Abstract
Abstract Fiber-reinforced polymers (FRP) are widely used in structural applications. Long-term properties of such materials exposed to water are of high concern and interest, especially for subsea and offshore applications. The objective of this study is to identify the mechanisms and to identify whether drop in properties of diamine-cured mixed DGEBA-HDDGE is reversible upon drying the material to its initial water content. The properties of interest are mechanical strength, elastic properties and fatigue performance, as well as changes in chemical structure. The effect of absorbed water on the properties of the resin is evaluated, and hygrothermal effects and aging mechanisms are discussed. Furthermore, it is shown experimentally that the tension fatigue S-N curve of a wet epoxy resin can be estimated by shifting the S-N curve of a dry material proportionally to a reduction in static tensile strength due to hygrothermal effects.
Highlights
Epoxy resins are well known for their relatively high strength, stiffness, low volatility, chemical resistance, and low shrinkage on curing [1, 2]
The objective of this study is to identify the mechanisms and to identify whether drop in properties of diamine-cured mixed DGEBA-hexanediol diglycidyl ether (HDDGE) is reversible upon drying the material to its initial water content
It is shown experimentally that the tension fatigue S-N curve of a wet epoxy resin can be estimated by shifting the S-N curve of a dry material proportionally to a reduction in static tensile strength due to hygrothermal effects
Summary
Epoxy resins are well known for their relatively high strength, stiffness, low volatility, chemical resistance, and low shrinkage on curing [1, 2]. Glycidyl ether derivatives of bisphenol A, i.e. DGEBA, are the most widely used epoxy resins in structural applications and constitute more than 75% of epoxy resins sold worldwide [3]. A decrease in Tg is generally attributed to plasticization and deterioration (i.e. chain scission), while an increase in Tg is derived from additional crosslinking [14]. The degradation of the tensile strength can be attributed to the plasticization and deterioration of the resin [14, 20]. The percentage reduction in the tensile strength of epoxies is related to the hydrophilicity of the resin blend, which may be measured by Hoy’s solubility parameter for hydrogen bonding [21]. Fatigue life reduction is still not completely understood, and while some authors report significant degradation, others do not observe noticeable changes after water absorption [17]
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