Fatigue of adhesive bonds in aircraft alloys under wet and dry conditions

摘要

Currently, there is considerable interest in the development of surface preparations for the structural adhesive bonding of aircraft that does not use chromate containing materials or other environmentally undesirable materials. Silane coupling agents have been extensively investigated as one possible solution. However, the resistance of the fabricated joints to degradation in the presence of moisture has usually only been measured under static loading using the wedge test (ASTM D3762-79). This test exposes samples to a tensile force under hot humid conditions (typically 50 °C and 95% R.H. or higher). The applicability of this method to predicting the life of the bonded joint under shear loading is not clear. Also it is not obvious whether there is a correlation between the results of this static test and the performance under fatigue loading conditions. Finally, it has been questioned whether or not results obtained at 50 °C can be correlated with those obtained at lower temperatures. It has been shown that the form of oxide grown at 50 °C is pseudoboehmite whereas Bayerite is the favoured form at lower temperatures.