Abstract
The effect of sustained loading on adhesively bonded systems has been investigated. This has been done through a combination of experimental and numerical work. Two contrasting adhesives were selected and were tested at room temperature and at 50°C. Bulk tensile properties and creep compliance data were obtained for both adhesives through uniaxial tensile tests in a screw driven Instron test machine. Several configurations of joints have also been tested, looking at adhesive shear and peel performance for joints loaded at various percentages of their quasi-static strength. Results from shear tests indicate that below a certain percentage ultimate strength joint failure will not be reached within a period of 20 months. From the creep compliance data for the bulk adhesive a material model was developed. Several models were investigated and the final model selected was a scaled version of the standard Abaqus model. This provided a good representation of the bulk behaviour of the adhesive and when applied to adhesive joints, through finite element analysis, led to a close correlation with experimental results. This model was used subsequently to analyse the changes, over time, in stress and strain distributions for several joint configurations loaded at various percentages of their quasistatic strength. The results showed a re-distribution of the stresses within the joints with time, resulting in a reduction in the peak stresses found at the ends of joint overlaps. An increase in joint overlap length gave a reduction in the peak stresses attained and consequently a reduction in the overall creep strain. At the centre of the long overlap the creep strain level is reduced significantly, but is not removed altogether, contrary to current expectation.