyperelastic analysis was compared with global and local linear elastic analysis. While the global results agree within a tolerable error range, the local analysis shows significant differences. Since failure occurs locally, non-linear analysis is recommended for the prediction of the locus of failure and failure prediction as well as for geometrical optimisation.

Furthermore, a pragmatic linear elastic approach for strength prediction was developed for joints with rigid adhesives. The approach uses a failure criterion developed from coupon testing, including knockdown and safety factors. The method is conservative and was verified by component tests for bondship application

The design methods for flexible and for rigid adhesive joints will also be parts of recommendations in the guidelines provided by DNV.

The methods can be directly used at current shipyard conditions. The education programme for the European Adhesive Engineer will use the results of the project for further spreading the information to other application areas. The implementation of the results to the specific sites needs some further effort, which can be supplied by IFAM within further co-operations and partnerships.

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