Hygrothermal Aging of Pultruded Fiber–Polymer Composite with Predictions for Design Service Lives

Abstract

This study presents the findings from an in-depth study into the influence of hygrothermal aging on the material properties of a pultruded flat sheet composite composed of electrical-corrosion resistant (E-CR) glass fibers and an unsaturated polyester-based matrix. By discussing the impact of hygrothermal aging across 10 material properties, assessing the suitability of test procedures, and presenting a framework, this study evaluates the suitability of the experimental test results for use with two service life models. This study offers an open and critical evaluation of the currently accepted methods. Across 102 batches, which consist of 476 coupons, immersed in distilled water at 25°C, 40°C, 60°C, and 80°C, with exposure times of 28, 56, 112 and 224 days, the changes in tensile, compressive, in-plane shear, and pin-bearing properties are evaluated alongside mass changes. An understanding is discussed of the relationships that were obtained for moisture uptake and for material property retentions over time, which identified evidence termed nonconsistent fluctuating trends. This study highlights the possibility of misleading results that arise from the impact of the forced drying of coupons before coupon testing. For longitudinal tensile properties, a direct comparison is made between coupons termed Dried and Wet (to represent field conditions) coupons, which indicates the need for careful consideration in characterization work for the determination of the long-term material properties of composites. With the development of a framework for the evaluation of two service life prediction models, the quality of 11 sets of experimental results is evaluated. Using the four most reliable sets of predictions, the acceleration factors and service lifetimes are reported. From the evaluation of the experimental findings, testing methodologies, and the application of service life prediction techniques, this study puts forward an understanding of how to execute experimental programs with accelerated aging with the aim of obtaining meaningful test results for the long-term material properties of fiber–polymer composites. The contribution of this study to the knowledge and understanding of how the mechanical properties of fiber–polymer composites might change over time due to the durability effects of moisture and temperature is important for the determination of adjustment factors for end-user conditions in North American standards and the conversion factors for moisture and temperature effects in the Eurocode standard. These factors are used in structural design codes to adjust the short-term material properties (characteristic values) so that the design values of material properties might be appropriate to the service lives of fiber–polymer composite structures of approximately 50 years.