Prediction of moisture uptake in the adhesive
layer of a lapjoint subject to water immersion 

NPL has a long history of materials modelling. In recent years some of this modelling work has involved the use of the Abaqus software package to carry out finite element analysis (FEA). FEA is a useful tool, which allows the prediction of deformation behaviour, along with the visualisation of various parameters such as stress and strain distributions. Within the materials research area at NPL finite element analysis has been used routinely for a range of applications such as:

• Modelling deformation behaviour of adhesives and adherends
• Assessing the validity of test specimens/procedures
• A tool to assess the effect of geometric changes (parametric studies)
• Predicting stess/strain concentrations - a way of predicting failure?

Without accurate materials data, finite element predictions can be meaningless. At NPL, we have a wealth of knowledge regarding materials testing, enabling us to produce accurate materials property data for inclusion in FE analyses.

To optimise the output from finite element analyses, the relevant materials model must be used, along with accurate materials properties. Much of the modelling work within the adhesives area has concentrated on choice of materials models and accurate calculation of materials parameters to enable predictions of both deformation behaviour and stress/strain.

Types of adhesives studied include flexible and rubber-toughened adhesives, which require different materials models and data. NPL reports, measurement notes and Good Practice Guides have been produced on the modelling of adhesive materials.