Combined Effects of Loading Rate and Fiber-breakpoint Initialization on Fracture of Composites

The mechanical properties of single glass-fiber/epoxy composites were found to be affected by either the loading rate or the type of the fiber embedded, which was contrary to the traditional assumption. Stress—strain measurements, optical microscopy, and electron microscopy observations (in situ and ex situ) revealed that the sample embedded with a thick fiber (φ42 μm) underwent a brittle fracture while the sample embedded with a thin fiber (φ26 μm) exhibited a ductile fracture at the same loading rate of 2 × 10 ^-5 s ^-1 . But both the fiber composites underwent a ductile fracture at the loading rate of 4 × 10 ^-6 s ^-1 and a brittle fracture at 2 × 10 ^-2 s ^-1 . The origin of this phenomenon is attributed to the fracture initialized by the fiber breakpoint inside the matrix and the external tensile loading rate.