Effect of hybrid mode on mechanics and failure behavior of C/GFRP hybrid rod: Experimental and theoretical analysis

Fiber hybrid technology is an effective means to achieve high performance of fiber reinforced polymer composites (FRP), which can effectively promote the innovative application of FRP in civil engineering structures. In the present paper, three types of carbon/glass fiber reinforced epoxy hybrid rods are produced by pultrusion technology, including randomly hybrid rod with bundle-by-bundle dispersion (UDH rod) and coated hybrid rod with shell and core structures (GCH and CGH rod). The effect of fiber hybrid mode on mechanical performances is investigated experimentally, and the hybrid effect, failure mechanism and hybrid theory of hybrid rod are elucidated. The results show that the weak interfacial layer at the shell-core interface is a key factor influencing the mechanical performance of GCH and CGH, while fiber random hybrid can eliminate the weak layer of shell-core interface and give full play to the bridging effect of glass fiber, which leads to the pseudo-ductility behavior for UDH. The residual stress and stress concentration of interface lead to the negative hybrid effect of mechanical strength, while the compressive residual strain generated within the carbon fiber bundles during curing and cooling leads to the positive hybrid effect of fracture strain. Failure of UDH begins in the outer carbon fiber bundles, and the progressive fragmentation of these bundles contributes to the observed pseudo-ductility behavior. Failure of GCH and CGH begins in the fracture of carbon fiber layer, and the rods exhibit brittle failure characteristic of the CFRP layer. Prediction models of stress-strain of hybrid rod are established based on theoretical analysis, and the predicted results are in good agreement with the experimental results.