The mechanical behavior of glass fiber–reinforced, glass bubble–filled epoxy composites in a moisture-rich environment is a critical area of study, especially for applications in marine, automotive, aerospace, and structural components where lightweight and durability are key. Here’s a breakdown of the core aspects:
Mechanical Behavior Changes Due to Moisture
1. Moisture Absorption Mechanism
- Epoxy absorbs water through diffusion.
- Water acts as a plasticizer, reducing glass transition temperature (Tg).
- Interfacial degradation between epoxy–glass fiber and epoxy–glass bubble interfaces.
2. Influencing Factors
- Glass fiber orientation and content: More fibers improve mechanical retention under wet conditions.
- Glass bubble volume fraction: Higher GB content = lower density but more moisture-sensitive.
- Void content and GB integrity: Defective bubbles or poor dispersion can create micro-cracks or moisture paths.
- Surface treatments: Silane treatments on GBs and sizing agents on GF can reduce moisture ingress.
Conditioning & Testing Protocols
- Immersion in water or salt solution (NaCl) at room temperature or elevated temps (e.g., 60–90°C).
- Moisture uptake measurement via weight gain over time.
- Mechanical testing after various immersion durations (24h to 1000+ hours).
- Use of Scanning Electron Microscopy (SEM) to inspect fracture surfaces.
Mitigation Strategies
- Use hydrophobic epoxy systems.
- Surface-modify GBs and GF with silane coupling agents.
- Add nanofillers (e.g., nanoclays, graphene) to reduce permeability.
- Apply moisture-resistant coatings to final composite parts.
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