Tension-tension fatigue performance of a large-diameter pultruded carbon/glass hybrid rod

A novel pultruded large diameter glass fiber shell (GFS) and carbon fiber core (CFC) hybrid rod (19 mm) was developed for structural applications. In the present paper, the tension-tension fatigue performances of the hybrid rod were studied with three stress levels (41.7%, 33.4% and 25.0%) and a fixed stress ratio of 0.4. The fatigue life of the hybrid FRP rod conformed to the classic logarithm regression model. The fatigue damage of the hybrid FRP rod initiated by debonding of GFS/CFC interface, leading more load to be transferred to GFS. The fatigue failure mode is that GFS split and separate from CFC, while no obvious damage is found on CFC. A 2D simulation confirmed the occurrence of CFC/GFS debonding during fatigue. Based on the fatigue life and failure mechanism, a three-stage fatigue failure model was proposed at different stress levels to provide a preliminary guidance for actual application of the large-diameter hybrid FRP rod. The rod after fatigue failure or 2 million fatigue cycles were tested to further understand the fatigue mechanisms. As found, bonding strength of GF/resin of the GFS layer, and CFC/GFS interface decreased significantly, supporting the above assumption.