Durability under hygrothermal exposure of vacuum infused GFRP composites produced with polyester and vinyl ester resins
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Tarikul HASAN , João R. CORREIA (PORTUGAL), Mário GARRIDO , Susana CABRAL-FONSECA , José SENA-CRUZ (PORTUGAL), Marco JORGEAbstract :
In the construction sector, many FRP structures are often exposed to the effects of moisture, for instance in maritime (e.g., piers, lock doors) or other outdoor applications (e.g., bridges, roofs); however, moisture is known to cause degradation of the polymer matrix, the reinforcing fibres and their interface and, therefore, this environmental degradation factor should be properly addressed in the service life of such structures.
Therefore, when designing FRP structures, the effects of moisture exposure should be duly considered, namely through the selection of appropriate conversion (or “knock down”) factors considering the reduction of mechanical properties during service life. The recent Technical Specification CEN/TS 19101:2022, “Design of fibre-polymer composite structures”, provides moisture conversion factors for different exposure classes, depending on the frequency and severity of exposure to moisture. The values of the moisture conversion factor were derived from data available in the literature and statistical considerations. However, such data was found to present several limitations, namely (i) high scatter, (ii) lack of results for long-term exposure, and (iii) gaps for several combinations of constituent materials and manufacturing methods; in particular, very few data is available for relatively thick composites (the ones used in construction) produced by vacuum infusion.
To address those gaps and to further assess the appropriateness of the design provisions given in CEN/TS 19101:2022, this paper presents an ongoing experimental and analytical study about the effects of hygrothermal exposure on the thermomechanical and mechanical behaviour of glass-FRP (GFRP) composites. Relatively thick (6.5 mm) GFRP laminates were produced by vacuum infusion using multi-axial reinforcement and two alternative resin systems: (i) isophthalic polyester and (ii) vinyl ester. The laminates were immersed in water at three different temperatures (20 °C, 40 °C and 60 °C), for periods of 3, 6, 12 and 24 months (additional results will be obtained up to 240 months), during which water absorption measurements were carried out. For each period and condition, the performance of the two types of laminates was assessed through dynamic mechanical analysis, and tensile, compressive, flexural, in-plane shear and interlaminar shear tests. The mechanical property retentions were then modelled using Arrhenius type degradation models, and 50-year predictions were derived for the GFRP composites. The results obtained were finally compared with design provisions given in CEN/TS 19101:2022 to assess their applicability to the type of composites used in the present study.
Therefore, when designing FRP structures, the effects of moisture exposure should be duly considered, namely through the selection of appropriate conversion (or “knock down”) factors considering the reduction of mechanical properties during service life. The recent Technical Specification CEN/TS 19101:2022, “Design of fibre-polymer composite structures”, provides moisture conversion factors for different exposure classes, depending on the frequency and severity of exposure to moisture. The values of the moisture conversion factor were derived from data available in the literature and statistical considerations. However, such data was found to present several limitations, namely (i) high scatter, (ii) lack of results for long-term exposure, and (iii) gaps for several combinations of constituent materials and manufacturing methods; in particular, very few data is available for relatively thick composites (the ones used in construction) produced by vacuum infusion.
To address those gaps and to further assess the appropriateness of the design provisions given in CEN/TS 19101:2022, this paper presents an ongoing experimental and analytical study about the effects of hygrothermal exposure on the thermomechanical and mechanical behaviour of glass-FRP (GFRP) composites. Relatively thick (6.5 mm) GFRP laminates were produced by vacuum infusion using multi-axial reinforcement and two alternative resin systems: (i) isophthalic polyester and (ii) vinyl ester. The laminates were immersed in water at three different temperatures (20 °C, 40 °C and 60 °C), for periods of 3, 6, 12 and 24 months (additional results will be obtained up to 240 months), during which water absorption measurements were carried out. For each period and condition, the performance of the two types of laminates was assessed through dynamic mechanical analysis, and tensile, compressive, flexural, in-plane shear and interlaminar shear tests. The mechanical property retentions were then modelled using Arrhenius type degradation models, and 50-year predictions were derived for the GFRP composites. The results obtained were finally compared with design provisions given in CEN/TS 19101:2022 to assess their applicability to the type of composites used in the present study.