Flexural performance and damage evolution of multiple fiberglass-reinforced UV-CIPP composite materials-- A view from mechanics and energy release

Fiberglass-reinforced ultraviolet cured-in-place pipe (UV–CIPP) composite material is one of the most trenchless materials for underground pipelines’ rehabilitation. In this paper, the bending resistance and damage evolution mechanism of glass fiber-reinforced UV-CIPP composites were investigated under the influence of glass fiber structure, the number of layers of glass fibers, the angle of fiber layups, and the thickness of the material by high-definition video, SEM and infrared thermal imaging. The results indicate that the damage evolution modes of UV-CIPP materials mainly include: (1) fiber pull-out and overall fiber bundle tensile failure caused by strong interfacial bonding, (2) fiber/matrix debonding and delamination, fiber fracture, and matrix cracking caused by weak interfacial bonding. Furthermore, among the seven different fiberglass structures of UV-CIPP materials, the [0°/90°] warp-knit axial/short-cut felt fiberglass fabric exhibit the best flexural performance, with a bending strength of 412 MPa and a bending modulus of 16.1 GPa for the 4 layers glass fiber fabric. Moreover, in the bending process of UV-CIPP materials, the surface temperature rises primarily due to fiber break, the temperature transition aligning with the stress transition. Finally, the energy release is mainly caused by the failure of the glass fibers, but the resin contributed comparatively little. This study provides a scientific reference for the structural design and optimization of UV-CIPP materials.