The use of a modified peel specimen to assess the peel resistance of aircraft fuel tank sealants

The aim of this study was to comprehensively review the traditional peel specimen for assessing adhesion of aircraft fuel tank sealants. A modified peel specimen was proposed that overcomes the inherent problems of the traditional test, which are associated with inaccurate geometry definition and clamping, and avoids any subjective interaction during testing from the knife cuts used to re-initiate the crack at the metallic interface. Artificial defects, which are easy to apply consistently, were introduced during manufacturing of the peel specimens and it was shown that these can act as precise knife cuts during testing. Two aircraft fuel tank sealants were tested using two different peel angles (135° and 180°), several sealant layer thicknesses (1.5, 2, 3 and 4 mm), various substrates (aluminium and mild steel) and chromate epoxy primers (low and conventional VOC). For those specimens that failed cohesively, the peel resistance increased significantly with the peel angle and the sealant layer thickness. On the other hand, the use of chromate epoxy primers did not affect either the peel resistance of the sealants or the failure mode.