Progressive study of water pressure-induced damage in hollow glass microsphere/epoxy resin composite materials based on the theory of elastic strain energy

The application of hollow glass microsphere/epoxy resin (HGMs/ER) composites is critical for deep-sea submersibles. This study proposes a progressive damage theory for HGMs/ER composites under hydrostatic pressure, based on elastic strain energy derived from self-consistent theory. We determined the ultimate strain energy limit of the HGMs and established their strain energy density distribution and probability distribution functions. The model predicted a chain fracture threshold pressure of 128.0 MPa for the composite material (density: 0.68 g/cm³). Below this threshold, water absorption remained low (e.g., 0.63% at 115 MPa), whereas above it, the water absorption rate increased exponentially with pressure, reaching 1.67% at 165 MPa. This sharp increase was quantitatively linked via an established absorption model to the volume fraction of fractured HGMs. Theoretical predictions of water absorption rates showed excellent agreement with experimental data, providing rigorous validation of the proposed progressive damage theory. These findings provide quantitative failure-prediction criteria and optimization guidelines for deep-sea buoyancy materials.