Stress transfer through the interphase in curved-fiber pullout tests of nanocomposites

The properties of nanoscale interphase significantly influence the mechanics of load transfer and hence the macroscopic behavior of fiber-reinforced composites. Herein, we present a theoretical framework to study the mechanics of stress transfer through both homogeneous and inhomogeneous interphases in a curved-fiber pull-out test and analyse the stress field in the three-phase composite system based on the shear-lag theory. Explicit expressions are derived to estimate the normal and shear stresses in the fiber, interphase and matrix. The results from the analytical model are validated with those obtained from a finite element analysis. Furthermore, influence of radially modulus graded interphase, according to linear and power laws, on the pull-out performance is also investigated. Graded interphases are observed to reduce the interfacial shear stresses by up to 40% as compared to the homogeneous interphases. The stress transfer in three-phase curved-fiber pullout test considering interfacial debonding and sliding has also been studied. Finally, models are simplified for straight-fiber pullout case considering both homogeneous and graded interphases. The study can serve as a framework to investigate the pull-out characteristics of a curved fiber in nanocomposites.