Influence of interfacial debonding and free edges upon compressive strength of unidirectional FRP composites

The uniaxial compressive behavior of fiber-reinforced polymer (FRP) composites is investigated in this paper. In the present study, the analytical model developed by the authors in previous studies is applied to investigate the effect of free edges and interfacial debonding upon the compressive strength of unidirectional composites. Results show that interfacial debonding has a great effect on the compressive strength, with fiber microbuckling strength falling to zero for the extreme case of complete fiber/matrix debonding with a frictionless interface. It is also found that free edges significantly affect the microbuckling behavior of unidirectional FRP composites by lowering the compressive strength of fibers located along a free edge as compared to that of inner fibers. Furthermore, the model indicates that the compressive strength of surface fibers can be strengthened by increasing the thickness of the outer matrix coating to the extent of theoretically being twice as high as the inner fibers. This finding may have significant practical implications for the strengthening of composite structures under compression by suppressing kink band initiation at free edges of the structure.