NOL-ring based evaluation of freeze and freeze–thaw exposure effects on FRP composite column wrap systems

Four different fiber reinforced polymer (FRP) composite column wrap systems are evaluated for durability after exposure to freeze (−15°F) and freeze–thaw conditions. Response and failure mechanisms are characterized through Naval Ordinance Laboratory-ring burst tests, short-beam-shear tests, dynamic mechanical thermal analysis and microscopy. It is shown that freeze–thaw exposure after salt soak can have a significant detrimental effect and results in reductions in both tensile strength and interlaminar shear strength. The adhesive layer used in the prefabricated adhesively bonded system is shown to be the weak link in that system with degradation and failure taking place either within the adhesive or at the adhesive–composite interface. Effects of incomplete ambient cure, pre-existing voids and process induced residual stresses are shown to be critical aspects for the other three systems. It is shown that, in comparison to the freeze–thaw conditions, sustained exposure to −15°F conditions has a much lower effect on all properties except modulus which is seen to increase due to matrix hardening and transition of material response to a predominantly brittle regime.