Short Beam Shear Strength Evaluations of GFRP Composites: Correlations Through Accelerated and Natural Aging

Abstract

Short Beam Shear Strength Evaluations of GFRP Composites: Correlations Through Accelerated and Natural Aging William Barker 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.

Time-Dependent Reliability Framework for Durability Design of FRP Composites

“…(Myers & Viswanath, 2006). Similar results for GFRP composites are also found by Barker (2019), Manalo et al (2020), and many other researchers.…”

“…For example, the research illustrates how a strength reduction factor of 0.3 for vinylester-based GFRP flexural members can be computed using accelerated and naturally aged testing data to provide 100 years of service life. Such results, although preliminary at this time, are close to what the FRP industry is experiencing (Barker, 2019, Manalo et al, 2020. 3.…”

“…One such study was undertaken by Keller et al (2007Keller et al ( , 2016 (Keller et al, 2007(Keller et al, , 2016 Another on-going long-term natural weathering study is at WVU Constructed Facility Center (Dittenber, GangaRao & Liang, 2014), where naturally aged FRP samples (manufactured between 1991 and 2006) were tested to document their aging behavior against their original values after 10+ years. This work was further advanced by Barker (Barker, 2019) particularly the older specimens, and material properties improved with aging, which can be potentially attributed to inadequate initial curing. Out of all properties evaluated, short beam shear strength appears to be the most sensitive to age-induced reduction since it correlates highly to known FRP matrix's degradation over time.…”

“…Barker (Barker, 2019) at WVU-CFC evaluated about 450 samples of 1/8" and 1/4" FRP (E-Glass Fibers in vinylester Resin, Fiber Volume Fraction of 0.34 by weight) for strength retention under accelerated testing ranging in duration from 150 days to 540 days, at temperatures of -23, 22, and 71 degree Celsius, in environments of acidic (HCL solution in tap water at pH =3), neutral (Tap water), and alkaline (NaOH solution in tap water at pH=13). Accelerated tests were calibrated using natural data from 11 to 18-year old naturally aged samples (exposed to indoor, partially outdoor, and fully exposed to outdoor environment).…”

“…The durability of FRP composites can be described in terms of gradual losses of chemical, physical, and mechanical properties over time. The continuous degradation of FRP properties over time without a threshold value or endurance limit has been well documented by many researchers such as GangaRao (2007GangaRao ( , 2011GangaRao ( , 2017, Manalo (2020), Vijay (2000), Karbhari (2003), and Barker (2019). The aging process involves many external and internal factors such as moisture, pH levels, temperature variations, sustained loading (or static fatigue), cyclic loadings (i.e., harmonic vibrations, dynamic fatigue or common fatigue), ultraviolet (UV) exposures, FRP architecture (i.e., fiber orientation, fiber volume fraction, manufacturing process, etc.…”