Effect of thermal cycling on tensile properties of degraded FML to metal hybrid joints exposed to sea water

In the present paper, the mechanical properties of hybrid bonded bolted joints between Fiber metal laminate (FML) and stainless steel adherends are investigated using experimental tensile tests. Three and five layered FMLs were fabricated using 430 stainless steel sheets and fiberglass prepreg layers. The adherends were bonded by AD-314 resin mixed with HA-34 hardener as adhesive and steel bolt was used for the mechanical fastening. The specimens were immersed into the sea water for 30 days and degradation of the mechanical strength of the joints was studied. Thermal cycles including heating (40 °C to100 °C) and cryogenic (−100 °C to −40 °C) cycles were applied in order to study their effects on the strength of the degraded joints. The failure mode for the adhesive bond was mixed failure and that of the bolted joint was the net-tension failure. The results showed 52% strength recovery in hybrid joints subjected to heating cycles. Cryogenic cycles also caused a 50% improvement in the tensile strength of the hybrid joints. In addition, the joint stiffness and absorbed energy of the specimens were improved significantly for both heating and cryogenic cycles. Moreover, the effect of FML stacking sequence on the results was also investigated. The results revealed that the mechanical fastening failure load for 5 layered FML joint is more affected by thermal cycles in comparison with 3 layered FML joint.