Estimation of carbon fiber/epoxy interfacial normal strength and interfacial shear strength by fiber bundle tests

The fiber/matrix interface is a vital region which determines, to a great extent, the ultimate strength of the fiber reinforced composites. The assessment of interfacial strength are usually based on the mechanical test of the single filament/resin specimens, i.e., Micro-indentation, fiber pull-out, fiber fragmentation and micro-bond tests have been extensively used in the past few decades. Recently, the transverse fiber bundle tensile (TFBT) test has been successfully utilized to estimate the fiber/matrix bonding strength under different interfacial modification conditions. Higher stress concentration in the normal direction occurs at the interphase. The interfacial normal strength (INS) can be evaluated by the combination of the experimental with analytical results. Besides, the 45° fiber bundle tensile (45FBT) test was firstly proposed to bridge the assessment of interfacial shear strength and fiber bundle test approach. The interfacial shear strength (ISS) can be also calculated based on experimental results and multiscale simulation. In this work, both the TFBT test and 45FBT test were used to determine the interfacial properties of carbon fiber and epoxy. The IFS results from the 45FBT test and the INS results from the TFBT test were contrasted.