BONDED COMPOSITE REPAIRS UNDER DRY/COLD AND HOT/WET ENVIRONMENTAL CONDITIONS

Composite structures are increasingly present in various types of structures, especially in the aircraft industry. As a result, suitable repair strategies have to be developed and tested. Hereby, an important part is testing under relevant environmental conditions. As a consequence, the current research work is focused on the influence of (1) testing at -30 °C in dried condition and (2) testing at 70 °C after 100 cycles between -30 °C and 70 °C / 85 % r. h. on the tensile strength of repair specimens. Specimens were repaired with 2 different taper ratios using a soft patch repair approach. Prior to tensile testing, the moisture absorption was assessed during conditioning at 70 °C / 85 % r. h. and during cyclic conditioning. For the cyclic conditioning, computed tomography (CT) was additionally performed in order to assess possible damage evolution between the dried and the conditioned state (after 100 cycles). Tensile testing showed a reduction in tensile strength in comparison to the non-repaired specimens for both taper ratios. The failure mode of the repair specimens changed from fiber failure to failure in the vicinity of the bondline with the steeper taper angle. CT images showed no indication of evolving defects in the vicinity of the bondline as a result of the cyclic conditioning.