Transparent Glass Fiber-Reinforced Polymers and Their Applications

Abstract

Stiff and transparent materials are essential across industries such as aerospace, defense, and consumer electronics. Traditional materials like glass and ceramics, while effective, have limitations due to brittleness, high density, and low impact resistance. Consequently, there is a demand for lightweight, durable materials with favorable optical properties. Fiber-reinforced polymers (FRPs) offer high strength-to-weight ratios and greater impact resistance than glass and ceramics. Given the low light absorption of glass fibers in the visible spectrum, transparent glass fiber-reinforced polymers (TGFRPs) show promise as replacements for traditional transparent materials.

This thesis explores two main aspects: (1) optimizing TGFRP transparency through manufacturing parameters and (2) leveraging TGFRP transparency for damage detection and stress analysis. In the first phase, findings demonstrate that achieving high surface smoothness and maximizing light transmission within the green spectrum (520–600 nm) are crucial for enhancing TGFRP transparency. This is best controlled via post-curing, a more stable approach than adding methyl methacrylate (MMA) as suggested in existing literature. Sizing was also found to play a critical role in transparency, ensuring optimal bonding between glass fibers and the matrix. Additionally, minimizing the number of glass fiber fabric layers improved transparency by reducing transmission losses across visible wavelengths.

The second phase investigated the transparency of TGFRP for visualizing internal damage and stress distributions. Confocal microscopy was used to observe cracks at various depths within TGFRP samples, while image processing techniques, such as thresholding, were employed to calculate crack density. The results indicate that a higher crack density corresponds to reduced light transmittance across the visible range. However, some limitations were encountered, as cracks and scratches on the upper layers cast shadows on the lower layers, complicating the detection of deeper damage.

During tensile testing of open-hole specimens, significant opacity changes were observed in high-strain regions, suggesting that opacity correlates with localized stress. Digital image correlation (DIC) and grayscale histogram analysis provided insights into the strain thresholds at which opacity changes begin. Future work could build on this by examining the extent to which opacity changes are due to refractive index variations alone, independent of crack formation, using these strain levels as a baseline.

Furthermore, verifying the reversibility of opacity changes through post-test spectrophotometry could position TGFRPs as highly effective materials for developing innovative and reliable non-destructive testing, damage detection, and stress visualization methods in glass fiber-reinforced polymer composites.