Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Develop numerical methods for joint presentation in large structural assessment

The application of flexible adhesives to join structural elements with similar or dissimilar materials is becoming more and more common in the last years. The finite element method provides versatile numerical tools for the investigation of the behaviour of the bonded joints under operational loading conditions. Non linear finite element methods with hyperelastic material model are required for detailed joint analysis. For the design of large structures a cost efficient modelling method is necessary: for the modelling of adhesive layer in large structures, a substitute system of spring elements can be applied.

In order to perform a global finite element analysis of a large bonded structure, a substitute system of spring elements has been developed to take into account the stiffness contribution of the adhesive layer. Three translational spring elements, connecting correspondent nodes of the adherent, constitute a discrete substitute model of the continuum adhesive in the global FE model. The stiffness moduli for each spring have been evaluated based on the test results performed on butt joint and lap shear joint. Assigning variable values to stiffness moduli, the complex dependency and the nonlinearity of the adhesive material on the loading rate, temperature, load type and cross section geometry can be directly accounted for.

The analysis with the hyperelastic material model enables refined detections of local stress and strain gradients in the adhesive layer. Nonlinear analysis can be performed. On one side, this method requires minimum assumption, but on the other side large models and long computational time are required.

The modelling method with a substitute system of spring elements allows for a reasonable element size of the adherents even with small joint thickness. Linear or nonlinear analysis can be performed. The deformations and forces across the joint are calculated.

Numerical simulation of a benchmark test on a bond-ed structure with flexible adhesive has been performed. The adhesive layer is represented either by so-lid elements characterised by hyperelastic material, or by spring elements with equivalent joint stiffness. The analysis re-sults have been compared with the first loading curve of the mechanical test. Both modelling methods enable a sufficiently accurate prediction of the overall stiffness behaviour of the bonded structures, if compared with the test results.

The stress evaluation of the adhesive is dependent upon the modelling method: the analysis with solid elements model provides local stress and strain. With spring elements model the nominal stress and strain is derived, which can be compared with permissible stress and strain provided by adhesive supplier directly. The correlation between local and nominal stress can be established by a sub-modelling.

Reported by

Alcan Alesa Engineering Ltd./ Alcan MTS
Max Högger-Strasse 6
8048 Zurich
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