Experimental and theoretical investigation on the cyclic tensile behavior of interlayer hybrid composites of polypropylene and glass fiber

Abstract This study combined polypropylene (PP) (rupture strain >20%) and glass fiber (rupture strain <3%) in an epoxy matrix to develop an interlayer hybrid fiber reinforced polymer (FRP) element. Cyclic tensile tests were conducted on this hybrid FRP composite system to investigate the hysteretic behavior, and a restoring force model describing the cyclic tensile stress–strain relationship was proposed. The experimental findings indicate that the cyclic tensile stress–strain response of the hybrid FRP composite follows an approximately linear envelope curve prior to the rupture of the glass fiber layer with minimal plastic strain observed. Subsequently, the hybrid FRP composite transitions to being solely supported by the PP fiber layer, exhibiting a reduced plastic strain growth rate (slope = 0.52) compared to a single PP FRP composite system (slope = 0.58). This characteristic enhances structural repairability following seismic events. Finally, a restoring force model incorporating the envelope curve and unloading/reloading rules of the hybrid FRP composite was developed and implemented in Abaqus software for finite element (FE) analysis, successfully predicting its cyclic tensile stress–strain response. The proposed restoring force model and FE modeling approach provide valuable guidance for practical design of structural members strengthened with the hybrid FRP element. Highlights Hysteretic behavior of hybrid FRP under cyclic loads is investigated. Hybrid FRP exhibits superior seismic repairability compared to steel. A restoring force model of hybrid FRP is proposed.