Fiber/epoxy interfacial shear strength measured by the microdroplet test

In this study, we analyzed the interfacial shear strength between epoxy and carbon fibers, measured from microdroplet specimens adhered onto a single carbon fiber. Microdroplet specimens exhibited different results of the interfacial strength according to the range of embedded fiber lengths and the calculation methods. The shear stress distributions along the interface were calculated by using the finite element analysis of the droplet, sphere and cylinder model types. The stress analysis showed that a larger shear stress concentration arose along the interface for the droplet model than for the cylindrical one. A compensation factor for the conventional shear lag model is suggested to deduce the real interfacial shear strength on the basis of the average octahedral shear stress calculated from the distortional energy for a unit volume.