Methods for shrinkage measurement considering stress development of curing structural adhesives

Joint strength and methods for their determination play a crucial role for component design within the development phase of adhesively bonded components. Shrinkage-induced stresses due to adhesive's curing may reduce the maximum strength of the bonded components; conversely, ignoring their effects may overestimate the design value thereof. Accordingly, the accurate prediction of residual stresses is of high importance, and so is determination of relevant material parameters. Adhesive properties, such as Young's modulus and shrinkage, change significantly throughout curing. These have to be determined according to various material models, which are tributary to the experimental determination of corresponding material parameters. In this paper, the effects of shrinkage and residual stresses on simple joint geometries are transiently determined using the extended rheometer (ExRheo). The ExRheo proved to be a reliable method to determine volume shrinkage through successful validation by mercury dilatometry. Furthermore, shrinkage of constrained specimens can be measured using ExRheo and showed to be lower compared to specimens that could shrink freely. Material-specific properties like onset of vitrification could also be detected with the presented method. Based upon these experimental results of thermo-analytical characterisation of structural adhesives during curing, data for finite element analysis (FEA) is gathered. Aforementioned results will lead to improvements of stress prediction for industrial applications.