Low-velocity impact damage behavior of glass fiber reinforced composites with different crack propagation

Glass fiber-reinforced resin matrix composites are widely used and studied for their good mechanical and impact resistance properties. In this paper, five glass fiber reinforced nylon 6 (PA6)-based composites were prepared by mechanical blending combined with the molding process. The flexural strength, shear strength, pendulum impact strength, and low-velocity impact properties of five composites were comparatively investigated. The crack extension modes of the composites were characterized and analyzed by light microscopy, scanning electron microscopy (SEM), and computerized X-ray tomography (XCT), and the effects of different crack extension modes on the mechanical and impact resistance properties of the composites were researched. Experimental results show that: (1) Cracks in the composite material mainly exist in two expansion modes: transverse propagation parallel to the direction of fiber layup and longitudinal propagation perpendicular to the direction of fiber layup; (2) Different crack extension modes will cause different damage situations to the composites, however, the crack extension mode has minimal impact on the flexural, shear and pendulum impact strength of the composites; (3) The flexural and shear strengths of the composites co-reinforced using fly ash and glass fibers were preferably 484.5 and 46.1 MPa; (4) The crack extension mode has a significant impact on low-velocity impact performances of the composite material. The composite co-reinforced with glass beads (GB) and glass fibers had the best impact resistance, with maximum impact force (Pmax), residual impact force (Pr), and absorbed energy (Ea) of 7015.2 N, 6273.6 N and 15.4 J, respectively.Highlights The propagation of cracks inside the composites was observed using SEM and XCT etc. A relationship between crack propagation mode and low-velocity impact resistance of composites was established. The low-velocity impact properties of composites are carefully analyzed. (A) and (B) Mode of propagation and distribution of cracks in FPB-GF/PA6 composites in low velocity impact tests, (C) Force-time curves for low-velocity impact testing of composite materials. image