Mechanical Performance of Aged Long Fibers: Direct Water Exposure and Temperature Effect

Long fiber-reinforced composite materials consist of continuous fibers with high strength and modulus embedded in either a thermoset or thermoplastic matrix. The resulting composite material provides a combination of properties that cannot be achieved with either of the constituents acting alone. In composite structures, fibers are the primary load-carrying element, whereas the matrix transfers stress to and between the fibers while protecting them from adverse environmental conditions and mechanical damages. While thermosetting matrices provide a high level of protection against water permeation, exposure to moisture may still be significant in certain thermoplastics. Therefore, the effect of moisture on the reinforcing elements and the degradation rate may be considerable. The presented study investigated the effects of environmental aging conditions on different commercially available continuous fibers, i.e., glass fiber, carbon fiber, and basalt fiber. The fibers were soaked in water at room and elevated temperature to investigate the degradation mechanisms and, ultimately, the mechanical performance of the fibers. Mechanical testing was performed with wet fibers and dried fibers after aging. In addition, scanning electron microscopy was employed to explore the responsible mechanism for fiber degradation by environmental aging.