Effect of Temperature on the Residual Stresses in an Integral Structure with a Crack-Retarding Patch

The application of bonded straps has been proposed for extending the fatigue life of aircraft structures, particularly for integral structures with low inherent crack-retarding capability. A potential disadvantage in the use of bonded crack retarders is the difference between the coefficients of thermal expansion between the strap and substrate materials, which causes residual stresses when the temperature deviates from the curing or assembly temperature. The evolution of these stresses in flight is important to take into account to accurately assess the fatigue crack growth behaviour of the structure. In this work, the residual strains in an aluminium compact-tension sample adhesively reinforced with a titanium strap have been measured with neutron diffraction and modelled with a finite element approach at room temperature and at -50 degrees C. It was found that a linear elastic approach could accurately be used to predict the residual stresses. The residual stresses were found to be about twice as large at -50 degrees C as at room temperature.