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 degreesF) and f reeze-thaw conditions. Response and failure mechanisms are characterized th rough 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 an d results in reductions in both tensile strength and interlaminar shear str ength. The adhesive layer used in the prefabricated adhesively bonded syste m 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 interf ace. Effects of incomplete ambient cure, pre-existing voids and process ind uced residual stresses are shown to be critical aspects for the other three systems. It is shown that, in comparison to the freeze-thaw conditions, su stained exposure to -15 degreesF 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. (C) 2001 Elsevier Science Ltd. All rights reserved.