Date of Graduation
Statler College of Engineering and Mineral Resources
Civil and Environmental Engineering
Fiber Reinforced Polymers (FRP) composites have been materials of interest in replacing or reinforcing steel, wood, and concrete, but lack of understanding of degradation under physical and chemical aging is a main concern. Through many years of research, the understanding of aging or durability of GFRPs has improved. To be able to evaluate aging related degradation rates, an accelerated aging methodology under varying environments is introduced. Accelerated aging is a concept used to age composites in a lab controlled environment under varying pH conditions (2 to 13) and temperatures (~ -20° to +160°F). Once acceleratedly aged testing is completed, Arrhenius relationships and Time-Temperature Superposition principles can be used to correlate the accelerated data with the naturally aged data to create strength reduction (knock-down) factors for 100-year service life.
In this work, accelerated and natural aged data for glass fiber reinforced vinyl-ester composites was collected through in-lab testing and literature data. Knowing that interlaminar shear strength (ILSS) is the most detrimental mechanical property, this work was solely focused on the degradation of ILSS of glass fiber reinforced vinyl-ester under varying pH environments and temperatures. The degradation of ILSS in composites has been found to follow two aging trends. Most of the ILSS degradation occurs within the first 3-10 years of service followed by a more gradual trend. The focus of this report is to understand the reason behind a large amount of strength loss in the initial service life. Accelerated testing was also performed on vinyl ester composites with different thicknesses, as well as pure vinyl ester samples. Examining how degradation occurs with varying thicknesses and the resin system apart from the composite is very crucial in understanding the reasons behind aging.
To achieve 100-year service knock-down factors, a correlation between acceleratedly aged and naturally aged data was formulated. In this study, the correlation was possible in a neutral pH environment due to the lack of natural aged data in alkaline and acidic environments. Therefore, alkaline and acidic environment knock-down factors are based solely on the plots shifted with acceleratedly aged data. Through hundreds of samples tested, alkaline environment is found to be the most detrimental compared to other chemical aging conditions, especially under elevated temperatures (~150°F). Under high alkaline (pH ~ 13) conditions, significant strength loss of up to 70% within the first thirty days of aging was observed, especially under high temperature conditions. 100-year service knock-down factors were arrived at using the Arrhenius relationship. This relationship is formed through reaction rates based solely on temperature dependency.
Barker, William Todd, "Short Beam Shear Strength Evaluations of GFRP Composites: Correlations Through Accelerated and Natural Aging" (2019). Graduate Theses, Dissertations, and Problem Reports. 3776.